473
From: Contemporary Cardiology: Heart Disease Diagnosis and Therapy:
A Practical Approach, Second Edition
Edited by: M. Gabriel Khan © Humana Press Inc., Totowa, NJ
15 Syncope
C
ONTENTSP
ATIENTE
VALUATIONN
EURALLYM
EDIATEDS
YNCOPEP
OSTURALH
YPOTENSIONC
EREBROVASCULARD
ISEASEC
ARDIACC
AUSESU
NEXPLAINEDS
YNCOPEB
IBLIOGRAPHYSyncope is defined as transient loss of consciousness associated with the loss of postural tone that is a result of sudden transient and inadequate cerebral blood flow; an acute fall in systolic blood pressure to less than 70 mmHg causes an interruption of cerebral blood flow for more than 8 seconds. Syncope is a common problem representing up to 1% of medical admissions to general hospitals and 3 to 7% of all U.S. emergency room visits.
Causes of syncope are often elusive, and the following points deserve attention:
• An obvious cardiac cause can be defined by the history, physical examination, electro- cardiogrm (ECG), and Holter monitoring in approximately 10% of cases (Fig. 15.1. and Table 15.1.).
• Vasodepressor or vasovagal syncope, also termed neurally mediated syncope or neuro- cardiogenic syncope, the common form of which is the simple faint, accounts for approximately 40% of cases of syncope. It is therefore most important to exclude this benign problem.
A Framingham study of 822 patients with syncope revealed the following causes:
unkonown 36.6%; vasovagal 21.2%; cardiac 9.5%; orthostatic 9.4%; medication 6.8%;
stroke or transient ischemic attach 4.1%; and others 7.5%.
The majority of patients with neurally mediated syncope do not sustain significant injuries. In a small subset of patients, syncope occurs without warning and serious inju- ries occur. I prefer to label this subset of patients as having malignant vasovagal syncope and clinical trials utilizing pacemakers, and medical therapy is required in this pure subset to obtain appropriate treatment strategies. Dr. Kapoor, in an excellent review, also makes this distinction.
Unexplained syncope constitutes a large group (35%), but in patients who have struc-
tural heart disease and unexplained syncope, electrophysiologic (EP) testing is rewarding
in identifying a significant number of cardiac causes of syncope and increases the total
Fig. 15.1. Assessment of syncope. *Approximate incidence percent. **SeeFig. 15.3.
cardiac cause of syncope to approximately 22%. Unfortunately, EP testing does not uncover all cases of sinoatrial (SA) and atrioventricular (AV) node disease or tachyarrhythmias.
Syncope may also be the clue to possibly life-threatening underlying cardiac diseases.
Cardiac syncope carries a 24% incidence of sudden death in 1 year, as opposed to less than 2% sudden death per year in the remaining 78% of individuals. One-year mortality of patients with cardiac syncope ranges from 15 to 30%, versus less than 2% for individuals with unexplained syncope and without structural heart disease.
Postural hypotension is an important cause of syncope. It commonly occurs because of a decrease in preload and often occurs in patients on cardiac medications that cause venous pooling. Less often, syncope has a neurogenic cause, being a troublesome feature of autonomic neuropathy (Table 15.2.).
The assessment of syncope is often difficult, but intriguing. Figure 15.1. gives an algorithmic approach to the assessment of syncope.
Dizziness is often a feature of presyncope and has several causes that are difficult to
determine.
Figure 15.2. indicates steps to consider.Table 15.1.
Obvious Cardiac Causes of Syncope and Approximate Incidence
Causes Approximate incidence (%)
Tachyarrhythmias 45
Sustained and nonsustained VT Torsades de pointes
Atrial fibrillation
Supraventricular tachycardia Long QT syndrome
WPW syndrome Pacemaker-mediated
Bradyarrhythmias 35
Sinus node dysfunction (sick sinus syndrome) AV block: second and third degree
Drug-induced
Carotid sinus syncope 3
Obstruction to stroke volume 10
Aortic stenosis
Hypertrophic cardiomyopathy Tight mitral stenosis
Atrial myxoma or thrombus Cardiac tamponade
Prosthetic valve dysfunction Pulmonary embolism Pulmonary hypertension Pulmonary stenosis
Others 7
Brugada syndrome Mitral valve prolapse Myocardial infarction Severe ischemic heart disease Coronary artery spasm Pacemaker syndrome Aortic dissection Fallot’s tetralogy Myocarditis Chagas’ disease
VT, ventricular tachycardia; WPW, Wolff-Parkinson-White; AV, atrioventricular.
PATIENT EVALUATION
The management of syncope entails the elucidation of the cause so that appropriate
advice, medications, or corrective measures may be used to prevent bodily injury or threat
to life. Because most cardiac causes pose a threat to life, it is important to use a methodical
approach to solving the cause of syncope in a given individual. This medical solution calls
for a sound knowledge of basic internal medicine and cardiology and should commence
with a detailed history and physical examination.
Table 15.2.
Noncardiac Causes of Syncope
Vasodepressor (vasovagal) (neurally mediated syncope, neurocardiogenic syncope) Postural hypotension
Decrease preload
Venous pooling, caused by extensive varicose veins, postexercise vasodilation, venous angioma in the leg
Drugs: nitrates, diuretics, ACE inhibitors
Decreased blood volume: blood loss, dehydration, vomiting, diarrhea, excessive sweating, Addison’s disease
Drug-induced α-Blockers Ganglion blockers Bromocriptine
L-Dopa
Neurogenic decrease autonomic activity Bed rest
Neuropathies/diabetes Shy Drager syndrome Idiopathic
Mastocytosis Cerebrovascular disease
Transient ischemic attack Subclavian steal
Basilar artery migraine
Cervical arthritis, allanto-occipital dislocation compression vertebral artery Situational
Cough, sneeze, micturition, defecation Others
Drugs/alcohol Hypoglycemia Hypoxemia Hypoventilation Hysterical Panic Attacks Unexplained
SeeFigs. 15.2. and 15.3.
Differential diagnosis includes epilepsy, which can often be difficult to distinguish from syncope. Of the precipitants, prodromal symptoms and complaints during the spell and symptoms after the episode are useful in distinguishing syncope and seizures.
A confusional state postsyncope lasting minutes to hours indicates seizures, as this does not occur with syncope; patients are most often fully alert within a minute or two of a syncopal episode.
Syncope is usually associated with the following:
• Loss of consciousness precipitated by pain or occurring after exercise, micturition, def- ecation, and stressful events is generally owing to syncope, whereas aura may precede a seizure.
• Symptoms, such as sweating and nausea, during the episode are associated with syncope.
• A long duration of loss of consciousness (>5 minutes), disorientation after the event, and slowness of return to consciousness suggest a seizure. Rarely, syncope can result in seizure-like activity, but when rhythmic movements (such as clonic or myoclonic jerks) are reported, seizure is the likely diagnosis.
Those who should be admitted to a hospital include the following:
• Patients with suspected cardiac cause.
• Patients with significant bodily injury.
• The elderly patient in whom a readily identifiable cause is lacking.
• Recurrent syncope of undetermined etiology in patient who have no prodrome and are at risk for injury to themselves or others.
Fig. 15.2. Algorithm for evaluating patients with dizziness.
History and Physical Examination
A detailed relevant history and physical examination are mandatory and should include the following steps:
• Check the blood pressure (BP) on the patient recumbent for more than 3 minutes and then on standing, to elicit postural hypotension, if positive, assess causes of postural hypoten- sion (Fig. 15.1.).
• Determine the BP in the arms and legs.
• Listen for bruits over the subclavian and carotid arteries.
• Look for finger clubbing and cyanosis as signs of congenital cyanotic heart disease.
• Perform a full cardiovascular examination. Check for left ventricular hypertrophy, pres- ence of thrills, the murmur of aortic stenosis, hypertrophic cardiomyopathy (HCM), mitral stenosis, mitral valve prolapse, and the presence of prosthetic heart valve (Table 15.1. and see Chapter 11).
• Assess for tachyarrhythmias and bradyarrhythmias.
The history should exclude the most common cause of syncope, that is, vasodepressor or vasovagal syncope. All known causes of syncope should be methodically excluded (see
Tables 15.1., 15.2., andFig. 15.1.).LABORATORY INVESTIGATIONS
After exclusion of the simple faint, obvious cardiac causes, postural hypotension, vasodepressor syncope, and cerebrovascular and situational causes, request complete blood count, electrolytes, blood urea, serum creatinine, and serum calcium. The follow- ing routine tests are not usually helpful:
• Chest X-ray.
• ECG.
• Echocardiogram.
• 24- or 48-hour Holter monitoring is advisable but has a low yield.
• Implantable loop recorder. Insertable loop recorders are the diagnostic test of choice to detect bradyarrhythmias in patients with rare recurrent symptoms.
• Head-up tilt testing. Head-up tilt testing has been used to delineate the pathophysiology, diagnosis, and management of patients with no detectable heart disease and unexplained syncope. Forty to 70% of patients with unexplained syncope experience syncope on being tilted 60° for 45 minutes. There is no standard protocol for the test, but current recommendations indicate the need for:
• At least 60° tilt.
• Duration of 15–45 minutes.
• Use of foot-plate support rather than saddle.
• Isoproterenol infusion improves sensitivity with decreased tilt time of 10 minutes at 80° tilt. The use of isoproterenol has the disadvantage of dosing difficulty and reduced specificity.
Isoproterenol infusion increased the provocation of symptoms produced by head-up
tilt from 2 to 87% in individuals with unexplained syncope over a 10-minute study period
and from 0 to 73% in those with diagnosed cardiopressor syncope, during a 15-minute
tilt at 60°. However isoproterenol is not recommended in patients over age 50 because
of cardiac adverse effects. Where edrophonium results in a negative head-up tilt test,
isoproterenol does not reveal a positive test. In a study by Kapoor et al., isoproterenol
infusion resulted in a nonsignificant difference in the rate of positive tests in 20 young patients with unexplained syncope and controls matched by age, sex, and absence of underlying heart disease. The study by Kapoor et al. questions the low specificity of this test. As discussed in the section “Neurally Mediated Syncope,” there is very little reason for tilt testing if a meticulously relevant history and physical examination is completed.
Head-up tilt testing confirms the diagnosis of neurocardiogenical syncope, but this diag- nosis can be made in more than 90% of patients with this benign condition. Head-up tilt testing adds to the cost of health care and has little justification, particularly when this test has caused death in one patient and cerebral destruction in another and with other cases pending settlements.
Head-up tilt using 60° for 45 minutes does not appear to be useful in youthful subjects with typical vasovagal syncope, but in this group, the clinical diagnosis is usually apparent.
In unexplained syncope, both head-up tilt testing and EP evaluation are complimen- tary and can identify the underlying cause in approximately 74% of patients presenting with unexplained syncope.
• The results of a positive tilt test are difficult to replicate on subsequent days, and thus it is difficult to use repeat tilt testing in treatment planning.
• Treatment of neurally mediated syncope is recommended only when syncope is recurrent or severe, and tilt testing should generally be reserved for these patients.
• Chemical stimulation with isoproterenol or sublingual nitroglycerin is required to achieve high rates of positive responses (65%) in unexplained syncope; nitroglycerin use is simpler and better tolerated, particularly in elderly and in patients with ischemic heart disease (IHD). Specificity and positive response rates are similar for both agents.
• There is an overuse of tilt testing for the workup of patients who have a benign ailment that should respond to increased salt intake and clarification of the prodrome, followed, if needed, by β-blocker therapy or disopyramide.
• Tilt testing causes minor degrees of asystole, but this can be occasionally prolonged and can cause cerebral damage, albeit rarely. A death has been reported, and one patient has suffered irreparable extensive brain damage. The court settlements do not adequately compensate the bereaved families. Other cases are before the courts. Calkins et al. made the point that it is distressing to observe the many patients with syncope who have been referred to tertiary centers. Diagnosis, in most cases, can be made clinically because of the prodromal symptoms, occurrence in the upright or seated position, and absence of confusion after syncope. The cost per patient is approximately $4700 for Holter, echocardiogram, stress testing and unnecessary electroeucephalogram, computed tomog- raphy and tilt testing. The test should be reserved for patients with unexplained syncope that has no prodrome and has caused injuries, that is, patients with malignant vasovagal syndrome.
NEURALLY MEDIATED SYNCOPE
The simple faint is the most common cause of syncope and is easily recognized.
Neurally mediated syncope (also called neurocardiogenic syncope) virtually never oc-
curs in a patient in the recumbent position. Precipitating circumstances are almost always
present and typically occur in young individuals and, occasionally, in older patients in the
setting of exhaustion, hunger, prolonged standing or sitting in a hot crowded room,
sudden severe pain or trauma, venipuncture, fright, and sudden emotional stress.
The simple faint usually gives a warning of seconds to minutes. Some warnings include the following:
• The feeling of weakness, nausea, vague upper abdominal discomfort, diaphoresis, yawn, sighing, hyperventilation, unsteadiness, blurring of vision, and unawareness before fainting.
• Vertigo is not a symptom associated with a simple faint, and these patients do not get syncopal attacks. Thus, a good history identifies the faint and may save expensive and time-consuming investigations.
• Dizziness, presyncope, drop attacks, and vertigo do not lead to a loss of consciousness.
Loss of consciousness for more than 5 minutes, disorientation after the event, and slow- ness of return to consciousness suggest a seizure.
Neually mediated syncope may present as the following:
• Vasodepressor: a profound fall in peripheral vascular resistance and marked reduction in BP occurs, but the heart rate usually remains above 60 beats per minute (BPM).
• Vasovagal: predominantly cardioinhibitory; a fall in BP occurs, but there is marked vagal induced bradycardia of less than 60 BPM;
• A combination of vasodepressor and vasovagal features. The vasodepressor component with marked reduction in BP appears to play an important role in loss of consciousness.
Bradycardia plays a secondary role. These features explain the poor response to atropine.
Thomas Lewis, in 1932, in his classic paper, stated that “while raising the pulse rate up to, and beyond, normal levels during the attack, leaves the blood pressure below normal and the patient still pale and not fully conscious.” Abboud makes the relevant comment that “60 years later, Sra et al. can make the same statement with respect to the implan- tation of a pacemaker.” Thus, the marked vasodilatation causes temporary, but profound, hypotension, with SBP of less than 65 mmHg which produces syncope even when the heart rate is 60–80 BPM. The marked vasodilatation is caused by the inhibition of sym- pathetic vasoconstrictor activity at the very moment when arteriolar vasoconstriction is necessary to combat the marked fall in BP. In most patients, the onset of bradycardia is consistently preceded by hypotension. Sra et al. have shown that an increase in myocar- dial contractility and a decrease in left ventricular (LV) systolic dimensions occur 2–4 minutes before the onset of syncope.
The constant findings in vasodepressor syncope are the following:
• A sudden marked fall in total peripheral resistance, resulting in a drastic fall in BP.
• Decreased cerebral perfusion causing loss of consciousness.
• Loss of consciousness usually occurs within 10 seconds of onset of diminished perfusion.
• Return of consciousness in seconds to minutes if the individual remains flat with the legs elevated.
• Injuries are most uncommon with vasodepressor syncope.
• Bradycardia of less than 55 BPM is not a feature.
The exclusion of epilepsy is relatively easy, but occasionally syncope may be confused with akinetic seizures. Bradycardia in association with seizures has been described. The aura, if any, in epilepsy is transient but tells a story; convulsive movements occur with loss of consciousness. Injuries, including lip and tongue biting, and incontinence with a prolonged postictal state may occur.
In patients with neurocardiogenical syncope, the diagnosis can be made in virtually all
patients from a relevant history and physical. Head-up tilt testing, although commonly
done in tertiary hospitals, is not necessary for confirming this diagnosis. If symptoms are
bothersome and structural heart disease has been excluded, a trial of increased sodium intake is advisable. Patients with vasovagal syncope should be taught to recognize their prodromal symptoms and to try the following:
• crossing their legs and squeezing.
• sitting down or lying down abruptly and elevate the legs higher than the hips.
Because cardiac sympathetic overstimulation, vigorous LV contraction, and stimula- tion of intramyocardial mechanoreceptors (C fibers) appear to be important underlying mechanisms in the genesis of unexplained syncope without structural heart disease, β- blockers or disopyramide have been given as rational therapy and have proven successful in some patients with disabling syncope.
Atenolol (25 mg) or metoprolol (100 mg) or pindolol (5 mg) daily may produce a salutary response. IV esmolol may be used to predict the outcome of oral β-blocker therapy; the trial of timolol, a noncardioselective β-blocker with greater vasoconstrictive properties than selective agents, should be tested in clinical trials. One short-term ran- domized trial and a large number of uncontrolled studies of β-blockers claim effective- ness of these drugs, but several controlled trials did not show effectiveness. A randomized trial of paroxetine showed reduced recurrences at 2 years but needs further confirmation.
Although volume expansion with increased salt and fluid intake, moderate exercise, and tilt training are relatively safe measures, beneficial effects have not been documented in randomized trials.
Midodrine was shown to be beneficial in a small randomized trial when compared with no treatment, but there was no placebo arm to the study.
Fitzpatrick and Sutton described 40 patients who had syncope associated with injuries because these patients had no prodrome. Tilt testing showed mostly vasovagal syncope with a profound bradycardia; some patients had other forms of bradycardias. Dual- chamber pacing appeared to prevent syncope during a 2-year follow-up. These patients were, however, over age 65 and may have had undetected SA or AV node disease. It is unusual for patients with neurocardiogenic syncope to sustain injuries, and fortunately this type of patient is uncommon. In patients who experience no prodrome and sustain injuries, a full workup is necessary. If EP studies are negative, prognosis is usually good, but some patients may have undetected SA or AV node disease. If injuries continue to occur, a subcutaneous monitoring device (Medtronic, Inc.) can be used. An implantable
“loop recorder” as described by Krahn and Klein et al. may provide helpful information.
In 14 patients with previous syncopal episodes and negative head-up tilt, the recorder revealed sinus arrest in three, complete heart block in two, supraventricular tachycardia (ST) in one, ventricular tachycardia (VT) in one, vasodepressor syncope in two, hemo- dynamic in one, and psychogenic in one. These authors concluded that an implantable
“loop recorder” is useful for making a diagnosis when episodes are too infrequent for standard monitoring techniques (see
Fig. 15.3.).Pacemakers
Pacemakers may be a treatment option in patients with severe recurrent syncope that have caused injuries (malignant vasovagal syndrome).
The few small clinical trials that have assessed this therapy had many flaws and most were negative and have not clarified the role of pacemakers.
The Vasovasal Pacemaker Study (VPS) II study by Connolly et al., addressed the issue
of the placebo effect associated with pacemaker intervention. Of the 52 patients random-
ized to a pacemaker with sensing but without pacing. Twenty-two (42%) had recurrent suncope within 6 months versus 16 (33%) of 48 patients in the pacemaker with rate–drop response. Lead dislodgement or repositioning occurred in seven patients. Vein thrombo- sis, pericardial tamponade leading to removal of the pacemaker system, and infection involving the pacemaker generator occurred in three patients. In only 15 to 23% of the patients, the lowest heart rate recorded was less than 40 BPM.
The authors concluded that pacing therapy did not reduce the risk of recurrent syncope in patients with vasovagal syncope. Because of the weak evidence of efficacy of pace- maker therapy and the risk of complications, pacemaker therapy should not be recom- mended as first-line therapy for patients with recurrent vasovagal syncope. It must be reemphasized that this was not a study of the malignant vasovagal syndrome.
In VASIS, the Vasovagal Syncope International Study, 42 patients who had experi-
enced three or more episodes of syncope during the past 2 years and had a cardioinhibi-
tory response on tilt testing (almost all without drug provocation), which was defined as
Fig 15.3. Algorithm for the management of unexplained syncope. *Use is abused: may not assist further with therapeutic strategies and is not without dangers of cortical damage.a heart rate of less than 40 BPM for more than 10 seconds or asystole for more than 3 seconds received a pacemaker with rate hysteresis. During a mean follow-up period of 3.7 years, syncope recurred in 5% of patients with pacemakers and 61% of patients without pacemakers.
Most importantly, the results of the four trials raises the question of whether the differences in the study results could be owing to differences in the study populations or in tilt testing methods. In VPS and VPS II, fewer than 30% of patients had relatively severe bradycardia that was prominent in VASIS and the Syncope Diagnosis and Treat- ment Study (SYDIT); 85% of patients in VASIS and 60% of patients in SYDIT had asystole.
Relative bradycardia on tilt testing does not appear to be an important predictor of the response to pacemakers but that asystole is. In VASIS and SYDIT, tilt testing was rea- sonably standardized, but it was not standardized in VPS or VPS II.
Pacemakers are not expected to benefit patients with neurally mediated syncope who manifest prominent vasodilatation (vasodepressor).
Importantly, patients in VASIS and SYDIT were older, and a different pathophysi- ological mechanism may operate in this subset of patients, requiring different treatments.
POSTURAL HYPOTENSION
Several cardiac medications may cause orthostatic hypotension, particularly in the elderly. Assess the following:
• Check the BP with the patient recumbent for at least 3 minutes and then on standing; a reduction in SBP of 20 mmHg or more represents orthostatic hypotension.
• Check for evidence of decrease in preload, which may manifest itself by venous pooling that may occur on sudden standing after vigorous exercise or because of extensive vari- cose veins. Preload reducing agents, particularly, nitrates. Angiotensin-converting enzyme inhibitors or α-blockers may be implicated. Blood loss and dehydration are obvious causes, but an occult cause of the latter is Addison’s disease.
• If conditions causing a decrease in preload are not present, inquire about the use of medications that cause arterial dilatation, particularly α1-adrenergic blockers, such as prasozin and labetalol, ganglion-blocking drugs, L-dopa, bromocristine, and rarely, nifedipine.
• If drug use is excluded, postural hypotension may be caused by autonomic imbalance or neurological diseases. Complete bed rest and a lack of leg exercise, plus a decrease in autonomic activity, commonly result in postural hypotension. Neuropathy, especially owing to diabetes, Shy Drager, and other neurologic problems must be excluded.
Standing from a recumbent or sitting position causes immediate pooling of blood in the lower limbs and a consequent fall in BP that normally triggers a baroreceptor response and sympathetically mediated vasoconstriction and an increase in heart rate. As indicated above, conditions that impair baroreceptor function and decrease sympathetically medi- ated α
1vasoconstriction may precipitate postural hypotension.
Orthostatic hypotension as a consequence of autonomic neuropathies and autonomic
failure is difficult to treat successfully. It may respond to increased sodium intake or
fludrocortisone (Florinef), 0.1–0.2 mg daily. The management of orthostatic hypoten-
sion caused by autonomic failure can be successfully managed in properly selected
patients with midodrine (Amatine), a selective peripherally acting postsynaptic α
1adr-
energic agonist. Salutary effects are caused by an increase in arterial and venous tone;
venous pooling is prevented. An initial dosage of 2.5 mg three times daily with monitor- ing of supine BP is used and then increased in 2.5-mg increments at weekly intervals to a maximum of 10 mg three times daily. Caution is needed because the action of midodrine is identical to that of other α-adrenergic receptor stimulants, such as methoxamine or phenylephrine; an increase in total systemic resistance may cause supine hypertension that can precipitate heart failure (HF), myocardial ischemia, infarction, or stroke in susceptible individuals. Supine hypertension is more common during the initiation of midodrine therapy; during the titration period, adverse effects include supine hyperten- sion, which may cause headaches and pounding in the ears. Reflex bradycardia may occur, and caution is needed when the drug is combined with agents that cause bradycar- dia (digoxin, β-blockers, diltiazem, and verapamil). Urinary retention is an important adverse effect in elderly males. The drug is contraindicated in patients with significant coronary heart disease, HF, renal failure, urinary retention, thyrotoxicosis, and pheochro- mocytoma. Midodrine is renally excreted, and care is necessary to decrease the dose and increase the dosing interval in patients with renal dysfunction.
In patients who are not responsive to midodrine or fludrocortisone and have sustained injuries, atrial pacing with a heart rate of 100 BPM may afford some amelioration if combined with increased salt intake, fludrocortisone, elevation of the head of the bed during sleep, and full-length leotards to enhance venous return.
A release of histamine, prostaglandin D, and other vasodilators from mast cell prolifera- tion (mastocytosis) causes vasodilatation and is a rare cause of postural hypotension.
Instruct the patient to change posture slowly and to engage in calf muscle flexion before standing. Elevating the head of the bed and a gradual change in posture may provide a salutary response.
CEREBROVASCULAR DISEASE Subclavian Steal
Occlusion of the subclavian artery proximal to its vertebral branch may produce symp- toms when exercising the arm on the affected side. Blood is directed from the basilar system down the vertebral artery to the arm. The steal of blood may be sufficient to cause clouding of consciousness and syncope. A bruit maximal over the supraclavicular area near the origin of the vertebral artery may be heard. Subclavian steal is not common, and syncope is a rare occurrence.
Transient Ischemic Attack
Syncope occurs in approximately 7% of individuals with transient ischemic attack (TIA) and is more common with vertebral-basilar artery TIA. Associated symptoms include vertigo, diplopia, ataxia, and loss of postural tone in the legs. A drop attack without loss of consciousness is more common than syncope. Treatment with enteric- coated aspirin (80–325 mg once daily) is advisable. Patients who are unable to take aspirin should be tried on clopidogrel. Poor responders should be considered for stenting.
Aortic Arch Syndrome
Pulseless disease (Takayasu’s disease) is an arteritis-producing occlusion of the aortic
arch vessels, and syncope may result. The BP is lower in the arms than the legs.
CARDIAC CAUSES
The major determinant in cardiac syncope is a decrease in cardiac output owing to reduced heart rate or ineffectual cardiac contractions secondary to arrhythmia. A diag- nosis of cardiac syncope connotes a guarded prognosis with a mortality of up to 24% in 1 year, although this varies greatly according to the mechanism of the arrhythmia. Early diagnosis with appropriate therapy is lifesaving. Obvious causes of cardiac syncope are listed in Table 15.1.
Tachyarrhythmias sustained rapid ventricular tachycardia (VT), that is, VT duration greater than 30 seconds, or symptomatic nonsustained VT commonly causes syncope.
When VT is not apparent on the ECG rhythm strip or Holter monitoring, the underlying mechanism may be revealed by EP testing.
Atrial fibrillation or other ST with fast ventricular rates may cause syncope, especially in the elderly, or when rapid rates supervene in patients with Wolff-Parkinson-White (WPW) syndrome.
Torsades de Pointes
This arrhythmia is usually caused by class IA agents (quinidine and procainamide) and class III agents (sotalol causes syncope mainly in the presence of hypokalemia;
amiodarone rarely causes torsades). Because torsades is a brady-dependent arrhythmia, acceleration of the heart rate using isoproterenol or by pacing constitutes effective modes of therapy. Magnesium sulfate IV will usually terminate the attacks pending initiation of more definitive therapy (see Chapter 6).
Aortic Stenosis and HCM
Syncope in aortic stenosis is typically exertional and suggests significant disease with life expectancy of 1–3 years. With HCM, syncope may be precipitated by exercise but can occur with normal activities or at rest (see Chapters 11 and 14).
Acute Myocardial Infarction
Syncope is an uncommon mode of onset of myocardial infarction (MI). Approxi- mately 64% of patients with acute inferior MI have significant bradycardia and hypoten- sion that predispose syncope. Rarely, patients with extensive coronary artery (CAD) disease present with exertional syncope.
Sinus Node Dysfunction and Sick Sinus Syndrome
Severe bradycardia (30–40 BPM), sinus arrest, and brady- or tachyarrhythmias may cause lightheadedness, dizziness, confusion, memory loss, or presyncope. One or more of these associated symptoms usually produce a 1- to 10-second warning before syncope;
however, syncope can occur without warning in this category of patients and injuries may occur.
The setting is usually IHD with old infarction. The ECG may be normal or show
evidence of old infarction, bradycardia, or sinus arrest. A 48-hour Holter gives about a
70% chance of detecting a significant arrhythmia, with symptoms noted in the patient’s
diary, as opposed to less than 48% with a single 24-hour Holter monitoring. Fairly often,
repeat 48-hour Holter monitoring is necessary once or twice over a couple of weeks to
identify a bradyarrhythmia that is symptomatic. Treatment of sinus node dysfunction is
given in Chapter 17. Sinus node dysfunction and severe bradycardia causing presyncope or syncope may be owing to drug therapy that inadvertently depresses sinus node func- tion. Verapamil, diltiazem, digitalis, β-blockers, class I antiarrhythmic agents, amiodarone, and especially their combinations, may cause severe bradycardia, AV block, and asystole in susceptible individuals. Discontinuation of the causative agent or agents is unfortunately rarely practical and pacing is usually indicated.
AV Block and Stokes-Adams Attacks
Patients with Mobitz type II or third-degree AV block may suddenly have an occur- rence of transient asystole or ventricular fibrillation (VF) with complete cessation of cerebral blood flow. Because VF is instantaneous, the cerebral circulation is suddenly deprived of perfusion, resulting in loss of consciousness usually without warning. Epi- sodes can happen while sitting, lying, or walking. The unconscious patient appears very pale and, on arousal, becomes flushed as blood rushes to the head. When a patient is assessed hours or days later, ECG may show manifestations of Mobitz type II or complete AV block, right bundle branch block or left bundle branch block (LBBB), or bilateral disease. Cardiac pacing should be instituted.
Prolonged QT Syndrome
Recurrent syncope in children and young adults with a positive family history may be owing to the prolonged QT syndrome. Episodes of life-threatening arrhythmias appear to be precipitated by increased sympathetic stimulation. Thus, β-blockers have a role in management, despite a tendency for bradycardia in many of these patients. Propranolol in doses of 80–160 mg daily or a similar noncardioselective β-blocker without agonist activity is preferred.
When recurrent syncope is uncontrolled by β-blockers, combined pacing and β-blocker therapy may be required. In uncontrolled cases, excision of the left stellate ganglion may be a last resort (see Chapter 6).
Carotid Sinus Syncope
Carotid sinus syncope produces loss of consciousness most often by a cardioinhibitory bradycardiac mechanism and rarely, by vasodepressor effects. This uncommon condi- tion represents less than 3% of patients with cardiac syncope and occurs mainly in men aged 61–76 years. Males outnumber females 4:1. The history of syncope occurring with sudden turning of the head, shaving, or a tight shirt collar should alert the physician.
Episodes may occur in clusters or with dizzy spells. In some patients, attacks are rarely
associated with any head movement or pressure on the neck. Right, left, or bilateral
carotid sinus involvement occurs in approximately 60, 22, and 22%, respectively. In a 17-
year follow-up of 89 patients, hypersensitivity of the right carotid sinus was 7:1 compared
with the left. Because carotid sinus massage, even for 2–3 seconds, carries a risk in the
elderly male, a provisional diagnosis is made by exclusion of other causes before attempt-
ing carotid sinus massage, which typically results in ventricular asystole for more than
3 seconds or a decrease in BP of 30–50 mmHg, without change in heart rate. Carotid sinus
massage is best done in a hospital setting with resuscitative equipment standby, although
if necessary, the transient asystole is usually easily terminated by asking the patient to
cough or by giving one or more light chest thumps. Complications are TIA, rare hemiple-
gia, and asystole.
Because of the high spontaneous remission rate and good outcome in patients with carotid sinus syncope, only patients with recurrent syncope, particularly those with or- ganic heart disease, should be considered for ventricular pacing and with programming the pacemaker rate well below the patient’s sinus rate. In a 2- to 8-year follow-up study by Brignole et al., patients with carotid sinus syncope had an overall mortality rate that was not significantly different from control patients (5.8/100 person-years).
Other Causes of Cardiac Syncope Additional causes of cardiac syncope include the following:
• Obstruction of blood flow may occur with massive pulmonary embolism.
• Myxoma and left atrial thrombosis may cause syncope precipitated by suddenly sitting up or leaning forward.
• Syncope occurring in patients with a prosthetic heart valve presents a particularly life- threatening emergency requiring admission to exclude prosthetic valve malfunction or obstructing thrombus (see Chapter 11).
• WPW syndrome or cardiac tamponade should present no problems in diagnosis. Fallot’s tetralogy produces hypoxic spells that cause arterial vasodilatation. β-Blockers inhibit right ventricular contractility and decrease the right to left shunt; also, these agents produce peripheral vasoconstriction. supraventricular tachycardia is controlled. These actions may ameliorate hypoxic syncope.
UNEXPLAINED SYNCOPE
Approximately 35% of syncopal attacks occur without a readily defined cause. From 10 to 25% of total EP studies done in several large EP laboratories in the United States are for the resolution of the diagnosis of unexplained syncope. An algorithm for the management of unexplained syncope is given in Figure 15.3.
EP Study
A provocative EP study is useful in revealing a cardiac cause in more than 33% of patients with unexplained syncope. Approximately 21% of these patients with negative studies is subsequently diagnosed as having intermittent high-degree AV block or sinus node disease. Caution is therefore necessary because an EP study is not a sensitive test to expose symptomatic bradycardia.
EP studies have been shown to initiate sustained monomorphic VT in approximately 18% of patients and nonsustained VT in approximately 23%. Nonsustained VT, espe- cially if only for a few seconds duration, carries a minimal risk in patients with syncope and requires no arrhythmia therapy. Patients with syncope and sustained monomorphic VT do not appear to benefit from antiarrhythmic therapy, and the incidence of syncope is not reduced except when amiodarone is used as therapy.
The exact incidence of sudden death is unknown but appears to be low in patients with syncope unresolved by extended Holter monitoring and EP testing.
In patients with structural heart disease, especially IHD or cardiomyopathy, and
severely impaired ventricular function, with Holter manifesting sustained monomor-
phic VT or EP-initiated sustained VT, amiodarone therapy is advisable. Holter monitor
documentation of sustained VT is a strong predictor of EP-induced sustained monomor-
phic VT, but the use of EP testing is of dubious value in these patients.
Signal-averaged ECG in the absence of LBBB and LV ejection fraction (EF) of less than 30% correlates well with the EP induction of sustained monomorphic VT, but signal- averaged ECG is not advisable because regardless of results, EP studies are indicated in virtually all patients with structural heart disease and unexplained syncope.
EP studies appear to be justifiable in patients who have a high probability of induction of sustained monomorphic VT, such as the following:
• Post-MI patients with unexplained syncope.
• LVEF less than 30%.
• LV aneurysm.
• Complex ventricular ectopy on Holter.
Patients who have undergone a detailed assessment, including a relevant history and physical investigation, and remain with syncope of unknown cause and a negative EP study, have a low (2%) incidence of sudden death. EP studies are falsely negative in over 20% of patients who continue to have syncope. Close follow-up with extended Holter monitoring or a second assessment of HV intervals (the conduction time from the His bundle to the ventricle) and tests of sinus node function may reveal sinus node dysfunc- tion or high-degree AV block.
In patients with recurrent symptoms, particularly in those with unexplained syncope that result in injuries insertable loop recorders are the diagnostic test of choice. A loop recorder may be implanted subcutaneously. The device is able to record 7–15 minutes of continuous ECG signal and is triggered by magnet application by the patient or compan- ion. The data can be retrieved by telemetry. An event recorder has a role in patients who have sufficient warning to activate the instruction and the event is retrieved by telemetry.
β-Adrenergic Blocker
Patients without structural heart disease and neurocardiogenic syncope respond to increase salt intake and a trial of 0.1 mg of Florinef and a β-adrenergic blocking drug daily should be given a trial. These agents have been shown to prevent neurocardiogenic syncope in 50–75% of patients. Atenolol (25 to maximum 50 mg), metoprolol sustained release (100 mg), 5 mg of timolol twice daily, or nadolol (20 mg). Propranolol is benefi- cial, but adverse effects are often bothersome. Sra et al. have shown esmolol to be effective in predicting the outcome of head-up tilt response to oral metoprolol. All patients who had a negative head-up tilt test response with esmolol IV had a negative test during oral metoprolol therapy. Timolol, a nonselective β-blocker, causes greater arteriolar vasoconstriction than does atenolol or other cardioselective β-blockers and should provide salutary effects without the need for an abuse of tilt testing.
Disopyramide has a negative inotropic effect and a tendency to increase peripheral vascular resistance. Disopyramide (100–150 mg) sustained-release twice daily may be given a trial in patients in the absence of structural heart disease and in patients who have failed to respond to β-blockers.
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