How To Differentiate Right Ventricular Outflow Tract Tachycardia from Arrhythmogenic Right Ventricular Cardiomyopathy?

Tachycardia from Arrhythmogenic Right Ventricular Cardiomyopathy?

C. W

, C. E

, C. V

, R. S

, M. B

Introduction

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a disease char- acterised by partial replacement of myocardial tissue by fibrofatty tissue.

Ventricular tachycardia may originate from the diseased areas and cause haemodynamically non-tolerated ventricular tachycardia, syncope, or sud- den death already in young patients.

Time of first diagnosis is usually before the age of 40 and not infrequent- ly already in adolescence. The aetiology of ARVC varies and there are differ- ent hypotheses as to how ARVC develops [1, 2]. Among affected patients, there is a predominance of males and early reports suggested that in some cases the disease may be familial. Moreover, a number of different gene mutations in desmosomes have been identified, such as mutations in cytoskeletal proteins, plakoglobin, and desmoplakin, and both autosomal- dominant and autosomal-recessive modes of inheritance have been report- ed. In some patients disease is also manifested in the left ventricle [3, 4].

Right ventricular outflow tract (RVOT) tachycardia is a benign condition.

In the absence of structural heart disease, it is considered to be primary elec- trical defect that results in ventricular extra beats, salvos, or sustained tachy- cardias mainly from the right ventricular outflow tract, but also infrequently from other regions in the right ventricle, above the pulmonary valve or the sinus valsalva. A variety of mechanisms have been suggested, including cAMP-triggered activity through late after-depolarisation. RVOT tachycardia is also mainly observed in young patients, predominantly females, and often

1

Department of Medicine-Cardiology, University Hospital Mannheim, Faculty of

Clinical Medicine of the University of Heidelberg, Mannheim, Germany

becomes symptomatic already in young adults. When confronted with a patient with left bundle-branch-block tachycardia with inferior axis, a diag- nosis of idiopathic RVOT tachycardia can be made only after exclusion of ARVC. The differential diagnosis of ARVC is based on the criteria of the Task Force of the Working Group Myocardial and Pericardial Disease of the European Societ y of Cardiolog y and of the Scient ific Council on Cardiomyopathies of the International Society and Federation of Cardiology.

Classification is based on electrocardiographic patterns of depolarisation and repolarisation, echocardiography, endomyocardial biopsy findings, mag- netic resonance imaging results, arrhythmia history, and other criteria [5].

However, clinical presentation alone does not allow a diagnosis to be made in the majority of patients. To differentiate between ARVC and RVOT tachy- cardia is a clinical challenge, and an intense work up is essential to making the correct therapeutic decision.

Electrocardiogram in Sinus Rhythm

There are different signs in the surface ECG of patients with arrhythmogenic right ventricular cardiomyopathy, most strikingly, the T-wave inversion and an epsilon-wave in lead V1 or V2. In addition, a localised increase of the QRS duration of > 110 ms in leads V1–V3 or positive late potentials are signs for a potential ARVC [1, 6, 7]. However, they are not observed in every patient and especially not during early stages of the disease. Although patients with a normal ECG at rest are less likely to suffer from ARVC, in the studies of Niroomand [6] and O’Donnell [7], repolarisation abnormalities in the pre- cordial leads varied between the two studies from 66% to 52% in patients with ARVC, and from 23% to 6% in patients with RVOT tachycardia.

The ECGs of patients with ARVC often display an incomplete right bun- dle-branch block or T-wave inversion in the right precordial leads, some- times also until V4, V5. In Niroomand’s study, T-wave inversion was seen in 13/15 patients (87%), while 14% of patients displayed epsilon waves [6].

O’Donnell observed positive late potentials on the signal-averaged electro- gram in 78% of patients with ARVC and in none of the patients with idio- pathic RVOT tachycardia.

Electrocardiogram During Ventricular Tachycardia

In patients with ARVC, the ventricular tachycardia (VT) shows a pattern of

left bundle-branch block. The QRS axis is shifted to the right when the VT

originates in the pulmonary infundibulum. The axis may also be shifted to

the extreme left when the VT arises from the diaphragmatic wall or is locat-

ed in the right ventricular apex or close to the tricuspid annulus [1, 2]. In patients with ARVC, the upstroke of the QRS complex seems to have some

‘slurring’ and a slew rate that is less steep. The QRS complex also appears broader. In the study by Niroomand et al., the axis during VT in ARVC was inferior in 48%, intermediate in 27%, and left/superior in 20% of patients. In contrast, in patients with idiopathic RVOT tachycardia, it was inferior in 90%

and intermediate or superior in only 5% [6].

The most common clinical presentation of RVOT tachycardia is a frequent, nonsustained repetition of uniform, monomorphic VT alternating with peri- ods of sinus rhythm. Isolated ventricular extra systoles present the same mor- phologic pattern as observed in tachycardia. The cycle length of sustained ventricular tachycardia commonly ranges from 140 to 180 bpm [8, 9].

Transthoracic Echocardiography

The structural major abnormalities in ARVC can be detected by echocardio- graphy, but minor abnormalities are seen only by magnetic resonance imag- ing (MRI). The signs of the disease are dilation of the right ventricle, the presence of aneurysm during diastole, and dyskinetic areas in the infero- basal region. Therefore, if there is any doubt about the diagnosis after transthoracic echocardiography, the patient should undergo cardiac MRI.

Nuclear Magnetic Resonance Imaging

Patients with right ventricular tachycardia should undergo MRI before inter- vention in order to detect aneurysms, intramyocardial fat, or advanced wall thickening before catheter ablation, if not distinct on echocardiography or right ventricular ventriculography [10].

Electrophysiological Study

Electrophysiological studies (EPSs) may help to differentiate RVOT tachycar- dia due to ARVC from idiopathic RVOT-VT. In the setting of ARVC, the sig- nals of the endocardial electrograms may be significantly altered in terms of activation delay, fragmentation, amplitude decrease, or dense scarring. These features are not likely to be found in idiopathic RVOT tachycardia patients.

Some investigators have analysed the endocardial electrograms by using an

electroanatomical mapping tool. Using this approach, Boulos et al. found a

significant difference between patients with ARVC and those with idiopathic

RVOT tachycardia [11]. They also compared the duration and amplitude of

the electrogram between normal probands, patients with RVOT-VT, and patients with an ARVC, and could demonstrate that while there was no dif- ference between normal probands and patients with an idiopathic RVOT-VT, there was a very large difference compared to ARVC patients [11]. Areas with a strong disposition to fibrofatty degeneration and therefore areas to look for fragmentation or scarring are the RVOT, the subtricuspidal base of the ventricle, and the RV-apex. Another indicator for VT in structural heart dis- ease is repetitive inducibility by programmed stimulation and the presence of a critical coupling interval. O’Donnell found that, in contrast to idiopathic RVOT-VT patients (3%), VT was induced by extra stimulation in 82% of pat ients w ith ARVC w hich indicates a re-ent rant mechanism [6].

Furthermore, in that study, in patients with idiopathic RVOT tachycardia there was usually only one morphology in premature beats or VT, whereas 71% of patients with ARVC presented from one to six morphologies charac- teristic of inducible tachycardia. Therefore, in the presence of VT pleomor- phism an ARVC should be suspected. Finally, the study also noted that frag- mented diastolic electrograms occurred in 82% of patients with ARVC [6].

Inducibility maybe facilitated by infusion of isoproterenol in both clinical entities and is therefore not a criterion to discriminate between the two dis- eases.

Triggering Factors for VT and Symptoms

Idiopathic ventricular tachycardia from the RVOT and VT in ARVC are diffi- cult to discriminate based on circumstances of onset, because sustained tachycardia and salvos tend to be induced by stress, catecholamines, or phys- ical exercise in both cases [1, 2, 6]. However, there is a difference in symp- toms in terms of severity for the overall population. Whereas syncope is more frequent in ARVC and cardiac arrest does practically not occur in idio- pathic RVOT-VT, in idiopathic VT there are more mild to moderate palpita- tions and dizziness due to bradycardia with bigeminus and resulting periph- eral pulse deficit. In ARVC, intensive physical activity or extreme anxiety is known to cause fast and recurrent VT with a considerable risk of sudden death. Therefore, it should be absolutely avoided in those patients [1].

Conclusions

The diagnosis of an idiopathic RVOT-VT is made by exclusion of ARVC or

any other structural heart disease. If there are no signs of RV myocardial

changes, such as dilatation, dyskinesia, hypokinesia, or aneurysms and wall

thickening, and there are no electrocardiographic signs of ARVC, the patient

most likely has an idiopathic RVOT-VT. However, especially in families with a history of sudden death, close follow-up may be useful. When enough minor or major criteria are met, the patient should be risk-stratified and treatment options should be tailored to the individual, taking into considera- tion the risks and benefits. In some younger patients with, e.g. syncope and one other minor criterion and RVOT-VT, this decision is often very difficult and will probably remain difficult. Genetic testing should be performed in all patients with a family history in order to detect relatives at risk.

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