UNIVERSITA’ DI PISA
SCUOLA DI SPECIALIZZAZIONE IN MALATTIE DELL’APPARATO CARDIOVASCOLARE
Direttore: Prof Roberto Pedrinelli
PREVALENCE AND PROGNOSTIC IMPACT OF
NON-ISCHEMIC LATE GADOLINIUM ENHANCEMENT
IN PATIENTS UNDERGOING STRESS PERFUSION
CARDIAC MAGNETIC RESONANCE
CANDIDATO Dr Ignazio Alessio Gueli
PRIMO RELATORE ACCADEMICO Prof Roberto Pedrinelli
Abstract:
Background: Stress perfusion cardiac magnetic resonance (stress-CMR)
provides information on myocardial ischemia and fibrosis using Late Gadolinium Enhancement (LGE). The ischemic pattern of LGE (I-LGE) is usually expected as it is the most frequent finding. However, non-ischemic LGE (NI-LGE) can be occasionally found suggesting alternative diagnosis.
Aim: To assess the prevalence and prognostic significance of NI-LGE in
patients undergoing stress-CMR.
Methods: Stress-CMR with either dipyridamole or adenosine was
performed in 283 patients (228 males, 81%) including perfusion imaging, wall motion evaluation and LGE. Follow-up was completed in all enrolled patients (median time: 1850 days; interquartile range: 1225-2705 days). Composite endpoint included cardiac death, ventricular tachycardia, myocardial infarction, stroke, hospitalization for cardiac cause and coronary revascularization performed beyond 90 days from stress-CMR scans.
Results: One hundred and twelve patients (40%) had negative LGE
(no-LGE), 140 patients (49%) I-LGE and 31 patients (11%) NI-LGE. Twenty-five events occurred in the no-LGE group, 68 in I-LGE and 11 in the NI-LGE group. On survival curves, patients with NI-NI-LGE had worse prognosis than patients with no-LGE regardless of the presence of
inducible perfusion defects (IPD). No significant prognostic differences were found between I-LGE and NI-LGE.
Conclusions: NI-LGE can be detected in 11% of patients during
stress-CMR providing a diagnosis of non-ischemic cardiac disease. Patients with NI-LGE have worse prognosis than those with no-LGE.
Introduction:
Over the last few decades, cardiac magnetic resonance (CMR) has established its role in both ischemic [1,2] and non-ischemic cardiomyopathies [3,4]. CMR diagnostic and prognostic value is nowadays unquestionable, representing a powerful tool in currently available diagnostic armamentarium. Stress-CMR has gained approval as an excellent tool for ischemia detection [5,6] with a significant impact in patient clinical care [7]. Stress-CMR correctly identifies ischemic burden and patients who may benefit from coronary revascularization [8] and international guidelines recommend its use when appropriate in order to act as gatekeeper of invasive coronary procedures [9].
CMR first-pass myocardial perfusion imaging is used to analyse blood flow through the myocardial capillary bed. CMR perfusion imaging is usually performed using vasodilator stressors such as adenosine or dipyridamole that induce maximal vasodilation. Hence, through the coronary steal mechanism the stenotic vessel, which is already completely vasodilated, suffers from coronary ‘theft’ causing ischemia. The perfusion defect is detectable as an area of hypointensity as the contrast agent does not reach the myocardium perfused by the stenotic vessel. Stress-CMR is defined positive if 2 or more adjacent segments show perfusion defects or at least 3 out of the total 16 segments demonstrate kinetic alterations.
Stress-CMR is a multiparametric technique with a diagnostic and prognostic role since evidence of a perfusion defect has an important impact for the prognosis of the patient. Moreover, its gives important information about inducible wall motion abnormalities and scar detection by late gadolinium enhancement (LGE). According to CEMARC study, which was the greatest population study comparing stress-CMR and SPECT, stress-CMR demonstrated higher accuracy than SPECT [5,6] for ischemia detection. CMR-stress demonstrated high sensitivity (91%) and good specificity (81%) in comparison with angiography [7]. Furthermore stress-CMR, without exposing patients to ionizing radiations, has a better spatial resolution than SPECT, being the latter not able to distinguish between subendocardial and transmural defects. Another advantage of stress-CMR is the possibility to match wall motion abnormality, a more specific sign, with perfusion defect, a more sensitive feature. In fact, perfusion defect is the first step of the ischemic cascade, whereas wall motion abnormalities, ECG alterations and symptoms are subsequent phenomena. Then, perfusion defects may be an early sign of ischemia but also be associated to false positive results. On the contrary, inducible wall motion abnormalities are very specific for ischemia but may be falsely negative in case of subendocardial ischemia.
During stress-CMR, in order to detect inducible perfusion defects (IPD), first pass perfusion sequences are mandatory. However, additional
sequences such as cine images and T1-weighted post-contrast are being easily and frequently acquired, allowing morphological and functional cardiac characterization. By performing these additional sequences, the assessment of biventricular function and mass, thickness as well as presence, extent and type of myocardial fibrosis by late gadolinium enhancement (LGE) is straightforward. Therefore, various forms and degrees of non-ischemic cardiac damage previously unsuspected may be unraveled. The prevalence and importance of non-ischemic LGE (NI-LGE) has been reported for resting CMR, showing how it may provide accurate answers not only to specific clinicians' questions but also detecting previously unsuspected cardiac findings [10]. Stress-CMR may share the same potential with resting CMR, however this hypothesis has not been proven yet. The aim of the current study was to define the prevalence, type and prognostic importance of unsuspected non-ischemic cardiac disease defined by the presence of NI-LGE in patients undergoing stress-CMR.
Materials and methods:
Patients with a clinical query of inducible myocardial ischemia and a referral for stress-CMR were consecutively enrolled from 2004 to 2016 and stress-CMR sequences and reports were retrospectively analysed. Stress-CMR was performed either with adenosine or dipyridamole. No patients enrolled in the study underwent regadenoson or dobutamine stress-CMR. All patients enrolled in the study gave their informed consent prior to their inclusion. Exclusion criteria were: incomplete or poor quality CMR scan, claustrophobia, age < 18 years old. Demographics and clinical data of all patients enrolled were collected from available clinical files. CMR reports were collected and available data extracted regarding biventricular volumes and systolic function as well as stress test result, based on the presence of perfusion defects. Patients' clinical indication regarding subsequent diagnostic-therapeutic management was at the discretion of patients’ personal physician. In particular, stress-CMR based decision on appropriate anti-ischemic medical treatment and/or indication and type of coronary revascularization (percutaneous/surgical/hybrid) was made according to internationally accepted clinical guidelines [11]. Two independent and experienced CMR operators reviewed all scans in order to detect potential non-ischemic cardiac findings and accordingly classified them as: isolated non-ischemic fibrosis when non-ischemic LGE was found in the absence of additional pathological findings; hypertrophic
cardiomyopathy (HCM), arrhythmogenic right ventricular dysplasia (ARVD), cardiac amyloidosis and dilated cardiomyopathy (DCM) when CMR criteria for each of the abovementioned diagnosis were met [12-14]. Follow-up was obtained by ambulatory visits, hospitalization following stress-CMR and/or telephone call. A composite endpoint was considered for survival analysis, including the following major adverse cardiac events (MACE): cardiac death, significant ventricular tachycardia documented in 24-hour tape, acute myocardial infarction, stroke, hospitalization for cardiac cause (angina, heart failure, significant arrhythmias) and coronary revascularization (beyond 90 days from CMR scan).
Statistical analysis:
Continuous variables, presented as mean and standard deviation when normally distributed were compared with ANOVA with Bonferroni post-hoc correction. When distribution was not normal, logarithmic transformation was performed before statistical analysis. Nominal data are presented as number and percentages and were compared using a chi-squared test or Fischer exact test as appropriate. Kaplan Meier curves were used to assess prognosis. All tests were 2-tailed, and p value < 0.05 was considered statistically significant. All statistical analyses were performed using MedCalc Statistical Software version 16.4.3 (MedCalc Software, Ostend, Belgium).
Results:
Two hundred and eighty-three patients (228 males, 81%) were consecutively enrolled with 243 (86%) of them undergoing dypiridamole stress-CMR and 40 (14%) adenosine stress-CMR. All patients with non-ischemic findings presented evidence of non-non-ischemic fibrosis. Based on the pattern of LGE, patients were divided in: No-LGE, non-ischemic LGE (NI-LGE) and ischemic LGE (I-LGE). NI-LGE was observed in 31 patients (10.9%; 21 with isolated non-ischemic LGE, 6 with HCM, 2 with ARVC, 1 with DCM and 1 with cardiac amyloidosis), 140 patients showed I-LGE and 112 no-LGE. Demographic data and cardiovascular risk factors of each group are summarized in Table 1.
On the total, 90 patients (31.8%) had evidence of IPD, of whom 84 showing I-LGE and 6 NI-LGE.
Prognostic evaluation
Follow-up was completed in all patients with a median follow-up time of 1850 days (interquartile range: 1225-2705 days). A total number of 104 MACE occurred, including 9 cardiac deaths of which 1 in the no-LGE and 8 in the I-LGE group. MACEs in the no-LGE group were 25, with 68 and 11 MACE respectively in the I-LGE and in the NI-LGE group. The survival free from MACE probability of no-LGE, I-LGE and NI-LGE was evaluated on Kaplan Meier curves analysis (Figure 1). Both patients with I-LGE and NI-LGE had worse prognosis than those with no-LGE
(respectively Log-rank p <0.0001 and p <0.005) as seen in figures 2 and 3. No difference in terms of prognosis was noted between patients with I-LGE and NI-I-LGE.
Among patients with NI-LGE, 25 (9% of total population) had normal myocardial perfusion and absence of significant coronary artery stenosis, whereas 6 (2%) had evidence of IPD. Among these 6 latter patient, 3 had normal epicardial coronary artery (microvascular disease) and 3 had significant stenosis (dual pathology).
The prognostic role of IPD among patients with NI-LGE was further investigated as showed in Kaplan Meier curve of figure 4: no significant prognostic difference was found between patients with and without IPD (p =0.31, Figure 4).
Discussion:
The main findings of our study are:
1) CMR is the only imaging technique permitting to make alternative diagnosis of non-ischemic cardiac disease during stress test. In fact, results of the current study demonstrated that in patients with clinical suspicion of ischemic heart disease, stress-CMR identified about 11% of patients with non-ischemic findings. The majority of them had only isolated areas of non-ischemic fibrosis, but cases of HCM, ARVD, DCM and cardiac amyloidosis were also diagnosed;
2) Patients with LGE had worse prognosis than patients without, regardless of the ischemic or non-ischemic origin;
3) Among patients with NI-LGE, 25 (9% of total population) had normal myocardial perfusion, whereas 6 (2%) had evidence of IPD, probably due to microvascular disease;
4) Prognosis of patients with NI-LGE did not differ based on the additional presence of IPD.
Initial forms of non-ischemic chronic cardiac disease may remain asymptomatic for years before an overt clinical presentation occurs [15]. Therefore, it is not surprising that patients affected from a non-ischemic cardiomyopathy may discover its presence when diagnostic tests are being performed for a different reason. The Euro-CMR registry, a multi-centre archive with consecutive enrolment of 27000 patients, has showed how CMR was able to provide a completely new and unexpected diagnosis in nearly 9% of scans [10]. This percentage is similar in our patient population primarily referred to stress CMR, demonstrating nearly 11% of NI-LGE in patients with clinical suspicion of ischemic heart disease. Considering this high percentage and the prevalence of CAD in the general adult population, it is possible to have a dual pathology (ischemic and non-ischemic disease) as we found in 3 patients in our study.
Moreover, the prevalence of NI-LGE of the current study highlights the important diagnostic role of CMR. Despite some forms of non-ischemic cardiomyopathy such as HCM could have been potentially diagnosed or at least suspected by different diagnostic techniques, most patients in our study population had isolated non-ischemic fibrosis not detectable by other techniques. CMR is the non-invasive gold standard for the detection of myocardial fibrosis and, even though different techniques such as SPECT or stress-echocardiography are considered diagnostically accurate for ischemia detection, they do not allow myocardial fibrosis detection. Especially in the 9% of patients with NI-LGE and no IPD, it is clear that by performing whichever other test for ischemia detection, these patients would have been considered "healthy" and dismissed without the need for additional testing, follow-up or family screening.
CMR diagnostic potential to reveal previously unsuspected non-ischemic cardiac findings is the main but not the only important finding of our study. The prognostic significance of CMR in NI-LGE [3,16], HCM [17], ARVD [18], DCM [19] and cardiac amyloidosis [20] is well established. Findings from our study support this evidence, since a diagnosis of one of the abovementioned pathologies pertained a negative prognosis, regardless the presence of associated IPD. Patients with I-LGE and NI-LGE showed a worse prognosis than patients without LGE. This result is in keeping with abundant scientific evidence both for ischemic and
non-ischemic patterns of presentation. By separately considering prognosis of patients with NI-LGE, IPD was not found to be a prognostic marker, even though stress-CMR allowed to detect patients with dual pathology. The presence of IPD in patients with non-ischemic heart disease may also suggest the presence of microvascular disease in the absence of significant stenosis of epicardial coronary arteries. In various cardiomyopathies the presence of microvascular disease may constitute a trigger for arrhythmic events and be associated to progression of the disease. Previous studies have already described the prognostic importance of myocardial perfusion abnormality in various forms of non-ischemic cardiomyopathy, mainly HCM [22, 23] and DCM [24]. By detecting previously unsuspected NI-LGE and associated evidence of IPD, stress-CMR allows to detect and correctly stratify a population at high-risk for MACE that need appropriate and intensive diagnostic and therapeutic management. Prognostic results in this subgroup and the lack of a significant difference between NI-LGE with and without IPD need to be interpreted with caution given the small number of patients in each group and low number of MACE.
Study limitations:
Some limitations of the study should be mentioned.
At the time of patient enrolment, parametric imaging sequences were not available yet, therefore no data on the potential effectiveness on non-ischemic diagnosis of these novel techniques could be evaluated. T1 mapping and extracellular volume (ECV) may permit detection of microscopic fibrosis that could improve the differential diagnosis between various forms of heart disease with strong prognostic ramification both in ischemic [25] and non-ischemic heart disease [26]. Recent studies suggest that T1 mapping could be also more effective than first pass perfusion technique in the perfusion defects assessment and distinction between IPD caused by stenosis of epicardial coronary artery or microvascular disease [27].
Conclusions:
NI-LGE was detected in 10.9% of patients during stress-CMR providing diagnosis of non-ischemic cardiac disease that could have been likely missed by alternative diagnostic test. Patients with NI-LGE had worse prognosis than those with no-LGE.
Competency in medical knowledge:
Non-invasive functional tests for myocardial ischemia have adequate diagnostic accuracy and are generally considered comparable as reported in the Guidelines on ‘Diagnosis and Management of Chronic Coronary Syndromes’. Indeed, guidelines indicate these tests for patients with intermediate likelihood of disease, basing the choice among stress-echocardiography, SPECT, PET and stress-CMR on the local expertise and availability only.
However, the results of this study highlight a proper diagnostic ability of stress CMR: the capability of providing alternative diagnoses to ischemic cardiac disease. Indeed, CMR detected non-ischemic cardiac diseases in 11% of patients undergoing stress-CMR, most of them having just small islands of fibrosis that would have not been found with other techniques. The advantage of making alternative diagnoses makes stress-CMR a complete diagnostic tool, enabling the clinician to address patients to targeted diagnostic and therapeutic pathways and to a full risk stratification. The only limitation remains the availability of CMR and trained imagers.
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Table 1: Demographics and cardiovascular risk factors, LV systolic function,
evidence of ischemic heart disease and adverse events in patients with I-LGE,
NI-LGE and no-NI-LGE.
NI-LGEa I-LGEb No-LGEc p value
Patients (nr) 31 140 112 - Male 25 (81%) 118 (84%) 85 (76%) 0.3 Age 59 ± 11b 64 ± 10a, c 60 ± 10b 0.003 Family history of CAD 9 (29%) 70 (50%) 54 (48%) 0.7 Dyslipidemia 9 (29%) b 89 (64%) a, 66 (59%) 0.08 Hypertension 14 (45%) b 99 (71%) a, 70 (62%) 0.3 Smokers 5 (16%) 32 (23%) 18 (16 %) 0.4 Diabetes 9b (29%) 39a (28%) 13 (12 %) 0.001 Sum of CV risk factors 2 (1-3) 2 (2-3)c 2 (1-3)b 0.011 LVEF 60 ± 15b 53 ± 16a, c 67 ± 8b <0.001 LV dysfunction (LVEF<50%) 6c (19%) 36c (26%) 0a,b 0.0001 Perfusion defects 6b,c(19%) 84a, c (60%) 0a, b <0.0001 FOLLOW-UP PTCA/CABG 3 (9%) 24c(17 %) 7b (6%) 0.003 Myocardial infarction 1 (3%) 9 (6%) 2 (2%) 0.2 Significant ventricular arrhythmias 3c(9%) 6c (4%) 0a,b 0.002 Cardiac death 0 8 (6%) 1 (1%) 0.07 Cardiac cause of hospitalization 8 (26%) 57c (41 %) 24b (21%) 0.004 MACE 11c (35%) 68b(49%) 25a,c(22%) 0.0001
Abbreviations: LGE: late gadolinium enhancement; nr: number; CAD: coronary artery disease; CV: cardiovascular; LV: left ventricular; PTCA: percutaneous transluminal coronary angioplasty; CABG: coronary artery bypass graft
. a = significant p value vs no-LGE; b = significant p value vs I-LGE; c = significant p value vs NI-LGE
Figure 1: Kaplan-Meier curve analysis showing prognosis of patients without
(no-LGE) and with ischemic (I-(no-LGE) and non-ischemic LGE (NI-(no-LGE) regardless of perfusion defects on stress-CMR.
(p <0.0001)
Abbreviations: MACE: major adverse cardiac events; LGE: late gadolinium enhancement
Figure 2: Kaplan-Meier curve analysis showing significant difference in terms of
prognosis between patients without (no-LGE) and with ischemic LGE (I-LGE) ( p <0.0001)
Abbreviations: MACE: major adverse cardiac events; LGE: late gadolinium enhancement
Figure 3: Kaplan-Meier curve analysis showing significant difference in terms of
prognosis between patients without (no-LGE) and with non-ischemic LGE (NI-LGE), ( p = 0.005).
Abbreviations: MACE: major adverse cardiac events; LGE: late gadolinium enhancement
Figure 4: Kaplan-Meier curve analysis showing no difference in terms of prognosis
between patients with non-ischemic LGE (NI-LGE) regardless of inducible perfusion defects (IPD) on stress-CMR.
(p 0.31)
Abbreviations: MACE: major adverse cardiac events; LGE: late gadolinium enhancement
Image: Stress-CMR with perfusion stress (top row) and rest (mid row) images and
evidence of septal midwall late gadolinium enhancement (arrows, bottom row).
