INTRODUCTION

Untreated sudden cardiac arrest (SCA) leads to sudden cardiac death (SCD), which accounts for 15%–20% of all deaths [1]. Cardiovascular diseases, particularly coronary artery disease, have been reported to be the most common cause of SCD [2], except in individuals younger than 30 years, in whom the predominant diagnosis is unexpected, idiopathic cardiac death [3].

METHODS

We retrospectively reviewed the medical records (electrocardiography, echocardiography, coronary angiography/coronary artery computed tomography, electrophysiology study) of all patients who underwent CMR between 2008 and 2017 in our hospital. In this study, we enrolled SCA survivors with an initially (before the CMR exam) unexplained or unclear cause of SCA. We included patients with a normal or slightly decreased ejection fraction, as worsening systolic function could be caused by SCA. The study was approved by the local ethics committee. All participants gave written informed consent for the CMR examination.

Cardiac magnetic resonance study

Cardiac magnetic resonance studies were performed on a 1.5 Tesla scanner (Avanto or Avantofit, Siemens, Erlangen, Germany) using breath-hold cines in the long-axis view and sequential slices in the short-axis view. All patients underwent a CMR study with a gadolinium-based intravenous contrast agent at standard dosage.

Each study was reported by a team of at least two skilled investigators. The final diagnoses were made using all available data.

Statistical analysis

Statistical analysis was performed using MedCalc software, version 10.03 (Ostend, Belgium). The Student t-test was used to compare normally distributed variances. A P-value <0.05 was considered significant. Non-normally distributed data were tested using the Mann-Whitney test. P <0.05 was considered significant.

RESULTS AND DISCUSSION

From all consecutive patients referred for CMR in our hospital between 2008 and 2017 (n = 8630), 57 patients were referred due to sudden cardiac arrest. We included 31 patients (16 male) in whom the SCA cause was unclear before CMR. The mean age (standard deviation [SD]) was 36.7 (12.2) years, and the mean (SD) left ventricular ejection fraction was 59.8 (7.6)%. Late gadolinium enhancement (LGE) was observed in 13 cases (41.9%), whereas in 1 case, right ventricular LGE was present.

Cardiomyopathies were diagnosed in 3 patients: one patient was found to have dilated cardiomyopathy (DCM), one had left ventricular non-compaction (LVNC), and one had arrhythmogenic right ventricular cardiomyopathy. In patients with DCM and arrhythmogenic right ventricular cardiomyopathy, LGE was observed. All of them had SCA as the first symptom of heart disease, and echocardiography was inconclusive.

There were no statistically significant differences in patients with normal cardiac function with and without fibrosis with regard to age (mean [SD]: 38.8 [12.2] years vs. 37.6 [13.0] years; P = 0.81), left ventricular ejection fraction (mean [SD]: 57.7 [6.8] % vs. 62.3 [7.0] %; P = 0.12), left ventricular end-diastolic volumes (median [interquartile range, IQR]: 82.0 [68.7–97.9] ml/m2 vs 82.5 [76.8–94.4] ml/m2; P = 0.54), and left ventricular end-systolic volume (mean [SD]: 34.2 [10.3] ml/m2 vs. 33.7 [11.0] ml/m2; P = 0.90, respectively).

SCA is a major medical problem associated with poor outcomes, with a survival rate of only 9.6% [4]. In Poland, the out-of-hospital cardiac arrest incidence is 69.7 per 100 000 inhabitants [5]. Many cardiovascular diseases are associated with an increased risk of SCA events.

Our cohort consisted of patients with normal or inconclusive echocardiographic findings, whereas in 3 (9.7%) of them cardiomyopathy was diagnosed by CMR. In the rest, mechanical cardiac function was grossly normal. In a large cohort of patients with normal echocardiography and ventricular arrhythmias (including aborted SCA) [6], structural heart disease was found in 25.5% of patients.

In patients with idiopathic DCM, approximately 30% of deaths are sudden [7] and strongly correlated with the presence of LGE [8]. LVNC is associated with a higher risk of SCD and ventricular arrhythmias than age-matched DCM [9]. Arrhythmias in patients with LVNC occur even if LGE is not present [10]. Accordingly, in patients with arrhythmogenic right ventricular cardiomyopathy, life-threatening arrhythmias can occur before detection of histological and imaging features [11].

In 87.1% of patients with normal cardiac function, there were no other causes according to a previous (pre-CMR) investigation. The CMR examination led to the finding of a potential arrhythmic substrate (represented by LGE) that might cause VT/VF leading to SCA in 11 of 27 patients with IVF.

In multiple studies analyzing causes of SCD in the US and European countries (Italy, Denmark, and the United Kingdom), the most common cause was unexplained SCD in patients with structurally normal hearts [12]. In the out-of-hospital cardiac arrest real-life cohort registry, IVF was diagnosed in 6.8% of SCAs among all survivors of SCAs with cardiac etiologies [13].

SCA survivors with CMR-based diagnosis have been found to have a worse prognosis than patients with a normal scan or minor nonspecific changes [14]. Moreover, the presence and extent of LGE correlate with a worse prognosis [15].

Limitation and strength

CONCLUSION

In a cohort of unexplained SCA survivors, the CMR study led to the finding of underlying cardiomyopathy in 3 patients (9.7%) and of potential arrhythmic substrates in 11 (35.5%) patients with idiopathic ventricular fibrillation. In 16 (51.6%) patients with IVF, the CMR scan was normal. The role of CMR in SCA survivors needs further investigation.

Article information

Conflict of interest: None declared.

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REFERENCES