CARDIOVASCULAR JOURNAL OF AFRICA • Volume 34, No 3, July/August 2023 152 AFRICA from a single-chamber ICD was performed in 1/38 (5.6%). The primary diagnoses are presented in Table 2 and Fig. 2. Three patients (7.9%) in the overall patient population had no identifiable primary diagnoses made after investigation for the aetiology of ventricular arrhythmia or SCD. After a median (IQR) follow up of 32 (14–90) months, 3/38 (7.9%) patients died and 2/38 (5.2%) received a heart transplant. During the follow-up period, 16/38 (42.1%) patients received at least one appropriate ICD shock therapy and 7/38 (18.4%) received at least one inappropriate shock therapy. The causes of inappropriate shock therapies are depicted in Fig. 3. There was no mortality difference between the patients who received primary-prevention ICDs and those who received secondaryprevention ICDs (6.3 vs 9.1%, log rank p = 0.87) (Fig. 4). There was a non-statistically significant trend towards increased mortality rate in patients who received appropriate ICD shocks versus those who did not get ICD shocks (Fig. 5A). In addition, inappropriate ICD shocks were not associated with increased mortality rates (Fig. 5B). Discussion The main findings of this study are: (1) patients ≤ 35 years of age comprised at least 14.6% of patients implanted with ICDs. This number was almost equally distributed between secondary prevention and primary prevention. (2) Non-ischaemic dilated cardiomyopathy and ARVC were the leading identifiable clinical diagnoses in this cohort. (3) On long-term follow up, 42.1% received appropriate ICD shocks and 18.4% received inappropriate ICD shocks; and (4) there was a trend towards increased mortality rates in patients receiving appropriate ICD shocks. Furthermore, 13.2% of our patients underwent heart transplantation or died. Most of our knowledge on the mechanisms and causes of SCD in young adults and children comes from autopsy analysis of athletic SCD victims or SCD events occurring during exercise or performance of sports activities.18 There are regional variations on the predominant causes of SCD in young patients. For example, analysis of the US National Registry of Sudden Cardiac Death in athletes and the National Collegiate Athletic Association showed hypertrophic cardiomyopathy was the leading cause of SCD, followed by congenital coronary anomalies.18,19 In contrast, in a Spanish multicentre, retrospective study based on forensic autopsies, myocarditis accounted for the majority of all SCD cases and non-sport-related SCD cases.21 In the same study, SCD cases related to sport were commonly due to arrhythmogenic cardiomyopathy (37%), followed by hypertrophic cardiomyopathy (24%).21 Similarly, in a 21-year prospective clinico-pathological study in the Veneto region of Italy assessing 300 adolescent and young adults with SCD, arrhythmogenic cardiomyopathy (23%) was the leading cause of SCD, followed by atherosclerotic coronary artery disease (19%).22 Our study is not a direct comparison to the above studies. However, it offers a surrogate for identification of the causes of SCD in our community, particularly when looking at our secondary-prevention cohort, who presented with VT (34.2%) and VF (18.4%) or survived cardiopulmonary rescuscitation (5.3%). In our secondary-prevention patient population, Table 1. Patient characteristics Variable Overall population, n = 38 Secondary prevention, n = 22 Primary prevention, n = 16 p-value Age, mean (SD) years 25.1 (7.6) 22.6 (7.9) 28.5 (5.9) 0.016 Male gender, n (%) 24 (63.2) 15 (68.2) 9 (56.3) 0.510 Systemic hypertension, n (%) 3 (7.9) 1 (4.5) 2 (12.5) 0.562 Diabetes mellitus, n (%) 1 (2.6) 1 (4.5) 0 – LVEDd, mean (SD) (mm) 54.5 (17.1) 44.8 (12.5) 66.9 (14.0) < 0.0001 LVESd, mean (SD) (mm) 43.6 (18.6) 32.8 (11.0) 57.3 (17.3) < 0.0001 Ejection fraction, mean (SD) (%) 42.8 (22.1) 54.1 (15.8) 28.7 (21.1) < 0.0001 NYHA functional class I/II , n (%) 27 (71.1) 16 (72.7) 11 (68.8) 0.573 NYHA functional class III, n (%) 5 (13.2) 1 (4.5) 4 (25.0) 0.084 Beta-blocker, n (%) 31 (81.6) 17 (77.3) 14 (87.5) 0.472 NDP CCB, n (%) 1 (2.6) 1 (4.5) – – Amiodarone, n (%) 7 (18.4) 5 (22.7) 2 (12.5) 0.333 Sotalol, n (%) 2 (5.3) 1 (4.5) 1 (6.3) 0.685 ACE inhibitor/ARB, n (%) 16 (42.1) 3 (13.6) 13 (81.3) < 0.0001 Warfarin, n (%) 5 (13.2) 3 (13.6) 2 (12.5) Months of follow up, median (IQR) months 32.0 (14.0–90.0) 39.5 (17.3–96.3) 20.5 (9.3–44.0) 0.043 Heart transplantation, n (%) 2 (5.2) 0 2 (12.5) 0.171 Mortality, n (%) 3 (7.9) 2 (9.1) 1 (6.3) 0.748 SD, standard deviation; NYHA, New York Heart Association; LVEDd, left ventricular end-diastolic dimension; LVESd, left ventricular end-systolic dimension; NDP CCB, non-dihydropyridine calcium channel blocker; ACE, angiotensin converting enzyme; IQR, interquartile range. Aetiology of inappropriate shocks Atrial fibrilation Sinus tachycardia Unknown supraventricular tachycardia 14.3% 42.9% 42.9% Fig. 3. Aetiology of inappropriate shocks; patient number 7.
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