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. 2022 Aug 12;34(3):150–156. doi: 10.5830/CVJA-2022-039

Clinical profile and outcomes of young patients treated with implantable cardioverter defibrillators at a South African tertiary hospital: a review of two decades of implantable cardioverter defibrillator implantation and follow up

Philasande Mkoko 1,2, Ashley Chin 2, Philasande Mkoko 3,4, Kayla Solomon 4, Ashley Chin 4
PMCID: PMC10658728  PMID: 35960158

Summary

Aim

In young patients without atherosclerotic coronary artery disease, the aetiology of sudden cardiac death (SCD) has been described in Europe and North America. However, there are important regional variations and there are limited data on the aetiology and outcome of SCD in South Africa. The objective of this study was to determine the profile and outcomes of young patients treated with implantable cardioverter defibrillators (ICDs) at a South African tertiary hospital.

Methods

OThis study was designed as a retrospective review of patients aged 35 years or younger implanted with ICDs at Groote Schuur Hospital.

Results

During the study period, 38 patients younger than 35 years were implanted with ICDs. The mean (standard deviation) age at ICD implantation was 25.1 (7.6) years and 63.2% were male. A secondary-prevention ICD was implanted in 57.9% of the patient population, and primary prevention in the remaining 42.1%. Patients with secondary-prevention ICDs presented with ventricular tachycardia (59.1%), ventricular fibrillation (31.8%) and receipt of cardiopulmonary resuscitation but no recorded electrocardiograms (9.1%). Arrhythmogenic right ventricular cardiomyopathy (ARVC) was the leading cause of SCD in the secondary-prevention patient population (36.4%). Idiopathic dilated cardiomyopathy accounted for 50% of the primary-prevention patient population. After a median (interquartile range) follow up 32 (14–90) months, 7.9% died and 5.2% received a heart transplant; 42.1% of the study population received appropriate ICD shock therapies and 18.4% received inappropriate shock therapies.

Conclusion

In this single-centre study from South Africa, ARVC and repaired congenital heart disease were the leading causes of SCD in patients younger than 35 years treated with secondary-prevention ICDs. Primary-prevention ICDs were frequently implanted for idiopathic dilated cardiomyopathy.

Cardiovascular diseases claim approximately 17 million lives globally each year. More than 75% of these deaths are in low- and middle-income countries and 25% are sudden cardiac deaths (SCD).1,2 SCD is defined as sudden and unexpected death occurring within an hour of the onset of symptoms or occurring in patients found dead within 24 hours of being asymptomatic and presumably due to a cardiac arrhythmia or haemodynamic catastrophe.2,3 In Europe and North America, SCD is reported to account for more than 350 000 deaths per year.4-6

Ventricular arrhythmias are an important cause of SCD. In 157 patients who suffered SCD while wearing a Holter monitor, de Luna and colleagues reported that 84% had ventricular tachycardia (VT) or ventricular fibrillation (VF) and 16% had a bradyarrhythmia as the cause of SCD.7 This finding has been confirmed in more contemporary data.8

Although SCD is uncommon in young adults, with an estimated annual incidence of one per 100 000 in people younger than 35 years of age, compared to one per 1 000 for those older than 35 years of age;4,9 SCD in young adults is emotionally overwhelming for families and the community. Implantable cardioverter defibrillators (ICDs) are well established as an important therapeutic intervention for the prevention of SCD by terminating ventricular arrhythmias in patients at risk of SCD or those who have survived SCD.10-14

Implantation of ICDs for primary and secondary prevention of SCD is supported by contemporary guidelines.2,3 However, access to ICDs in low- and middle-income countries is limited due to the high cost of these devices and the shortage of adequately trained physicians to select appropriate patients, implant the device, manage the complications and follow up the patients.15-17 Therefore there are limited data on the patient profile and outcomes of patients implanted with ICDs in sub-Saharan Africa. We performed a retrospective study to determine the profile and outcomes of patients younger than 35 years of age implanted with ICDs in a South African referral centre.

Methods

This study was designed as a retrospective review of patients, aged 35 years or younger, implanted with ICDs at Groote Schuur Hospital from 1 January 1998 to 31 December 2020. Groote Schuur Hospital is a 900-bed tertiary- and quaternarycare centre located in the in the Western Cape province of South Africa and affiliated to the University of Cape Town. This study was approved by the University of Cape Town Human Research Ethics Committee, HREC ref no: 505/2019.

Patients implanted with ICDs are followed up in our device clinic at six weeks post implantation with a clinical review, chest radiograph, electrocardiogram and device interrogation. The clinical review, ECG and device interrogation are then repeated every six months. Patients with cardiac resynchronisation therapy plus a defibrillator (CRT-D) perform a six-minute walk on each visit. Patients are advised to immediately come into hospital when they experience an ICD shock.

Clinical notes, ICD device information and follow-up data were reviewed. A standardised data-collection form was used to collect baseline demographic data, information on clinical presentation and ICD follow-up data for a history of ICD shock therapies. Device-stored electrograms were reviewed to determine whether the delivered shock therapy was appropriate or inappropriate.

Statistical analysis

Normally distributed continuous variables are reported as means ± standard deviations (SD), and as medians and interquartile ranges (IQR) when skewed. Discrete data are presented as numbers and percentages. The chi-squared test and Student’s t-test were used to calculate differences between the primary- and the secondary-prevention groups, accordingly. The Kaplan– Meier and log rank tests were used to assess the cumulative survival differences between the primary-prevention versus secondary-prevention group, any ICD shock therapy versus no ICD shocks and appropriate ICD shocks versus no ICD shocks. A p-value < 0.05 represents a statistically significant difference. Statistical analyses were performed using SPSS Statistics for Macintosh version 24.0 (IBM, USA).

Results

A total of 260 patients were implanted with ICDs at Groote Schuur Hospital during the study period. After excluding seven patients with missing records and 215 patients older than 35 years of age, 38 patients were analysed (Fig. 1). The patient characteristics are presented in Table 1. The mean (SD) age at ICD implantation was 25.1 (7.6) years and 63.2% were male. At presentation, the ejection fraction on echocardiography was 42.8% (22.1%).

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
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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.

Fig. 1.

Fig. 1

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Study flow chart.

A secondary-prevention ICD was implanted in 22/38 (57.9%) of the patient population and primary-prevention ICD in the remaining 16/38 (42.1%) (Table 2). Patients with secondaryprevention ICDs presented with VT [13/22 (59.1%)], VF [7/22 (31.8%)] and confirmation of cardiopulmonary resuscitation, but no recorded electrocardiograms in 2/22 (9.1%). A singlechamber ICD was implanted in 24/38 (63.2%), dual-chamber ICD in 8/38 (21.1%) and CRT-D in 6/38 (15.8%). An upgrade 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.

Table 2. Device characteristics, indications and outcomes.

Variable Overall patient population, n=38 Secondary prevention, n = 22 Primary prevention, n = 16 p-value
Arrhythmic indication for ICD, n (%)
Ventricular tachycardia 13 (34.2) 13 (59.1) 0 < 0.0001
Ventricular fibrillation 7 (18.4) 7 (31.8) 0 0.014
CPR, no documented arrhythmia 2 (5.3) 2 (9.1) 0 0.329
Type of ICD implanted, n (%)
Single-chamber ICD 24 (63.2) 20 (90.9) 4 (25) < 0.0001
Dual-chamber ICD 8 (21.1) 2 (9.1) 6 (37.5) 0.05
CRT-D 6 (15.8) 0 6 (37.5) 0.003
CRT-D upgrade from single-chamber ICD 1 (2.6) 0 1 (6.3)
Primary cardiac diagnoses, n (%)
Idiopathic dilated cardiomyopathy 10 (26.3) 2 (9.1) 8 (50) 0.007
Peripartum cardiomyopathy 4 (10.5) 0 4 (25) 0.025
Hypertrophic cardiomyopathy 1 (2.6) 0 1 (6.3) 0.421
Arrhythmogenic right ventricular cardio- myopathy 10 (26.3) 8 (36.4) 2 (12.5) 0.09
Cardiac sarcoidosis 1 (2.6) 0 1 (6.3) 0.421
Long-QT syndrome 2 (5.3) 2 (9.1) 0 0.329
Surgically repaired CHD, n (%) * 5 (13.2) 5 (22.7) 0 0.05
Myocarditis 2 (5.3) 2 (9.1) 0 0.329
No primary diagnoses made 3 (7.9) 3 (13.6) 0 0.183
Appropriate ICD shock 16 (42.1) 12 (54.5) 4 (25) 0.06
Inappropriate ICD shock 7 (18.4) 6 (27.3) 1 (6.3) 0.10
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*Four patients with repaired tetralogy of Fallot and one patient with a repaired ventricular septal defect.

ICD, implantable cardioverter defibrillator; CRT-D, cardiac resynchronisation therapy plus a defibrillator; CPR, cardiopulmonary resuscitation; CHD, congenital heart defects.

Fig. 2.

Fig. 2

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Identified substrate for arrhythmia or possible SCD; patient number 38.

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).

Fig. 3.

Fig. 3

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Aetiology of inappropriate shocks; patient number 7.

Fig. 4.

Fig. 4

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Kaplan–Meier curves depicting the cumulative survival difference between the primary- and secondary-prevention groups.

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).

Fig. 5.

Fig. 5

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A: Kaplan–Meier curves depicting the cumulative survival difference between patients who received appropriate ICD shock therapies and those who did not get appropriate ICD shocks. B: Kaplan–Meier curves depicting the cumulative survival difference between patients who received inappropriate ICD shock therapies and those who did not get inappropriate ICD shocks.

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, arrhythmogenic cardiomyopathy was the leading cause of SCD, responsible for 21.1% of patients, followed by post-surgery congenital heart disease (13.2%).

At least 40% of SCD children and young adults have a negative autopsy or have a structurally normal heart. This is described as sudden arrhythmic death syndrome (SADS).23 A clinically relevant cardiac gene mutation is detected in 13 to 27% of patients in whom post mortem genetic testing is performed.23,24 For example, Lahraouchi and colleagues performed post mortem genetic testing on 302 SCD victims with negative autopsy studies, and pathogenic or likely pathogenic variants were detected in 13%, mostly for catecholaminergic polymorphic ventricular tachycardia (CPVT) and long-QT syndrome, which accounted for six and 4%, respectively.24 This is important, as these findings have implications on family screening and management.2,25 For example, evaluation of families of SADS victims identifies inheritable disease in 40 to 50% of families.26,27

Although access to advanced cardiac imaging, such as cardiac magnetic resonance imaging, in addition to echocardiography is available in our centre and therefore the diagnosis of structural overt arrhythmogenic cardiomyopathies such as hypertrophic cardiomyopathies, arrhythmogenic right ventricular cardiomyopathy and so forth is not curtailed, we do not perform genetic testing or provocation testing to unmask possible concealed channelopathies. Furthermore, we do not have the processes and protocols of assessing non-surviving SCD victims and their families. Therefore, this presents a major limitation in our hospital and region in assessing and managing survivors of SCD, non-surviving victims and their families.

Real-world data indicate that the one- and five-year incidence of appropriate ICD shock is eight and 23% respectively.28 This therapy is often directed to monomorphic VT, polymorphic VT/ VF, or a combination of the two.28 Appropriate ICD shocks are a marker of severe cardiovascular disease and haemodynamic progression and are associated with increased mortality rates. For example, recipients of appropriate ICD shocks in the MADIT-II trial had a three-fold increase in hazard ratio for mortality after an appropriate ICD shock.29 Furthermore, in the SCD-HeFT trial, patients who suffered appropriate ICD shocks had a five-fold increase in mortality rate. Additional appropriate shocks resulted in an eight-fold increase in the risk of death.30

A meta-analysis assessing the association of appropriate ICD shock and mortality, involving 10 studies, found a strong association between appropriate ICD shocks and mortality; the hazard ratio for cardiac death was 2.95 (95% CI: 2.12–4.11; p < 0.001).31 In our study, 16/38 (42%) of the overall patient population, 12/22 (54%) in the secondary-prevention patient group and 4/16 (25%) in the primary-prevention group received appropriate ICD shocks. Furthermore, there was a trend towards increased mortality rates in patients who received appropriate ICD shocks (log rank p = 0.06). Considering this finding on the backdrop of larger studies, appropriate shocks portend worse outcomes and these data suggest that patients receiving appropriate ICD shocks should be followed up closely and carefully to optimise appropriate medical therapies.

Implantation of ICDs in young patients as part of primary or secondary prevention has become a common practice with global trends on an upwards trajectory.32 Young recipients of ICDs are often confronted with psychological stress from inappropriate ICD shocks, a lifetime of generator changes and prohibition in sport participation and/or intensive exercise.2,25,33,34

In landmark ICD trials, the rates of inappropriate ICD shocks ranged between 11 and 20%.35 However, the rates of inappropriate ICD shocks in young adults and children vary between 25 and 45%.34 In the current study, the overall rate of inappropriate ICD shocks was 18.4% (7/38). This was higher in the secondary-prevention (6/22) than the primary-prevention group (1/16) (27.3 vs 6.3%, p = 0.10). Similarly to previous reports, supraventricular tachycardia (SVT), including atrial fibrillation and sinus tachycardia were the common causes of inappropriate shocks in this young cohort.35 This is particularly important as both sinus tachycardia and SVT tend to have higher rates in young patients, predisposing them to device misdiagnoses as a ventricular arrhythmia.37

Clinical trials studying ICD algorithms to reduce inappropriate shocks either included patients implanted with dual-chamber ICDs or CRT-D or excluded patients with channelopathies or previous surgery for congenital heart diseases.38-41 Therefore, the strategies we use to minimise ICD shocks in this patient population are extrapolated from studies mainly enrolling adult patients with ischaemic heart disease. Our study did not detect any mortality difference between patients receiving inappropriate ICD shocks and those who did not. Although the association between inappropriate shock and mortality has been contradictory, these are associated with important psychological stress, anxiety, depression and physical pain.33,34 These incur significant costs to health systems by resulting in early battery depletion and the need for box change and frequent hospitalisations.37

Our study has several limitations. This was a small, singlecentre study, with a selection bias of survivors of SCD (secondary-prevention group) and our assessment of SCD was incomplete (no genetic testing or provocation testing to unmask channelopathies). Furthermore, assessment and screening of relatives of SCD victims was not performed. This study highlights the gaps in practice and missed opportunities in SCD evaluation in our centre and possibly in other parts of sub-Saharan Africa and Africa at large. There are obvious cost implications and cultural barriers that must be addressed to achieve comprehensive evaluation of SCD survivors, victims and their families.

Conclusion

We set out to define the patient characteristics of young patients treated with ICDs in a South African referral hospital over the past two decades. The devices were almost equally distributed between primary and secondary prevention, with dilated cardiomyopathy and ARVC being the most frequent indications, respectively. Over the follow-up period, there was no mortality difference between the primary- and the secondary-prevention groups. However, there was a trend towards increased mortality rates in patients who received appropriate ICD shocks.

Contributor Information

Philasande Mkoko, Email: Mkkphi002@myuct.ac.za, Cardiology and Angiology Department, Alexandria University, Alexandria, Egypt.

Philasande Mkoko, Cardiology and Angiology Department, Alexandria University, Alexandria, Egypt.

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