Hypertrophic cardiomyopathy – do the old sporting restrictions still apply?

25th June 2023, Dr Chee L Khoo

Sudden cardiac death

Consensus cardiology recommendations previously supported the ’blanket’ disqualification of athletes with hypertrophic cardiomyopathy (HCM) from competitive sport. Clinically, it is almost impossible to exclude HCM from physical examination. Thus, sudden cardiac death (SCD) is always on our minds when we are asked to sign off on a clearance to participate in sporting activities. We can’t refer all those requesting clearance for echocardiography. Do exercise restrictions actually lower the risk of SCD in HCM anyway? Conversely, is there a subgroup of athletes with HCM who may be able to safely participate in intensive exercise? How common is SCD in patients with HCM?

What is HCM?

The prevalence of HCM estimated is 1:200-1:500 (1). Most genetically and clinically affected individuals probably remain undiagnosed, largely free from disease-related complications. So, those estimates are probably under-estimations. The left ventricular hypertrophy (LVH) is classically described as asymmetric and commonly the interventricular septum is affected; hence, the term asymmetric septal hypertrophy. The asymmetric patterns of left ventricular hypertrophy (LVH) may be diffuse involvement of ventricular septum and free wall or segmental confined to the basal anterior septum or distal [apical] chamber. Although LV thickness is usually unchanged throughout adulthood, it can be dynamic, increasing in asymptomatic adolescents and young adults, or regressing with progressive evolution to end-stage HF.

You would have noticed that the earlier terminologies, hypertrophic obstructive cardiomyopathy (HOCM) and idiopathic hypertrophic sub-aortic stenosis are no longer used to describe this entity. Patients present with or without left ventricular outflow tract (LVOT) obstruction. Resting or provocative LVOT obstruction occurs in 70% of patients and is the most common cause of heart failure. In other words, not all HCM have obstructive outflow. Hence, the omission of obstructive in the new terminology.

HCM also presents an unpredictable arrhythmogenic substrate demonstrating myocardial disarray and interstitial and myocardial scarring as a result of microvascular ischaemia (1). Athletes engaging in intense exercise undergo powerful adrenaline surges, extreme metabolic stresses and dehydration, all of which could provoke a ventricular tachyarrhythmia in the setting of a pathological myocardial substrate.

The inheritance

HCM can be inherited as a Mendelian autosomal dominant disorder with variable penetrance, associated with variants in genes encoding proteins of the cardiac sarcomere involved in contractile function. However, only 30% of clinically diagnosed HCM patients have evidence of a genetic aetiology with pathogenic disease-causing mutations and therefore most patients fulfilling a clinical HCM diagnosis do not have a sarcomere mutation (2-5).

Genetic testing has a role in family screening and identification of HCM phenocopies but sarcomere mutations do not predict sudden death, prognosis or future clinical course of individual patients. Genetic testing can identify clinically silent genetically affected family members without LVH. This is known as “gene positive–phenotype negative,” and has capacity for transmission to offspring but is associated with both negligible adverse event rates and relatively infrequent phenotypic conversion during adulthood.

The clinical profiles

Testing optimally include echocardiography, 12-lead ECG, ambulatory ECG monitoring (via Holter or wireless patch), contrast cardiac magnetic resonance (CMR), exercise (stress) echocardiography to provoke outflow gradient if absent or mild at rest, and possibly genetic testing (see later). In most age groups, maximum LV thickness ≥ 15 mm at any site in the chamber is consistent with identification of HCM. 13 to 14 mm can be diagnostic if associated with HCM family history, typical dynamic outflow obstruction, or distinctly abnormal ECG patterns. Stress echocardiography is an important test in HCM with the capability of provoking labile physiologic LV outflow gradients.

Patients with HCM can be affected by a variety of evolving clinical profiles:

  • Stable benign clinical profile without need to recommend a major treatment intervention
  • Increased arrhythmic sudden death risk with consideration for an implantable cardioverter-defibrillator (ICD)
  • LVOT obstruction with significant heart failure (HF) symptoms, as potential candidates for invasive septal reduction intervention to abolish subaortic gradient and reverse HF
  • Nonobstructive end-stage phase with consideration for advanced HF therapies
  • Atrial fibrillation and risk for embolic stroke with indication for anticoagulation  

Sudden cardiac death (SCD) in HCM

In a series of 1306 athletes with SCD in the USA, 842 had an autopsy-confirmed cardiovascular diagnosis. HCM was the leading identified structural disorder but only represents 36% of confirmed diagnoses and 23% of all cardiovascular cases (6). Similarly, an analysis of SCD in college athletes from the USA as well as a prospective study of elite adolescent soccer players from the UK both found that HCM represented about one-third of SCD cases (7,8).

SCD is more common in younger patients (age 5–25 years) compared with HCM-related stroke and heart failure as the cause of death in older patients.

Early studies reported an annual mortality rate of approximately 4% in children with HCM (9,10). In a 1976 study of 35 children under 15 years with HCM followed for 7.4 years, one-third of patients died suddenly (4% mortality per year) (9). Conventional risk markers for patients with HCM include a prior cardiac arrest, family history of HCM-related sudden death, unexplained recent syncope, multiple episodes of non-sustained ventricular tachycardia (VT), massive LVH (wall thickness ≥30 mm), left ventricular apical aneurysm or an ejection fraction <50% (1).

A modern risk stratification and prevention model may avert most SCD in a general population of predominantly older patients with HCM. With the utilisation of implantable cardioverter devices (ICD) and contemporary management strategies, annual mortality rate was only 0.1% (11).

What about ICD in young athletes?

The ICD sports safety registry studied 328 patients (mean age 33 years) for ICD events over a median follow-up of 31 months and documented no deaths or resuscitated cardiac arrests (12). However, only 60 patients were competitive athletes and only 13 participants had HCM. Primary prevention ICD implants as a strategy to permit participation of at-risk HCM patients in competitive sports is not recommended, given the high shock rates reported.

Uncool exercises in HCM

Intense sports participation can increase arrhythmic risk, supporting consideration for prudent disqualification to prevent catastrophic events on the athletic field. HCM patients are discouraged from sports activities involving accelerated running (sprinting) associated with abrupt increase in heart rate or development/increase in LVOT obstruction, or isometric weight training. Athletic situations that are restrictive and in which it is difficult for participants to terminate independently (should potential cardiovascular symptoms arise) are not recommended.

There is no compelling evidence that participation in regular recreational and noncompetitive aerobic-type physical exercise of moderate intensity itself elevates arrhythmic risk or promotes disease progression in HCM. The Randomized Exploratory Study of Exercise Training in Hypertrophic Cardiomyopathy trial established that 16 weeks of moderate-intensity exercise resulted in a small but significant increase in exercise capacity in older adult patients (mean age 50.4 years) with HCM (13).

These modest increases in cardiorespiratory fitness may be associated with reductions in cardiovascular mortality. Retrospective survey of adult patients with HCM (mean age 49 years) suggested that lifetime vigorous exercise correlated with favourable diastolic function and was not associated with ventricular arrhythmias (15).

Does competitive exercise restriction decrease SCD?

A 1998 study reported on 33 335 screened athletes (mean age 19 years) from the Veneto region of Italy (16) HCM was identified in 22 athletes, all of whom were disqualified from competitive sport and survived over 8 years of follow-up. One athlete with undetected HCM died, compared with 16 HCM-related deaths in the unscreened (non-athlete) general population. While the study was not powered to provide definitive conclusions, early detection of HCM in competitive athletes followed by sports disqualification led to a 73% risk reduction in mortality.

Similarly, 11 168 elite adolescent soccer players (mean age 16.4 years) from the UK underwent cardiovascular screening and were followed for a mean of 10.6 years (17). Five athletes were diagnosed with HCM through screening; three athletes stopped competitive soccer and survived, while two athletes continued playing against medical advice and died during exercise.

HCM screening

Screening for HCM in first-degree and other close family relatives is recommended. Distinctly abnormal 12-lead ECG patterns (ST-T abnormalities, increased voltages, deep Q waves, or pre-excitation) can raise suspicion of HCM in family members, sometimes even before LVH is evident by imaging.

Diagnostic imaging, the preferred strategy for screening family members for HCM phenotypes usually begins at 12 years, extending to 18 to 21 years of age. imaging can be repeated at about 5-year intervals, in the absence of resolution by genetic testing.

In summary, intense competitive sporting activities is still strongly discouraged in young athletes with HCM. Moderate noncompetitive aerobic exercise programs to improve cardiorespiratory fitness, as part of developing healthy lifestyles, are acceptable and in fact, is encouraged. SCD is more common in the young while strokes and heart failure are more common in older patients.

References:

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