17 Apr, 12 | by BMJ Group
Fabrice Muamba was discharged from hospital yesterday, after he collapsed during a football match due to a cardiac arrest on 17 March. His collapse reminds us of the sensational nature of sudden unexpected death in a young person, not least an elite athlete. Sudden cardiac death (SCD) is estimated to be responsible for 60 000 deaths per year in the United Kingdom with the majority in people over 35 years of age, and with ischaemic heart disease the commonest aetiology in this age group. The disease profile in those younger than 35 is different and more common causes here include cardiomyopathies (such as hypertrophic cardiomyopathy (HCM) and arrhythmogenic right ventricular cardiomyopathy (ARVC)), inflammatory disorders (such as sarcoidosis, myocarditis), congenital heart disease, drug causes, and arrhythmia syndromes (such as Wolff-Parkinson-White syndrome, Long QT syndrome (LQTS), and Brugada syndrome). Death during physical activity is a feature of some of these conditions (eg. HCM, LQTS 1).
The investigation of a cardiac arrest survivor requires screening for electrolytes and toxicological (including QT prolonging drugs) screens as well as ruling out microbiological and autoimmune causes as necessary (for example Coxsackie B in myocarditis). The 12-lead ECG must be studied closely. In addition to ST elevation and heart block, notable findings include a slurred QRS complex (pre-excitation), prolonged QT interval, and the distinctive ST elevation of Brugada syndrome.
Pre-morbid ECGs should be sought, as signs associated with arrhythmia syndromes can be transient. Ambulatory monitoring and exercise ECGs may reveal intermittent abnormalities. The signal averaged ECG is another useful tool, created by further filtering the ECG and enhancing the latter portion of the QRS complex to look for late potentials that can support a diagnosis of ARVC.
Transthoracic echocardiography is the first line modality in assessing cardiac structure but magnetic resonance scanning provides powerful diagnostic capability (for detecting subtle right ventricular wall motion abnormalities and fibrofatty replacement in ARVC for example). Invasive investigations include coronary angiography, cardiac biopsy, and cardiac electrophysiological studies as necessary.
If all the above investigations are negative, doctors should be highly suspicious of the ion channelopathies, so called as the main pathological feature is defective ion channels causing activation-repolarisation abnormalities within the heart. They include LQTS, short QT syndrome, Brugada syndrome and catecholaminergic polymorphic ventricular tachycardia (CPVT). The patient may have a history of palpitations or syncope and a family history of sudden unexpected death, and the circumstances of death may provide a clue (diving/exertion in LQT 1, auditory triggers in LQT 2 and sleep in LQT 3 and Brugada syndrome). Drug provocation testing may bring out ECG patterns associated with LQT 1 (adrenaline) or Brugada (ajmaline or flecainide).
The hereditary nature of several of the conditions causing SCD makes the screening of family members an essential undertaking. In addition to cardiac investigations, genetic testing has a role here, and can be of diagnostic and prognostic value, by informing treatment decisions in LQTS, for example.
In the absence of a reversible cause, the secondary prevention of cardiac arrest would require an implantable an implantable cardioverter defibrillator. Beta blockade and other anti-adrenergic measures (left cervical sympathectomy) can effectively manage arrhythmia in LQTS and CPVT. Lifestyle modifications, such as avoiding exercise and certain drugs, may be necessary.
The death of an athlete is rare, with an incidence of between 1 in 50 000 to 1 in 200 000 a year, and screening elite athletes for such conditions is not compulsory in the United Kingdom. Italy is the only country where pre-participation screening of competitive athletes is required by law. A nationwide programme was launched in 1982 and reported to significantly reduce mortality. The price has been excluding large numbers of otherwise healthy individuals who may have never had a problem. Difficulty arises from racial variation and non-specific ECG findings – at which point is the pathological threshold crossed? Serious discussion is required, however, as some highly trained individuals may secretly harbour a ticking time bomb.
Justine Bharamato is a clinical research associate at UCL and the Heart Hospital, UCLH Foundation Trust. She holds a clinical research training fellowship awarded by Heart Research UK. She is doing a PhD in Autonomic Modulation in Brugada Syndrome.