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Assessing the risk of sudden cardiac death in a patient with hypertrophic cardiomyopathy

2004; BMJ; Volume: 90; Issue: 5 Linguagem: Inglês

10.1136/hrt.2003.020529

2053-5864

M. Frenneaux,

Cardiovascular Function and Risk Factors

ypertrophic cardiomyopathy (HCM) is an inherited disease (or perhaps more correctly, in view of its genetic heterogeneity it should be considered as a group of diseases).It exhibits pronounced phenotypic variability, including extent of hypertrophy, presence and severity of symptoms, and natural history.The early literature, derived from a small group of tertiary referral centres, suggested that it was a relatively uncommon but extremely malignant disorder, with annual mortality rates of 2-4% in adults and 6% in adolescents and children, the majority of these deaths being sudden.w1 More recently it has become apparent that HCM is in fact a common disorder, with a prevalence estimated from echocardiographic population screening of 0.2%.w2 However, it is also now clear that HCM is overall much more benign than these earlier studies had suggested, with an annual mortality rate in large unselected series of approximately 1%, at least half of these deaths being sudden, and the remainder principally caused by heart failure and stroke. 1 Nevertheless, HCM is an important cause of sudden cardiac death (SCD); in most (but not all) series it is the most important cause of SCD in young adults and in athletes. 2Many of these deaths occur in patients with minimal or no symptoms (indeed the diagnosis of HCM is sadly often made first at the postmortem examination, following the sudden cardiac death of a previously healthy individual).With the development of automatic implantable cardioverterdefibrillators (AICDs), effective preventive therapy is now available.The challenge is to distinguish high risk from low risk patients with HCM in order to target prophylactic therapies (AICD ¡ amiodarone) to those at risk.The need for such risk stratification is more than simply one of health economics.Compared with patients with coronary artery disease who undergo AICD implantation, HCM patients who are implanted are much younger, and have a much lower annual event (or AICD discharge) rate.It is likely that their lifetime risk of serious AICD related complications will be high. 3 SUDDEN CARDIAC DEATH IN HCM: TRIGGER VERSUS SUBSTRATE cThe terminal event in patients who die suddenly from HCM is probably most commonly ventricular fibrillation (VF) (fig 1).Data from HCM patients who have received appropriate AICD discharges have shown that these discharges have occurred in response to sustained monomorphic ventricular tachycardia (VT), VT leading to VF or unheralded VF. 3 However, even in those patients in whom an AICD has been implanted because of a documented resuscitated episode of VT or VF, the annual rate of appropriate AICD discharge is only 11%. 3 This leads to the conclusion that the development of a malignant arrhythmia requires the coalescence of triggers at a critical moment in time as well as a pro-arrhythmic substrate.The substrate is most likely the presence of extensive myocyte disarray and/or fibrosis.These changes probably predispose to re-entrant ventricular arrhythmias.Myocyte disarray is more extensive at postmortem examination in patients with HCM who die suddenly.w3 Similarly, troponin T mutations, generally associated with a high risk of sudden cardiac death, are associated with minor left ventricular hypertrophy, but extensive myocyte disarray.w4 Various triggers are postulated to be involved in the development of malignant ventricular tachyarrhythmia in HCM.These include myocardial ischaemia, hypotension caused by inappropriate vasodilation or by exacerbation of outflow tract obstruction, altered autonomic tone, rapid atrioventricular conduction along an accessory pathway, conduction system disease, and paroxysmal atrial fibrillation.AICD interrogations and/or Holter recordings have demonstrated that the development of VT or VF may be preceded by sinus tachycardia or bradycardia, by AV block, or by pronounced ST segment changes.w5 Observations such as these support the concept that ventricular arrhythmia may not be a primary event in many cases.