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Hypertrophic Cardiomyopathy: Prevention of Sudden Death

Dr. P. Elliott
London, United Kingdom

K. Schwartz (Paris, France). Molecular diagnosis of the disease–its value for risk stratification
Hypertrophic cardiomyopathy (HCM) is defined by the presence of left ventricular hypertrophy in the absence of any haemodynamic or systemic cause. The majority of adult patients with HCM have mutations in one of at least 12 genes that encode proteins of the cardiac sarcomere. In a recent analysis of 197 patients, 63% of patients carried a sarcomeric gene mutation; the most frequently affected were cardiac myosin binding protein C (42%) and ß-myosin heavy chain (40%).
Some genetic studies in HCM suggest that particular gene abnormalities are associated with specific clinical phenotypes. In particular, families with cardiac troponin-T mutations have mild hypertrophy and a high risk of sudden death whereas myosin binding protein C mutations are associated with late-onset disease. More recently, however, detailed family studies have shown that the expression of these mutations is heterogeneous with examples of severe hypertrophy in the case of troponin T and childhood disease in myosin binding protein C.
Dr. Schwartz highlighted some of the impediments to the use of genetic testing in clinical risk stratification in HCM: many mutations are novel and therefore have no data on prognosis; HCM is characterised by intra- and inter-familial variation; and published data are derived from small numbers of families. Moreover, many described mutations are probably non-pathogenic sequence variations.

Conclusions
Detailed genetic analysis of families with HCM has shown that there are trends towards particular phenotypes in association with specific genetic mutations. However, the confounding effect of variable clinical expression limits the use of genotyping in the assessment of sudden death risk.

G. Breithardt (Münster, Germany). Role of electrophysiological testing for risk stratification.
A high proportion of patients with HCM have non-sustained ventricular arrhythmias, but the frequency of sudden cardiac death in such individuals is relatively low. Current ACC/ESC consensus guidelines suggest that invasive electrophysiological studies (programmed ventricular stimulation) should not be performed in patients with HCM for the purposes of stratifying risk. Professor Breithardt reviewed the literature on which this recommendation is based. Many small studies have demonstrated little additional value of EPS in HCM. A single study of 230 patients indicated that EPS identified a cohort of patients with a history of ventricular arrhythmia and syncope; however, this study failed to examine the incidence of provocable ventricular arrhythmias in a comparative control group. Several studies have demonstrated slowing and fragmentation of the paced electrogram; this has been interpreted as the electrical manifestation of the pathological substrate in HCM–myocyte disarray. New unpublished data on the predictive value of ECG fractionation were presented–the study is consistent with previously published data showing increased fractionation in patients that have experienced a VF arrest. The value of the technique in patients that have not had an event (the majority of patients) remains to be determined.

Conclusion
There are insufficient data to support the use of EPS in clinical risk stratification in patients with HCM.

 T. Wichter (Münster, Germany). Strategies for sudden death prophylaxis
Sudden cardiac death is a relatively uncommon event in patients with HCM, but fortuitous clinical observation has identified a number of potential triggers for ventricular arrhythmia; these include supraventricular arrhythmia, abnormal blood pressure responses, myocardial ischaemia, and outflow tract obstruction.
Irrespective of the presence of identifiable triggers, all patients with HCM should be assessed for the presence of clinical features that are associated with an increased risk of sudden death. Patients with a cardiac arrest have a 40% chance of recurrence in the next four years and should receive prophylactic antiarrhythmic therapy. Risk factors in patients without a history of syncopal ventricular arrhythmia include non-sustained ventricular tachycardia on Holter monitoring, a failure of blood pressure to rise (or a fall) during upright exercise, severe left ventricular hypertrophy (wall thickness ≥30 mm), family history of sudden death, and unexplained syncope. Dr Wichter demonstrated that in spite of the low predictive value of individual risk factors, their co-existence in the same patient is associated with a substantially increased risk of sudden death.

Conclusion
All patients with HCM should undergo clinical risk stratification; those with multiple risk factors should be considered for ICD therapy. In uncertain cases, the power of the individual risk factors should guide treatment.

P Spirito (Genoa, Italy). Primary and secondary prevention with implantable cardioverter-defibrillators.
Evidence from multi-centre studies suggests that patients with cardiac disease and a high risk of sudden cardiac death are best treated with an implantable cardioverter defibrillator (ICD). Professor Spirito reviewed evidence from an Italian-American registry; in this study the annual appropriate ICD shock rate in patients with a history of cardiac arrest was 11%; in high risk patients without such a history it was 4.5%. Fourteen per cent of patients had device related complications, mostly relating to lead failures. Professor Spirito suggested that such complications might be reduced with the use of single lead systems rather that dual chamber devices, but acknowledged that the high risk of atrial arrhythmias in some patients means that dual chamber devices may help to reduce inappropriate shocks. Longitudinal data from single and multicentre studies will help to clarify the most appropriate devices and programming parameters in patients with HCM

Conclusion
ICDs are an effective in preventing sudden cardiac death. However, the fact that many patients with HCM are young and will have a device for many years, means that further research on who should receive them, and in what configuration, is required.

Professor William McKenna (London, United Kingdom). Hypertrophic Cardiomyopathy and the risk of sudden death in athletes.
Deaths in athletes are uncommon, but the high profile of successful young sportsmen and women means that they have high emotional impact in the public mind; HCM accounts for approximately 50% of all such deaths. Athletic training causes reversible physiological changes in cardiac structure and function that can mimic some of the features seen in patients with HCM. Professor McKenna reviewed the characteristic ECG and echocardiographic changes seen in young athletes and contrasted them with those seen in HCM. The most common ECG abnormalities seen in athletes are sinus bradycardia and increased QRS voltage, in the absence of significant repolarisation abnormalities. In contrast, patients with HCM frequently have left axis deviation, pathological Q-waves and marked ST-T wave abnormalities–isolated voltage criteria for LVH are rarely seen in HCM. Similarly, the degree of hypertrophy seen on echocardiography in most patients with HCM is rarely if ever seen in athletes; the presence of diastolic abnormalities and small ventricular cavities also suggests HCM rather than athletic adaptation. Guidelines on exercise in patients with HCM were also reviewed. Professor McKenna considered the paradox of the current guidelines that advise total avoidance of exercise with the fact that up to two thirds of HCM deaths occur at rest or during minimal exertion–a review of European guidelines is pending.

Conclusion
The grey zone between the physiological changes seen in the athlete’s heart and HCM is in reality very small.

Autor: Dr. P. Elliott

Fuente: European Society of Cardiology

Ultima actualizacion: 2 DE OCTUBRE DE 2004

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