Short QT syndrome is characterized by consistently short QT intervals, usually below 300 msec, which does not lengthen with bradycardia. There is a propensity for sudden cardiac death and atrial fibrillation. Family history of sudden death may be forthcoming. Electrophysiologically short QT syndrome is characterized by short refractory periods and inducible VF (ventricular fibrillation) at EP (electrophysiological) study.

Shortening of QT interval can occur in tachycardia, hyperthermia and hypercalcemia. Digoxin can also shorten the QT interval. These should be excluded before considering a diagnosis of short QT syndrome.

Treatment options for short QT syndrome are limited. Some have reported lengthening of QT interval with quinidine. Most patients with short QT syndrome and a risk of sudden cardiac death get an ICD (implantable cardioverter defibrillator) implanted.

In another article in the same issue of the journal, Thoppil et al describe the successful treatment of post myocardial infarction electrical storm by targeting the Purkine potentials [Thoppil PS et al. Indian Pacing Electrophysiol J. 2008; 8: 298-303].

Traditionally it is thought that sympathoadrenergic system activation is compensatory in heart failure. This is true in acute heart failure. But in chronic heart failure, sympathoadrenergic system becomes counter productive and maladaptive. It increases the afterload and myocardial cell necrosis as well down regulation of beta receptors. This is why betablockers have been considered in the treatment of chronic heart failure. Studies have shown that if you treat 100 patients with heart failure, it will prevent 4 deaths and 4 hospitalisations. Carvedilol, bisoprolol and metoprolol succinate have been shown to improve the survival in heart failure in various studies, but bucindolol failed to do so in the BEST trial. Even though COMET trial showed superiority of carvedilol over metoprolol tartarate, there were several criticisms about the methodology of the trial questioning whether it was a fair comparison. Metoporolol tartarate was a short acting preparation compared to the metoprolol succinate extended release preparation which was shown to be useful in heart failure earlier. Hence the superiority of carvedilolol over metoporlol in heart failure is not yet fully accepted. Betablockers are indicated in all patients with symptomatic heart failure. But they have to be started only only when they are stable and not on inotropic support or intravenous diuretics.

What is the role for devices in heart failure management?

All patients need optimal pharmacological therapy and life style modifications. But in a small subset, there is a definite role for devices. Ventricular tachycardia in a scar of old myocardial infarction may necessitate the implantation of an implantable cardioverter defibrillator (ICD). Hypotensive ventricular tachycardia in heart failure is an important cause for sudden cardiac death (SCD) as it can degenerate into ventricular fibrillation in a short time. Those who have survived a SCD are those at a higher risk of recurrence and benefit maximum with an ICD implantation. ICD improves the life expectancy by 6 years in these high risk individuals.

Intraventricular dyssynchrony in the presence of severe left ventricular dysfunction is an important indication for cardiac resynchronization therapy (CRT). Delay between the contractions of the septum and the lateral left ventricular wall causes reduced left ventricular stroke volume. The important surrogate of ventricular dyssynchrony is an increased QRS duration. In CRT, septum and lateral left ventricular wall contracts simultaneously producing improvement in the left ventricular stroke volume. This is achieved by pacing the lateral wall of the left ventricle through a coronary vein along with right ventricular endocardial pacing. CRT improves the symptomatic status and survival of heart failure patients with left ventricular dyssynchrony. But still there is a 30% non-responder rate of patients who do not respond to CRT.

What is the implication of Starlings law of the heart?

It is the volume of the heart which determines the force of contraction. Increase in muscle fibre length increases the force of contraction upto a certain level. Beyond this level, further increase in the volume of the heart produces deterioration of cardiac output. 2.2 microns is the critical sarcomere length at which there is optimal force of contraction, due to good overlap of actin and myosin filaments.