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.

Causes

Coronary artery disease: 80%

CAD is by and large, the most important cause of SCD.

Cardiomyopathy: 15%

Left ventricular hypertrophy is a strong independent risk factor for SCD. ARVD is being recognized as an important cause of exercise induced SCD.

Others: 5%

Aortic stenosis

Channelopathies – Long QT syndrome, Brugada syndrome, Short QT syndrome

Coronary anomalies – Anomalous origin of left coronary artery from pulmonary artery (ALCAPA)

Aortic valve endocarditis

Myocarditis

Sarcoidosis

Operated Tetralogy of Fallot

Predictors of SCD

1. LV ejection fraction

LV ejection fraction < 30% is the single most powerful independent predictor of SCD. The incidence of SCD increases as the ejection fraction decreases, but the proportion of SCD to all deaths due increase in deaths due to pump failure.

2. NYHA class is similar to LV ejection fraction, but patients may shift from one class to another frequently.

3. Non sustained ventricular tachycardia (NSVT) is a predictor in a small group of patients

4. Signal averaged ECG – Late potential predict SCD. It has a high negative predictive value. It is not useful in patients with bundle branch block.

5. QRS duration – higher QRS duration is an indicator.

6. T wave alternans – very good marker of SCD in ischemic and non-ischemic cardiomyopathy.

7. QT dispersion is the variability in QT interval between the leads – does not give any meaningful prognostic information.

8. QT interval variability is the variability in QT interval during the period of ECG recording – predictive of SCD, but more studies are needed.

9. Barorecetor sensitivity – sensitivity of change in heart rate with change in blood pressure.

10. Heart rate variability in short term and long term – short term heart rate variability is a predictor of SCD while long term heart rate variability is a predictor of total mortality.

11. Hear rate turbulence – transient slowing of heart rate after the post ventricular ectopic beat followed by an acceleration. Heart rate turbulence is an important predictor of SCD.

12. Heart rate recovery following a treadmill exercise test is a predictor of SCD.

13. Inducible ventricular tachycardia on EP study

Problems with preventive strategy: 80% occurs at home, only 15% occur in streets or in public places

Risk stratification is easy at individual level, but not at a community level

Reluctance to start resuscitation due to unwillingness to give mouth to mouth breathing and also the worry about legal problems in case of unwitnessed death

Chain of survival was described in 1991: early access to Emergency Medical Service, early CPR, early defibrillation, early ACLS

Markers of futility:

Unwitnessed cardiac arrest – almost no survival

Response time more than 8 min – survival < 0.3%

If the initial rhythm is asystole or pulseless electrical activity

AED should be available in airports, convention centres, sporting arenas, casinos, shopping malls and large office building.

Public access to defibrillation trial: NEJM 2004; 20,000 Volunteers, 1600 AEDs, 239 episodes of SCD. Only those with bystander CPR successful. Prevented 16 extra deaths at a huge expense

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.