SICK SINUS SYNDROME

(Tachycardia bradycardia Syndrome, SSS)

DEFINITION AND AETIOLOGY

SSS includes conditions of sinus arrest, sinoatrial exit block, persistent sinus bradycardia combined with tachycardia due to paroxysmal atrial or junctional tachycardia, atrial fibrillation or flutter. Coronary atherosclerosis is an uncommon cause. Coronary arteriosclerosis with or without hypertension, rheumatic or diphtheritic heart disease; thyrotoxicosis; myocarditis; drugs like Digitalis, Quinidine, Procainamide, Propranolol, Verapamil; Congenital heart disease, cardiomyopathy; Chagas’ disease, amyloidosis, sacoidosis may be present in association with SSS.

MECHANISM

This is due to abnormal pace-maker function of SA node or defective conduction of it from SA node to AV node as a result of patchy fibrosis of sinus node, atrium, AV node or His- Purkinjee system.

CLINICAL FEATURES OF SICK SINUS SYNDROME

This occurs most commonly in elderly patients. From time to time there may be bradycardia followed by tachycardia. The bradycardia is due to sinus bradycardia, sinus standstill, sinus arrest, sinoatrial block, AV junctional escape rhythm and ectopic atrial impulse. There may be long pause following atrial premature beat. Prolonged sinus node recovery time is determined by atrial pacing. In presence of chronic atrial fibrillation or recurrent repetitive atrial fibrillation there may be slow ventricular rate, sometimes preceeded or followed by sinus bradycardia, sinus arrest or SA block. There may be failure of restoration of sinus rhythm following cardioversion or combined AV-block with interventricular block. Tachycardia is due to paroxysmal supraventricular tachycardia, atrial fibrillation or flutter, etc. Patient may not have any symptom at all. There may be syncope, near syncope and chest pain or there may be palpitation. In some, there may be anginal pain, heart failure or confusion, palpitation.

Atropine test

IV Atropine 0.5 mg normally increases the heart rate to 100 beats/minute or above. But here it will never be more than 90 beats per minute even after 1 mg IV. Also resistant to Isoproterenol.

Exercise test

Even after moderate exercise the heart rate is never more than 110 per minute.

TREATMENT

Pharmocologic therapy is difficult. Sinus slowing is preventedby inserting an artificial pace-maker. Most symptomatic patients will require permanent pacing. Dual chamber pacing is better because ventricular pacing is usually associated with subsequent atrial fibrillation and AV block.

Treatment for tachyarrhythmia by pharmacologic agents is often difficult without prior pacing as digoxin and other antiarrhythmic drugs may exacerbate bradycardia. It should also be remembered that symptomatic relief following pacing is not always consistent.

.SICK SINUS SYNDROME.

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