Abnormality of sinoatrial node (SAN) function or
The syndrome may be acquired or congenital.
Between 2 and 6% of cases are familial and inherited as an autosomal
Sinoatrial node depolarization is irregular or
fails, resulting in bradycardia or sinus arrest. In the presence of sinus
arrest or extreme sinus bradycardia, a junctional escape rhythm may develop.
Irregular depolarization of the sinus node, however, causes paroxysms of
tachycardia (supraventricular tachycardia/atrial fibrillation) between
episodes of bradycardia. Acquired causes include surgical trauma, fibrous,
inflammatory, or degenerative infiltration of the sinus node and ischemia.
Clinical history, ECG with or without Holter monitoring.
May remain asymptomatic. Symptoms include
dizziness, syncope, palpitations, and chest pain. A 12-lead ECG should be
examined for sinus bradycardia, sinus arrest, and junctional escape rhythm;
however, a single recording may appear normal. Continuous monitoring may be
necessary to demonstrate alternating episodes of bradycardia and
tachycardia. Episodes of tachycardia may be controlled with digoxin or beta
blockade. If beta blockade is used, cardiac pacing (dual-mode, dual-pacing,
dual-sensing) usually becomes necessary to prevent profound bradycardia.
Acquired sick sinus syndrome may be caused by lithium and carbamazepine
Obtain a complete medical history of
frequency of syncope/palpitations, drug history, and pacemaker details. Attempt to define
etiology of the sick sinus syndrome in the individual patient may be impossible. If the
syndrome is newly diagnosed, consider temporary pacing. Cardiovascular
assessment: review recent ECG(s). Further investigations must be carried on
medical grounds. Metabolic considerations: check serum electrolytes.
Decreased systemic vascular resistance
caused by volatile agents or major regional blockade may result in profound
hypotension because a reflex tachycardia is not generated. Stroke volume is
the primary determinant of cardiac output, therefore myocardial
contractility and optimal filling pressures should be maintained. Complete
atrioventricular block during anesthesia is also reported.
Atropine will not treat the
bradycardia. Chronotropic agents have minimal effect on heart rate.
Burt D: The sick sinus syndrome: A complication during anesthesia.
Iinuma Y, Maruyama K, Hara K. Complete atrioventricular block during anesthesia in a
patient with sick sinus syndrome under atrial pacing. J Anesth 19(1):92, 2005.
Underwood S, Glynn C: Sick sinus syndrome manifest after spinal anesthesia.
Zipes DP. Specific arrhythmias: diagnosis and treatment, in Braunwald E
(ed): Heart Disease: A Textbook of Cardiovascular Medicine. 5th ed. Philadelphia, WB Saunders, 1996, pp.