Sick Sinus Syndrome (SSS)
Sick sinus syndrome (SSS) occurs from sinoatrial node dysfunction and may manifest in multiple different ways including:
- Tachycardia-bradycardia syndrome (i.e. pauses after converting to sinus rhythm)
- Severe sinus bradycardia
- Sinus pauses/sinus arrest
- Sinoatrial nodal exit block
- Chronotropic incompetence (failure of heart rate to increase during exercise)
Clinical symptoms depend on the mechanism. Severe bradycardia results in dizziness, fatigue, generalized weakness and dyspnea on exertion. Pauses can result in syncope and even sudden death. Sick sinus syndrome is the leading indication for permanent pacemaker implantation. Withholding drugs that suppress the sinoatrial nodal function, if possible, can frequently improve the symptoms and potentially avoid the need for pacemaker insertion. These drugs include beta-blockers, calcium channel blockers amiodarone, digoxin, anti-arrhythmic drugs and some older drugs (reserpine, guanethidine, clonidine, cimetidine, lithium).
The actual cause of sick sinus syndrome is related to replacement of the sinus node with fibrinous tissue. This usually occurs concomitantly with similar changes throughout the entire conduction system including the AV node and increases with age. On rare occasions, ischemia to the SA node or other infiltrative disease can cause SSS.