Sick sinus syndrome


Sick sinus syndrome is a condition in which the sinoatrial node is not able to perform its pacemaker function well enough all the time. Many etiologies can cause the syndrome such as aging, intrinsic defects of the SA node, systemic conditions that also affect the heart (inflammatory diseases, infections), and substances such as toxins or medications (beta-blockers, CC blockers, antiarrhythmic drugs). The majority of cases happen on patients over 65 years old. It may lead to bradycardia episodes, tachycardia episodes, tachycardia-bradycardia episodes or difficulty to adapt the heart rate during exercise.

SIGNS AND SYMPTOMS:

Patients can be asymptomatic or present with intermittent symptoms of low cardiac output (fatigue, lightheadedness, dizziness, pre-syncope, syncope). Patients may also present with episodes of palpitations or chest pain (angina) or dyspnea on exertion. The events rarely occur at the beginning, but their frequency increases as the disease progresses.

There is also an increased risk of thromboembolic events (stroke, peripheral or visceral vascular occlusion).

DIAGNOSIS:

Diagnosis is often difficult and is made based in a correlation of history, symptoms and EKG findings.

Resting EKG and exercise stress test may be used. Exercise stress test may show chronotropic incompetence (inability to reach at least 80% of the maximum predicted HR during exercise)

If resting ECG and stress test do not help, ambulatory ECG monitor (holter) with associated symptom diary for up to 4 weeks may be necessary.

Pharmacological challenges (with atropine and isoproterenol) or electrophysiological studies may also help some cases, although they are not routinely recommended for most cases.

ECG CHANGES:

It can produce a variety of manifestations, such as:

  • Sinus bradycardia
  • Sinus arrest (with or without junctional escape)
  • Sinoatrial exit block
  • Ectopic atrial bradycardia
  • Paroxysmal supraventricular tachycardia
  • Atrial flutter
  • Atrial fibrillation
  • Atrial tachycardia

These arrhythmias can alternate over time.

TREATMENT:

Patients with reversible causes such as medications should have them managed. Patients with persistent symptoms due to bradycardia should receive a permanent pacemaker to reduce symptoms. Dual-chamber pacing is often preferred since there is a risk of progressive dysfunction of the conduction system.

Individuals suffering from tachycardia-bradycardia syndrome with episodes of atrial fibrillation may benefit from oral anticoagulation (check CHA2DS2-VASc and HAS-BLED for considerations).

SOURCES & FURTHER READING:

  1. Gregoratos G. Sick Sinus Syndrome. Circulation. 2003;108:e143-e144.
  2. Ewy GA. Sick Sinus Syndrome. Journal of the American College of Cardiology. Volume 64, Issue 6, August 2014.
  3. Adan V., Crown LA. Diagnosis and Treatment of Sick Sinus Syndrome. Am Fam Physician. 2003 Apr 15;67(8):1725-1732.
  4. Vavetsi S. et al. Consecutive administration of atropine and isoproterenol for the evaluation of asymptomatic sinus bradycardia Europace (2008) 10 (10): 1176-1181.
  5. Brubaker PH, Kitzman DW. Chronotropic Incompetence: Causes, Consequences, and Management. Circulation. 2011 Mar 8; 123(9): 1010–1020.