Introduction
Sinus node dysfunction (SND) is defined as an insufficient heart rate for physiologic demands. It may manifest as sinus bradycardia or slow heart rate, sinus pauses, sinus arrest with no heartbeat for a period of time or heartbeats generated by an “escape” mechanism from another part of the heart, or chronotropic incompetence, the inability of appropriate heart rate increase to match increased demand.
Tests
A careful history and physical exam should be performed with attention to identifying any potentially reversible contributors to the bradycardia, including medications, ischemia (insufficient blood flow), and autonomic imbalance. Blood tests may be done to check electrolytes and thyroid function. An echocardiogram is often performed to evaluate cardiac function, as cardiac dysfunction both may impact symptoms and management decisions, for example suggesting that consideration should be given to potentially implanting a more complex cardiac device, such as an implantable cardioverter-defibrillator and/or biventricular pacemaker.
Treatment
Implantation of a permanent pacemaker is the mainstay of treatment. A pacemaker is a small electronic device inserted under the skin via a small incision below the collarbone near the shoulder. Wires extend from the device through blood vessels to the heart to stimulate the heart to beat. Pacemaker implantation is generally considered a relatively low risk procedure, with infection, bleeding, and lead dislodgement among the most common complications. Virtually all patients with SND have symptomatic improvement following pacemaker placement. Notably, there is no data clearly documenting survival benefit with pacemaker insertion for patients with SND.
Some patients do have a strong indication to remain on a medication that contributes to symptomatic bradycardia, for example a patient with angina related to coronary artery disease; in this case, continuation of the medication and placement of a permanent pacemaker is appropriate. Notably, patients with vasovagal syncope, who experience symptomatic bradycardia associated with peripheral vasodilation, may not benefit from pacemaker implantation, which is unable to negate the associated blood pressure drop through heart rate support. Patients who have tachycardia-bradycardia syndrome should additionally have their stroke risk carefully assessed to consider appropriateness of anticoagulation therapy.
Melvin Scheinman MD and Cara Pellegrini MD, San Francisco, USA
References
Circulation Cardiology Patient Page “Sick Sinus Syndrome”. http://circ.ahajournals.org/content/108/20/e143.full
Circulation Cardiology Patient Page “Cardiac Pacemaker From the Patient’s Perspective”.http://circ.ahajournals.org/content/105/18/2136.full