Cardiac Rhythms and Arrhythmias

node as the region responsible for activation of the heart.1 Laslett first suggested sinus node dysfunction as a cause of bradycardia in 1909, and during the 1950s and 1960s Short, Ferrer, Lown, and others described the clinical spectrum of sinus node dysfunction that is commonly called the “sick sinus syndrome resting sinus bradycardia.”2-5 Sinus node dysfunction can have multiple electrocardiographic manifestations including sinus pauses, the bradycardia-tachycardia syndrome, and inappropriate sinus node response to exercise (chronotropic incompetence).