A man in his 80s presented to the emergency department after falling in his bathroom. There was no associated loss of consciousness, chest pain, dyspnea, or palpitations. For the past several weeks he had noted generalized weakness and fatigue. His medical history was pertinent for a dual-chamber pacemaker implant 3 years earlier for intermittent symptomatic second-degree atrioventricular (AV) block. Additional comorbidities included hypertension and well-controlled type 1 diabetes with no recent changes in his medications. Initial vital signs showed a systolic blood pressure of 110 mm Hg and results of physical examination demonstrated clear lungs. Results of cardiovascular examination demonstrated no gallops, murmurs, or rubs. Results of electrocardiography performed on admission are shown in Figure 1. His pacemaker was programmed to a DDDR (dual-chamber, rate-adaptive) pacing mode with an AV delay of 300 milliseconds and tracking rates from 60 to 110 pulses per minute. The postventricular atrial refractory period was programmed to 200 milliseconds.