Hyperkalemia and atrial pacemakers: what can the electrocardiogram tell you?

A 73-year-old white male with a history of coronary artery disease, congestive heart failure, diabetes mellitus, and pacemaker/implantable cardioverter defibrillator placement presented to the emergency department with a chief complaint of abnormal laboratory tests. On arrival, he complained of nausea, vomiting, diaphoresis, and shortness of breath. Physical examination revealed pulmonary rales and peripheral edema. His presenting and previous ECGs are shown in Figure 1 and Figure 2, respectively. The patient was found to be hyperkalemic secondary to acute renal insufficiency, and after standard emergency department treatment and emergent dialysis, the patient was stabilized and discharged home in 2 days.