Atrio-Ventricular Nodal Block Associated with Methamphetamine Use

BACKGROUND Methamphetamine use has dramatically increased among young adults worldwide, contributing to a surge in cardiovascular complications. While typically associated with QT prolongation, nonspecific ST-T wave abnormalities, and tachyarrhythmias, high-grade atrio-ventricular (AV) blocks are exceedingly rare. Methamphetamine's sympathomimetic effects usually enhance AV nodal conduction, making bradyarrhythmia an unusual presentation. CASE REPORT A 40-year-old man with methamphetamine dependence presented with dyspnea, bilateral lower-extremity edema, and intermittent chest pain. He admitted to recent methamphetamine use earlier that day and requested detoxification. Initial vital signs revealed sinus tachycardia (123 bpm) and systolic blood pressure in the 130 s to 150 s mmHg. A physical exam showed an S3 gallop, a displaced point of maximal impulse, and a soft systolic murmur. Continuous telemetry monitoring later revealed a 2: 1 AV block. Subsequent electrocardiogram captured a transient 3: 1 AV block preceded by PR prolongation, following a period of sinus tachycardia and coinciding with apnea and oxygen desaturation for both events. Echocardiography showed severe global hypokinesis and a left ventricular ejection fraction (LVEF) of 20%. Cardiac MRI demonstrated severe biventricular dilation and dysfunction, prominent trabeculations, and a suspected LV thrombus without late gadolinium enhancement. Nuclear imaging was negative for amyloidosis. The patient underwent dual-chamber implantable cardioverter-defibrillator (ICD) placement for primary prevention of sudden cardiac death and pacing support and was discharged in stable condition. CONCLUSIONS This case illustrates the potential for methamphetamine toxicity to unmask distal conduction system disease. Early recognition is critical, as such presentations can progress to complete heart block requiring permanent pacing.