Diagnosing Myocardial Infarction in Paced Patients

Primary Diagnostic Challenges

The American Heart Association recommends that ventricular pacing be recognized as a factor that fundamentally obscures the ST-segment and T-wave changes essential for MI diagnosis, due to altered ventricular depolarization creating secondary repolarization abnormalities that mimic or mask ischemic changes in patients with pacemakers 1
The European Society of Cardiology notes that the anticipated morphology in paced rhythms shows QRS-to-ST-segment-T-wave discordance, meaning ST depression naturally occurs in leads with positive QRS complexes and ST elevation occurs in leads with negative QRS complexes, which directly conflicts with the standard STEMI criteria requiring ST elevation ≥0.1-0.25 mV in contiguous leads in the general population 2, 3, 4

The American College of Cardiology recommends applying modified Sgarbossa criteria when paced rhythm is present, rather than standard STEMI criteria, which includes ST-segment elevation ≥5 mm in leads with negative QRS complexes, ST-segment elevation ≥1 mm in leads with positive QRS complexes, and ST-segment depression ≥1 mm in leads V1, V2, or V3 in patients with suspected myocardial infarction 3, 4
The European Heart Journal suggests performing serial ECGs or continuous ST-segment trend monitoring to demonstrate dynamic changes characteristic of acute ischemia, and comparing with previous ECGs when available to identify new changes from baseline paced morphology in patients with pacemakers 1, 3, 4

The American Heart Association recommends maintaining a low threshold for urgent angiography when clinical suspicion is high despite non-diagnostic ECG, as some patients with acute coronary occlusion present without interpretable ST changes, and considering reprogramming the pacemaker to allow evaluation of intrinsic rhythm in patients who are not pacemaker-dependent 1
The European Society of Cardiology notes that the ECG by itself is often insufficient, even in non-paced patients, and this limitation is magnified in paced rhythms, requiring aggressive clinical judgment and low threshold for invasive evaluation rather than reliance on traditional ECG criteria in patients with suspected myocardial infarction 2, 3, 4