Evolving Myocardial Infarction

Abstract

Scenario: This electrocardiogram (ECG) was obtained from a 66-year-old male patient being admitted to the coronary care unit (CCU) as a “direct admit.” The patient had gone to an urgent care center 1 hour earlier with complaints of weakness and shortness of breath. Based on the symptoms and ECG (similar to the one below), he was sent via ambulance to the CCU. Past medical history includes hypertension and hypercholesterolemia. The patient stated he has not been feeling well for about 3 weeks, and was especially “sick” this day. He decided to go to work but a coworker urged him to get medical help, and at the end of his shift he went to the urgent care center.Acute inferior myocardial infarction (MI) with posterior wall involvement, nonspecific intraventricular conduction delay that may be related to ischemia or incomplete right bundle branch block, and accelerated junctional rhythm.Acute MI in the inferior part of the heart is identified by ST segment elevation in the inferior leads II, III, and aVF. The ST segment elevation in lead II is less than 1 millimeter, but its shape is abnormal and suggests acute ischemia. Importantly, because this patient delayed seeking treatment, it is likely these changes represent evolutionary ST segment changes of an MI and indicate necrosis has occurred. This is further supported by the Q waves seen in these 3 leads. Q waves greater than 30 milliseconds in leads II and aVF indicated “old” inferior infarction.The ST segment depression seen in the precordial leads V4 through V6 are reciprocal changes that may occur with inferior wall MI. Worth noting is the ST segment depression and delayed R wave in leads V1 and V2,- which suggest posterior wall injury. Because ECG leads are not placed on the posterior thorax for a standard 12-lead ECG, clinicians cannot diagnose posterior wall infarction using ST segment elevation criteria. Rather, one would see ST segment depression in the lead opposite the posterior wall (V1 to V3). The R wave in leads V1 and V2 are wide and also indicate “old” MI in the posterior wall. Criteria for this diagnosis is an R > 40 milliseconds in V1 and > 50 milliseconds in V2. Accelerated junctional rhythm is present and P waves can be appreciated in the T waves in leads V2 to V4.This patient’s condition and ECG indicate an acute MI. He likely exceeded the time frame for reperfusion with primary percutaneous coronary intervention or thrombolytics because the time from symptom onset to presentation should be less than 90 minutes. Immediate interventions include bedside ECG monitoring, intravenous access, oxygen, nitrates, analgesia for chest pain, aspirin, serum biomarker, and a beta blocker. Be prepared for lethal cardiac arrhythmias given the ischemic conditions and the lack of sinus rhythm.