21 ST Depression in AVL Differentiates Inferior ST Elevation Myocardial Infarction From Benign Causes of Inferior ST Elevation

Abstract

Background: ST segment elevation in leads II, III, and/or aVF due to inferior ST elevation acute myocardial infarction may be misdiagnosed as pericarditis or as benign early repolarization. Conversely, these non life-threatening etiologies of ST elevation may be confused for inferior STEMI. Study Objectives: We sought to determine if the presence of any (reciprocal) ST-segment depression in lead aVL would differentiate inferior STEMI from these less serious etiologies of ST elevation. Methods: Retrospective study of 3 populations with ST elevation in inferior leads: group 1 with inferior STEMI; group 2 with pericarditis, and group 3 with inferior ST elevation due to early repolarization. For group 1, we searched the cardiac catheterization laboratory database at Hennepin County Medical Center for all cases coded as acute Inferior STEMI from January 2002 through March 2008. For group 2, we searched for all patients with a discharge diagnosis of pericarditis from 1996 to 2010 who presented to the ED with chest pain and ≥ 1 mm of ST elevation in ≥ 1 inferior lead. For group 3, we assessed the resting baseline ECGs of 5489 asymptomatic patients from the Finnish Health 2000 survey (44% men, mean age 50.5 years) and selected those with at least 1 mm of ST elevation in 2 consecutive inferior leads as measured by both custom software and visual analysis. All cases were reviewed and the presenting ECG, as well as the first ECG that was used for diagnosis of acute STEMI, were analyzed. ST segments were measured at the J-point relative to the PR segment. Results: Group 1: There were 156 patients with inferior STEMI. Whether or not they met reperfusion criteria (n=134, 86%), 155 had some amount of ST depression in lead aVL (sensitivity 99%; 95% CI: 96%-100%). Group 2: there were 67 ED pericarditis patients with chest pain; 23 were excluded for absence of ST elevation and 5 were excluded because the medical record could not be found, leaving 39; all rule out for acute myocardial infarction. All 39 had some inferior ST elevation and 19 met inferior reperfusion criteria (1 mm of ST elevation in 2 consecutive inferior leads); none of the 39 had any ST-segment depression in lead aVL, or any other lead (specificity, 100%; 95% CI: 89%-100%). Group 3: there were 71 patients who met inferior reperfusion criteria; after excluding patients with a paced rhythm (2), left bundle branch block (2) and Wolff Parkinson White Syndrome (1), none of 66 had any ST depression in lead aVL (specificity, 100%; 95% CI: 93%-100%). Overall diagnostic performance of STD in aVL for STEMI versus no-acute myocardial infarction were sensitivity 99% (95% CI: 96%-100%) and specificity 100% (95% CI: 95.6%-100%). Limitations: We did not include cases with left ventricular hypertrophy by limb lead voltage; these are known to often have baseline reciprocal STD in lead aVL. Conclusion: When there is inferior ST segment elevation in the presence of normal conduction (no left bundle branch block, paced rhythm, LVH, or Wolff Parkinson White Syndrome), the presence of any ST depression in lead aVL is highly sensitive and specific for inferior STEMI versus early repolarization or pericarditis.