2017 Resarch Forum

RBFM: C-1

Applicant: Verna L Marquez MD Principal Investigator: Tana Parker MD

Posterior myocardial infarction: the blind spot in the heart Tana Parker MD, Verna L Marquez MD, Corinne Verghese MS III

INTRODUCTION: Posterior myocardial infarction (PMI) is a diagnosis often missed. Standard 12 lead electrocardiogram does not image the posterior wall, known as “ the blind spot of the heart.” Specific indicators of PMI on 12 lead ECG have been studied, but are not widely known by physicians. The addition of posterior ECG leads (V7-V9) improves diagnostic sensitivity, though not routinely used in clinical practice. Delays in the timely revascularization of these patients can occur, increasing morbidity and mortality. PURPOSE: A 52-year-old Hispanic male (hypertension, hypercholesterolemia) presented with chest pain for over 12 hours. The pain started acutely (jaw radiating to mid sternum and left upper arm) during yard work. It was pressure-like, associated with shortness of breath, and partially relieved with rest. Initial 12L ECG showed normal sinus rhythm (probable LAE); troponin was 0.116. The patient was admitted for management of NSTEMI. Pain persisted over the next few days, troponin levels trended up, reaching 20.7. Repeat 12-lead ECG showed abnormal R wave progression with “no evidence of acute infarction”. The patient was transferred to an outside facility, left heart catheterization revealed 90% stenosis in the second obtuse marginal (OM2) branch of the left circumflex artery. Angioplasty with stent placement was performed. DISCUSSION: Isolated PMI often do not receive appropriate reperfusion treatment (rarity and lack of classical ST- elevation on 12L ECG). There are no unique symptoms that would indicate PMI presence; occurrence of only 3-7% makes it difficult to detect. Our patient presented with symptoms consistent with Acute Coronary Syndrome, and routine work up led us to treat him for NSTEMI initially. The posterior wall is mainly supplied by the left circumflex artery, the least commonly infarcted coronary artery. Research has shown that ST-segment depression in the precordial leads is one of the more specific indicators of true PMI on standard 12-lead ECG. This finding represents the inverse of what would be seen in the posterior leads (ST elevation of V7-V9). Additional criteria for PMI include prominent R wave, R/S wave ratio >1.0 in lead V2, prominent upright T wave, and co-existing acute inferior and/or lateral MI. In our patient, an initial diagnosis of NSTEMI was made, given ECG findings. In retrospect, initial ECG’s failed to demonstrate the above indicators for PMI as well. Subsequent ECGs were obtained due to persistence of chest and jaw pain and up-trending Troponin: prominent R waves with R/S wave ratio >1.0 in lead V2 were noted. CONCLUSION: Lack of evidence of STEMI on 12-Lead ECG, and no reported unique symptoms to indicate isolated PMI makes the diagnosis difficult. Physician familiarity with specific indicators that can be found on 12 lead ECG, and addition of posterior leads V7-V9 will increase sensitivity in diagnosing this condition.