A 65-year-old female with hypertension and hyperlipidemia develops substernal chest pressure with dyspnea. Physical exam is notable for the following:
12-lead electrocardiogram reveals the following:
What is the most likely mechanism of this patient’s dyspnea?a. Pulmonary embolism
Correct Answer: B
The patient presents with a clinical syndrome suggestive of an acute coronary syndrome (ACS). The 12-lead electrocardiogram demonstrates most notably ST segment depressions in the right precordial leads (V1-V3) with prominent R-waves. These findings could suggest a posterior myocardial infarction versus anterior subendocardial ischemia. The presence of prominent R-waves is suspicious for posterior pathologic Qwaves and makes the ST segment depressions more suggestive of infarction. Posterior leads, placed alongside the inferior border of the left scapula (at the same horizontal level as V6), could also be obtained to confirm suspicion of a transmural infarct. Portable echocardiography can be considered to clarify the diagnosis of ST elevation myocardial infarction (STEMI). Early recognition and revascularization are key to managing a posterior STEMI.
The mitral valve has two papillary muscles. The anterolateral papillary muscle receives dual blood supply from the left anterior descending artery and the left circumflex. The posteromedial papillary muscle is supplied only by the posterior descending artery which in most patients branches off the right coronary artery. In posterior myocardial infarctions, attention should be paid to the increased risk of papillary muscle ischemia leading to acute mitral regurgitation. Clinical exam may reveal a holosystolic murmur at the left sternal border with pulmonary edema that corroborates the diagnosis. A murmur, however, may not be heard in up to 50% of cases.