A 52-year-old man with no past medical history presented to the ED with six days of chest pain. He had been seen in the ED two days earlier and sent home because his serial troponins were negative with four days of pain, which "ruled out coronary disease," according to the account of his first visit.
A more detailed history revealed that he actually had had intermittent pain with two to three episodes per day, each lasting two to five minutes, but that night, it had been happening for more than an hour. He reported no syncope, shortness of breath, nausea, sweating, or other complaints.
His vital signs were normal except for a pulse of 110 bpm, and his exam was otherwise normal.
The initial differential diagnosis was tachydysrhythmia, electrolyte abnormality, pulmonary embolism, and acute coronary syndrome.
This was his initial ECG.
The computer read this as sinus tachycardia, an inferior infarct, possibly acute, with a lateral injury pattern. Do you agree with the computer? What should you do next?
The computer read was correct but incomplete. There was some ST elevation in lead II, V6, and possibly a bit in I and aVL. There was also evidence of a posterior MI with ST depression and relatively tall R waves in V1-V4. These findings were most likely due to a posterolateral STEMI. The ECGs from his visit two days earlier were checked and deemed to be normal, but they were done while the patient was free of pain.
The patient's troponin I was elevated at 2.7 (99% URL <0.030: troponin I immunoassay, Abbott Laboratories). He went to the cath lab, and had a 100% proximal left circumflex artery occlusion. This case was a classic example of new-onset angina with a normal ECG and troponin followed by an acute MI a few days later. A good history is the key to picking up unstable angina before the MI because the ECG and troponin rarely will. A repeat troponin was 365.
The ECG is much less sensitive when the patient is free of pain, as in unstable angina. Troponins should be expected to stay normal with episodic chest pain lasting less than 15-30 minutes, as in unstable angina. It is really the history alone that makes the diagnosis of unstable angina, so take a good one!
Untreated unstable angina often leads to MI (or death) in the following week or two.
Posterior MI is considered a STEMI equivalent. Other STEMI equivalents include de Winter's pattern, ROSC, shark fin pattern, and Smith-Modified Sgarbossa criteria in left bundle branch block, or paced rhythms. De Winter's and posterior MI share some features, but de Winter's, which is anterior ischemia, has briefer ST depression and taller T-waves than posterior MI.
This post was peer-reviewed by Stephen W. Smith, MD, of Dr. Smith's ECG Blog.
Source: Emergency Medicine 1-Minute Consult Pocketbook