aka Cardiovascular Curveball 014
An ECG is done:
Q1. Describe this ECG.
The ECG demonstrates
- underlying sinus rhythm with a rate of 75 bpm and normal axis.
- antero-lateral ST elevation.
- auto-analysis of the ECG states ‘ACUTE MI’.
The patient looks well. His observations are normal, and despite aspirin and GTN he is still complaining of 7/10 chest pain.
Q2. Is the auto-analysis interpretation correct? Is this an Acute MI?
Thankfully Prof. Steve Smith, an emergency physician and creator of Dr Smith’s ECG Blog thinks he can help…
Dr Smith has created a formula using logistical regression to aid in differentiating between subtle anterior STEMI and benign early repolarisation (BER). This formula is to be used when the diagnosis is in doubt i.e. not an obvious STEMI and no LVH, LBBB, or reciprocal ST depression. [Original Article] [Blog Reference]
Subtle Anterior STEMI Calculation = (1.196 × [ST-segment elevation 60 ms after the J point in lead V3, in mm]) + (0.059 × [QTc in ms]) – (0.326 × [R-wave amplitude in lead V4 in mm]).
- if result is > 23.4 then the sensitivity and specificity for subtle MI is around 90%, the higher the value the more likely the diagnosis is MI.
Q3. How does this apply to our patient?
- QTc was calculated by the ECG machine at 410ms
- The result from Dr Smith’s formula = 21.6
- This makes the ECG findings suggestive of BER rather than subtle anterior STEMI.
Q4. What would you do now?
- Cardiology were urgently consulted
- On review they were convinced the ECG changes represented a STEMI
- The patient was taken to the cardiac cath lab post haste.
Q5. The angiogram report
- Left Main coronary artery – Normal
- Left Anterior Descending coronary artery – Bridging with ?spasm mid-vessel
- Left Circumflex coronary artery – smooth and angiographically normal
- Right coronary artery – Dominant, smooth and angiographically normal
- Left ventriculogram – mild hypokinesis anterior wall, overall normal ejection fraction
- Impression – Nil occlusive coronary artery disease, Left anterior descending coronary artery bridging with ?spasm
After reading the angiogram report and subsequent findings of no obstructive lesion and with a lesson concerning the finer points of ECG interpretation on my lips I checked the patient’s blood tests which revealed a high sensitivity troponin of 3010 ng/L (<26ng/L).
Despite the Dr Smith’s formula predicting BER over Acute Coronary Syndrome the patient has a significantly raised troponin and a regional wall motion abnormality, however there is no occlusive coronary artery disease.
Q6. Would you have activated the cardiac cath lab?
- I was fortunate enough to see this patient at 0900 on a Tuesday in a tertiary hospital with a well staffed cardiac cath lab. It would have been difficult to argue against going to the lab given the resources at hand.
- I also happen to work in a state that is massive and the effort and cost of retrieving a patient from some of the locations in my state can be considerable. Having tools such as Steve Smith’s calculator at hand can be an amazing boon for those who don’t have the ease of access to a cath lab that I do, where they can present objective evidence to the fact that ‘this is not a STEMI’ when people come in with chest pain that you know is not suffering from ACS.
- In this case the patient did not have a fixed obstruction in his coronaries to account for his regional wall motion abnormality and significantly raised troponin and so the formula was right. Wasn’t it?
Q6a. What is this ‘bridging’ they mention in the coronary cath report report?
- Myocardial bridging is a congenital anomaly in which a segment of a coronary artery takes a “tunneled” intramuscular course under a “bridge” of overlying myocardium.
- This causes vessel compression in systole, resulting in hemodynamic changes that may be associated with angina, myocardial ischaemia, acute coronary syndrome, left ventricular dysfunction, arrhythmias, and even sudden cardiac death.
- Smith SW, Khalil A, Henry TD, et al. Electrocardiographic differentiation of early repolarization from subtle anterior ST-segment elevation myocardial infarction. Ann Emerg Med 2012;60(1):45-56. PMID: 22520989
- MDCalc – Subtle Anterior STEMI Calculator
- Lee MS, Chen C. Myocardial Bridging: An Up-to-Date Review. J Invasive Cardiol 2015 Nov;27(11): 521-528. PMCID: PMC4818117
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