Myocardial infarction in the presence of LBBB
See brief interpretation of 12 lead EKG above
This is a classic example of ischemic EKG changes in the presence of left bundle branch block (LBBB). The Sgarbossa criteria may be used to detect myocardial infarction in the presence of pre-existing LBBB. The Sgarbossa criteria are:
1. ST segment elevation of 1 mm or more in the same direction (concordant) as the QRS complex in any lead — score 5.
2. ST segment depression of 1 mm or more in any lead from V1 to V3 — score 3.
3. ST segment elevation of 5 mm or more discordant with the QRS complex — score 2
In the EKG above there is concordant ST elevation in the inferior leads (II, III, aVF) which yields a Sgarbossa score of 5 indicating myocardial infarction. Studies have shown that a score of at least 3 points indicate myocardial infarction albeit with low sensitivity, i.e. if these changes are not present the patient may still have an infarction. A patient with LBBB and newly onset of chest pain or dyspnea should always be discussed with an invasive cardiologist.
When ST elevations are present in the inferior leads the most likely location for the culprit lesion is in the right coronary artery (RCA). This is exactly where the invasive cardiologist found it, as shown in the coronary angiography below:
The Sgarbossa criteria may also be applied to diagnose myocardial infarction in paced rhythm, though they are less specific.
– Troels
