The Deceptive Ears of a Rabbit

This particular ECG resulted in a great deal of discussion. Though I don't have the actual details of the patient encounter, its clear that the ECG machine, the paramedic student, the preceptor, and the emergency physician all contest the actual interpretation of the following tracing. ECGs like this one represent fantastic learning opportunities. When confronted with a bunch of squiggly lines and conflicting information, it is imperative to stay focused and proceed through the ECG interpretation in a stepwise fashion. Judging from all of the hashmarks, pen marks, and circles, there wasn't any resolution by the time the paramedics had cleaned their stretcher and left for their station!

1) What's the rate?
2) What's the rhythm?
3) Are concerning ST/T segment changes present?
4) Where are my defibrillator / pacer pads?

12 lead ECG

12 lead ECG interpretation and discussion

The ECG tracing reveals a regular rhythm. Before getting distracted by rabbit ears or conduction delays, it is important to discern whether or not a sinus rhythm is present. P waves are occasionally visualized, but there is simply no fixed PR ratio. The absence of a fixed PR suggests that a high grade block is present. Considering the widened QRS, it is likely that the tracing represents a third degree heart block. Further corroborating that interpretation is the relatively fixed R to R interval. Putting this together: wide QRS + fixed R to R + varied PR interval  = third degree heart block. By definition, a right bundle branch block or left bundle branch block CANNOT be diagnosed in the absence of a sinus rhythm.

The ST/T segments are grossly abnormal. The large QS wave present in leads III and aVF suggest a prior inferior wall myocardial infarction. In addition, there is poor R wave progression across the precordial leads. The R wave is still of decreased amplitude in lead V4. Recall that the R wave should transition to a mostly positive deflection by lead V4. There is minimal ST segment elevation in the inferior leads as well. Though this patient may be suffering from acute ischemia, the presence of a third degree block is requires aggressive management and expeditious transport. This rhythm, in the presence of anginal symptoms, warrants chemical or electrical therapy. Transport to an interventional facility, patient stability permitting, is a good strategy.

Fix the rate first!

Final interpretation

Probable third degree heart block, probable inferior wall myocardial infarction, old anterior wall myocardial infarction