Expected ECG Findings
The easiest way to explain the heart rhythm is to refer back to an electrocardiogram (ECG - as depicted below). For review, we will go over the basics of an ECG first:
-P Wave: depolarization of atria (starting at the SA node, then spreading out to the atria)
-PR Interval: time it takes for the electrical pulse to get from the SA node to the AV node)
-QRS Complex: depolarization of ventricles (starting at the AV node; re-polarization of atria hidden here)
-T Wave: re-polarization of ventricles
This patient in particular, as you recall, had 3 pulses followed by a pause. This likely signifies a Second Degree AV Block: Mobitz Type I (Wenckebach). This would be depicted at a slowly increasing PR interval, before a lack of QRS complex occurs. The cycle then restarts. Basically this means the signal from the SA node to the AV node slows until it doesn't make it through to initiate ventricular contraction, before the next SA node initiates again to restart the cycle.
If you've ever struggled with interpretting ECG's, I recommend reading this book by Dale Dubin. It provides a step-by-step understanding and asssessment of ECG's along with the associated pathologies, at an MD level. It is an excellent source for reviewing for a CardioPulm course or preparing for the Cardiovascular section of the boards!