I recently performed both of these ECGs a few days apart during the same work week. They were recorded on an outpatient basis. It wasn’t until I recorded the second ECG that I realized I had a good pair of ECGs to illustrate this comparison.
At a superficial glance, both of these appear to represent the same thing and some people might even argue that both of these ECGs have identical interpretations but they would be wrong. One of these represents a conventional example that is intrinsic to the heart and it's conduction system. The other is a lesser-known example and is extrinsic to the heart. Admittedly, they do share similar characteristics however there are several contrasting features as well.
Fig. # 1
Patient's clinical data: 68-year-old white man. History of hypertension.
Fig. # 2
Patient's clinical data: 57-year-old black man.
The computer interpreted Fig. # 2 as:
Marked sinus bradycardia with marked sinus arrhythmia 1st degree AV block
DO YOU AGREE WITH THE COMPUTER?
What are the causes of the pauses and the "group beating"? Do either of these patients need a pacemaker?
Hint: In Fig. # 2, pay careful attention to the sinus P-P intervals and their correlation with the timing of the pauses. Compare the PR intervals and their corresponding RP intervals. Also contrast the lengths of the longest and shortest RR intervals. This will help to differentiate it from Fig. # 1.