The best method for measuring irregular heart rates with varying R-R intervals is to count the number of R waves in a 6-sec strip (including extra beats such as PVCs, PACs, and PJCs) and multiply by 10. This gives the average number of beats per minute.

The heart rate is 70 bpm (counting the blocked beat), 75 bpm in the underlying rhythm (1,500/20 = 75). The rhythm is irregular due to the blocked beat. The interpretation (see Tab-ECGs) is sinoatrial (SA) block.