A basic rhythm with normal PQRST intervals/durations with a beat-to-beat variation in the P-P interval producing an irregular ventricular rate. Variation in the P-P interval of more than 120 ms. The P-P interval gradually lengthens and shortens in a cyclical fashion, usually corresponding to the phases of the respiratory cycle. Normal Sinus P-waves with a constant morphology (i.e. no evidence of premature atrial contractions). Constant P-R interval but with widely varying R-R intervals, such that the longest R-R interval is greater than 35% and less than 100% longer than the interval immediately preceding it.

Sinus Arrhythmia (54-76 BPM)