Which term describes a heart rhythm with alternating normal and abnormal R-R intervals?

The term that describes a heart rhythm characterized by alternating normal and abnormal R-R intervals is sinus arrhythmia. Sinus arrhythmia is a common physiological phenomenon, especially seen in younger individuals, where the heart rate fluctuates in coordination with the respiratory cycle. During inhalation, the heart rate may increase, while exhalation leads to a decrease in heart rate, resulting in variability of the R-R intervals observed on an electrocardiogram (ECG). This variability is considered normal as long as it remains within certain healthy limits and does not indicate an underlying pathological condition.

While atrial flutter is characterized by a rapid and organized atrial rhythm, leading to a consistent R-R interval that is not varying, ventricular fibrillation presents as chaotic electrical activity with no discernible pattern, indicating a severe cardiac emergency. Respiratory sinus tachycardia would imply a faster heart rate but does not account for the alternating nature of the intervals present in sinus arrhythmia. Therefore, sinus arrhythmia accurately captures the described heart rhythm with its alternating R-R interval pattern.