RRinterval

The RR interval is the time between successive R waves on an electrocardiogram (ECG). The R wave marks ventricular depolarization, so the RR interval represents one completed cardiac cycle at the ventricles. RR intervals are typically measured in milliseconds and are inversely related to heart rate (HR = 60,000 divided by the RR interval in milliseconds; or HR = 1 divided by the RR interval in seconds).

In a healthy adult at rest, RR intervals commonly range from about 600 to 1000 milliseconds, corresponding to a heart rate of roughly 60 to 100 beats per minute. RR intervals shorten as heart rate increases (during activity or stress) and lengthen with slower rates (rest or sleep).

RR interval variability, the beat-to-beat variation in RR intervals, is a key component of heart rate variability (HRV). HRV is influenced by autonomic nervous system activity, reflecting the balance between sympathetic and parasympathetic inputs. Higher HRV generally indicates greater autonomic flexibility, while reduced HRV has been associated with various health conditions and increased cardiovascular risk.

Clinical use and limitations: RR intervals are central to rhythm analysis, Holter monitoring, and stress testing. Abnormally short or long intervals, or highly irregular intervals, can indicate arrhythmias such as tachycardia, bradycardia, pauses, or atrial fibrillation. Accurate RR interval assessment requires high-quality ECG data; ectopic beats, noise, or artifacts can distort measurements. Wearable devices and photoplethysmography can estimate RR-related metrics, but ECG remains the reference standard for precise interval measurement.