Heart Rate Variability (HRV) Calculator

Heart Rate Variability (HRV): SDNN and RMSSD: Explanation and Clinical Context Heart Rate Variability (HRV) is a non-invasive marker of autonomic nervous system function and cardiac health. SDNN (Standard Deviation of NN intervals) represents overall HRV and reflects both sympathetic and parasympathetic influences. RMSSD (Root Mean Square of Successive Differences) reflects short-term parasympathetic activity and is sensitive to vagal tone.

Low HRV, particularly low SDNN and RMSSD, has been associated with higher risk of cardiovascular events, mortality, and autonomic dysfunction. These parameters are calculated from consecutive normal-to-normal RR intervals obtained from ECG recordings, typically over 5 minutes (short-term) or 24 hours (long-term Holter monitoring). Clinical interpretation: SDNN <50 ms or RMSSD <20 ms indicates high risk and impaired autonomic function, whereas values above 100 ms (SDNN) or 50 ms (RMSSD) indicate normal autonomic regulation.