Applications

Autonomic dysfunction

Standardized five-minute HRV may contribute to the assessment of autonomic function in diabetes mellitus with suspected cardiovascular autonomic neuropathy, heart failure with reduced or preserved ejection fraction, neurodegenerative disorders including Parkinson disease and multiple system atrophy, post-acute infection syndromes, orthostatic intolerance syndromes and rehabilitation monitoring. In each context, HRV findings are interpreted alongside other study measures and the recording context, and are not independently diagnostic.

Orthostatic intolerance and POTS

The consensus-based diagnostic framework for postural orthostatic tachycardia syndrome in adults requires all of the following: chronic (≥3 months) orthostatic symptoms that worsen with upright posture and improve with recumbency; a sustained heart-rate increase of at least 30 beats per minute within ten minutes of upright posture (40 bpm in adolescents aged 12–19 years); the absence of orthostatic hypotension (a sustained fall of at least 20 mmHg systolic or 10 mmHg diastolic); and exclusion of alternative explanations such as dehydration, anaemia, hyperthyroidism, medications that affect heart rate, and other causes of sinus tachycardia. Resting five-minute HRV may characterize associated autonomic patterns, but the diagnosis of POTS is established through symptoms and orthostatic heart-rate and blood-pressure assessment, not HRV alone.

Studies of short-term HRV in POTS cohorts have reported a range of group-level findings including reduced RMSSD, reduced HF power, reduced SDNN in some populations, and relative LF predominance in a subset of recordings. These group patterns are not mandatory for diagnosis, are not present in all individuals with POTS, and should not be used in isolation to confirm or exclude the condition.

Post-acute infection syndromes, ME/CFS and Long COVID

Post-acute infection syndromes (PAIS), including myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and the post-COVID-19 condition (“Long COVID”), are characterized by a complex constellation of symptoms that may include orthostatic intolerance, post-exertional malaise, sleep disturbance, chronic fatigue, cognitive dysfunction and palpitations. A growing body of evidence points to a bidirectional relationship between the immune system and the autonomic nervous system in these conditions, with reduced vagal-related HRV metrics observed in some cohorts.

Within this context, standardized five-minute HRV recording may provide a non-invasive objective autonomic measure, support cohort characterization in research studies, serve as an outcome measure in interventional trials, and facilitate longitudinal monitoring. A specific HRV pattern does not diagnose Long COVID or ME/CFS, and HRV findings in these populations remain an area of active research.

Cardiometabolic and neurological applications

Reduced HRV has been associated with adverse outcomes in several cardiovascular conditions, although five-minute HRV must not be substituted for validated 24-hour risk models. In neurological research, short-term HRV may support the assessment of autonomic involvement in Parkinson disease, multiple system atrophy and other neurodegenerative disorders.

Longitudinal monitoring

Standardized short-term HRV recordings can be repeated over time to track changes in autonomic function in response to interventions, rehabilitation or disease progression. Reliable longitudinal comparison requires consistent recording conditions, equipment and analysis methods across sessions.

Research applications

Standardized resting five-minute HRV recordings can be integrated into research protocols for baseline autonomic assessment, comparison of autonomic profiles between cohorts, pre- and post-intervention analysis, correlation with orthostatic testing and validated symptom scales, and reproducible short recordings suitable for larger studies.

Minimum reporting standards

The following items should be reported in any study using short-term HRV to ensure reproducibility and comparability:

• Device used for recording
• ECG or PPG methodology
• Sampling rate (Hz)
• Recording duration
• Position during recording
• Rest duration before recording
• Breathing protocol (spontaneous or paced)
• Time of day
• Rhythm exclusions (ectopy, arrhythmia)
• Ectopy threshold applied
• Artefact-correction method
• HRV software and version
• Time-domain metrics reported
• Frequency-domain units and transformation
• Age and sex of the study population

Worked case

Case background

Female, 20 years old, 27 months after SARS-CoV-2 infection. Symptoms include palpitations, cognitive dysfunction and orthostatic dizziness.

Orthostatic findings

Supine heart rate: 65 bpm, supine blood pressure: 104/76 mmHg. Standing heart rate after two minutes: 112 bpm, standing blood pressure: 107/74 mmHg. The heart-rate increase reaches the adult increment threshold after two minutes. A complete orthostatic assessment is required to establish that the increase is sustained and to exclude alternative causes.

Five-minute HRV

Interpretation

Interpreted using the female 18–29 reference range: RMSSD below the 5th percentile, SDNN between the 5th and 25th percentile, indicating reduced short-term beat-to-beat and overall variability, with relative LF predominance. These findings are compatible with associated autonomic dysregulation but are not diagnostic by themselves.