triangular_index

Hrv Triangular Index

Definition

HRV triangular index. Formally: N / max(histogram_weights).

What does normal look like?

Fitted normative prior: Gamma(α = 5.937, θ = 1.737), KS p = 1.2e-14, n = 61715.

Empirical distribution over the pooled nsrdb+nsr2db normative windows (360-beat windows, 120-beat stride), overlaid with the fitted Gamma prior density. Vertical lines mark the median and the 5–95% range.

Normal-range summary (pooled nsrdb+nsr2db)

n varies by feature only through per-window validity over the full pooled nsrdb+nsr2db table (n up to 61 715; e.g. sampen/mse drop windows where the statistic is undefined). ulf is the one exception: a 360-beat (~5 min) window contains no ULF-band power, so it uses a long-window NSRDB-only extraction (see its own page).

Use cases

• Geometric, artifact-robust overall-HRV magnitude from the RR histogram.
• 24-h Holter analysis where noise defeats SDNN.
• Post-MI risk stratification (Malik et al. 1989).

Applications by area

Evidence is reported at the measure-family level; a specific variant may not be the exact index measured in every cited study.

Clinical

Coverage: statistics. A pooled literature; reviews or meta-analyses exist.

HTI (and TINN) are original 1996 Task Force geometric measures that remain recurring prognostic markers: reduced HTI/TINN is associated with higher post-MI and atrial-fibrillation mortality and reduced diabetic autonomic integrity: except one hemodialysis-AF cohort reporting a U-shaped, not monotonic, relationship.

Dominant reported direction: down: lower HTI/TINN → worse outcome (one U-shaped exception).

Key references: (Task Force, European Society of Cardiology / North American Society of Pacing & Electrophysiology, 1996); (Stuckey et al., 2014).

Sports & peak performance

Coverage: individual papers. A small, scattered literature with no pooled meta-analysis.

Not the sports-science metric of choice: a 138-athlete profiling study and dedicated exercise-HRV meta-analyses bypass HTI/TINN entirely in favor of SDNN/RMSSD/LF-HF. Where it is reported, HTI rises with higher aerobic/endurance training status.

Dominant reported direction: up with endurance training status (rarely reported).

Key references: (Stuckey et al., 2014).

Contemplative practice

Coverage: sparse or none. Essentially no dedicated application literature found.

Six targeted searches of the most relevant meditation/mindfulness HRV papers found none reporting HTI or TINN: these studies uniformly use SDNN/RMSSD/LF-HF instead, plausibly because typical meditation-session recordings (5–20 min) are too short for a stable NN-interval histogram (the Task Force recommends ≥20 min, ideally 24 h).

Dominant reported direction: no data harvested for this domain.

Key references: (Task Force, European Society of Cardiology / North American Society of Pacing & Electrophysiology, 1996).

See the effect-distribution meta-analysis page for the harvested per-study effect sizes/p-values behind these domain summaries (docs/zoo_gen/effect_stats.csv).

Resources

Resource-intensity rank ◍◍◌◌◌ low is measured: median wall-clock time and allocations over a 360-beat window on synthetic realistic RR (docs/zoo_gen/bench_resources.jl; full grid in resource_bench.csv).

Cold = fresh memoization caches (builds every shared representation from scratch); warm = shared representations (diff, periodogram, Poincaré coords, DFA fluctuation) already cached, so only this feature is recomputed. The tier is derived from the cold cost; see Geometric subgraph (Poincaré coords / RR histogram + reductions). Warm (shared representation cached) is 3× cheaper.

Citation

HRV triangular index, Malik et al. (1989); standardised by the Task Force (1996).

Seminal reference(s): (Malik et al., 1989); (Task Force, European Society of Cardiology / North American Society of Pacing & Electrophysiology, 1996).

See the References page for the full bibliography.