Absence of low frequency oscillations in short-term heart rate variability: a common and adverse finding after myocardial infarction

Heart rate variability (HRV) analysis is proposed as a reliable tool for estimation of the sympatho-vagal control of the heart. The GISSI-3 Arrhythmias Substudy studied short-term HRV in a relatively unselected population of patients with recent MI. Ten minutes of single-lead ECG recorded 13±7 days after MI from patients in standard comparable conditions and pharmacological wash-out were transmitted by telephone line from 8 enrolled cardiac care units to the core laboratory for centralised analysis. After discharge of no-sinus rhythm ECGs, data from 324/374 patients were available. Time (SD: R-R standard deviation) and Frequency (VLF, LF, HF) HRV analysis was performed on 300 consecutive RR intervals. Power spectral densities were estimated by applying an autoregressive model. HRV indexes showed a non-parametric distribution, generally skewed around the lowest values. In 75 patients (23%) no LF power was detected by PSD analysis. This result was associated to markers of increased sympathetic activity as lower cycle length and standard deviation (R-R = 902 vs. 940 ms and SDNN = 25.4 vs. 29 ms; p 65 years) and blood pressure hypertension showed an independent and significant correlation to absence of LF power. In the thrombolytic era nearly one quarter of post MI patients doesn't show any oscillations in the LF band. The lack of LF rhythms identifies a subgroup of patients with adverse clinical predictors after M