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Traditional and Nonlinear Heart Rate Variability Are Each Independently Associated with Mortality after Myocardial Infarction


  • This research was supported by Grant NHLBI R0-3.

  • Manuscript received 26 April 2004; Revised manuscript received 23 July 2004; Accepted for publication 25 August 2004.

Phyllis K. Stein, Ph.D., Washington University School of Medicine HRV Laboratory, 4625 Lindell Boulevard, Suite 402, St. Louis, MO 63108. Fax: 314-286-1394; E-mail:


Introduction: Decreased heart rate variability (HRV) and abnormal nonlinear HRV shortly after myocardial infarction (MI) are risk factors for mortality. Traditional HRV predicts mortality in patients with a range of times post-MI, but the association of nonlinear HRV and outcome in this population is unknown.

Methods and Results: HRV was determined from 740 tapes recorded before antiarrhythmic therapy in Cardiac Arrhythmia Suppression Trial patients with ventricular premature contractions (VPCs) suppressed on the first randomized treatment. Patients were 70 ± 121 days post-MI. Follow up was 362 ± 241 days (70 deaths). The association between traditional time and frequency-domain HRV and mortality and nonlinear HRV and mortality were compared for the entire population (ALL), those without coronary artery bypass graft post-MI (no CABG), and those without CABG or diabetes (no CABG, no DIAB) using univariate and multivariate Cox regression analysis. Strength of association was compared by P values and Wald Chi-square values. Nonlinear HRV included short-term fractal scaling exponent, power law slope, and SD12 (Poincaré dimension). For ALL and for no CABG, increased daytime SD12 had the strongest association with mortality (P = 0.002 ALL and P < 0.001 no CABG). For no CABG, no DIAB increased 24-hour SD12 hours had the strongest association (P < 0.001) with mortality. Upon multivariate analysis, increased SD12, decreased ln ULF (ultra low frequency), and history of prior MI and history of congestive heart failure each remained in the model.

Conclusion: Nonlinear HRV is associated with mortality post-MI. However, as with traditional HRV, this is diluted by CABG surgery post-MI and by diabetes. Results suggest that decreased long-term HRV and increased randomness of heart rate are each independent risk factors for mortality post-MI.