Does heart rate variability correlate with long-term prognosis in myocardial infarction patients treated by early revascularization?

Abstract

Aim: To assess the prevalence of depressed heart rate variability (HRV) after an acute myocardial infarction (MI), and to evaluate its prognostic significance in the present era of immediate reperfusion.

Methods: Time-domain HRV (obtained from 24-h Holter recordings) was assessed in 326 patients (63.5 ± 12.1 years old; 80% males), two weeks after a complicated MI treated by early reperfusion: 208 ST-elevation myocardial infarction (STEMI) patients (in which reperfusion was successfully obtained within 6 h of symptoms in 94% of cases) and 118 non-ST-elevation myocardial infarction (NSTEMI) patients (percutaneous coronary intervention was performed within 24 h and successful in 73% of cases). Follow-up of the patients was performed via telephone interviews a median of 25 mo after the index event (95%CI of the mean 23.3-28.0). Primary end-point was occurrence of all-cause or cardiac death; secondary end-point was occurrence of major clinical events (MCE, defined as mortality or readmission for new MI, new revascularization, episodes of heart failure or stroke). Possible correlations between HRV parameters (mainly the standard deviation of all normal RR intervals, SDNN), clinical features (age, sex, type of MI, history of diabetes, left ventricle ejection fraction), angiographic characteristics (number of coronary arteries with critical stenoses, success and completeness of revascularization) and long-term outcomes were analysed.

Results: Markedly depressed HRV parameters were present in a relatively small percentage of patients: SDNN < 70 ms was found in 16% and SDNN < 50 ms in 4% of cases. No significant differences were present between STEMI and NSTEMI cases as regards to their distribution among quartiles of SDNN (χ² =1.536, P = 0.674). Female sex and history of diabetes maintained a significant correlation with lower values of SDNN at multivariate Cox regression analysis (respectively: P = 0.008 and P = 0.008), while no correlation was found between depressed SDNN and history of previous MI (P = 0.999) or number of diseased coronary arteries (P = 0.428) or unsuccessful percutaneous coronary intervention (PCI) (P = 0.691). Patients with left ventricle ejection fraction (LVEF) < 40% presented more often SDNN values in the lowest quartile (P < 0.001). After > 2 years from infarction, a total of 10 patients (3.1%) were lost to follow-up. Overall incidence of MCE at follow-up was similar between STEMI and NSTEMI (P = 0.141), although all-cause and cardiac mortality were higher among NSTEMI cases (respectively: 14% vs 2%, P = 0.001; and 10% vs 1.5%, P = 0.001). The Kaplan-Meier survival curves for all-cause mortality and for cardiac deaths did not reveal significant differences between patients with SDNN in the lowest quartile and other quartiles of SDNN (respectively: P = 0.137 and P = 0.527). Also the MCE-free survival curves were similar between the group of patients with SDNN in the lowest quartile vs the patients of the other SDNN quartiles (P = 0.540), with no difference for STEMI (P = 0.180) or NSTEMI patients (P = 0.541). By the contrary, events-free survival was worse if patients presented with LVEF < 40% (P = 0.001).

Conclusion: In our group of patients with a recent complicated MI, abnormal autonomic parameters have been found with a prevalence that was similar for STEMI and NSTEMI cases, and substantially unchanged in comparison to what reported in the pre-primary-PCI era. Long-term outcomes did not correlate with level of depression of HRV parameters recorded in the subacute phase of the disease, both in STEMI and in NSTEMI patients. These results support lack of prognostic significance of traditional HRV parameters when immediate coronary reperfusion is utilised.

Keywords: Autonomic nervous system; Heart rate variability; Left ventricle ejection fraction; Long-term prognosis; Myocardial infarction; Non-ST-elevation myocardial infarction; Primary percutaneous coronary intervention; ST-elevation myocardial infarction.

Figure 1

Kaplan-Meier major clinical events-free survival curves for: Patients with recent ST-elevation myocardial infarction vs patients with recent non-ST-elevation myocardial infarction (A), patients with preserved left ventricle ejection fraction (> 40%) vs patients with depressed left ventricle ejection fraction (≤ 40%) (B). STEMI: ST-elevation myocardial infarction; NSTEMI: Non-ST-elevation myocardial infarction; MCE: Major clinical events.

Figure 2

Kaplan-Meier survival curves for patients with lowest quartile of standard deviation of all normal-to-normal intervals vs patients in the other standard deviation of all normal-to-normal intervals quartiles: Major clinical events-free survival curves (A), all-cause mortality curves (B). HRV: Heart rate variability; SDNN: Standard deviation of all normal-to-normal intervals; MCE: Major clinical events.

Figure 3

Kaplan-Meier all-cause mortality curves for ST-elevation myocardial infarction patients (A) and non-ST-elevation myocardial infarction patients (B) divided between cases with lowest quartile of standard deviation of all normal-to-normal intervals vs cases in the other standard deviation of all normal-to-normal intervals quartiles. HRV: Heart rate variability; SDNN: Standard deviation of all normal-to-normal intervals; STEMI: ST-elevation myocardial infarction; NSTEMI: Non-ST-elevation myocardial infarction.