Background and purpose: Heart rate variability (HRV) is a physiological phenomenon which reflects the influence of the autonomic nervous system on the heart work. The research in HRV has not been limited to the domain of basic and clinical cardiology, mostly with the aim of stratifying the risks of sudden death from malignant arrhythmias among patients with myocardial infarction (MI), but over the past few years the research has been done and studies have been published also in the area of neurology. Likewise acute MI, acute ischemic stroke leads to autonomic dysbalance and lowered HRV. However, literature lacks relevant data on autonomic dysbalance after the acute phase of ischemic stroke. The aim of this study was to assess the level of autonomic dysbalance in patients after the acute phase of ischemic stroke.
Patients and methods: This prospective study included 86 consecutive patients who had suffered ischemic stroke (59 men and 27 women, mean age 56 +/- 13 years) and 86 age-matched healthy control subjects (62 men and 24 women, mean age 53 +/- 9 year). In the acute phase of the disease, along with clinically manifest neurologic deficit, there is ischemic hemispheric lesion verified by computed tomography (CT) scan. Lesion of the left and right cerebral hemisphere was detected in 56% and 44% of patients, respectively. After the acute phase of the disease, patients were hospitalized at one of the neurologic departments of the Hospital for Medical Rehabilitation in Krapinske Toplice, Croatia, where rehabilitation was carried out (mean duration 20 +/- 9 days) in the 1999-2002 period. Inclusion criteria were: age under 70 years, first ischemic stroke verified by CT scan within 2-12 weeks of the acute phase of the disease, Barthel index 30-50, and stable sinus rhythm in ECG. Exclusion criteria were: a history of previous ischemic stroke, intracerebral hemorrhage, MI, percutaneous coronary intervention or surgical revascularization of the myocardium, clinical signs of coronary artery disease, acute heart failure, diabetes mellitus, chronic atrial fibrillation, sinus node disease, AV block grade II or III, and the use of beta adrenergic blockers or antiarrhythmic agents class Ic or III in medication. Twenty-four hour Holter ECG was performed 58 +/- 23 days after the stroke (14 +/- 5 days from the beginning of rehabilitation). HRV was analyzed from the Holter ECG data. The values of the HRV parameters in stroke patients were compared with those recorded in the control group. Most of the variables proposed by the Task Force on HRV were analyzed. Time domain analysis included: mean RR, mean of R-R intervals for normal beats; SDNN, standard deviation of all normal R-R intervals; SDNN-i, mean of 5-minute standard deviations of RR intervals; SDANN-I, standard deviation of the 5-minute means of R-R intervals; rMSSD, square root of the mean of the squared successive differences in R-R intervals; and pNN50, percentage of R-R intervals that are by at least 50 ms different from the previous interval. Frequency domain analysis included: TP, total power (0.0-0.5 Hz); VLF, very low (0.0033-0.04 Hz); LF, low (0.04-0.15 Hz); HF, high (0.15-0.40 Hz) frequency components; and LF/HF, low to high frequency ratio. Statistical analysis was performed using the commercial software package, Microsoft SPSS for Windows, Version 8.0.
Results: Patients who had suffered an ischemic stroke had a significantly lower overall HRV and shorter mean RR interval than healthy subjects from the control group: SDNN 96 +/- 27 vs. 136 +/- 31 ms, p < 0.001; TP 1962 +/- 1338 vs. 3968 +/- 2857 ms2, p < 0.001; and mean RR 869 +/- 104 vs. 892 +/- 117 ms, p = 0.02.
Conclusion: As in MI, the values of HRV stay significantly lower after the acute phase of the disease in patients who have suffered ischemic stroke compared to healthy persons of the same age.