Heart rate variability patterns before ventricular tachycardia onset in patients with an implantable cardioverter defibrillator

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Abstract

Time- and frequency-domain analysis of heart rate variability (HRV) has been proven effective in describing alteration of autonomic control mechanisms and in identifying patients with increased cardiac and arrhythmic mortality. Patients with implantable cardioverter defibrillators offer the opportunity to evaluate HRV patterns before ventricular tachycardia (VT) and under control conditions. We therefore analyzed time- and frequency-domain parameters of short-term HRV and power-law behavior of RR interval time series at rest, at 15 to 30 minutes, and immediately before VT. In comparison to control conditions, lower values of mean cycle length duration and total power were observed before VT. Spectral analysis indicated that the low- to high-frequency ratio was significantly higher (5.5 ± 0.6 vs 2.8 ± 0.3) immediately before VT than during rest. Both findings were consistent with the shift of sympathovagal balance toward sympathetic predominance and reduced vagal tone. Before VT, a more negative value of the scaling exponent β of the power-frequency relation (−1.57 ± 0.04 vs −1.33 ± 0.04) also confirmed the presence of an altered HRV pattern in comparison to controls. Thus, both abnormal autonomic modulation and dynamic patterns of HRV seem to characterize the minutes before arrhythmia onset in these patients.

Section snippets

Patient population

From September 1, 1997, to December 1, 1998, the stored electrographic time series before detected arrhythmic events of 60 patients implanted with Medtronic 7220 to 7223 devices (Minneapolis, Minnesota) were collected. This procedure was performed at the time of device interrogation after an arrhythmic event perceived by the patient, during a scheduled control examination or after the patient’s admission to the emergency room (35%, 50%, and 15% of the cases, respectively). A control recording

Arrhythmic events

Sixty-eight episodes of VT were analyzed. Most of the episodes (77%) occurred during daytime while the patients were not engaged in physical activity; a few episodes (7%) occurred during some form of exercise, whereas the remaining events occurred during the night. The mean cycle length of VT was 322 ± 6 ms. Antitachycardia pacing effectively treated most of the episodes (71%). Cardioversion terminated VT in 29% of cases.

Analysis of short-term recordings

The period immediately before VT onset was compared with control and VT20.

Discussion

Our study describes for the first time the changes in HRV before VT in patients with an implantable defibrillator. Three major findings are notable and distinguish the minutes before VT onset from control periods: a reduction in cycle length duration and in total power, an increase in LF/HF ratio, and a more negative scaling exponent β.

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    This study was partially supported by a grant from Ministero dell’Università e della Ricerca Scientifica, Rome, Italy. Manuscript received March 9, 2000; revised manuscript received and accepted May 5, 2000.

    The participating centers are listed in the .

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