Recovery of heart rate variability and ventricular repolarization indices following exercise

Abstract

Background: There is a heightened risk of sudden cardiac death related to exercise and the postexercise recovery period, but the precise mechanism is unknown. We have demonstrated that sympathoexcitation persists for ≥45 minutes after exercise in normals and subjects with coronary artery disease (CAD). The purpose of this study is to determine whether this persistent sympathoexcitation is associated with persistent heart rate variability (HRV) and ventricular repolarization changes in the postexercise recovery period.

Methods and results: Twenty control subjects (age 50.7 ± 1.4 years), 68 subjects (age 58.2 ± 1.5 years) with CAD and preserved left ventricular ejection fraction (LVEF), and 18 subjects (age 57.6 ± 2.4 years) with CAD and depressed LVEF underwent a 16-minute submaximal bicycle exercise protocol with continuous ECG monitoring. QT and RR intervals were measured in recovery to calculate the time dependent corrected QT intervals (QTc), the QT-RR relationship, and HRV. QTc was dependent on the choice of rate correction formula. There were no differences in QT-RR slopes among the three groups in early recovery. HRV recovered quickly in controls, more slowly in those with CAD-preserved LVEF, and to a lesser extent in those with CAD-depressed LVEF.

Conclusion: Despite persistent sympathoexcitation for the 45-minute recovery period, ventricular repolarization changes do not persist for that long and HRV changes differ by group. Additional understanding of the dynamic changes in cardiac parameters after exercise is needed to explore the mechanism of increased sudden cardiac death risk at this time.

Figure 1

The corrected QT interval (QTc) is plotted at rest, every minute during exercise, and every minute during 30 minutes of recovery for control subjects, those with coronary artery disease and preserved left ventricular ejection fraction (CAD‐Preserved LVEF), and those with coronary artery disease and depressed left ventricular ejection fraction (CAD‐Depressed LVEF). Mean data are shown for each group; standard errors are shown at baseline and every 5 minutes.

Figure 2

The QT–RR slope is plotted every minute in recovery for control subjects, those with coronary artery disease and preserved left ventricular ejection fraction (CAD‐Preserved LVEF), and those with coronary artery disease and depressed left ventricular ejection fraction (CAD‐Depressed LVEF). Mean data are shown for each group; standard errors are shown every 5 minutes.

Figure 3

Plot of the root mean square residual (RMS) at rest, every minute for the first 5 minutes of recovery, and then every 5 minutes. Mean data ± standard errors are shown for each group—abbreviations as in Figure 2.

Figure 4

Plot of the root mean squared successive differences (MSSD at rest, every minute for the first 5 minutes of recovery, and then every 5 minutes. Mean data ± standard errors are shown for each group—abbreviations as in Figure 2.