The Relationship between Ventricular Repolarization Duration and RR Interval in Normal Subjects and Patients with Myocardial Infarction

Abstract

Objectives: When either ventricular myocardium becomes ischemic or autonomic nervous system activity changes with age, the relationship between ventricular repolarization duration and RR interval will change as well. We studied the relationship between ventricular repolarization duration and RR interval among normal subjects in different age groups and between patients with myocardial infarction (MI) and age-matched healthy subjects. Methods: Ventricular repolarization duration variability (RDV) spectra were separated into RR-dependent and RR-independent components. We compared spectral measures among normal subjects in different age groups and between patients with MI and age-matched healthy subjects. Results: The RR-dependent component of RDV spectra, which is correlated with autonomic nervous system activity, significantly decreased with age for healthy subjects. The RR-independent component significantly increased in MI patients compared to age-matched healthy subjects. Conclusions: We demonstrated the increase in RDV upon decreasing age and in the presence of MI. Our results support the idea that the RR-dependent part corresponds to the physiology-related part of the RDV spectra and the RR-independent part corresponds to the pathology-related part of the RDV spectra. Our study suggests that these spectral measures are likely to be helpful in the evaluation of a patient with MI and merit further investigation.

Relation between QT interval variability and muscle sympathetic nerve activity in normal subjects

“…Elevated beat-to-beat variability in ventricular repolarization duration, measured as changes in QT interval [QT variability (QTV)] on body surface ECG has been attributed to increased sympathetic outflow to the ventricles (32,46). Although it is widely believed that QTV is predominantly driven by heart period (RR interval) variability (RRV) under normal conditions during rest (34), several studies across a range of condi-tions, including healthy subjects (2), patients post-myocardial infarction (50), heart failure patients (25), and patients with diabetes mellitus (39), showed that a large part of QTV could not be solely attributed to RRV. An increased decoupling between RRV and repolarization variability was reported in healthy subjects following head-up tilt, a maneuver well known to increase sympathetic nerve activity (12), and QTV unrelated to RR and respiration (35) was shown to increase under similar experimental conditions.…”

Augmented Oscillations in QT Interval Duration Predict Mortality Post Myocardial Infarction Independent of Heart Rate

“…This attenuation of the QT-RR relationship has also been found in MI patients with reduced LVEF when compared to those with coronary artery disease but no MI (Sosnowski et al, 2002). Others found no difference in the RR dependent component of QTV when comparing MI patients to healthy subjects (Lombardi et al, 1998;Zhu et al, 2008). These aggregate results suggest that the attenuation in QT-RR relationship is only prevalent in high-risk patients rather than in all patients post MI.…”

Ventricular Repolarization Spectra

“…While they inevitably lost some of the repolarization time that might be an important indicator of ischemic myocardium with the longest repolarization delay, these spectral measures are likely to be helpful in the evaluation of areas of infarction in patients with MI. In the study by Zhu et al [1] , HRD significantly decreased with age in healthy individuals, but in MI patients, HRI significantly increased compared to agematched controls.…”

“…Separating the autonomic component from the tissue component of repolarization variability is a contribution made by Zhu et al [1] . Perhaps future studies assessing outcome in patients with cardiomyopathies using these techniques will further advance our understanding of repolarization variability and help to prognosticate the risk for a poor outcome.…”

“…In this issue of Cardiology , Zhu et al [1] determine ventricular repolarization duration variability (RDV) spectra to provide another noninvasive tool to evaluate the risk of arrhythmias and treatment outcome. They assessed ECG at rest for 20 min, and RDV was derived by software analysis of the ECG into heart rate-dependent (HRD) and -independent (HRI) components.…”