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Elevated myocardial repolarization lability and arterial baroreflex dysfunction in healthy individuals with
Anna Myredal1, Peter Friberg, Mats Johansson
1Department of Internal Medicine, Varberg Hospital, Varberg, Sweden. anna.myredal@lthalland.se
Insights
The nondipping blood pressure pattern in healthy individuals is linked to autonomic nervous system dysfunction. This is evidenced by increased QT variability and reduced baroreflex effectiveness, indicating higher cardiovascular risk.
Area of Science:
- Cardiology
- Autonomic Nervous System Function
- Hypertension Research
Background:
- The nondipping blood pressure pattern (NDP), lacking nocturnal BP reduction, is associated with increased cardiovascular morbidity and mortality.
- Reduced vagal control and heightened cardiac repolarization lability are linked to ventricular arrhythmia and sudden cardiac death.
Purpose of the Study:
- To assess temporal QT variability, arterial baroreflex sensitivity (BRS), and baroreflex effectiveness index (BEI).
- To compare these parameters between healthy subjects with normal BP patterns ('dippers') and those with nondipping BP patterns ('nondippers').
Main Methods:
- Ninety-five healthy subjects underwent 24-h ambulatory BP monitoring.
- Electrocardiogram (ECG) and beat-to-beat BP were recorded to calculate QT variability index (QTVI), BRS, and BEI.
Main Results:
- Nondippers exhibited significantly increased QTVI (elevated myocardial repolarization lability) compared to dippers.
- Nondippers demonstrated a significantly decreased BEI (impaired baroreflex function) compared to dippers.
- No significant differences in BRS were observed between the groups.
Conclusions:
- A nondipping BP pattern in healthy individuals is associated with myocardial repolarization lability and impaired baroreflex function.
- These findings suggest underlying autonomic nervous system dysfunction in individuals with NDP.
- NDP may represent a preclinical marker for cardiovascular risk in seemingly healthy subjects.
Background:
The "nondipping" pattern (NDP) of blood pressure, characterized by the absence of the reduction in blood pressure (BP) that typically takes place during the night time, has been associated with elevated cardiovascular morbidity, including stroke, myocardial infarction, and sudden cardiac-related death. In various cardiovascular diseases, reduced vagal control of cardiac function and elevated lability of cardiac repolarization have been associated with increased risk for ventricular arrhythmia and sudden death. The aim of this study was to assess temporal QT variability, arterial baroreflex sensitivity (BRS), and baroreflex effectiveness index (BEI) in two groups of otherwise healthy subjects, one group consisting of those with a normal BP pattern and the other with a nondipping BP pattern.
Methods:
Ninety-five healthy subjects underwent 24-h ambulatory BP (AMBP) monitoring. A minimum of 10% reduction in BP during the night relative to daytime levels is considered normal (as found in "dippers"). These individuals were classified as "dippers" (n = 59) and individuals without 10% reduction in BP during night were classified as "nondippers" (n = 36). Electrocardiogram (ECG) readings and beat-to-beat BP were recorded at 1,000 Hz with the subjects at rest in the supine posture for 20 min. BRS, BEI, and QT variability index (QTVI) were calculated.
Results:
There were no differences between the study groups with respect to age, gender, and average BP. Nondippers showed an increase in QTVI (-1.28 +/- 0.48 in nondippers vs. -1.52 +/- 0.29 in dippers, P < 0.05) and a decrease in BEI (0.34 +/- 0.17 in nondippers vs. 0.43 +/- 0.17 in dippers, P < 0.05), whereas BRS did not differ between the groups.
Conclusion:
A nondipping BP pattern in healthy subjects is associated with elevated myocardial repolarization lability and impaired baroreflex function, suggesting dysfunction of the autonomic nervous system.
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Monitoring Both Arms:
Monitoring BP in both arms during the initial assessment is advisable, as the systolic value may differ by five to ten mm Hg between arms. For subsequent BP assessments, use the arm with the higher reading.