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Beat-to-beat QT interval variability: novel evidence for repolarization lability in ischemic and nonischemic dilated
R D Berger1, E K Kasper, K L Baughman
1Johns Hopkins School of Medicine, Baltimore, Md 21287, USA. ron@tachy.cdisc.jhu.edu
Insights
Dilated cardiomyopathy (DCM) patients show increased beat-to-beat QT interval variability, indicating temporal instability in ventricular repolarization. This heightened variability is linked to disease severity but not ejection fraction.
Area of Science:
- Cardiology
- Electrophysiology
- Heart Failure Research
Background:
- Dilated cardiomyopathy (DCM) is a significant risk factor for malignant ventricular arrhythmias and sudden cardiac death.
- Ventricular repolarization abnormalities are implicated in DCM-related arrhythmias.
- While spatial repolarization heterogeneity is studied, temporal fluctuations remain under-explored.
Purpose of the Study:
- To investigate beat-to-beat QT interval variability in DCM patients.
- To compare QT interval variability between DCM patients and healthy controls.
- To explore the relationship between QT interval variability, heart rate variability, and clinical parameters in DCM.
Main Methods:
- Utilized automated analysis of 256-second surface ECG records from 83 DCM patients and 60 controls.
- Calculated QT variability index (QTVI) using normalized QT variance and heart rate variance.
- Assessed coherence between heart rate and QT interval fluctuations via spectral analysis.
Main Results:
- DCM patients exhibited significantly higher QT variance and QTVI compared to controls.
- Heart rate variance was reduced in DCM patients.
- QTVI correlated with New York Heart Association functional class but not ejection fraction or etiology.
Conclusions:
- DCM is characterized by increased beat-to-beat QT interval variability, suggesting temporal repolarization lability.
- This variability is uncoupled from heart rate fluctuations and worsens with functional class severity.
- Findings highlight temporal repolarization instability as a key feature of DCM.
Background:
Dilated cardiomyopathy (DCM) is associated with a high incidence of malignant ventricular arrhythmias and sudden death. Abnormalities in repolarization of ventricular myocardium have been implicated in the development of these arrhythmias. Spatial heterogeneity in repolarization has been studied in DCM, but temporal fluctuations in repolarization in this setting have been largely ignored. We sought to test the hypothesis that beat-to-beat QT interval variability is increased in DCM patients compared with control subjects.
Methods And Results:
Eighty-three patients with ischemic and nonischemic DCM and 60 control subjects served as the study population. Beat-to-beat QT interval variability was measured by automated analysis on the basis of 256-second records of the surface ECG. A QT variability index (QTVI) was calculated for each subject as the logarithm of the ratio of normalized QT variance to heart rate variance. The coherence between heart rate and QT interval fluctuations was determined by spectral analysis. In patients, ejection fractions were assessed by echocardiography or ventriculography, and spatial QT dispersion was determined from the standard 12-lead ECG. DCM patients had greater QT variance than control subjects (60.4+/-63.1 versus 25.7+/-24.8 ms2, P<.0001) despite reduced heart rate variance (6.7+/-7.8 versus 10.5+/-10.4 bpm2, P=.01). The QTVI was higher in DCM patients than in control subjects, with a high degree of significance (-0.43+/-0.71 versus -1.29+/-0.51, P<10[-12]). QTVI did not correlate with ejection fraction or spatial QT dispersion but did depend on New York Heart Association functional class. QTVI did not differ between DCM patients with ischemic and those with nonischemic origin. Coherence between heart rate and QT interval fluctuations at physiological frequencies was lower in DCM patients compared with control subjects (0.28+/-0.14 versus 0.39+/-0.18, P<.0001).
Conclusions:
DCM is associated with beat-to-beat fluctuations in QT interval that are larger than normal and uncoupled from variations in heart rate. QT interval variability increases with worsening functional class but is independent of ejection fraction. These data indicate that DCM leads to temporal lability in ventricular repolarization.