A Time-Varying Nonparametric Methodology for Assessing Changes in QT Variability Unrelated to Heart Rate Variability

Abstract

Abstract-Objective: To propose and test a novel methodology to measure changes in QT interval variability (QTV) unrelated to RR interval variability (RRV) in non-stationary conditions. Methods: Time-frequency coherent and residual spectra representing QTV related (QTVrRRV) and unrelated (QTVuRRV) to RRV, respectively, are estimated using time-frequency Cohen's class distributions. The proposed approach decomposes the nonstationary output spectrum of any two-input one-output model with uncorrelated inputs into two spectra representing the information related and unrelated to one of the two inputs, respectively. An algorithm to correct for the bias of the timefrequency coherence function between QTV and RRV is proposed to provide accurate estimates of both QTVuRRV and QTVrRRV. Two simulation studies were conducted to assess the methodology in challenging non-stationary conditions and data recorded during head-up tilt in 16 healthy volunteers were analyzed. Results: In the simulation studies, QTVuRRV changes were tracked with only a minor delay due to the filtering necessary to estimate the non-stationary spectra. The correlation coefficient between theoretical and estimated patterns was > 0.92 even for extremely noisy recordings (SNR in QTV = −10dB). During head-up tilt, QTVrRRV explained the largest proportion of QTV, whereas QTVuRRV showed higher relative increase than QTV or QTVrRRV in all spectral bands (P ≤ 0.05 for most pairwise comparisons). Conclusion: The proposed approach accurately tracks changes in QTVuRRV. Head-up tilt induced a slightly greater increase in QTVuRRV than in QTVrRRV. Significance: The proposed index QTVuRRV may represent an indirect measure of intrinsic ventricular repolarization variability, a marker of cardiac instability associated with sympathetic ventricular modulation and sudden cardiac death.

Sequential Electro-Anatomical Mapping Methodology and Preliminary Results for Reentry Vulnerability Index Estimation

“…A sequential mapping method assumes that the activation-repolarization sequence of consecutive beats is identical. In practice, this assumption is not verified as beat-to-beat variability of repolarization [4,5], and, to lesser extent, activation exists. To measure RT i and AT i from different Figure 1.…”

Nocturnal ventricular arrhythmias are associated with the severity of cardiovascular autonomic neuropathy in type 2 diabetes

“…It has been demonstrated that CAN is associated with several cardiovascular risk factors, such as hypertension, smoking, and obesity, cardiovascular disease and the use of antihypertensive drugs . Cardiovascular autonomic neuropathy is also an independent risk factor for silent ischemia, myocardial dysfunction, and major cardiovascular events . In addition, definite CAN is not only a predictor for recurrent cardiovascular disease, but has been also associated with increased all‐cause mortality in diabetic patients …”

“…One factor is autonomic neuropathy, which may result in ion channel disorder and cardiac electrophysiological disorder . Previous studies have shown that QT interval variability associated with cardiac repolarization increases with the severity of CAN, which may be responsible for the recurrence of ventricular arrhythmias . The presence of CAN also causes a significant increase in P‐wave duration and dispersion, indicating the occurrence of atrial fibrillation .…”

“…2 Cardiovascular autonomic neuropathy is also an independent risk factor for silent ischemia, myocardial dysfunction, and major cardiovascular events. [3][4][5][6] In addition, definite CAN is not only a predictor for recurrent cardiovascular disease, 7 but has been also associated with increased all-cause mortality in diabetic patients. 8 There have been several studies of nocturnal arrhythmias associated with sudden death or dead-in-bed syndrome.…”

“…17 Previous studies have shown that QT interval variability associated with cardiac repolarization increases with the severity of CAN, 18 which may be responsible for the recurrence of ventricular arrhythmias. 4 The presence of CAN also causes a significant increase in P-wave duration and dispersion, indicating the occurrence of atrial fibrillation. 19 Although above studies have shown an association between cardiac repolarization and CAN, only a few studies have examined the correlation between nocturnal arrhythmias or repolarization and CAN.…”