Vito Starc

Beat-to-Beat QT Interval Variability in Coronary Patients☆

Changes in ventricular repolarization have been described in patients after myocardial infarction, whereas data for coronary patients without prior myocardial infarction are lacking. This study was designed to evaluate ventricular repolarization in coronary patients with effort angina pectoris. Beat-to-beat QT interval variability (QTV) using 5-minute resting high-resolution ECG recordings was measured in 26 men (mean age 62.1 years) with effort angina pectoris and without prior myocardial infarction, and in 30 age-matched men without clinically evident coronary heart disease (controls). To evaluate the degree of coronary artery disease in coronary patients, coronary angiography was performed. Coronary patients displayed significantly higher values of QTV compared with the control patients (P < .001). Rate adaptation of QT interval correlated significantly with the degree of coronary artery disease in the study group patients (P < .05). The significant association between QTV and coronary heart disease suggests altered ventricular repolarization in coronary patients without prior myocardial infarction.

Atorvastatin Therapy May Reduce the Incidence of Sudden Cardiac Death in Patients With Advanced Chronic Heart Failure

BACKGROUND In retrospective studies, statin therapy has been related to decreased incidence of sudden cardiac death (SCD) in heart failure. We sought to prospectively investigate a relation between atorvastatin therapy and SCD in patients with advanced chronic heart failure. METHODS AND RESULTS We enrolled 110 patients with heart failure with a left ventricular ejection fraction less than 30% and cholesterol level greater than 150 mg/dL. Fifty-five patients were randomized to atorvastatin (10 mg/day) (statin group); the remaining 55 patients received no statins (controls). Patients were followed for 1 year. At baseline, the two groups did not differ in age, sex, left ventricular ejection fraction, cholesterol, B-type natriuretic peptide, heart rate variability, or QT variability. During follow-up, 29 patients died (26%) and 2 patients (2%) underwent heart transplantation. Of the 29 deaths, 13 were attributed to pump failure, 15 were attributed to SCD, and 1 was attributed to noncardiac causes. All-cause mortality was lower in the statin group (9/55, 16%) than in controls (20/55, 36%) (P = .017). The same was true of the SCD rate (3/55 [5%] vs. 12/55 [22%], P = .012), but not of the pump failure (5/55 [9%] vs. 8/55 [15%], P = .38). SCD-free survival was 2.3-times higher in the statin group than in controls (P = .01). CONCLUSIONS Atorvastatin therapy seems to be associated with decreased incidence of SCD in patients with advanced chronic heart failure. Larger studies are ongoing to confirm this hypothesis.

Conventional QT Variability Measurement vs. Template Matching Techniques: Comparison of Performance Using Simulated and Real ECG

Increased beat-to-beat variability in the QT interval (QTV) of ECG has been associated with increased risk for sudden cardiac death, but its measurement is technically challenging and currently not standardized. The aim of this study was to investigate the performance of commonly used beat-to-beat QT interval measurement algorithms. Three different methods (conventional, template stretching and template time shifting) were subjected to simulated data featuring typical ECG recording issues (broadband noise, baseline wander, amplitude modulation) and real short-term ECG of patients before and after infusion of sotalol, a QT interval prolonging drug. Among the three algorithms, the conventional algorithm was most susceptible to noise whereas the template time shifting algorithm showed superior overall performance on simulated and real ECG. None of the algorithms was able to detect increased beat-to-beat QT interval variability after sotalol infusion despite marked prolongation of the average QT interval. The QTV estimates of all three algorithms were inversely correlated with the amplitude of the T wave. In conclusion, template matching algorithms, in particular the time shifting algorithm, are recommended for beat-to-beat variability measurement of QT interval in body surface ECG. Recording noise, T wave amplitude and the beat-rejection strategy are important factors of QTV measurement and require further investigation.

Advanced electrocardiographic predictors of mortality in familial dysautonomia

OBJECTIVE To identify electrocardiographic predictors of mortality in patients with familial dysautonomia (FD). METHODS Ten-minute resting high-fidelity 12-lead electrocardiograms (ECGs) were obtained from 14 FD patients and 14 age/gender-matched healthy subjects. Multiple conventional and advanced ECG parameters were studied for their ability to predict mortality over a subsequent 4.5-year period, including representative parameters of heart rate variability (HRV), QT variability (QTV), T-wave complexity, signal averaged ECG, and 3-dimensional ECG. RESULTS Four of the 14 FD patients died during the follow-up period, three with concomitant pulmonary disorder. Of the ECG parameters studied, increased non-HRV-correlated QTV and decreased HRV were the most predictive of death. Compared to controls as a group, FD patients also had significantly increased ECG voltages, JTc intervals and waveform complexity, suggestive of structural heart disease. CONCLUSION Increased QTV and decreased HRV are markers for increased risk of death in FD patients. When present, both markers may reflect concurrent pathological processes, especially hypoxia due to pulmonary disorders and sleep apnea.

Contraction wave in axial direction in free wall of guinea pig left ventricle

Mechanical activation of the normal left ventricle (LV) is not simultaneous; however, the potential consequences of the ejection function of the ventricle are not entirely known. We studied contraction of the LV free wall to determine whether it reveals a contraction wave in the axial direction during ejection. Seven guinea pig hearts in situ were studied via thoracotomy. In each heart, the ventricular and aortic pressures were measured by two microtipped manometers (2-Fr, Millar). Contraction of the LV free wall was assessed with a video system (Dalsa D6-0256 camera and EPIX PIXCI D32 frame grabber; acquisition rate, 500 frames/s), and 15-18 epicardial markers were used to divide the region into 20-25 triangular areas. The area sizes were studied during contraction to locate the position of the contraction wave. For each triangular area, two variables were determined as follows: the time (t(c)) from the end of diastole until the size of the area reached 80% of maximum size reduction (normalized with the duration of systole) and the normalized latitude (L(ax)) of the area (determined at the end of diastole). A relationship between these two variables was determined by regression analysis. We found that the t(c) at which the contraction wave reached a triangular area was in positive correlation with the L(ax) value for that triangular area with a slope of 0.25 +/- 0.09 and a linear correlation coefficient of 0.41 +/- 0.08. Thus contraction in the guinea pig LV free wall occurs progressively from apex to base with successive areas reaching 80% contraction.

The effect of aging and cardiac disease on that portion of QT interval variability that is independent of Heart Rate Variability

Our goal was to remove all readily explainable (extrinsic) portions of beat-to-beat QT interval variability (QTV) from total QTV so as to derive the purest possible measure of intrinsic QTV. For this purpose we developed a model that describes extrinsic QTV based on other factors ascertainable from the ECG, such as changes in RR intervals, voltage amplitudes and QRS-T angles. Five-min supine high-fidelity 12-lead ECGs were acquired from 101 individuals, including from 20 healthy young men (age 21plusmn1) and from three groups of middle-aged individuals (52plusmn11 years) with increasing levels of cardiac disease. By fitting our model data to the measured QT interval signal, we calculated the explained (extrinsic) part of QTV, and the difference between the measured and the calculated QT signal represented the ldquounexplainedrdquo (or intrinsic) part of QTV. Results suggest that the ratio of unexplained to explained QTV increases with both age and cardiac disease.

Coronary Artery Disease Alters Ventricular Repolarization Dynamics in Type 2 Diabetes

Ventricular repolarization dynamics (VRD) is an important predictor of outcome in diabetes.We examined the potential impact of coronary artery disease (CAD) on VRD in type 2 diabetic patients. We recorded 5‐minute high‐resolution resting electrocardiograms in 38 diabetic patients undergoing elective coronary angiography, and in 38 age‐ and gender‐matched apparently healthy subjects (controls). Using leads‐I and ‐II, time‐domain indices of VRD were calculated. Coronary angiography was regarded as positive if ≥ 50% stenosis was found. Angiography was positive in 21 diabetic patients (55%). Patients with CAD had a significantly higher degree of VRD than controls (SDNN(QT): 15.81 ± 7.22 ms versus 8.94 ± 6.04 ms; P < 0.001, rMSSD(QT): 21.02 ± 7.07 ms versus 11.18 ± 7.45 ms; P < 0.001). Ventricular repolarization dynamics in diabetic patients with negative angiograms did not differ from VRD in controls (SDNN(QT): 8.94 ± 6.04 ms versus 7.44 ± 5.72 ms; P = 0.67, rMSSD(QT): 11.18 ± 7.45 ms versus 10.22 ± 5.35 ms; P = 0.82). CAD increases VRD in patients with type 2 diabetes. Therefore, changes in ventricular repolarization in diabetic patients may be due to silent CAD rather than due to diabetes per se.

Reliability and reproducibility of advanced ECG parameters in month-to-month and year-to-year recordings in healthy subjects

Advanced resting ECG parameters such the mean vector angle between the QRS complex and T wave (spatial QRS-T angle), and the QT interval variability index (QTVI) have important diagnostic and prognostic utility, but their reliability and reproducibility (R&R) are not well characterized. We hypothesized that the spatial QRS-T angle would have relatively higher R&R than parameters such as QTVI that are more responsive to transient changes in the autonomic nervous system. The R&R of several conventional and advanced ECG parameters were studied via intraclass correlation coefficients (ICCs) and coefficients of variation (CVs) in: (1) 15 supine healthy subjects from month-to-month; (2) 27 supine healthy subjects from year-to-year; and (3) 25 subjects after transition from the supine to the seated posture. As hypothesized, ICC for the spatial mean QRS-T angle was higher than QTVI (0.95 vs. 0.61), and CV lower (3.8 vs. 8.1%, respectively), suggesting that the former parameter is more reliable and reproducible.

Improved ECG pre-processing for beat-to-beat QT interval variability measurement

The aim of this study was to enhance the ECG pre-processing modalities for beat-to-beat QT interval variability measurement based on template matching. The R-peak detection algorithm has been substituted and an efficient baseline removal algorithm has been implemented in existing computer software. To test performance we used simulated ECG data with fixed QT intervals featuring Gaussian noise, baseline wander and amplitude modulation and two alternative algorithms. We computed the standard deviation of beat-to-beat QT intervals as a marker of QT interval variability (QTV). Significantly a lower beat-to-beat QTV was found in the updated approach compared the original algorithm. In addition, the updated template matching computer software outperformed the previous version in discarding fewer beats. In conclusion, the updated ECG preprocessing algorithm is recommended for more accurate quantification of beat-to-beat QT interval variability.

Diabetes Does Not Affect Ventricular Repolarization and Sudden Cardiac Death Risk in Patients with Dilated Cardiomyopathy

Background: We studied the effects of diabetes on ventricular repolarization parameters and sudden cardiac death in patients with dilated cardiomyopathy (DCM).