Marcelo O. Biagetti

Developmental changes of cardiac repolarization in rabbits: implications for the role of sex hormones.

OBJECTIVESnFirstly, to compare gender-dependent differences of cardiac repolarization in both adult and young rabbits. Secondly, to analyze the effect of gonadectomy on these gender differences in cardiac repolarization.nnnMETHODSnWe evaluated potential gender differences in cardiac repolarization with both microelectrode and ECG recordings. QT(end), JT(end), and T(peak-end) intervals and action potential durations at 30%, 50% and 90% of full repolarization were used to assess ventricular repolarization in adult (normal and gonadectomized) and young rabbits of both sexes.nnnRESULTSnAdult rabbits exhibited clear gender-related differences in repolarization evidenced by significantly longer JT(end) and T(peak-end) intervals and significantly longer APD30, APD50 and APD90 in females. These gender-related differences in repolarization were absent in young rabbits and were abolished by gonadectomy.nnnCONCLUSIONSnDevelopmental changes of repolarization are present in rabbits. These changes are in agreement with those reported in humans and may further support the role played by sex hormones in the modulation of cardiac repolarization.

Unsupervised classification of ventricular extrasystoles using bounded clustering algorithms and morphology matching

Ventricular extrasystoles (VE) are ectopic heartbeats involving irregularities in the heart rhythm. VEs arise in response to impulses generated in some part of the heart different from the sinoatrial node. These are caused by the premature discharge of a ventricular ectopic focus. VEs after myocardial infarction are associated with increased mortality. Screening of VEs is typically a manual and time consuming task that involves analysis of the heartbeat morphology, QRS duration, and variations of the RR intervals using long-term electrocardiograms. We describe a novel algorithm to perform automatic classification of VEs and report the results of our validation study. The proposed algorithm makes use of bounded clustering algorithms, morphology matching, and RR interval length to perform automatic VE classification without prior knowledge of the number of classes and heartbeat features. Additionally, the proposed algorithm does not need a training set.

Role of Dipolar and Nondipolar Components of the T Wave in Determining the T Wave Residuum in an Isolated Rabbit Heart Model

Introduction: Repolarization heterogeneity has been shown to constitute a substrate for malignant ventricular arrhythmias. Noninvasive measurement of abnormal repolarization through assessment of QT interval dispersion from the resting standard 12‐lead ECG initially had shown promise in assessing arrhythmia risk but was challenged recently. The relative T wave residuum (TWR) has been proposed recently to reflect regional repolarization dispersion more accurately. We analyzed the role played by the dipolar and nondipolar components in determining TWR.

Lack of Effect of Conduction Direction on Action Potential Durations in Anisotropic Ventricular Strips of Pig Heart

Anisotropy and Repolarization. Introduction: The influence of activation sequence on the rate of rise of the depolarization phase of action potentials in atrial or ventricular muscles has been well established. However, whether myocardial fiber orientation is important in modulating the repolarization process is unclear.

Enhanced modified moving average analysis of T-wave alternans using a curve matching method: a simulation study

T-wave alternans (TWA) are beat-to-beat amplitude oscillations in the T-waves of electrocardiograms (ECGs). Numerous clinical studies have demonstrated the link between these oscillations and ventricular arrhythmias. Several methods have been developed in recent years to detect and quantify this important feature. Most methods estimate the amplitude differences between pairs of consecutive T-waves. One such method is known as modified moving average (MMA) analysis. The TWA magnitude is obtained by means of the maximum absolute difference of even and odd heartbeat series averages computed at T-waves or ST–T complexes. This method performs well for different levels of TWA, noise, and phase shifts, but it is sensitive to the alignment of the T-waves. In this paper we propose a preprocessing stage for the MMA method to ensure an optimal alignment of such averages. The alignment is performed by means of a continuous time warping technique. Our assessment study demonstrates the improved performance of the proposed algorithm.

Influence of Filtering Techniques on the Time-Domain Analysis of Signal-Averaged P Wave Electrocardiogram

Differences in P Wave Filtering Techniques. introduction: The advent of signal‐averaged ECG (SAECG) systems for P wave analysis has made it important to determine if the use of different filtering techniques in these systems is diagnostically equivalent.

Beat-to-Beat Repolarization Variability Measured by T Wave Spectral Variance Index in Chronic Infarcted Animals

Background: Recent experimental and clinical studies have shown that beat‐to‐beat variability of repolarization morphology is associated with an increased risk for developing malignant ventricular arrhythmias. However, few data exist on the relationship between beat‐to‐beat repolarization variability and myocardial infarction itself.

Chronic versus acute effects of amiodarone on the Vmax-conduction velocity relationship and on the space constant in canine myocardium

Isolated tissue experiments (canine ventricular epicardium) and computer simulations were used to characterize the relationship between changes in maximum rate of depolarization during upstroke (Vmax) and the conduction velocity (theta) induced after long-term therapy with amiodarone and to compare these data with those obtained after acute superfusion with either desethylamiodarone or the parent compound. After chronic amiodarone, the changes in Vmax were linearly related to the square of the changes in theta during longitudinal propagation (LP) (slope = 0.93, r = 0.93, p = NS with respect to slope = 1), whereas during transverse propagation (TP), the slope of the relationship between both variables was slightly decreased (slope = 0.88, r = 0.96, p < 0.05 with respect to slope = 1). Similar results were observed after acute superfusion with desethylamiodarone (LP), (slope = 1, r = 0.05, p = NS with respect to slope = 1). In contrast, a significant increase in slope (p < 0.05 with respect to slope = 1) was observed after acute superfusion (slope = 1.45, r = 0.85 and slope = 1.48, r = 0.75 during LP and TP, respectively). In addition, the space constant (lambda) after chronic amiodarone (1.05 +/- 0.06 mm) was not significantly different from control (0.98 +/- 0.04 mm), but was slightly though significantly increased after acute amiodarone administration (1.07 +/- 0.03 mm, p < 0.03). Data are mean +/- SEM. Experimental data from chronic amiodarone were well fitted in a one-dimensional Beeler-Reuter-based discrete cable by reducing sodium conductance (GNa) exclusively. In contrast, data from acute superfusion were fitted only when junctional resistance (rj) and GNa were simultaneously reduced. These data suggest that acute amiodarone may modify both active and passive membrane properties whereas chronic amiodarone appears to alter only the active properties; the data further indicate that desethylamiodarone may play an important role in the mechanism of action of chronic amiodarone treatment.

Differential Modulation of Electrocardiographic Indices of Ventricular Repolarization Dispersion Depending on the Site of Pacing During Premature Stimulation

Differential Modulation of ECG Indices of Dispersion. Introduction: Dispersion of ventricular repolarization has been shown to increase with premature stimulation. Moreover, a straight correlation between the amount of dispersion of repolarization and the vulnerability to ventricular fibrillation was reported. On the other hand, differences between right ventricular (RV) and left ventricular (LV) fibrillation threshold have been reported. However, no data exist regarding the influence of the site of stimulation on modulation of dispersion of repolarization.

Effect of electrode impedance in improved buffer amplifier for bioelectric recordings

We analysed the effects of electrode impedance on the transfer response of a one-stage improved buffer amplifier. The electrode DC resistance (Rd) modifies the one-stage buffer transfer response. We found a limit electrode resistance (Rd(lim)) which depends on the transfer damping factor (ϵ). If Rd is lower than 86.5u2009ku200aΩ, the transfer response of the buffer fulfils American Heart Association (AHA) recommendations, but when Rd is greater than Rd(lim) it must be cautiously weighed up because its influence in the transfer response becomes appreciable. The maximum Rd that can be driven by the buffer is 1.2u2009Mu200aΩ. Higher values do not fulfil AHA recommendations. Therefore, electrodes with higher impedance should not be used with this kind of buffer. In contrast, when this buffer is used to build in an instrumentation amplifier (IA) for bipolar recording, the common-mode rejection ratio (CMRR) is sensitive to the electrode type used.