Esteban Valverde

Geometrical and temporal ECG features for quantification of increased ventricular repolarization dispersion in an experimental heart rabbit model

Abnormal increase of ventricular repolarization dispersion (VRD) is an important risk factor for severe arrhythmia development. An increased VRD implies a modification of the spatio/temporal T wave morphology. Our objective is to study the ECG derived VRD feature markers that better represent the electrical modifications generated by increased VRD in an in vitro rabbit heart experiment which has global VRD induced, at all myocardium areas, by supplying d-Sotalol (dS) and by premature ventricular stimulation (PVS). Temporal (T-wave duration, T W) and geometrical (mean repolarization axis, ThetaXT , measured respect to a fix reference X axis) features were shown as the better markers of increased VRD, with the higher discrinant power in the T wave duration. Results are: TW:(95plusmn7 ms) vs (118plusmn15 ms) for Control vs PVS; TW:(78plusmn10 ms) vs (133plusmn29 ms) for Control vs dS; ThetaXT-(35plusmn51deg) vs (117plusmn49deg) for Control vs dS

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 86.5 k Ω, 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 1.2 M Ω. 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.

Beat-to-beat electrocardiographic analysis of ventricular repolarization variability in patients after myocardial infarction

Several studies have shown that the beat-to-beat variability of ventricular repolarization, which can be computed by T-wave spectral variance (TSV) index, constitutes a marker of cardiac risk. Moreover, the fact that properties of action potential duration are altered during the healing (days, weeks) and healed (months) infarct stages, have been reported. However, no data exist regarding the influence of the time elapsed after myocardial infarction (MI) on modulation of the beat-to-beat ventricular repolarization variability. In the present work we have evaluated TSV index during healing and healed stages of MI using 12 standard ECG leads. The ECG of control or healthy subjects (n = 49) and the ECGs in patients after MI (n = 38), one within the first seven days (MI7) and the other after 60 days (MI60) of cardiac infarction, have been analyzed. We have considered the preferential ECG leads as those leads in which TSV index have presented a relative change greater than 10 in MI7 respect to control. Results indicate that TSV index have shown a significant increase (p < 0.0005) in I, II, aVR, aVF, V3, V4, V5 and V6 leads in healing phase of MI (MI7) with respect to control. Further, in the healed phase of MI (MI60), the TSV index tends to decrease their values towards the control. Also, we have computed a multilead TSV index based on the preferential ECG leads. In that sense, the multilead criteria have shown better perfomance quantifying beat-to-beat repolarization variability than any single ECG lead considered. The sensitivity, specificity and AUC of TSV index were: 92%, 90% and 0.96 for MI7; and 76%, 84% and 0.81 for MI60, respectively. Moreover, the beat-to-beat ventricular repolarization variability has been quantified by the QT variability index (QTVI). Even though the results that we have obtained with TSV index have been comparable to those obtained with the QTVI, this latter has not reflected the modulation effect associated to time elapsed after MI. Also, the preferential ECG leads depending on MI site using TSV index have been computed, being lead V4 for anterior and lead aVF for inferior MI, respectively. Finally, this study might help understand the role of healing and healed stages following MI on beat-to-beat variability modulation of ventricular repolarization.

Effects of amiodarone and desethylamiodarone on the inward rectifying potassium current (IK1) in rabbit ventricular myocytes

We examined the effects of amiodarone (AMI) and desethylamiodarone (DAM) on whole-cell inward rectifying potassium current (IK1) in freshly isolated adult rabbit ventricular myocytes by using the whole-cell voltage-clamp technique, as an index of their effects on resting membrane resistance (Rm). Under control conditions, the current showed a strong inward rectification with a maximal inward current measured at -130 mV of -26.4 +/- 1.3 pA/pF and a maximal outward current measured at -50 mV of 3.5 +/- 0.3 pA/pF The current also exhibit a time-dependent activation, with a time constant of activation (tau(a)) that increased with depolarization. The maximal slope conductance normalized to cell capacitance was 0.509 +/- 0.019 nS/pE After exposure to both DAM (50 microM; n = 8) and AMI (50 microM; n = 7), rapid decrease in inward IK1 was observed. Block was restricted almost exclusively to the inward component. DAM caused a significant reduction of the maximal inward current (-20.0 +/- 2.0 pA/pF; p < 0.05), whereas AMI induced an even greater reduction of the same component (-14.1 +/- 1.2 pA/pF; p < 0.05 with respect to control and to DAM). The outward component of IK1 was not changed by either AMI or DAM (4.0 +/- 0.3 pA/pF and 3.4 +/- 0.4 pA/pF, respectively). AMI and DAM also decreased the maximal slope conductance significantly (0.297 +/- 0.019 nS/pF and 0.421 +/- 0.038 nS/pF, respectively). In addition, AMI but not DAM significantly increased the tau(a). However, the voltage dependence of the acceleration of tau(a) remained unchanged after both AMI and DAM exposure. These results allow us to conclude that AMI may induce a greater increase in the resting Rm than its main metabolite. This effect may counterbalance, at least in part, the conduction slowing due to its sodium channel-blocking properties.

Beat-to-beat ventricular repolarization variability evaluated during acute myocardial ischemia ☆

Abstract Experimental and clinical studies have shown that beat-to-beat variability of ventricular repolarization morphology, which can be measured by T-wave spectral variance (TSV) index based on the two-dimensional Fourier transform, is associated with an increased risk of developing malignant ventricular arrhythmias. In the present study we tested TSV index during percutaneous coronary intervention (PCI) procedure in the 12 standard ECG leads and in the orthogonal X , Y and Z leads. In addition, we analyzed the intrasubject and intersubject variability of TSV index, in order to determine reliable limits of significant repolarization variability due to an ischemic cardiac process. A total population of 62 patients, in which two ECG controls and one ECG recording during PCI procedure, were obtained. Results indicate that TSV index showed significant differences during PCI procedure with respect to control situation in all ECG leads ( p 0.0001 ). The relative change between PCI procedure and control situation showed that there is a preferential ECG lead to analyze the TSV index depending on the occlusion site. Moreover, TSV index presented a high stability in each patient and a significant larger variability among patients. Finally, we conclude that TSV index offers a robust tool for evaluating beat-to-beat repolarization variability during acute myocardial ischemia.

Assessment of delayed ventricular activation after myocardial infarction

Abstract Experimental and clinical studies have shown that after myocardial infarction (MI), increases the risk to develop cardiac arrhythmias. We have evaluated the ventricular activation during healing (MI7) and healed (MI60) stages after MI. We carried out a comparative study between the QRS spectral variance (QRSSV) index and late potentials (LPs) obtained by the Signal-averaged (SaECG) technique. The electrocardiograms of 48 healthy subjects (CTRL); 84 patients in MI7 and 41 in MI60 without VT/VF; and also 7 patients in MI7 and 6 in MI60 with VT/VF, were analysed utilizing the Frank leads. The QRSSV has increased (p