Guillermo C. Bertrán

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.

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.

Blockade of the inward rectifier potassium currents by zinc and nickel ions in voltage-clamped toad muscles

The inward rectifier is one of the voltage-sensitive K+ channels present in several tissues: Its conductance increases under hyperpolarization and decreases with depolarization. In this work we studied the effects of Zn2+ and Ni2+ (5-30 mM) on the macroscopic K+ current through the inward rectifier system. The experiments were performed in the short muscle fibers of the lumbricalis muscle of toads with a two-microelectrode voltage clamp technique. The fibers were equilibrated in a control solution containing 68 mM K2SO4 and then exposed to Zn2+ or Ni2+. We found that both cations reduced in a reversible manner the current carried by K+ ions, and this reduction was prevented by decreasing the external pH of the solution (pH 5). The blockade of current was slightly dependent on the membrane potential and time independent. Two mechanisms may be involved in the blocking action of these cations: Zn2+ and Ni2+ may either be blocking the pore of the channels or acting at a regulatory binding site on the extracellular surface in an unspecified manner.

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.

Electrocardiogram Delineation in a Wistar Rat Experimental Model

Background and Objectives The extensive use of electrocardiogram (ECG) recordings during experimental protocols using small rodents requires an automatic delineation technique in the ECG with high performance. It has been shown that the wavelet transform (WT) based ECG delineator is a suitable tool to delineate electrocardiographic waveforms. The aim of this work is to implement and evaluate the ECG waves delineation in Wistar rats applying WT. We also describe the ECG signal of the Wistar rats giving the characteristics of its spectrum among other useful information. Methods We evaluated a delineator based on WT in a Wistar rat electrocardiograms database which was annotated manually by experienced observers. Results The delineation showed an “overall performance” such as sensitivity and a positive predictive value of 99.2% and 83.9% for P-wave, 100% and 99.9% for QRS complex, and 100% and 99.8% for T-wave, respectively. We also compared temporal analysis based ECG delineator with the WT based ECG delineator in RR interval, QRS duration, QT interval, and T-wave peak-to-end duration. The results showed that WT outperforms the temporal delineation technique in all parameters analyzed. Conclusions Finally, we propose a WT based ECG delineator as a methodology to implement in a wide diversity of experimental ECG analyses using Wistar rats.

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.