Modelling of the electrocardiographic signal during an angioplasty procedure in the right coronary artery.

Dynamical models are useful tools to generate sets of varied morphological signals by synthesizing human electrocardiograms (ECGs). These signals are used for testing and improving algorithms of ECG delineation, patient monitoring and heart disease detection. This work presents a procedure based on the ECGSYN model to synthesize ECG morphological changes induced by a percutaneous transluminal coronary angioplasty (PTCA) procedure in the right coronary artery. We provide a set of parameters to be used in ECGSYN and generate heartbeats with altered ST-T complexes. These characteristic model parameters were obtained through a non-linear fitting algorithm applied to every available heartbeat. To extend these parameters, normal distributions were generated with their means and standard deviations obtained from the STAFF III database. Parameters were presented for P, QRS and T-waves at leads II, III and aVF. The synthesis procedure shows an average correlation and positive predictive value of 92.2% and 88.2%, respectively. In conclusion, we provide a technique capable of synthesizing electrocardiographic ischemic morphology with physiological plausibility. Then, the generation of data sets for algorithm testing can benefit from this system of ECG signal synthesis.

Deconvolution: It Fans Back, Out, and Ahead [Retrospectroscope].

The origins of convolution and its further and rather complex historical development were dealt with in detail by Alejandro Dominguez in a previous article [1]. We saw there that it can be traced back to the middle of the 18th century; however, its modern form and use are not more than 50 or 60 years old.

Identification of Patients with Myocardial Infarction. Vectorcardiographic and Electrocardiographic Analysis.

BACKGROUND: The largest morbidity and mortality group worldwide continues to be that suffering Myocardial Infarction (MI). The use of vectorcardiography (VCG) and electrocardiography (ECG) has improved the diagnosis and characterization of this cardiac condition. OBJECTIVES: Herein, we applied a novel ECG-VCG combination technique to identifying 95 patients with MI and to differentiating them from 52 healthy reference subjects. Subsequently, and with a similar method, the location of the infarcted area permitted patient classification. METHODS: We analyzed five depolarization and four repolarization indexes, say: a) volume; b) planar area; c) QRS loop perimeter; d) QRS vector difference; e - g) Area under the QRS complex, ST segment and T-wave in the (X, Y, Z) leads; h) ST-T Vector Magnitude Difference; i) T-wave Vector Magnitude Difference; and j) the spatial angle between the QRS complex and the T-wave. For classification, patients were divided into two groups according to the infarcted area, that is, anterior or inferior sectors (MI-ant and MI-inf, respectively). RESULTS: Our results indicate that several ECG and VCG parameters show significant differences (p-value<0.05) between Healthy and MI subjects, and between MI-ant and MI-inf. Moreover, combining five parameters, it was possible to classify the MI and healthy subjects with a sensitivity = 95.8%, a specificity = 94.2%, and an accuracy = 95.2%, after applying a linear discriminant classifier method. Similarly, combining eight indexes, we could separate out the MI patients in MI-ant vs MI-inf with a sensitivity = 89.8%, 84.8%, respectively, and an accuracy = 89.8%. CONCLUSIONS: The new multivariable MI patient identification and localization technique, based on ECG and VCG combination indexes, offered excellent performance to differentiating populations with MI from healthy subjects. Furthermore, this technique might be applicable to estimating the infarcted area localization. In addition, the proposed method would be an alternative diagnostic technique in the emergency room.

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.

Acute myocardial ischemia monitoring before and during angioplasty by a novel vectorcardiographic parameter set.

BACKGROUND: This work evaluates the vectorcardiographic dynamic changes in ischemic patients before and during Percutaneous Transluminal Coronary Angioplasty (PTCA). METHODS: Four QRS-loop parameters were computed in 51 ischemic and 52 healthy subjects with the objective of assessing the vectorcardiographic differences between both groups: maximum vector magnitude (QRS(mVM)), planar area (QRS(PA)), maximum distance between centroid and loop (QRS(mDCL)) and perimeter (QRS(P)).The conventional ST-change vector magnitude (STC(VM)), QRS-vector difference (QRS(VD)) and spatial ventricular gradient (SVG) were also calculated. RESULTS: Statistical minute-by-minute PTCA comparison against a healthy population showed that ischemic patients monitoring is greatly enhanced when all the QRS-loop parameters, in combination with the standard STC(VM), QRS(VD) and SVG indexes, are used in the classification. Sensitivity and Specificity, in turn, reached rather high values, 95.4% and 95.2%, respectively. CONCLUSIONS: These new vectorcardiographic set of complementary QRS-loop parameters, when combined with the classics STC(VM), QRS(VD) and SVG indexes, increase sensitivity and specificity for acute ischemia monitoring.

Novel set of vectorcardiographic parameters for the identification of ischemic patients.

New signal processing techniques have enabled the use of the vectorcardiogram (VCG) for the detection of cardiac ischemia. Thus, we studied this signal during ventricular depolarization in 80 ischemic patients, before undergoing angioplasty, and 52 healthy subjects with the objective of evaluating the vectorcardiographic difference between both groups so leading to their subsequent classification. For that matter, seven QRS-loop parameters were analyzed, i.e.: (a) Maximum Vector Magnitude; (b) Volume; (c) Planar Area; (d) Maximum Distance between Centroid and Loop; (e) Angle between XY and Optimum Plane; (f) Perimeter and, (g) Area-Perimeter Ratio. For comparison, the conventional ST-Vector Magnitude (ST(VM)) was also calculated. Results indicate that several vectorcardiographic parameters show significant differences between healthy and ischemic subjects. The identification of ischemic patients via discriminant analysis using ST(VM) produced 73.2% Sensitivity (Sens) and 73.9% Specificity (Spec). In our study, the QRS-loop parameter with the best global performance was Volume, which achieved Sens=64.5% and Spec=74.6%. However, when all QRS-loop parameters and ST(VM) were combined, we obtained Sens=88.5% and Spec=92.1%. In conclusion, QRS loop parameters can be accepted as a complement to conventional ST(VM) analysis in the identification of ischemic patients.

The allometric model in chronic myocardial infarction.

BACKGROUND: An allometric relationship between different electrocardiogram (ECG) parameters and infarcted ventricular mass was assessed in a myocardial infarction (MI) model in New Zealand rabbits. METHODS: A total of fifteen animals were used, out of which ten underwent left anterior descending coronary artery ligation to induce infarction (7-35% area). Myocardial infarction (MI) evolved and stabilized during a three month-period, after which, rabbits were sacrificed and the injured area was histologically confirmed. Right before sacrifice, ECGs were obtained to correlate several of its parameters to the infarcted mass. The latter was normalized after combining data from planimetry measurements and heart weight. The following ECG parameters were studied: RR and PR intervals, P-wave duration (PD), QRS duration (QRSD) and amplitude (QRSA), Q-wave (QA), R-wave (RA) and S-wave (SA) amplitudes, T-wave peak amplitude (TA), the interval from the peak to the end of the T-wave (TPE), ST-segment deviation (STA), QT interval (QT), corrected QT and JT intervals. Corrected QT was analyzed with different correction formulae, i.e., Bazett (QTB), Framingham (QTFRA), Fridericia (QTFRI), Hodge (QTHO) and Matsunaga (QTMA) and compared thereafter. The former variables and infarcted ventricular mass were then fitted to the allometric equation in terms of deviation from normality, in turn derived after ECGs in 5 healthy rabbits. RESULTS: Six variables (JT, QTB, QA, SA, TA and STA) presented statistical differences among leads. QT showed the best allometric fit (r = 0.78), followed by TA (r = 0.77), STA (r = 0.75), QTFRA (r = 0.72), TPE (r = 0.69), QTFRI (r = 0.68) and QTMA (r = 0.68). Corrected QT's (QTFRA, QTFRI and QTMA) performed worse than the uncorrected counterpart (QT), the former scaling allometrically with similar goodness of fits. CONCLUSIONS: QT, TA, STA and TPE could possibly be used to assess infarction extent in an old MI event through the allometric model as a first approach. Moreover, the TPE also produced a good allometric scaling, leading to the potential existence of promising allometric indexes to diagnose malignant arrhythmias.

Probability of ventricular fibrillation: allometric model based on the ST deviation.

BACKGROUND: Allometry, in general biology, measures the relative growth of a part in relation to the whole living organism. Using reported clinical data, we apply this concept for evaluating the probability of ventricular fibrillation based on the electrocardiographic ST-segment deviation values. METHODS: Data collected by previous reports were used to fit an allometric model in order to estimate ventricular fibrillation probability. Patients presenting either with death, myocardial infarction or unstable angina were included to calculate such probability as, VFp = δ + ß (ST), for three different ST deviations. The coefficients δ and ß were obtained as the best fit to the clinical data extended over observational periods of 1, 6, 12 and 48 months from occurrence of the first reported chest pain accompanied by ST deviation. RESULTS: By application of the above equation in log-log representation, the fitting procedure produced the following overall coefficients: Average ß = 0.46, with a maximum = 0.62 and a minimum = 0.42; Average δ = 1.28, with a maximum = 1.79 and a minimum = 0.92. For a 2 mm ST-deviation, the full range of predicted ventricular fibrillation probability extended from about 13% at 1 month up to 86% at 4 years after the original cardiac event. CONCLUSIONS: These results, at least preliminarily, appear acceptable and still call for full clinical test. The model seems promising, especially if other parameters were taken into account, such as blood cardiac enzyme concentrations, ischemic or infarcted epicardial areas or ejection fraction. It is concluded, considering these results and a few references found in the literature, that the allometric model shows good predictive practical value to aid medical decisions.

Prediction of ventricular fibrillation based on the ST-segment deviation: allometric model.

Based on some reported clinical data, we attempt to apply the allometric law for evaluating the probability of ventricular fibrillation when electrocardiographic ST-segment deviations are determined. The deviation is measured in millimeters at the standard calibration of 1mV = 10mm and the probability in percent. Using the equation VF(P) = δ + ß (ST) in log-log representation, the fitting procedure produced the following overall coefficients: Average ß = 1.11, with a maximum = 1.65 and a minimum = 0.78; Average δ = 0.83, with a maximum = 1.39 and a minimum = 0.41. For a 2mm ST-deviation, the full range of predicted ventricular fibrillation probability extended from about 6% at 1 month up to 47% at 4 years after the original cardiac event. These results, at least preliminarily, appear acceptable and still call for full clinical test. The model seems promising if other parameters were taken into account, such as cardiac enzyme concentration, ischemic or infarcted epicardial areas or ejection fraction. It is concluded, considering these results and a few references found in the literature, that the allometric model shows promising features in cardiology.

[Influence of sexual maturity and gonadectomy on cardiac electrical activity in male and female rabbits]. / Influencia de la madurez sexual y la castración sobre la actividad eléctrica cardiaca en conejos machos y hembras.

Sex-associated differences in cardiac electrical activity have already been document noted. Even though these differences are usually associated with the effect of maturity and sex hormones, there are still some controversial points to this respect. The aim of this study was to evaluate the effects of maturity and gonadectomy on the different parameters of surface electrocardiogram and the duration of the action potential in young and adult rabbits. The differences obtained in females were observed in late repolarization, whereas in males took place in early repolarization. There was a relationship between the differences observed in the duration from the peak to the end of the T wave and those observed in the duration of the action potential to 90% of repolarization in females, whereas in males the relationship exists between the duration from the point J to the peak of the T wave and the duration of the action potential at 30 and 50% of repolarization. Differences could be related to hormonal or non-hormonal factors.

Influencia de la madurez sexual y la castración sobre la actividad eléctrica cardíaca en conejos machos y hembras / Influence of sexual maturity and gonadectomy on cardiac electrical activity in male and female rabbits

Es bien conocida la existencia de diferencias en la actividad eléctrica cardíaca asociadas al sexo. Si bien estas diferencias habitualmente se relacionan al efecto de la madurez y de las hormonas sexuales gonadales, todavía existen controversias al respecto. El objetivo de este trabajo fue evaluar el efecto que la madurez sexual y la castración producen sobre los distintos parámetros del electrocardiograma de superficie y de la duración de los potenciales de acción (DPA). Se utilizaron conejos jóvenes (menores de un mes de edad) y adultos (mayores de seis meses de edad). Las diferencias obtenidas en las hembras se observan en la repolarización tardía, mientras que en los machos ocurren en la repolarización temprana. Existiría una relación entre las diferencias observadas en la duración desde el pico máximo hasta el fin de la onda T (Tpf) y las observadas en la DPA al 90% de la repolarización (DPA90) en las hembras, mientras que en los machos la relación existe entre la duración desde el punto J hasta el pico máximo de la onda T (JTp) y la DPA al 30 y 50% de la repolarización (DPA30 y DPA50). Si bien existen diferencias que podrían ser debidas a factores hormonales otras serían debidas a factores no hormonales.

Sex-associated differences in cardiac electrical activity have already been documented. Even though these differences are usually associated with the effect of maturity and sex hormones, there are still some controversial points to this respect. The aim of this study was to evaluate the effects of maturity and gonadectomy on the different parameters of surface electrocardiogram and the duration of the action potential in young and adult rabbits. The differences obtained in females were observed in late repolarization, whereas in males took place in early repolarization. There was a relationship between the differences observed in the duration from the peak to the end of the T wave and those observed in the duration of the action potential to 90% of repolarization in females, whereas in males the relationship exists between the duration from the point J to the peak of the T wave and the duration of the action potential at 30 and 50% of repolarization. Differences could be related to hormonal or non-hormonal factors.

Cuantificación de la dispersión espacial de la repolarización ventricular cardíaca a través del electrocardiograma de superficie / Quantification of Cardiac Ventricular Repolarization and its Spatial Dispersion through the Surface Electrocardiogram

La dispersión de la repolarización ventricular (DRV) está determinada esencialmente por la heterogeneidad de los potenciales de acción en diferentes regiones del miocardio. Con frecuencia el corazón responde a ciertos estados fisiopatológicos con la producción de un incremento de la DRV, fenómeno éste que puede devenir en una arritmia ventricular maligna y/o en la muerte súbita. Hace 25 años, con el objetivo de identificar a pacientes de riesgo cardíaco, se comenzó a cuantificar la DRV con diversos índices obtenidos por procesamiento computacional del electrocardiograma. Estos índices se basan en la detección de cambios en la duración o en la forma en la onda T en presencia de cardiopatías. En este trabajo se presenta una revisión de los índices de dispersión espacial y su potencialidad como herramienta de apoyo al diagnóstico de riesgo cardíaco.

The ventricular repolarization dispersion (VRD) is determined basically by the heterogeneity of the action potentials in different myocardial regions. Usually the heart responds to certain physiopathological states by producing a VRD increase, which may lead to a malignant ventricular arrhythmia and/or sudden death. For 25 years, the VRD has been quantified with several indexes obtained by computerprocessing the electrocardiogram, in order to identify cardiac- risk patients. These indexes are based on the detection of T wave changes in duration or form, in the presence of cardiopathies. A revision of the spatial dispersion indexes and their potential as supporting tool for the diagnosis of cardiac risk is presented in this work.

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. METHODS AND RESULTS: Singular value decomposition was applied to the repolarization signals obtained from isolated rabbit hearts using a 5 x 8 array multielectrode recording system during premature beats (N = 11) and after d-sotalol (N = 9) exposure. Both the dipolar and nondipolar components of the T wave increased significantly during premature stimulation and after d-sotalol exposure. The relative TWR decreased significantly during premature stimulation but did not change after d-sotalol. Changes in the dipolar and nondipolar components of the second half of the T wave were significantly greater than those corresponding to the first half during premature stimulation, and a significant correlation was observed between the nondipolar components of the second half of the T wave and the T(peak-end) interval. CONCLUSION: Conditions exist during which both the dipolar and nondipolar components can change simultaneously. Under these conditions, the relative TWR may not reflect regional heterogeneity of repolarization with accuracy. The nondipolar components of the second half of the T wave can be linked to assessment of the transmural dispersion of repolarization.

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

OBJECTIVES: Firstly, 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. METHODS: We 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. RESULTS: Adult 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. CONCLUSIONS: Developmental 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.

Lack of effect of conduction direction on action potential durations in anisotropic ventricular strips of pig heart.

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. METHODS AND RESULTS: We examined the influence of activation sequence on the repolarization phase of action potentials in epicardial tissues from the right and left ventricles of domestic pigs. Whereas cells from the right ventricle exhibited direction-dependent differences in action potential duration at 30%, 50%, and 90% of full repolarization (190.6 +/- 31.1 msec vs 181.8 +/- 32.8 msec, 240.3 +/- 23.5 msec vs 236.7 +/- 25.4 msec, and 291.3 +/- 23.7 msec vs 287.4 +/- 25.1 msec for longitudinal and transverse propagation, respectively; P < 0.001), a similar duration of repolarization during both directions of propagation was observed in cells from the left ventricle at 50% and 90% of full repolarization (241.4 +/- 39.4 msec and 285.5 +/- 39.5 msec vs 240.4 +/- 38.9 msec and 284.9 +/- 39.6 msec for longitudinal and transverse propagation respectively; P = NS). A slight but significant difference was found at 30% of full repolarization in cells from the left ventricle (190.4 +/- 39.0 msec vs 187.0 +/- 38.0 msec for longitudinal and transverse propagation, respectively; P < 0.05). In the left ventricle, the duration of repolarization did not change as the distance between the recording site and stimulation site increased. CONCLUSION: The direction of wavefront propagation with respect to fiber orientation may not play an important role in modulating the duration of repolarization in epicardial cells from the left ventricle.

Análisis experimental de la repolarización ventricular / Experimental analysis of the ventricular repolarization

En el presente trabajo se vuelca nuestra experiencia en el estudio de la repolarización ventricular. Hemos podido comprobar, en primer lugar, que las caracterísitcas anisotrópicas del tejido cardíaco son capaces de modular la repolarización ya que, en el epicardio del ventrículo derecho los potenciales de acción son más cortos tanto al 30 como al 50 y al 90 por ciento de la repolarización completa, durante la propagación transversal cuando se los compara con los obtenidos durante la propagación longitudinal o paralela al eje mayor de las fibras cardíacas. Sin embargo esto no se cumple en el ventriculo izquierdo (Tabla 1). Este comportamiento diferente en la modulación de la repolarización, probablemente ligado con la presencia de propiedades anisotrópicas no homogéneas entre ambos ventrículos, contribuye a su vez a modular la dispersión de la repolarización ventricular especialmente ante situaciones en las que el efecto electrotónico se vea favorecido por la presencia de conducción lenta. En segundo lugar pudimos comprobar que la evaluación de la dispersión de la repolarización incrementa su poder de discriminación si se la mide con una grilla de electrodos distribuídos homogeneamente en la superficie del tórax. En tercer lugar comprobamos que el incremento en la dispersión de la repolarización ventricular en función del intervalo de acoplamiento de un latido prematuro exhibe un comportamiento diferencial dependiente del sitio de estimulación. Esto es mientras la dispersión de la repolarización se incrementa monotónicamente a medida que se acorta el intervalo de acoplamiento de un latido prematuro cuando el sitio de aplicación de los estímulos se ubica en el ventrículo derecho. Cuando los estímulos fueron aplicados en el ventrículo izquierdo pudimos observar que la dispersión mostró una reducción incicial en función del período de acoplamiento hasta alcanzar un mínimo y a partir de allí exhibe un incremento monotónico. Finalmente, ha sido sugerido que cambios en la forma -mas que cambios en la duración- de la onda T son los que contribuyen a aumentar la heterogeneidad de la repolarización. En este sentido, se ha mostrado que la alternancia en la onda T, que es una manifestación extrema de anormalidades en la forma de la onda T, puede relacionarse con incremento del riesgo a las taquiarritmias ventriculares... (TRUNCADO)

Análisis experimental de la repolarización ventricular / Experimental analysis of the ventricular repolarization

En el presente trabajo se vuelca nuestra experiencia en el estudio de la repolarización ventricular. Hemos podido comprobar, en primer lugar, que las caracterísitcas anisotrópicas del tejido cardíaco son capaces de modular la repolarización ya que, en el epicardio del ventrículo derecho los potenciales de acción son más cortos tanto al 30 como al 50 y al 90 por ciento de la repolarización completa, durante la propagación transversal cuando se los compara con los obtenidos durante la propagación longitudinal o paralela al eje mayor de las fibras cardíacas. Sin embargo esto no se cumple en el ventriculo izquierdo (Tabla 1). Este comportamiento diferente en la modulación de la repolarización, probablemente ligado con la presencia de propiedades anisotrópicas no homogéneas entre ambos ventrículos, contribuye a su vez a modular la dispersión de la repolarización ventricular especialmente ante situaciones en las que el efecto electrotónico se vea favorecido por la presencia de conducción lenta. En segundo lugar pudimos comprobar que la evaluación de la dispersión de la repolarización incrementa su poder de discriminación si se la mide con una grilla de electrodos distribuídos homogeneamente en la superficie del tórax. En tercer lugar comprobamos que el incremento en la dispersión de la repolarización ventricular en función del intervalo de acoplamiento de un latido prematuro exhibe un comportamiento diferencial dependiente del sitio de estimulación. Esto es mientras la dispersión de la repolarización se incrementa monotónicamente a medida que se acorta el intervalo de acoplamiento de un latido prematuro cuando el sitio de aplicación de los estímulos se ubica en el ventrículo derecho. Cuando los estímulos fueron aplicados en el ventrículo izquierdo pudimos observar que la dispersión mostró una reducción incicial en función del período de acoplamiento hasta alcanzar un mínimo y a partir de allí exhibe un incremento monotónico. Finalmente, ha sido sugerido que cambios en la forma -mas que cambios en la duración- de la onda T son los que contribuyen a aumentar la heterogeneidad de la repolarización. En este sentido, se ha mostrado que la alternancia en la onda T, que es una manifestación extrema de anormalidades en la forma de la onda T, puede relacionarse con incremento del riesgo a las taquiarritmias ventriculares... (TRUNCADO) (AU)