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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 (QRSmVM), planar area (QRSPA), maximum distance between centroid and loop (QRSmDCL) and perimeter (QRSP).The conventional ST-change vector magnitude (STCVM), QRS-vector difference (QRSVD) 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 STCVM, QRSVD 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 STCVM, QRSVD and SVG indexes, increase sensitivity and specificity for acute ischemia monitoring. Fil: Correa Prado, Raul Oscar. Universidad Nacional de San Juan. Facultad de Ingenieria. Departamento de Electronica y Automatica. Gabinete de Tecnologia Medica; Argentina Fil: Arini, Pedro David. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Argentino de Matemática; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Instituto de Ingeniería Biomédica; Argentina Fil: Correa Prado, Lorena Sabrina. Universidad Nacional de San Juan. Facultad de Ingenieria. Departamento de Electronica y Automatica. Gabinete de Tecnologia Medica; Argentina Fil: Valentinuzzi, Maximo. Universidad de Buenos Aires. Facultad de Ingenieria. Instituto de Ingeniería Biomédica; Argentina Fil: Laciar Leber, Eric. Universidad Nacional de San Juan. Facultad de Ingenieria. Departamento de Electronica y Automatica. Gabinete de Tecnologia Medica; Argentina

Summary The electrocardiogram of the snake can be reliably recorded with two leads: one longitudinal, the other transverse. The longitudinal lead consists of a cephalad electrode located at 10% of the body length and a caudad electrode at 50% of the body length; both electrodes are on the ventral surface of the animal. The transverse electrodes are located bilaterally at the level of the heart (approximately 24% of the body length for the species reported here). The most appropriate calibration for adequately large deflections of the recording pen is 2cm=1mV or, in some cases, 3cm=1mV. A longitudinal and a transverse distribution of the cardiac potentials have been obtained for each of the three components of the ECG. They would agree qualitatively with the predictions of the dipole theory. With the two orthogonal leads described above, a reasonable estimate of the cardiac vectors can be obtained. Changes in the position of the heart, either by handling or by artificial respiration, may introduce significant changes in the magnitude and orientation of the vectors. When transverse leads are recorded, rotation around the YY-axis usually produces large variations in the amplitudes of the ECG waves. Spontaneous changes in T-amplitude are relatively common in the snake.

Summary o 1. Body surface electrocardiograms have been recorded in the anesthetized and unanesthetized snake from leads approximating the conventions of limb leads. 2. They shown evidences of a sequence of activity in this form: from a pacemaker in the sinus venous to the atria and to the ventricles, by an electrocardiogram including an SV complex preceding the P wave. 3. The ventricular T wave in the snake is generally in the same direction as the major deflection R; Q and S are poorly developed. The T wave varies greatly in amplitude and may become completely inverted without apparent change in the position of the leads relative to the heart. 4. Direct leads and myograms from the individual chambers of the snake heart confirm the designations applied to the body surface electrocardiogram. 5. T waves have been detected following the P wave as well as the SV wave in direct leads, confirming the potentially biphasic nature of all the complexes of the electrocardiogram. 6. Studies of the duration of electrical systole related to the cardiac cycle yield ratios of 0.20, 0.40, and 0.60 for the sinus venosus, atria, and ventricle in the same heart and in comparable circumstances. They suggest a growing preponderance of the contractile element of ventricular systole. 7. As the heart deteriorates and dies the relative and absolute amplitude of the SV complex recorded from direct leads increases remarkably. 8. Spontaneous premature sinus waves and sino-atrial blocks appear as clear-cut electrographic entities.

Summary The sinus venosus-atrial Wenckebach-Lucianiphenomenon was fully and directly demonstrated in snakes and turtles. Its pattern is similar to that shown by the phenomenon at the atrio-ventricular level, and presumably the mechanisms are the same. Since a continuum of arrhythmias was observed between the 1:1 ratio and the final 2:1 block, it is inferred that the synchronization theory of Roberge and Nadeau could be extended to this case postulating the existence of three coupled oscillators.

Summary Q-T changes have been demonstrated in the snake electrocardiogram when the heart rate HR is decreased by vagal stimulation. Two types of relationships were studied with this method: Q-T as a function of HR (or R-R interval) and Q-T/R-R as a function of HR. Second degree polynomial approximations were obtained for these data. The data were also used to determine Bazett's coefficient for the snake, which was 5.6 when Q-T=K/√HR or 0.724 when Q-T=K/√R-R, where Q-T and R-R are in sec. and HR in beats/min. The second variable Q-T/R-R was found to be a nearly linear function of heart rate in the same animal at room temperature. There was no essential difference when interindividual variations were considered, although the dispersion increased significantly and a tendency of the function to become constant appeared evident with higher heart rates. This means that the relative decrease of Q-T is smaller at higher cardiac frequencies than it is at lower frequencies, and the curve begins to deviate from a straight line with a slope given by the initial angle of the second degree polynomial fit. Also, if Q-T is assumed to be constant, a chart can be constructed and superimposed on the Q-T/R-R vs HR scattergram so that the range and most probable normal value of Q-T are easily identified.