Electrophysiologic effects of surgical isolation of the right ventricle

Pacing to Restore Right Ventricular Contraction After Surgical Disconnection for Arrhythmia Control in Right Ventricular Cardiomyopathy

Ventricular tachycardia in ARVC (arrhythmogenic right ventricular cardiomyopathy) is typically managed by ICD implantation, with a limited role of catheter ablation. Surgical disconnection of the right ventricular (RV) has been used to control ventricular tachycardia (VT) in ARVC, but it often led to refractory RV failure due to loss of RV contraction after surgery. We report multisite pacing to recruit the disconnected RV to prevent ventricular failure.

Cardiac Surgery for Arrhythmias

Cardiac arrhythmia surgery was initiated in 1968 with the first successful division of an accessory AV connection for the Wolff-Parkinson-White Syndrome. Subsequent surgical procedures included the left atrial isolation procedure and the right atrial isolation procedure for automatic atrial tachycardias, discrete cryosurgery of the AV node for AV nodal reentry tachycardia, the atrial transection procedure, corridor procedure and Maze procedure for atrial fibrillation, the right ventricular disconnection procedure for arrhythmogenic right ventricular tachycardia, the encircling endocardial ventriculotomy, subendocardial resection procedure, endocardial cryoablation, the Jatene procedure, and the Dor procedure for ischemic ventricular tachycardia. Because of monumental strides in the treatment of most refractory arrhythmias by endocardial catheter techniques during the past decade, the only remaining viable surgical procedures for cardiac arrhythmias are the Maze procedure for atrial fibrillation and the Dor procedure for ischemic ventricular tachycardia. Nevertheless, the 25-30 years of intense activity in the field of cardiac arrhythmia surgery provided the essential foundation for the development of these catheter techniques and represent one of the most exciting and productive eras in the history of medicine. In one short professional career, we have witnessed the birth of arrhythmia surgery, its adolescence as an "esoteric" specialty, its prime as an enlightening yet exhausting period, and finally its waning years as a source of knowledge and wisdom on which better methods of treatment have been founded. One could hardly ask for a more rewarding experience.

Cardiac Surgery for Arrhythmias

Cardiac arrhythmia surgery was initiated in 1968 with the first successful division of an accessory AV connection for the Wolff-Parkinson-White syndrome. Subsequent surgical procedures included the left atrial isolation procedure and right atrial isolation procedure for automatic atrial tachycardias, discrete cryosurgery of the AV node for AV nodal reentrant tachycardia, the atrial transection procedure, the corridor procedure, and the maze procedure for atrial fibrillation, the right ventricular disconnection procedure for arrhythmogenic right ventricular tachycardia, and the encircling endocardial ventriculotomy, subendocardial resection procedure, endocardial cryoablation, the Jatene procedure, and the Dor procedure for ischemic ventricular tachycardia. Because of monumental strides in the treatment of most refractory arrhythmias by endocardial catheter techniques during the past decade, the only remaining viable surgical procedures for cardiac arrhythmias are the maze procedure for atrial fibrillation and the Dor procedure for ischemic ventricular tachycardia. Nevertheless, the 25 to 30 years of intense activity in the field of cardiac arrhythmia surgery provided the essential foundation for the development of these catheter techniques and represent one of the most exciting and productive eras in the history of medicine. In one short professional career, we have witnessed the birth of arrhythmia surgery, its adolescence as an "esoteric" specialty, its prime as an enlightening yet exhausting period, and finally its waning years as a source of knowledge and wisdom upon which better methods of treatment have been founded. One could hardly ask for a more rewarding experience.

Spatiotemporal complexity of ventricular fibrillation revealed by tissue mass reduction in isolated swine right ventricle. Further evidence for the quasiperiodic route to chaos hypothesis

We have presented evidence that ventricular fibrillation is deterministic chaos arising from quasiperiodicity. The purpose of this study was to determine whether the transition from chaos (ventricular fibrillation, VF) to periodicity (ventricular tachycardia) through quasiperiodicity could be produced by the progressive reduction of tissue mass. In isolated and perfused swine right ventricular free wall, recording of single cell transmembrane potentials and simultaneous mapping (477 bipolar electrodes, 1.6 mm resolution) were performed. The tissue mass was then progressively reduced by sequential cutting. All isolated tissues fibrillated spontaneously. The critical mass to sustain VF was 19.9 +/- 4.2 g. As tissue mass was decreased, the number of wave fronts decreased, the life-span of reentrant wave fronts increased, and the cycle length, the diastolic interval, and the duration of action potential lengthened. There was a parallel decrease in the dynamical complexity of VF as measured by Kolmogorov entropy and Poincaré plots. A period of quasiperiodicity became more evident before the conversion from VF (chaos) to a more regular arrhythmia (periodicity). In conclusion, a decrease in the number of wave fronts in ventricular fibrillation by tissue mass reduction causes a transition from chaotic to periodic dynamics via the quasiperiodic route.

Left ventricular pressure effects on right ventricular pressure and volume outflow

Massive destruction of the right ventricular free wall has been shown to cause only mild hemodynamic alterations. Further, the derivative of right ventricular (RV) pressure (P) is broad or double peaked, with one peak occurring coincidentally with peak left ventricular (LV) dP/dt. Both observations suggest a direct LV assistance to RV function. Since the ventricles contract nearly simultaneously, the relative contribution of LV to RV pump function has been difficult to determine. This LV assistance was quantified in six canine experiments using a unique electrically isolated RV preparation. While on total cardiopulmonary bypass, the RV free wall was electrically isolated from the remainder of the heart. This preparation allowed for wide variations in the timing interval between RV and LV contractions. Double-peaked waveforms for RVP and pulmonary flow (RVF) occurred over a wide range (0 to 300 ms) of pacing intervals between the RV and LV. One derivative peak always followed RV contraction for RVP and RVF (r = 0.971 +/- .011, P less than 0.01: r = 0.972 +/- .012, p less than 0.01; respectively). The second derivative peak was unrelated to the RA-RV pacing interval (r = 0.297 +/- .191, P greater than 0.5 RVP; 4 = 0.237 +/- .278, P greater than 0.5 RVF), but corresponded to the maximal LVP rise. Additionally, the magnitude of the two derivative peaks was similar when the ventricles contracted synchronously. When RV contraction preceded or followed LV contraction, the derivative peak associated with LV contraction was significantly greater (P less than 0.05, range 2.1 +/- 0.6 to 6.7 +/- 1.6 for RVP; P less than 0.05 range 1.9 +/- 0.4 to 6.7 +/- 1.5 for RVF) than the derivative associated with RV contraction. These data demonstrate a normally present, large LV assistance to RV contraction and may help to explain the RV response to myocardial infarction.

Effect of the right ventricular isolation procedure on ventricular vulnerability to fibrillation

A certain critical mass of myocardium is believed to be necessary to initiate ventricular fibrillation. The right ventricular isolation procedure, employed clinically to confine ventricular tachyarrhythmias to the right ventricle, decreases the ventricular mass available for fibrillation by isolating the ventricles from each other. The effect of this procedure on ventricular fibrillation thresholds is unknown. Left and right ventricular fibrillation thresholds were measured before and after right ventricular isolation in 10 adult mongrel dogs utilizing a single 5 ms stimulus of increasing current strength applied to the epicardium during the vulnerable period. There were no significant differences in heart rate, aortic blood pressure, left atrial pressure, temperature, arterial blood gases or regional myocardial blood flow between the study periods. In 9 of the 10 dogs, the isolated right ventricle could not sustain ventricular fibrillation despite the utilization of stimulus strengths of up to 80 mA. In the 10th dog, the right ventricular fibrillation threshold increased 150%, from 20 to 50 mA. The left ventricular fibrillation threshold markedly increased in every dog, with an average increase from 23 +/- 2 to 40 +/- 4 mA (p less than 0.0005). To determine whether time, cardiopulmonary bypass or the right ventricular incision could cause similar changes in ventricular fibrillation threshold, five different dogs underwent the entire experimental protocol except for incomplete isolation of the right ventricle. There were no significant changes in ventricular fibrillation thresholds in these dogs. Thus, in the canine model, right ventricular isolation can prevent the occurrence of sustained fibrillation in the isolated right ventricle and can significantly increase the left ventricular fibrillation threshold.

Interpolating unipolar epicardial potentials from electrodes separated by increasing distances

In cardiac mapping, potentials for unexplored areas are estimated by interpolating values from nearest neighbor electrodes regardless of distances between these sites or wave front orientation. The effects of these variables on interpolated unipolar electrograms were analyzed two ways: with a computer model and with electrograms recorded 9.9 and 14.1 mm apart. For the model, wave fronts (n = 39) were generated from electrograms recorded during right ventricular (RV) activation in five dogs following the RV isolation procedure. Each wave front was assumed to propagate radially at 0.5 m/sec from a site 30 mm from the center of a square array with electrodes located at the center and corners. Each wave front crossed the array with its tangent at an angle of 0 degrees, 45 degrees, or 90 degrees to the diagonal line connecting opposite corner electrodes. Potentials for all five sites were generated from each wave front and were interpolated for the center site from the generated corner potentials. Generated and interpolated center site potentials were compared using correlation coefficients (r) and percent root mean square differences (%RMSD). Mean r values fell below 0.90 for interelectrode distances of 15.6 mm, 2.8 mm, and 1.4 mm at 0 degrees, 45 degrees, and 90 degrees wave front orientations, respectively. For experimentally measured potentials recorded 9.9 mm apart, results from interpolated electrograms were similar to results from the model at 0 degrees propagation. Electrograms interpolated from potentials measured 14.1 mm apart had poorer r and %RMS values than those from the computer model. Thus, with linear interpolation unipolar electrograms can be inaccurately interpolated from electrodes less than 3 mm apart or correctly interpolated from electrodes more than 14 mm apart depending upon wave front orientation.

Results of direct surgical ablation of ventricular tachycardia not due to ischemic heart disease

Surgical treatment of sustained ventricular tachycardia due to nonischemic causes is uncommon. Nonischemic ventricular tachycardia was treated in 14 patients by map-directed surgical ablation of an arrhythmogenic site. There were 9 male and 5 female patients. The mean age was 33 +/- 13.4 years (range, 15 to 57 years). The etiology was idiopathic in 4 patients, cardiomyopathy in 3, acute myocarditis in 1, arrhythmogenic right ventricular dysplasia in 2, tumor in 1, postoperative Tetralogy of Fallot in 2, and acute bacterial endocarditis in 1. Pre- and/or intraoperative electrophysiologic mapping was achieved in 13 of 14 patients. A variety of operations were performed without death. Two late deaths have occurred, neither of them, however, from arrhythmias. After operation two patients had recurrent arrhythmias. Surgery for nonischemic ventricular tachycardia is safe and effective and should be considered early in the course of these mostly young patients.

Four digital algorithms for activation detection from unipolar epicardial electrograms

The reproducibility of activation detection by each of four algorithms used to calculate maximum derivatives was tested on two sequential paced beats of right ventricular unipolar epicardial electrograms which represented either local activation of the right ventricle alone or synchronous activation of both ventricles. The methods were evaluated by comparing the shape of the two beats aligned on their selected activation times, i.e., the time at which the maximum negative deflection occurred, the differences in activation intervals for the two beats, and the effect on the activation time of superimposing distant events on local activation. The 17-point second-order data fit algorithm performed slightly better than the first-order difference, three-point Lagrange derivative, and five-point second-order data fit algorithms except that activation time selection by the 17-point technique was slightly, but significantly, delayed by the superposition of distant potentials. The 17-point second-order data fit technique is therefore recommended for use in detecting activation unless computation time is a major consideration. In that case, the five-point second-order data fit technique, which uses only four data values for each computation, can be used with only slight decreases in accuracy.

Right ventricular free wall isolation: effects on regional myocardial blood flow

The right ventricular isolation procedure was developed to treat medically refractory, nonischemic right ventricular tachycardia. The effect of this procedure on regional myocardial blood flow to the isolated right ventricle was evaluated in 10 adult mongrel dogs. There were no significant changes in aortic pressure, right ventricular systolic or diastolic pressure, or cardiac index following right ventricular isolation when the left ventricle and right ventricular free wall were synchronously paced. Myocardial blood flow to the isolated right ventricle was unchanged following the procedure (0.85 +/- 0.07 ml/min/gm to 0.87 +/- 0.08 ml/min/gm; p = not significant). Analysis of regional flow revealed that only a thin rim of right ventricular tissue near the ventriculotomy showed a significant decrease in blood flow (1.10 +/- 0.1 ml/min/gm to 0.29 +/- 0.04 ml/min/gm; p less than 0.05). Thus, this procedure leaves intact the blood supply to the great percentage of the right ventricular free wall. This finding supports the concept that the right ventricular isolation procedure is effective in isolating abnormal electrical activity without compromising regional myocardial blood flow.

Hemodynamic consequences of right ventricular isolation: the contribution of the right ventricular free wall to cardiac performance

Surgical isolation of the right ventricular free wall was performed in 10 dogs to evaluate both the hemodynamic effects of the procedure and the postoperative contribution of right ventricular free wall contraction to overall cardiac performance. Following the procedure, there was no significant differences in peak right ventricular systolic pressure, right atrial pressure, right ventricular stroke volume, or cardiac index. Cardiac index remained at preoperative levels over a wide range of filling pressures. However, there was a significant decrease in right ventricular stroke work (6.0 +/- 1.3 gm-m/m2 to 5.1 +/- 0.5 gm-m/m2; p less than 0.05). Pacing the isolated right ventricular free wall resulted in marked hemodynamic improvement compared with an electrically silent right ventricular free wall. Cardiac index increased from 1.7 +/- 0.2 L/min/m2 to 2.6 +/- 0.2 L/min/m2 (p less than 0.0005), and right ventricular stroke work went from 3.0 +/- 0.6 gm-m/m2 to 6.4 +/- 0.9 gm-m/m2 (p less than 0.0005). Right ventricular performance was also significantly related to the timing of right ventricular free wall contraction. Thus, the right ventricular free wall played an important role in the maintenance of normal cardiac hemodynamics.

Effects of distant potentials on unipolar electrograms in an animal model utilizing the right ventricular isolation procedure

The effects of distant potentials on local epicardial unipolar electrograms were examined utilizing a model that enabled both ventricles to be paced independently in five dogs. The right ventricular isolation procedure electrically isolates the right from the left ventricle. Right ventricular electrograms were separated into their local (right ventricular) and distant (left ventricular) components by altering the left-right ventricular pacing interval. Waveform configuration, peak to peak amplitude, magnitude of the slope and timing of the fastest downstroke were carefully evaluated at each electrode site, both with and without the presence of distant left ventricular potentials. Except for the timing of the fastest downstroke, all of these variables were significantly altered by distant potentials. Although the slope of the fastest downstroke was significantly affected by distant potentials, it remained a sensitive indicator of local versus distant activation. All electrograms of local right ventricular activation had a slope magnitude greater than 2.5 mV/2 ms whereas none of the right ventricular electrograms containing only distant left ventricular activity had a magnitude greater than 2.5 mV/2 ms. Computer-generated electrograms were calculated by digitally summing the recorded local right and distant left ventricular components. The simulated electrograms correlated well with the recorded electrograms during synchronous ventricular pacing. Thus, the configuration, amplitude and slope of unipolar electrodes were profoundly influenced by distant potentials. The timing of the fastest downstroke is largely independent of the effect of distant potentials and most closely represents local activation. The magnitude of the slope of the recorded electrogram accurately distinguishes local from distant activation.