- Email: [email protected]
Modeling propagation across adjacent anisotropic muscle layers
SELECTED ABSTRACTS
(A4-10) Low Energy Ablation of AV Conduction With a Suction-Held Catheter Peter J. Tarjan, Birinder Boveja, Donald Cohen, Thomas F. Joubert and Eileen Zalewski. Cordis Research Corporation, Miami, Florida. The bundle of His can be ablated experimentally with precision and low energy by the use of a combination catheterlead system. The specially-shaped, 7 F catheter has one ring electrode at its distal tip and another one about 10 mm proximal to the first. This “lead” is positioned so as to optimize the amplitude of the bipolar His potential, then adjusted further to maximize the His deflection between its tip and body surface electrode. Next, suction (100-200 mmHg) per the method of Polgar is applied through the lumen to hold the tip firmly against the tissue and the site is paced. If the stimulus to ventricular-potential interval (St-V) is short and the morphology of the ventricular complex is similar to that of a sinus beat, a shock of 10 or 20 joules (J) is delivered. If this does not produce complete heart block (CHB), additional shocks of increasing energy are delivered to the endocardial site. Should the St-V and ventricular morphology not be as desired prior to the shock, the suction is released and the catheter repositioned. Results: Use of this method of ablation of the His bundle in the canine model revealed that when the St-V is close to the HV interval, a single shock of 20 J always produced permanent CHB. An initial shock of 10 J, in contrast, always failed and further shocks of from 20 to 30 J were required to initiate CHB. Even then CHB did not always persist, but resulted in a longer PR interval. The dogs were paced for 60 days. Gross examination showed smooth endocardial surfaces at the site of injury with a nodule of about 2 mm diameter. Conclusion: This method produces permanent CHB with a shock of 20 J. It further permits a desired degree of precision in the positioning of the catheter.
73
with anterior Ml showed no mortality gradient, whereas inferior Ml groups showed a trend toward increasing mortality with increased extent of MI. Conclusion: In large multicenter studies, this code permits subset creation which enhances the role of the ECG as a clinical predictor.
(84-5) Ambulatory ST Segment Changes and Related Incidence of Silent ischemia F. Correia-Junior, M. Fiuza, J. Correia and F. Padua. Centro de Cardiologia da Universidade (LA 3) Lisbon, Portugal. Twenty-four hour ambulatory ECG recordings were performed in 200 patients (pts) with angina, in order to evaluate the possibility of diurnal ST changes in relation to painful and painless ischemic episodes and the eventual incidence of related arrhythmias. One hundred and forty pts (70%) did complain of chest pain during Holter monitoring and 57% of these showed significant ST changes. Of the 60 asymptomatic pts, 16 (27%) presented with ST changes during the register period. Painful ST segment changes occurred more frequently during daytime. Silent ST changes occurred more frequently during night, in particular between midnight and 6 AM. Although arrhythmias were more common accompanying ST changes related to painful episodes, severe forms of ventricular arrhythmias were also observed during painless ST alterations. Our results suggest that silent ischemia is more frequent than expected, mostly at night, and that dangerous arrhythmias are not unusual in this situation. Any program of prevention of sudden death should give consideration to the problem of silent ischemia.
Session D4 - Basic Research Session B4 - Clinical Research
(D4-1) Modeling Propagation Anisotropic Muscle Layers
(84-l) A New Electrocardiographic Classification for Post- Myocardial Infarction Clinical Trials.
Bruce M. Steinhaus. University of Utah, Salt Lake City, Utah. Action potential propagation across orthogonally oriented muscle layers was modeled using a P-dimensional sheet perpendicular to the layers. The model simulated 3dimensional plane wave propagation across the ventricular wall using the Beeler Reuter ionic current membrane model. Anisotropy was represented by higher coupling resistance in the transverse (t) than longitudinal (I) direction. Layers were homogeneously coupled with t-resistance values. Activation in the t-direction propagated with a higher safety factor than propagation in the I- direction as previously shown experimentally. This caused functional block at the boundary between orthogonal layers for a range of t-resistances, pacing frequencies and premature cycles; block was sensitive to propagation direction. With block, activation initiated in the tlayer which later reexcited the t- layer. Findings suggest that reentry can occur where adjacent layers are orthogonally oriented as they are normallly in the pulmonary conus. Increased t-coupling resistance as with disease and age would aggravate the abnormal activity. It follows that the normal gradual transmural rotation of cell orientation in the left ventricle would be protective against this reentrant activity.
Henry Greenberg, John Gillespie, Edward M. Dwyer, Jr. and the Multicenter Post Infarction Group (MPIP), St. Luke’sRoosevelt Hospital Center, Columbia University, New York, New York. Because of limitations in the clinical applicability of electrocardiograms (ECG) classified by the Minnesota Code, we designed a new system and have reread the ECGs of 653 first myocardial infarction (Ml) patients in the MPIP data base. For each of 45 anatomic regions - anterior, lateral, inferior, and posterior - Q-wave MI, non-Q wave MI, ischemic changes, and no changes were identified. To assess the usefulness of this classification, mean radionuclide ejection fraction (RNEF) and P-year mortality were analyzed using 14 Ml categories. RNEF was inversely related to the extent of anterior Ml (pcO.O05), falling from 50% for anterior to 40% for anterior Ml plus non-Q wave changes to 34% for anterior plus lateral Q-wave MI, but was unchanged for any variation of inferior Ml. Mortality was less (p
20(l),
1987
Across
Adjacent
(A4-10) Low Energy Ablation of AV Conduction With a Suction-Held Catheter Peter J. Tarjan, Birinder Boveja, Donald Cohen, Thomas F. Joubert and Eileen Zalewski. Cordis Research Corporation, Miami, Florida. The bundle of His can be ablated experimentally with precision and low energy by the use of a combination catheterlead system. The specially-shaped, 7 F catheter has one ring electrode at its distal tip and another one about 10 mm proximal to the first. This “lead” is positioned so as to optimize the amplitude of the bipolar His potential, then adjusted further to maximize the His deflection between its tip and body surface electrode. Next, suction (100-200 mmHg) per the method of Polgar is applied through the lumen to hold the tip firmly against the tissue and the site is paced. If the stimulus to ventricular-potential interval (St-V) is short and the morphology of the ventricular complex is similar to that of a sinus beat, a shock of 10 or 20 joules (J) is delivered. If this does not produce complete heart block (CHB), additional shocks of increasing energy are delivered to the endocardial site. Should the St-V and ventricular morphology not be as desired prior to the shock, the suction is released and the catheter repositioned. Results: Use of this method of ablation of the His bundle in the canine model revealed that when the St-V is close to the HV interval, a single shock of 20 J always produced permanent CHB. An initial shock of 10 J, in contrast, always failed and further shocks of from 20 to 30 J were required to initiate CHB. Even then CHB did not always persist, but resulted in a longer PR interval. The dogs were paced for 60 days. Gross examination showed smooth endocardial surfaces at the site of injury with a nodule of about 2 mm diameter. Conclusion: This method produces permanent CHB with a shock of 20 J. It further permits a desired degree of precision in the positioning of the catheter.
73
with anterior Ml showed no mortality gradient, whereas inferior Ml groups showed a trend toward increasing mortality with increased extent of MI. Conclusion: In large multicenter studies, this code permits subset creation which enhances the role of the ECG as a clinical predictor.
(84-5) Ambulatory ST Segment Changes and Related Incidence of Silent ischemia F. Correia-Junior, M. Fiuza, J. Correia and F. Padua. Centro de Cardiologia da Universidade (LA 3) Lisbon, Portugal. Twenty-four hour ambulatory ECG recordings were performed in 200 patients (pts) with angina, in order to evaluate the possibility of diurnal ST changes in relation to painful and painless ischemic episodes and the eventual incidence of related arrhythmias. One hundred and forty pts (70%) did complain of chest pain during Holter monitoring and 57% of these showed significant ST changes. Of the 60 asymptomatic pts, 16 (27%) presented with ST changes during the register period. Painful ST segment changes occurred more frequently during daytime. Silent ST changes occurred more frequently during night, in particular between midnight and 6 AM. Although arrhythmias were more common accompanying ST changes related to painful episodes, severe forms of ventricular arrhythmias were also observed during painless ST alterations. Our results suggest that silent ischemia is more frequent than expected, mostly at night, and that dangerous arrhythmias are not unusual in this situation. Any program of prevention of sudden death should give consideration to the problem of silent ischemia.
Session D4 - Basic Research Session B4 - Clinical Research
(D4-1) Modeling Propagation Anisotropic Muscle Layers
(84-l) A New Electrocardiographic Classification for Post- Myocardial Infarction Clinical Trials.
Bruce M. Steinhaus. University of Utah, Salt Lake City, Utah. Action potential propagation across orthogonally oriented muscle layers was modeled using a P-dimensional sheet perpendicular to the layers. The model simulated 3dimensional plane wave propagation across the ventricular wall using the Beeler Reuter ionic current membrane model. Anisotropy was represented by higher coupling resistance in the transverse (t) than longitudinal (I) direction. Layers were homogeneously coupled with t-resistance values. Activation in the t-direction propagated with a higher safety factor than propagation in the I- direction as previously shown experimentally. This caused functional block at the boundary between orthogonal layers for a range of t-resistances, pacing frequencies and premature cycles; block was sensitive to propagation direction. With block, activation initiated in the tlayer which later reexcited the t- layer. Findings suggest that reentry can occur where adjacent layers are orthogonally oriented as they are normallly in the pulmonary conus. Increased t-coupling resistance as with disease and age would aggravate the abnormal activity. It follows that the normal gradual transmural rotation of cell orientation in the left ventricle would be protective against this reentrant activity.
Henry Greenberg, John Gillespie, Edward M. Dwyer, Jr. and the Multicenter Post Infarction Group (MPIP), St. Luke’sRoosevelt Hospital Center, Columbia University, New York, New York. Because of limitations in the clinical applicability of electrocardiograms (ECG) classified by the Minnesota Code, we designed a new system and have reread the ECGs of 653 first myocardial infarction (Ml) patients in the MPIP data base. For each of 45 anatomic regions - anterior, lateral, inferior, and posterior - Q-wave MI, non-Q wave MI, ischemic changes, and no changes were identified. To assess the usefulness of this classification, mean radionuclide ejection fraction (RNEF) and P-year mortality were analyzed using 14 Ml categories. RNEF was inversely related to the extent of anterior Ml (pcO.O05), falling from 50% for anterior to 40% for anterior Ml plus non-Q wave changes to 34% for anterior plus lateral Q-wave MI, but was unchanged for any variation of inferior Ml. Mortality was less (p
20(l),
1987
Across
Adjacent