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Biomedical subjects

M E Harold

Publications and source records attributed to M E Harold.

7 recordsLinked to original sources
PubMed1993

Histologic study of chronic catheter cryoablation of atrioventricular conduction in swine.

To evaluate the efficacy of catheter cryoablation, we studied histologic changes of the atrioventricular (AV) junction in eight pigs 6 weeks after cryoablation of central conducting tissue. Cryothermia at -60 degrees C was applied to the AV junction through an 8F or 11F cryocatheter with no electrode and was maintained for 3 minutes after complete AV block was obtained. Six weeks later, gross inspection revealed a distinct, oval-shaped scar 5 to 8 mm in length along or above the septal leaflet of the tricuspid valve in each animal. Microscopically, ablated sites were discrete and were replaced by dense connective tissue with no signs of chronic inflammation. Neovascularization was often seen in scar tissue, and small branches of coronary vasculature within lesions appeared patent with mild intimal proliferation. Ablated lesions involved a small area of the summit of the muscular interventricular septum in three animals, but lesions were never found in the base of the aortic wall or aortic valve. The proximal AV conduction system, either the penetrating bundle or a portion of the AV node, was ablated in all five animals with complete AV block. Three animals that did not maintain complete AV block showed scar formation in the atrial septum above the AV node or penetrating bundle; two of these lesions had small islands of viable atrial myocardium embedded within scar tissue. Catheter cryoablation can produce lesions as effectively as those created during open-heart surgery and is a possible procedure for treatment of intractable supraventricular tachycardia. Improvements in technique or in the cryocatheter may be needed to create more reliably located and homogeneous scar.

Animals↗
PubMed1993

Prophylactic treatment of swine with bretylium for experimental cardiac catheterization.

We evaluated a cryothermic ablation catheter for potential use in treating supraventricular tachycardia by cardiac catheterization in miniature swine. Cardiac catheterization was performed on anesthetized miniature swine by using multiple catheters that were inserted bilaterally by either percutaneous or cutdown techniques into the femoral veins. We performed electrophysiologic tests according to standard atrial and ventricular electrical stimulation protocols. Manipulation of catheters in the tricuspid valve area and right ventricle was an essential part of the study. During an initial study of five swine, catheter manipulation produced sustained and nonsustained ventricular tachycardia and ventricular fibrillation. To prevent arrhythmias, bretylium (5 mg/kg) was administered intravenously 10 minutes before catheter manipulation and repeated every 30 minutes throughout the procedure. Since the use of bretylium was instituted, there have been no cases of ventricular fibrillation in a series of 20 animals. We determined that bretylium is effective in the suppression of ventricular arrhythmias in swine undergoing cardiac catheterization.

Animals↗
PubMed1991

The acute effects of flecainide in the swine heart failing from incessant supraventricular tachycardia.

The acute hemodynamic and electrophysiologic effects of flecainide in tachycardia-induced ventricular dysfunction were investigated using an animal model. Seven swine were initially (CON) evaluated by echocardiography and then by right heart catheterization and provocative electrical ventricular stimulation both before and after treatment with intravenous flecainide. Rapid atrial pacing at 210 to 240 beats/min (SVT) was then employed for 2 to 4 weeks until echocardiographic evidence of left ventricular dysfunction developed. Immediately upon termination of pacing, the above studies were repeated both before and after treatment with flecainide. Significant (p less than 0.0001) pacing-related hemodynamic effects on the cardiac output (CON:3.0 L/min versus SVT:1.6 L/min), right ventricular ejection fraction (CON:55% versus SVT:17%), and pulmonary wedge pressure (CON:8 mm Hg versus SVT:22 mm Hg) were observed. Pacing-related electrophysiologic effects included increases in the PR interval (CON:94 msec versus SVT:119 msec, p less than 0.001) and QTc interval (CON:418 msec versus SVT:450 msec, p = 0.016). With serum flecainide concentrations in the human therapeutic range, no significant effect on hemodynamic or electrophysiologic parameters in either the normal or failing heart were detected. Nonsustained ventricular tachycardia induced prior to pacing in one animal and after pacing in another animal was seen before but not following use of flecainide. No acute proarrhythmic effects were observed. In summary, intravenous flecainide had no significant acute adverse hemodynamic, electrophysiologic, or proarrhythmic effects in an animal model of tachycardia-induced ventricular dysfunction.

Animals↗
PubMed1990

Real-time, automated, interactive cardiac electrophysiology testing.

We describe a new automated interactive system that performs all of the functions required for complete evaluation of the intracardiac conduction system, for inducing, terminating and analyzing tachydysrhythmias, and for locating and characterizing accessory atrioventricular (AV) connections and ectopic foci. In the first year of operation, the system was used to conduct 210 electrophysiology studies. These ranged from simple postoperative evaluation of the conduction system to complete tachycardia studies during pharmacological manipulation of the patient. Patient age at time of catheterization ranged from 6 days to 70 years, with median age of 8 years and 7 months. Advantages accruing from automated electrophysiology testing with this system included great precision and accuracy of timing measurements, flexibility in designing and implementing pacing protocols, and rapid management of induced or spontaneous dysrhythmias. Significant savings of time and labor were achieved by computer generation of reports and graphs as opposed to manual data extraction and plotting. The single most significant advantage is the ability of the system to provide information on a real-time basis, permitting the electrophysiologist to analyze, modify, extend or curtail the procedure.

Adolescent↗
PubMed1990

Computer-enhanced mapping of activation sequences in the surgical treatment of supraventricular arrhythmias.

Surgical treatment of accessory pathways and ectopic foci requires accurate information on the physical locations of the arrhythmogenic substrates. Although electrophysiology studies during cardiac catheterization frequently provide accurate and reliable data, the physical locations of the sites to be ablated must be verified in situ by electrical activity mapping. We have developed a microcomputer-based system that facilitates creation of electrical activity maps, supplanting the manual method formerly used. Signals produced by mapping and reference electrodes, as well as cardiac diagrams with grid coordinates and times, are presented on a monitor in formats that are easily interpreted by the surgeon and cardiologist. The system is rapid, accurate, and reliable, and has reduced the time required to localize conduction abnormalities from 30 to 45 minutes for the manual method, down to an average of 12 minutes per case. The system is simple to operate, requiring only minimal training. All of the components of the system are commercially available; no specialized hardware is required.

Adolescent↗
PubMedDate not supplied

Percutaneous serial catheterization in swine: a practical approach.

In a model designed for experimental cryoablation of the His bundle in swine, a study that required multiple and follow-up cardiac catheterizations, femoral percutaneous cannulations were successfully performed in 14 of 15 swine: 6/6 Yucatan miniature, 5/6 Hanford miniature, and 3/3 Yorkshire farm pigs, weight range 15-50 kg. A follow-up cardiac catheterization was performed in 10 of these animals: 5 Hanford and 5 Yucatan. Femoral percutaneous cannulation was successful in 6. A cutdown approach was successful in the remaining 4 after failed attempts at percutaneous vascular access. The results show that percutaneous femoral cardiac catheterization is a feasible and practical technique for cardiovascular studies in swine, especially those that require multiple and serial catheterizations.

Animals↗