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I Parson

Publications and source records attributed to I Parson.

10 recordsLinked to original sources
PubMed1990

Transatrial balloon technique for activation mapping during operations for recurrent ventricular tachycardia.

Results of operations for recurrent ventricular tachycardia have improved since methods of mapping that allow a directed approach to the problem have been developed. With standard operative techniques (ventriculotomy and introduction of a hand-held probe or multiple electrode array), it has not always been possible to obtain satisfactory endocardial activation maps during the tachycardia. We have recently developed a new transatrial balloon approach that has greatly facilitated intraoperative mapping. This paper describes our total experience with the new approach and draws attention to details of the cardiopulmonary bypass technique and the surgical approach needed for safe balloon insertion across the mitral valve. We describe how correlation between position of target electrodes on the balloon and the internal geometry of the heart is achieved and discuss the choice and application of appropriate ablation techniques. In our series of 37 consecutive patients, 35% had a grade IV ventricle (ejection fraction less than 20%), 32% had a previous posterior infarct, 51% did not have a resectable aneurysm, and 54% had been receiving amiodarone within 1 month of the operation. These factors have been associated with poor operative results in other series. With the transatrial balloon technique, we were able to induce and map ventricular tachycardia in 100% of patients (average 2.6 +/- 1.3 morphologies per patient). Using a variety of ablation techniques (endocardial excision, cryoablation, or balloon electric shock ablation), we have achieved surgical control of the arrhythmias in 84% of patients with an operative mortality rate of 14%. We recommend transatrial balloon mapping as the procedure of choice for intraoperative identification of arrhythmogenic foci in patients with recurrent ventricular tachycardia.

Catheterization↗
PubMed1989

Balloon electric shock ablation. Effects on ventricular structure, function, and electrophysiology.

We have recently developed a transatrial balloon approach for intraoperative endocardial mapping of ventricular tachycardia, which can be performed in the intact ventricle. In selected patients, we have eliminated the arrhythmia by passing a series of electric currents through specific beads on the balloon array. The goal of this new technique, balloon electric shock ablation, is to create a homogenous scar in the subendocardial target area identified by mapping. Experimental data exist on the effects of catheter delivery of electric discharges to the myocardium, but no data are available on the effects of balloon electric shock ablation. We have performed balloon electric shock ablation in animals (nine cathodal shocks of 100 J given through a 4 cm2 electrode grid). Ventricular function was assessed at 6 weeks and compared with function after a simple ventriculotomy and with function in control animals having no operation. Gated nuclear ventriculograms were obtained during volume loading. Myocardial performance and diastolic pressure volume relationships were determined for the three groups. After balloon electric shock ablation or ventriculotomy, left atrial pressures were increased at similar end-diastolic volumes, which indicated decreased ventricular compliance. The trend reached statistical significance (compared with data from control animals) only in the group undergoing balloon electric shock ablation. Myocardial performance (stroke work index/end-diastolic volume relationship) was unchanged in the three groups. In the long-term balloon electric shock ablation preparation, an electrophysiologic study (including burst pacing) failed to induce ventricular arrhythmias. At 6 weeks, the lesion created by balloon electric shock ablation was a layer of homogenous mature scar with sharply defined borders. There was no evidence of additional injury to the surrounding myocardium or to the mitral valve apparatus. These studies show that delivery of a series of electric shocks through a 1 cm balloon grid of electrodes can create an area of homogeneous, electrically inert scar and that this procedure when performed in healthy dog hearts has no significant effect on the structure and function of the rest of the left ventricle.

Animals↗
PubMed1988

Electrical ablation with a balloon electrode array: chronic electrophysiologic response.

An intraoperative endocardial array of electrodes which permits simultaneous recordings from multiple sites in the intact ventricle is currently in clinical use and has provided the opportunity for exploring electrical ablation as an alternative to standard surgical ablative techniques requiring a ventriculotomy. A variation of the electrical ablative procedure adapted for this intraoperative purpose was studied in seven dogs to determine its long-term electrophysiologic and structural effects on ventricular myocardium. With the dogs on cardiopulmonary bypass, a mesh-covered latex balloon was introduced into the left ventricle via an atriotomy. Five damped sinusoidal discharges (4 of 200 J per 2 electrodes, one of 100 J to the remaining electrode) were delivered to nine silver bead electrodes sutured at 1 cm intervals onto the mesh and arranged in a 2 x 2 cm2 array. At 5-8 weeks following the ablation, no ventricular arrhythmias could be induced in any of the dogs using standard stimulation techniques. The scar produced by the ablation consisted of dense fibrous tissue, and was well demarcated from surrounding normal myocardium. Cellular electrophysiology confirmed that no action potentials could be recorded within the scarred area while at distances of 1 mm from the scar border, normal responses could be elicited from both muscle cells and Purkinje fibers. The adaptation of the described electrical ablative procedure produces an electrophysiologically inert scar.

Action Potentials↗
PubMed1988

A new intraoperative approach for endocardial mapping of ventricular tachycardia.

Results of operation for control of ventricular tachycardia have improved since endocardial mapping techniques have been developed that allow a directed approach to the problem. In some patients, a limitation of established techniques has been difficulty in initiating the arrhythmia after a ventriculotomy has been made to allow introduction of endocardial recording electrodes. This paper describes a transatrial approach for endocardial mapping with a balloon array of 112 electrodes, which has been used intraoperatively in 15 patients. Surgical success in this group has been compared to that obtained in a similar group of patients in whom standard techniques of intraoperative mapping were used. With our new balloon technique we have been able to easily induce and map multiple episodes of ventricular tachycardia in all cases. On the basis of detailed endocardial maps, the locations of earliest activation and possible reentry loops have been identified and ablated with either endocardial excision or application of the cryoprobe. When indicated, concomitant procedures including aneurysm resection (9/15) and bypass grafting (14/15) have been performed. Hospital mortality in this group was 20%. None of the deaths have been related to recurrent ventricular tachycardia or complications of the mapping technique. Postoperative electrophysiologic studies performed at 2 weeks have been normal in 11 of 12 or 92% of patients. To date (mean follow-up 12 +/- 6 months) there has been no clinical recurrence or evidence of ventricular tachycardia by Holter monitoring in these patients. We conclude that the transatrial balloon approach to endocardial mapping facilitates intraoperative induction of ventricular tachycardia, allows complete mapping during multiple runs of the arrhythmia without prolonging cardiopulmonary bypass time, and improves results of operation using standard ablation techniques.

Cardiac Pacing, Artificial↗
PubMed1987

Activation sequence of ventricular tachycardia: endocardial and epicardial mapping studies in the human ventricle.

Thirty-five patients with ischemic heart disease and ventricular arrhythmias underwent intraoperative activation mapping at the time of coronary artery bypass surgery. During ventricular tachycardia, the sequence of activation in the intact ventricle was recorded simultaneously from 110 endocardial or 110 epicardial sites, or both. A balloon array of electrodes, inserted across the mitral valve, was used to obtain endocardial recordings in the left ventricle, and this appeared to facilitate the induction of ventricular tachycardia. Of 61 episodes of tachycardia, 16 (15 patients) were recorded with the epicardial sock and 45 (20 patients) with the additional use of the endocardial balloon. The sequence of activation during tachycardia was observed to conform to one of four configurations: monoregional spread was the most common activation sequence recorded on both the endocardium and epicardium, while biregional activation and figure eight sequences were recorded exclusively on the epicardium and endocardium, respectively. The fourth sequence was a circular spread of activation observed on both surfaces. Continuous activation throughout the tachycardia cycle length was an infrequent finding. Simultaneous recordings of endocardial and epicardial activation were obtained in 45% of episodes. The sequence of activation recorded on one surface was matched by a similar sequence on the remaining surface in less than half of these. The onset of endocardial activation preceded that of the epicardium in greater than 90% of tachycardia episodes, and the duration of left ventricular endocardial excitation often exceeded that recorded epicardially over both ventricles. The epicardium, however, did appear to be an important determinant of surface electrocardiographic configuration.

Cardiac Catheterization↗
PubMed1987

Intraoperative electrical ablation of ventricular arrhythmias: a "closed heart" procedure.

Both intraoperative endocardial mapping and surgical ablation for ventricular arrhythmias have until now required a ventriculotomy. Such an incision may be associated with an increase in morbidity and mortality, especially when performed through friable myocardium. A "closed heart" technique of intraoperative endocardial mapping and ablation of ventricular arrhythmias was developed in which a balloon array of 112 electrodes was introduced into the left ventricular cavity by a transmitral approach. The array permitted safe delivery of repeated electrical discharges of up to 150 J at each electrode. In four patients with coronary artery disease and no ventricular aneurysm, this "closed heart" technique was used to map and treat seven distinct ventricular tachycardias. The time taken to map each tachycardia varied from 3 to 13 minutes. Between 100 and 150 J was then delivered at each of 10 to 42 electrode sites, and the ablation procedure took 7 to 16 minutes per patient to complete. One patient died 24 hours postoperatively from preexisting thrombocytopenic purpura. There was no significant deterioration in left ventricular function in the three survivors and all have remained arrhythmia free, without antiarrhythmic agents, for 4 to 11 months. This technique offers a new method of surgical treatment of ventricular tachycardia without ventriculotomy, and is particularly suited to patients without a discernible left ventricular aneurysm.

Arrhythmias, Cardiac↗
PubMed1984

Clinical instrumentation for the intra-operative mapping of ventricular arrhythmias.

Surgical treatment of ventricular arrhythmias has been greatly facilitated by intra-operative mapping. Present clinical mapping techniques are time-consuming, of limited accuracy, and are restricted to monoform sustained tachycardias. A previously reported on-line cardiac mapping system used in the research laboratory has been modified to provide epicardial maps of ventricular arrhythmias induced at the time of surgery. Changes such as a battery-operated multiplexer, patient electrical isolation, adjustable electrogram gain, time-code labeling and marker-matrix display, have all contributed to the intra-operative application of the original analog real-time mapping technique. These modifications were accomplished without compromising the spatial or temporal resolution (0.5 cm and 8.3 ms) of the laboratory system. An advantage of the present system is a decrease in cardiopulmonary bypass time as a direct result of the instantaneous analysis and display of epicardial activation information. In addition, it enables, for the first time, short salvos and polymorphic runs of ventricular tachycardia to be mapped intra-operatively.

Arrhythmias, Cardiac↗
PubMed1984

The acoustic impedance locus for normal human ears.

The ear's complex acoustic impedance locus for frequencies from 200 Hz to 2 kHz was obtained for 20 subjects screened for normal hearing. The purpose of the experiment was to observe "kinks" in the total driving point impedance locus of the ear, as measured by acoustic impedance in the ear canal at a depth comparable to that of clinical audiometry. Such impendance bumps or loops are expected to contribute to irregularities seen in high-frequency clinical tympanograms. The transducer probe consisted of two 1/8 inch condenser microphones inserted in the ear canal. The instrumentation used a continuous sinusoidal probe tone sweeping the frequency range in 90 seconds. Analog circuitry performed synchronous detection and filtering and provided the resistance and reactance of the impedance derived from the sound pressure measured in the ear canal. Data were recorded in the form of an impedance locus in the complex plane. These loci demonstrated kinks suggesting middle ear resonances, at 604 +/- 99 Hz, 986 +/- 94 Hz and 1 361 +/- 87 Hz. Ninety-seven percent of the ears demonstrated a single kink while 78% displayed two. In addition, a group of 5 normal subjects were measured 5 times. The variation within subjects was 5 to 10% of the mean impedance. It is concluded that there are resonances within the middle ear structure that manifest themselves as easily observed bumps or loops in the ear's impedance locus.

Acoustic Impedance Tests↗
PubMed1982

On-line cardiac mapping: an analog approach using video and multiplexing techniques.

A video and multiplexing system is described that provides a source of display in real-time, slow-motion, and stop-frame modes of ventricular activation. The displayed image, consisting of a matrix of 112 dots, is arranged to represent a polar projection of the ventricles. The dots brighten at the time of local cardiac activation, which is sensed by an electrode array monitoring the myocardium. Experiments in in situ canine hearts have provided detailed depictions at 8.3-ms intervals of the ventricular activation sequence during sinus and ventricularly paced rhythm. The origin of ventricular paced beats can be located with an accuracy of less than 5 mm. Coronary occlusion produces a defect in the displayed image that outlines the ischemic area and demonstrates regions of delayed conduction. This approach to ventricular mapping provides a detailed on-line display of activation with a recording capacity of 1 h. The system offers a practical, inexpensive alternative to computerized methods of investigating ventricular arrhythmias in both the experimental and intraoperative environment.

Animals↗