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Biomedical subjects

E Downar

Publications and source records attributed to E Downar.

At least 55 records · Page 3Linked to original sources
PubMed1984

On-line epicardial mapping of intraoperative ventricular arrhythmias: initial clinical experience.

An on-line automatic mapping system was developed for beat by beat display of epicardial activation during ventricular tachycardia induced at the time of cardiac surgery. A sock array of 110 button electrodes was used to record and display local activation on a video monitor at 8.3 ms intervals. On instant replay in slow motion, epicardial pacing sites were accurately localized to the nearest electrode. Local unipolar electrograms were also recorded, first from the sock array, then from an array of 16 transmural needle electrodes. The epicardial display was verified by retrospective manually derived maps using the recorded epicardial electrograms. In four patients with coronary artery disease and recurrent inducible ventricular tachycardia, earliest epicardial activation was located on slow motion replay within 1 minute. Subendocardial sites of early activation were located within 10 minutes by replay of electrograms from the needle array before ventriculotomy. Transmural and endocardial resection of these sites prevented inducibility of the tachycardia on postoperative electrophysiologic study in three of the four patients. There has been no clinical recurrence of ventricular tachycardia after 3 to 14 months of follow-up despite cessation of antiarrhythmic therapy in three of the patients. This technique has unique advantages over existing mapping methods. It provides beat by beat display of activation sequences so that clinical tachycardias that are short in duration or pleomorphic in configuration now become amenable to mapping. In addition, it markedly shortens total time on cardiopulmonary bypass.

Adult↗
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

Amiodarone-associated phospholipidosis and fibrosis of the liver. Light, immunohistochemical, and electron microscopic studies.

The hepatic morphological findings in 3 patients treated with amiodarone, a potent and effective antiarrhythmic drug, are reported. An enlarged liver and mild elevation of hepatic enzymes were the most important clinical findings. Fibrosis, cholangitis, mixed inflammatory infiltrate, and cytoplasmic granularity of the hepatocytes were the main histologic changes common to all cases. In 2 of the cases the presence of Mallory bodies was confirmed by electron microscopy. In 1 of these 2 cases, Mallory bodies were also confirmed by immunostaining. Ultrastructurally, numerous cytoplasmic inclusions with a membranous or lamellar structure identical to those described in phospholipidosis were the most striking features seen in hepatocytes, biliary epithelial cells, Kupffer cells, and endothelial cells.

Amiodarone↗
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↗
PubMed1981

Time course of changes in porcine myocardial phospholipid levels during ischemia. A reassessment of the lysolipid hypothesis.

This study was performed to determine the early and delayed metabolic effects of myocardial ischemia on the major membrane phospholipids and to reassess the potential role of lysophospholipids in the genesis of malignant dysrhythmias induced by ischemia. Samples taken from in situ hearts before ant at various intervals up to 40 minutes after abrupt ligation of LAD were extracted by the classical Folch technique with modifications to avoid artifactual lysophospholipid production and losses. Following thin layer chromatography of lipid extracts, phospholipid fractions were quantified by phosphorus estimation and lysophospholipids by a more sensitive method employing gas liquid chromatography. The total phospholipid content with the exception of lysophospholipids remained essentially constant throughout the early phases of acute ischemia, but fell by 6 and 14% after 8 and 24 ours, respectively. At 8 minutes, lysophospholipid levels n ischemic myocardium were significantly increased by 60% compared to pre-occlusion controls in the ischemic zone and by 25% in post-occlusion controls. They changed little thereafter. The molecular species of lysophospholipids remained unchanged throughout the period of ischemia studied. The mole fraction of other phospholipids as well as their fatty acyl and aldehyde profiles also were unchanged. Despite significant elevations in lysophospholipids levels, their absolute quantities were very small (0.6% of total phospholipid P) and 15-fold smaller than that reported in vitro to simulate electrophysiological manifestation of ischemia. However, such small amounts in vivo, if produced in the microenvironment of certain membrane-bound enzymes along with acidosis, hypoxia, and fatty acids, could be potentially deleterious to cell functions.

Animals↗
PubMed1980

Unidirectional block in Purkinje fibers.

Three methods of inducing focal conduction disturbances in free-running sheep Purkinje fibers (symmetric and asymmetric focal cooling and asymmetric focal crushing) were explored in 50 preparations. Complete unidirectional block was induced in only a minority of symmetrically cooled preparations whereas the asymmetric lesions generated this conduction disturbance in 80-85% of preparations. The block was more stable when induced by crushing than by asymmetric cooling but was more readily reversible with the latter. The direction of block coincided with the least abrupt gradient in the intensity of the lesion (82-94%), was reversible upon reorientation of the cooling lesion, and was independent of anatomic orientation or pre-existing asymmetries of conduction. The models of unidirectional block described in this paper may be useful in the elucidation of the mechanism of asymmetric conduction disturbances and in studies of the mechanism of action of antiarrhythmic drugs.

Action Potentials↗
PubMed1980

Valsalva termination of ventricular tachycardia.

Nine patients with recurrent ventricular tachycardia (VT) that could be repeatedly terminated by a Valsalva maneuver are described. In two, the tachycardia would cease for only a few seconds and then resume, whereas in seven, the tachycardia could be permanently and reproducibly terminated with a Valsalva maneuver. In all patients the tachycardia ended during the strain phase of the Valsalva maneuver, when blood pressure and radiographic measurement indicated that cardiac dimensions had been reduced dramatically. The speed with which the Valsalva maneuver terminated VT incresed in direct proportion to the strain pressure. Maneuvers such as standing or nitroglycerin, which independently reduce cardiac dimensions, enhanced the potency of the Valsalva maneuvers. Pretreatment with atropine or propranolol in four patients did not alter the response of VT to the Valsalva maneuver. Thus, it appears that a strong Valsalva maneuver can terminate some forms of VT, most likely related to an abrupt reduction in cardiac dimensions.

Adolescent↗
PubMed1980

The effect of antiarrhythmic drugs on depressed conduction and unidirectional block in sheep Purkinje fibers.

We studied the effect of therapeutic concentrations of lidocaine, procainamide, quinidine, propranolol, and diphenylhydantoin on two models of depressed conduction and unidirectional block produced by asymmetric focal cooling and crushing in sheep Purkinje fibers. All drugs were shown to induce reversible deterioration of conduction. Unidirectional block was converted to bidirectional block with each drug. Improvement of conduction was rare and conversion of unidirectional block to bidirectional conduction never was observed. These experiments suggest that all five drugs may act by a uniform mechanism of action in some reentrant ventricular arrhythmias involving a zone of depressed conduction or unidirectional block within the Purkinje network.

Animals↗
PubMed1977

The effect of "ischemic" blood on transmembrane potentials of normal porcine ventricular myocardium.

"Ischemic" blood was obtained in pigs from a local coronary vein on release of coronary artery occlusion. The effects of this blood on transmembrane potentials of muscle strips taken from the same heart were compared with control blood. Whereas action potentials remained stable in control blood, ischemic blood collected after more than 15 minutes of coronary occlusion produced shortening of action potential duration, reduction of resting potential, upstroke velocity and amplitude, then postrepolarization refractoriness and finally unresponsiveness. Ischemic blood collected after shorter periods of coronary occlusion produced only mild effects (shortening of action potential and postrepolarization refractoriness). These effects of ischemic blood could not be attributed to increased potassium concentration even in combination with acidosis, hypoxia and hypoglycemia. It appears that during ischemia unidentified factors are released which have potent depressant effects on the excitability of even normal myocardium.

Action Potentials↗
PubMed1977

The effect of acute coronary artery occlusion on subepicardial transmembrane potentials in the intact porcine heart.

Subepicardial transmembrane potentials were recorded from intact pig hearts to observe the changes induced by acute ischemia. Ischemia shortened action potential duration, and decreased its amplitude, upstroke velocity, and resting potential. The cells were unresponsive after 12 to 15 minutes of coronary artery occlusion, yet near normal action potentials could be restored by flushing the occluded artery with saline as late as 40 minutes after occlusion. The unipolar extracellular electrogram reflected unresponsiveness by a monophasic potential. Local refractory periods initially shortened by up to 100 msec. Later, postrepolarization refractoriness occurred and refractory periods lengthened often in excess of basic cycle length, thus resulting in 2:1 responses. The onset of early ventricular arrhythmias often coincided with a period of alternation and 2:1 responses, especially when these got out of phase in different regions. Reperfusion frequently led to ventricular fibrillation, and was associated with marked inhomogeneity in cellular responses. Re-entry within ischemic myocardium was the most likely mechanism for arrhythmias.

Action Potentials↗
PubMed1975

Antazoline therapy of recurrent refractory supraventricular arrhythmias--a preliminary report.

Seven patients with chronic or recurrent supraventricular tachyarrhythmias were selected for a trial of antazoline therapy because sinus rhythm or a controlled ventricular response could not be achieved with quinidine, procainamide, digitalis or propranolol. Sinus rhythm was established by either intravenous administration of antazoline or direct-current countershock, and has been maintained in all for 4 to 16 months by oral administration of antazoline. Side effects were minor. Antazoline is a sufficiently promising antiarrhythmic agent to warrant large-scale controlled studies.

Adolescent↗
PubMed1975

Self-conversion of drug-resistant paroxysmal atrial tachycardia.

A 56-year-old woman had paroxysmal atrial tachycardia (PAT) that was recurrent, drug-resistant and required frequent electroversion. The mode of onset and termination of initiated episodes of PAT suggested an AV junctional reentrant mechanism. The problem was successfully managed by a permanent electrode implanted transvenously in the coronary sinus and connected to a subcutaneous radio frequency receiver. For the past 24 months the patient has successfully terminated all episodes of PAT (at least 60) by activating an external radio frequency transmitter that transmits impulses to the implanted receiver and electrode catheter. Conversion to sinus rhythm requires 5 seconds or less of pacing.

Bundle of His↗