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Biomedical subjects

G N Kay

Publications and source records attributed to G N Kay.

100 records · Page 6Linked to original sources
PubMed1988

Incidence of reentry with an excitable gap in ventricular tachycardia: a prospective evaluation utilizing transient entrainment.

The demonstration of transient entrainment has been proposed as evidence of reentry, with an excitable gap as the probable mechanism of tachycardia. A prospective series of 27 consecutive patients with sustained ventricular tachycardia induced by programmed electrical stimulation was studied to determine the frequency with which transient entrainment can be demonstrated and to define the optimal location of pacing and recording electrodes. In all patients, electrodes for pacing and recording were placed in both the left and right ventricles during electrophysiologic study. Among the 19 patients in whom the response to rapid pacing could be evaluated (25 episodes of ventricular tachycardia), transient entrainment was demonstrated in 79% (76% of episodes). Ten of 12 episodes of ventricular tachycardia with a left bundle branch block QRS configuration in lead V1 and 9 of 13 episodes with a right bundle branch block QRS configuration could be transiently entrained (p = NS). Transient entrainment was demonstrated for 8 of 11 episodes of ventricular tachycardia with a left bundle branch block configuration during pacing from the left ventricle, but for only 2 of 10 episodes during pacing from the right ventricular apex (p less than 0.05). Conversely, 9 of 13 episodes of ventricular tachycardia with a right bundle branch block configuration were transiently entrained during pacing from the right ventricular apex, but 0 of 10 episodes were transiently entrained by left ventricular pacing (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Comparison of unipolar and bipolar active fixation atrial pacing leads.

The purpose of this investigation was to compare the acute pacing and sensing characteristics of a new bipolar active fixation atrial pacing lead with those of a unipolar atrial lead of similar design. Pacing threshold voltage and current, lead impedance, and atrial electrogram amplitude and slew rate were measured at the time of surgery in 28 consecutive patients undergoing DDD pacing system implantation. Eleven patients received a Medtronic 6957J-58 unipolar active fixation atrial lead and 17 patients were given a Medtronic 4016-58 bipolar lead. Both leads are polyurethane-insulated with the distal electrode being a platinum alloy screw-helix with a surface area of 8.0 mm2. There were no significant differences in the threshold voltage (1.01 V unipolar versus 1.05 V bipolar) or current (1.93 mA unipolar versus 1.78 mA bipolar) of the two leads. The mean impedance of the bipolar active fixation lead was 618 ohms compared to 479 ohms for the unipolar lead (p = 0.02). The mean amplitude of the atrial electrogram was 4.64 mV for the bipolar lead and 3.11 mV for the unipolar lead (p = 0.02). The atrial electrogram exceeded 5 mV in 10 of 17 patients with the bipolar lead but zero of 11 with the unipolar lead. There was no significant difference in the mean slew rate of the leads (1.09 V/s bipolar versus 0.73 V/s unipolar; p = 0.18). Over a follow-up period of up to 10 months, all patients remained in either the DDD or DDI modes with no episodes of atrial sensing or pacing failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Value of the 12-lead electrocardiogram in discriminating atrioventricular nodal reciprocating tachycardia from circus movement atrioventricular tachycardia utilizing a retrograde accessory pathway.

The value of the 12-lead electrocardiogram for distinguishing atrioventricular (AV) nodal reciprocating tachycardia from circus movement AV tachycardia utilizing a retrograde accessory pathway was studied in 100 patients with narrow QRS complex tachycardia. Intracardiac electrograms showed AV nodal reciprocating tachycardia in 40 patients and circus movement AV tachycardia in 60. The 12-lead electrocardiograms recorded during tachycardia were randomly sorted and reviewed by 4 experienced cardiac electrophysiologists who were blinded to the diagnosis associated with each tracing, the relative proportion of each arrhythmia and the hypotheses to be tested. Each reviewer was asked to indicate the location of the P wave relative to the QRS complex, electrical axis of the P wave in the frontal and horizontal planes and presence or absence of QRS alternation, and to interpret the most likely mechanism. The performance of published electrocardiographic criteria to differentiate AV nodal reciprocating tachycardia from circus movement AV tachycardia was evaluated. The overall accuracy of the reviewers' interpretations was 75%, similar to the accuracy of the predefined criteria when applied by these observers (71% correct, difference not significant). Interobserver agreement of reviewer interpretations was 76% and the intraobserver agreement was 78%. Features associated with circus movement AV tachycardia by univariable analysis were P waves after the QRS complex, faster tachycardia rates and QRS alternation. Multivariable analysis showed that only the location of the P wave relative to the QRS complex was independently associated with the mechanism of tachycardia (p = 0.002). QRS alternation was found by multivariate analysis to be associated with the rate but not the mechanism of the tachycardia.

Diagnosis, Differential↗
PubMed1987

Comparison of survival of amiodarone-treated patients with coronary artery disease and malignant ventricular arrhythmias with that of a control group with coronary artery disease.

Although amiodarone is effective in the treatment of ventricular arrhythmias, it is associated with serious toxic effects. In addition, the prognosis of patients with malignant ventricular arrhythmias and coronary artery disease treated with amiodarone remains poor. The survival of 54 consecutive patients with angiographically documented coronary artery disease and symptomatic ventricular tachycardia or ventricular fibrillation treated with amiodarone was compared with that of 5,125 medically treated patients with coronary artery disease. The amiodarone group was older, with worse left ventricular function and more peripheral and cerebrovascular disease. The 1 year survival probability was 0.73 for the amiodarone group and 0.94 for the control coronary artery disease group. At 2 years of follow-up, the survival probabilities were 0.60 and 0.90 for the amiodarone and the control group, respectively. When the survival curves were adjusted for group differences in baseline prognostic characteristics (integrated as a previously published hazard score), there was no difference in the prognosis of the two groups. These findings suggest that treatment with amiodarone of malignant ventricular arrhythmias associated with coronary artery disease maintains patients on an underlying survival curve determined by the degree of myocardial dysfunction, clinical characteristics and coronary anatomy, and that amiodarone does not have a deleterious effect on survival.

Aged↗
PubMed1986

Hemodynamic abnormalities in acute myocardial infarction.

Great strides have been made in the management of patients with acute myocardial infarction since the advent of coronary care units. However, congestive heart failure continues to be the major cause of in-hospital mortality. The accurate diagnosis and classification of hemodynamic abnormalities allow the application of specific therapies for each patient. Because clinicians can now routinely measure left and right ventricular preload, systemic and pulmonary vascular resistance, cardiac output, and arteriovenous oxygen difference, pharmacologic and surgical interventions can be applied in a scientific manner. In addition, mechanical complications can be promptly recognized and aggressively treated. Although the mortality rate for patients with severe left ventricular dysfunction after myocardial infarction remains high, expert management offers an improved prognosis for many patients.

Cardiotonic Agents↗
PubMed1986

Characterization of retrograde conduction by direct endocardial recording from an accessory atrioventricular pathway.

Accessory pathway electrograms are rarely recorded in patients with Wolff-Parkinson-White syndrome. In one patient, during electrophysiologic study, simultaneous local ventricular (V) accessory pathway (AP) and atrial (A) deflections were recorded during bipolar catheter endocardial mapping over the pathway. Analysis of changes in electrographic intervals during performance of the ventricular extrastimulus technique allowed characterization of the retrograde conduction properties of the pathway. As coupling intervals were decreased, an initial increase was seen in the AP2A2 interval with subsequent ventriculoatrial block between the accessory pathway and atrium. When coupling intervals were further decreased, the V2AP2 interval lengthened with ultimate block between the ventricle and accessory pathway. These findings support the concept of impedance mismatch as the cause of conduction block in accessory pathways with the distal junction of the accessory pathway being the most vulnerable.

Adult↗
PubMed1983

Torsade de pointes: the long-short initiating sequence and other clinical features: observations in 32 patients.

The clinical setting, precipitating factors, electrocardiographic features and response to treatment of 32 patients with torsade de pointes were reviewed. Thirty-one patients had underlying cardiac disease and 30 patients had a previous underlying cardiac arrhythmia. Antiarrhythmic medications, often in association with electrolyte abnormalities (such as hypokalemia and hypomagnesemia) were the most common precipitating factors. In 22 of 26 patients, the serum drug levels of the antiarrhythmic agents were found to be within the therapeutic range. However, before the administration of agents known to prolong the QT interval, 20 of the 32 patients had, either alone or in combination, baseline prolongation of the QT interval, hypokalemia or hypomagnesemia. All patients had QTc interval prolongation (mean 0.59 second) immediately before the development of torsade de pointes. Marked lability of T wave morphology was frequently noted. Cardiac pacing was the only consistently effective mode of therapy. A characteristic long-short ventricular cycle length as the initiating sequence was found in 41 of 44 episodes of torsade de pointes. Reported data support the high frequency of this electrocardiographic feature of torsade de pointes in which its onset could be analyzed. It is suggested that this electrocardiographic characteristic will aid in both establishing the diagnosis of torsade de pointes and distinguishing it from other polymorphic forms of ventricular tachycardia.

Adult↗
PubMedDate not supplied

Modeling and closed-loop pharmacologic control of the ventricular rate during induced atrial fibrillation in anesthetized dogs.

An automated drug delivery system that provides closed-loop feedback control of the ventricular rate during atrial fibrillation is described. The control system was designed using a mathematical model of the effect of esmolol infusion in the ventricular rate. The model was developed in system identification experiments with anesthetized dogs in which atrial fibrillation was induced and maintained by rapid atrial pacing. A control system of variable structure, which incorporates a transient controller and a regulator, was designed to perform satisfactorily over a wide range of subject responses to drug infusion. The transient controller brings the ventricular rate to the setpoint with little overshoot. When the ventricular rate is near the setpoint, the drug infusion rate is calculated by the regulator. The drug infusion rate is constrained to ensure smooth transitions in the hemodynamic state of the patient and for safety. Feasibility of the system was demonstrated in computer simulations and animal experiments.

Adrenergic beta-Antagonists↗