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Biomedical subjects

J W Mason

Publications and source records attributed to J W Mason.

At least 127 records · Page 7Linked to original sources
PubMed1983

The automatic implantable defibrillator: local ventricular bipolar sensing to detect ventricular tachycardia and fibrillation.

The first-generation automatic implantable defibrillator implanted in man sensed arrhythmias by monitoring a transcardiac electrocardiographic signal. This sensing system reliably detected ventricular fibrillation and sinusoidal ventricular tachycardia but failed to sense all nonsinusoidal ventricular tachycardias. To solve this problem, a new ventricular tachycardia detection scheme was developed using a local ventricular bipolar electrogram and electronic circuits using rate averaging and automatic gain control to permit sensing of electrograms down to 0.1 mV. This detection scheme was tested during electrophysiologic studies in 11 patients with ventricular tachycardia and fibrillation. All 22 episodes of induced ventricular tachycardia with a rate above the selected cutoff were detected after an average of 5.1 +/- 1.8 seconds. No episodes below the rate cutoff were detected. The bipolar circuits also reliably detected ventricular fibrillation. Arrhythmia detection and signal quality in 9 patients receiving automatic defibrillators using the new bipolar rate detection circuit were compared with the findings in 5 patients previously receiving units that sensed arrhythmias using the transcardiac electrocardiographic signal. Compared with the transcardiac monitoring units the newer bipolar units had shorter and more uniform sense times (5.5 +/- 1.4 versus 12.2 +/- 7.1 seconds). It is concluded that malignant ventricular tachyarrhythmias can be sensed accurately using bipolar rate detection and that this system has numerous advantages over the previously used transcardiac electrocardiographic signal.

Aged↗
PubMed1983

Efficacy of verapamil in chronic, recurrent ventricular tachycardia.

Verapamil, 0.25 mg/kg, was given to 24 patients with chronic, recurrent ventricular tachycardia (VT) whose clinical tachyarrhythmias were reproduced at electrophysiologic study. Seven patients (29%) responded acutely to verapamil: VT was not inducible in 5 and spontaneously terminated within 5 seconds of induction in 2 patients in whom it was previously sustained. Four of the 7 responders had no identifiable structural heart disease, and 3 had coronary artery disease. Responders were younger and had better left ventricular function than did nonresponders. Long-term therapy with verapamil, attempted in 5 of the 7 responders, was effective in 3, ineffective in 1, and of uncertain efficacy in 1. Verapamil therapy was discontinued because of worsened congestive heart failure in 2 patients. The short-term efficacy of verapamil in these patients compares favorably with the efficacy of other antiarrhythmic agents against VT induction in patients with long-term, recurrent, drug-refractory VT. The short-term efficacy of verapamil correlated with its long-term efficacy. These observations provide preliminary evidence that verapamil may be useful in the treatment of some patients with recurrent VT. When standard drugs are not effective, verapamil should be given a trial, especially in young patients with good left ventricular function.

Adult↗
PubMed1983

Safety and efficacy of intravenous quinidine.

The safety and efficacy of intravenous quinidine were evaluated in a patient population with a high prevalence of left ventricular dysfunction and intraventricular conduction delays. Quinidine gluconate (mean dose 9.1 +/- 1.6 mg/kg) was administered during electrophysiologic study to 100 patients with ventricular or supraventricular tachyarrhythmias. Clinical heart failure was present in 68 percent of the patients. Left ventricular end-diastolic pressure, cardiac index, and left ventricular ejection fraction were abnormal in 62, 48, and 70 percent, respectively. Major intraventricular conduction delays (QRS of 120 msec or more) were present in 27 percent, and the H-V interval was prolonged (over 55 msec) in 28 percent. Despite the prevalence of these abnormalities, quinidine was discontinued because of hypotension in only 10 patients. Saline solution was infused to maintain preload in 37 percent, and hypotension responded promptly to saline solution infusion or discontinuation of quinidine infusion in all subjects. Hypotension was not more common in patients with more severe left ventricular dysfunction. QRS duration, H-V interval, QTc, and right ventricular effective refractory period increased significantly (p less than 0.001) after quinidine administration. Heart block or QRS widening of 50 percent or more did not occur. Quinidine prevented arrhythmia induction in 26 percent of patients who received full doses. Ventricular tachycardia cycle length increased in all 41 patients in whom identical forms were induced before and after quinidine (287 +/- 71 msec versus 361 +/- 93 msec, p less than 0.001). Intravenous quinidine may be administered safely to patients with intraventricular conduction delays and moderate heart failure. When antiarrhythmic efficacy is assessed by electrophysiologic study, quinidine compares favorably with other antiarrhythmic agents.

Arrhythmias, Cardiac↗
PubMed1983

Clinical factors predicting successful electrophysiologic-pharmacologic study in patients with ventricular tachycardia.

Data from 142 patients who had sustained ventricular tachycardia or ventricular fibrillation were analyzed to determine if clinical variables predict response to antiarrhythmic drugs at electrophysiologic study. Effective antiarrhythmic drugs were identified for 43 patients (30%). Ten of 25 variables analyzed were univariate predictors of drug response at the probability (p) level of less than 0.05. Stepwise logistic regression identified three variables independently predictive of drug response: fewer coronary arteries with 70% or greater stenosis (p less than 0.001), female sex (p less than 0.002) and fewer episodes of arrhythmia (p less than 0.03). A function incorporating these three variables was constructed to predict the probability of drug response, and ranges of the predictor function corresponding to high, intermediate and low probabilities of drug response were identified. Response rates in the high (greater than 50%), intermediate and low (less than 10%) probability ranges were 28 (58%) of 48, 10 (27%) of 37 and 5 (9%) of 57, respectively. Thus 40% of the patients who had a less than 10% likelihood of benefit from electrophysiologic-pharmacologic study were classified into the low probability range. When the predictor function was applied prospectively to 25 additional patients, response rates in the three probability ranges were 3 (50%) of 6, 1 (12%) of 8 and 0 (0%) of 11. These data show that analysis of clinical variables can be used to estimate the probability of benefit from electrophysiologic-pharmacologic study.

Anti-Arrhythmia Agents↗
PubMed1983

Amiodarone: clinical efficacy and toxicity in 96 patients with recurrent, drug-refractory arrhythmias.

Ninety-six patients with recurrent, drug-refractory tachyarrhythmias were treated with amiodarone for 8.0 +/- 7.5 months (range 1 day to 27 months): 77 for recurrent ventricular tachycardia or ventricular fibrillation (VT/VF), two for complex ventricular ectopy, and 17 for supraventricular tachyarrhythmias. The actuarial incidence of successful amiodarone therapy was 52 +/- 7% at 12 months and 28 +/- 9% at 24 months for patients with VT/VF. Neither patient with complex ventricular ectopy was successfully treated. Among the patients with supraventricular tachyarrhythmias, 64.7% were successfully treated for 7.7 +/- 7.6 months (range 1 to 22 months). Amiodarone toxicity occurred in 66 of 91 patients (72.5%) treated for more than 1 week. Fourteen patients had therapy-limiting toxicity. Of these 14, six had pulmonary toxicity, four had arrhythmia exacerbation, one had hepatitis, one had renal toxicity, one had rash, and one had erythema nodosum. The actuarial incidence of therapy-limiting side effects was 27 +/- 7% at 15 months. We conclude that amiodarone is useful in the treatment of refractory tachyarrhythmias but that the rate of efficacy in VT/VF is lower and the incidence of significant toxicity is higher than has been generally appreciated.

Adult↗
PubMed1983

Prognostic significance of the number of induced ventricular complexes during assessment of therapy for ventricular tachyarrhythmias.

We analyzed 255 long-term trials of antiarrhythmic therapy, each of which had been evaluated at electrophysiologic study, to identify the maximum number of induced ventricular complexes consistent with the long-term efficacy of antiarrhythmic therapy. All patients had spontaneous and inducible sustained ventricular tachycardia or ventricular fibrillation. The incidence of therapeutic efficacy at 1 month and throughout follow-up was similar for trials in which zero, one, two, three, four, five, six to 10, and 11 to 15 complexes were induced, but significantly lower (p less than .001) for trials in which 16 or more complexes were induced. The cumulative incidence of efficacy at 1 year was 75 +/- 5% for 0 to 5 induced complexes, 72 +/- 11% for six to 10 complexes, 83 +/- 15% for 11 to 15 complexes, 42 +/- 10% for 16 complexes to 15 sec, and 48 +/- 6% for sustained ventricular tachycardia. At 1 year, the incidence of "sudden death-free" survival was higher for patients in trials that prevented initiation of sustained ventricular tachycardia than for those in trials that permitted initiation of sustained ventricular tachycardia (91 +/- 3% vs 75 +/- 6%; p = .01). The duration of the arrhythmia induced at therapy assessment was in the range of 11 to 20 complexes for only 4% of trials. Antiarrhythmic therapy is likely to be effective if as many as 15 complexes are induced at therapy assessment. The best cutoff, between 11 and 20 complexes, is difficult to identify because of the small fraction of trials in this range. Patients in whom initiation of sustained ventricular tachycardia is not prevented are at high risk for arrhythmia recurrence and sudden death.

Adult↗
PubMed1983

Can the laboratory director find the pathologists he needs?

Is the pathologist seeking a job the kind of pathologist the laboratory director wants to hire? The author of this article emphasizes that all pathologists, not just residency training program directors, must be aware of changing needs if new pathologists are to possess the necessary qualifications for practice in the 1980s and 1990s.

Hospital Departments↗
PubMed1982

Efficacy and cost of cardiac monitoring in patients receiving doxorubicin.

We compared the incidence of heart failure (CHF), CHF mortality and CHF severity in cancer patients (pts) treated with doxorubicin (DXR) in the presence and absence of cardiologic monitoring (CM). CM consisted of endomyocardial biopsy and right heart catheterization as definitive tests with and without echocardiograms and phonocardiographically derived systolic time intervals as screening tests. CHF incidence was very low (0.03) in non-CM pts without risk factors (RF). RF pts had a CHF incidence of 0.17 without and 0.06 with CM (P = 0.107). Five of 58 RF pts in the non-CM group and 0 of 49 RF pts in the CM group died of problems related to CHF. CHF symptomatology by NYHA criteria was less in CM RF pts than non-CM RF pts (P = 0.034). The prevention of CHF mortality and morbidity in CM pts was not due to administering less DXR, as CM pts actually received an average of 43 mg/m2 more DXR than non-CM pts. We conclude that pts without RF need no CM during treatment with DXR, and that CM can reduce CHF severity and CHF mortality in RF pts.

Adult↗
PubMed1982

Endomyocardial biopsy: its history, techniques and current indications.

Endomyocardial biopsy has found wide application as a diagnostic tool in the practice of cardiology and is of great clinical use in selected cardiac disorders. It is indispensable in the management of cardiac transplant recipients and has become increasingly valuable in the diagnosis of myocarditis and certain cardiomyopathies. Technical difficulties have been overcome, and the procedure is straightforward and of low risk in experienced hands. It is hoped that advances in endomyocardial biopsy will lead to a greater ability of physicians to diagnose and treat cardiac disease.

Biopsy↗
PubMed1982

Comparative clinical electrophysiologic effects of diltiazem, verapamil and nifedipine: a review.

The slow channel blocking agents--diltiazem, verapamil and nifedipine--have generated clinical interest for the treatment of a variety of cardiovascular disorders. These agents, despite a similar basic mechanism of action, produce disparate clinical cardiac electrophysiologic effects in human beings. In usual doses, the acute administration of diltiazem slows heart rate. Verapamil and nifedipine, however, increase heart rate. Although diltiazem and verapamil produce equivalent slowing of atrioventricular (A-V) nodal conduction, verapamil prolongs A-V nodal refractoriness to a greater degree. In contrast, nifedipine facilitates A-V nodal conduction and shortens A-V nodal refractoriness. Knowledge of these differences may aid in the appropriate selection of specific slow channel blocking agents in specific clinical situations.

Atrioventricular Node↗
PubMed1982

Decreased incidence of antiarrhythmic drug efficacy at electrophysiologic study associated with the use of a third extrastimulus.

Drug trials during electrophysiologic study were performed in 166 patients with sustained ventricular tachycardia (VT) or ventricular fibrillation. In the first 21 patients (group I), a maximum of two extrastimuli was used. In 145 subsequent patients (group II), drug efficacy was assessed using three extrastimuli if one or two failed to induce VT. The incidence of acute drug efficacy was 15 of 21 (71%) in group I, but only 44 of 145 (30%) in group II (p less than 0.01). To assess the influence of the third extrastimulus on the differing incidence of acute drug efficacy, we examined the 69 group II patients whose VT was initially induced by one or two extrastimuli. Acutely effective agents were identified for 19 of these 69 patients using up to three extrastimuli to define efficacy. In 24 of te 50 patients for whom no effective drug could be found, VT was induced with one or two extrastimuli during all drug trials. In the remaining 26 patients VT could be induced after drug administration only with use of three extrastimuli. If efficacy had been defined using a maximum of two extrastimuli, these 26 patients would have been considered responsive to drug testing. Overall, 45 to 69 (65%) rather than 19 of 69 (28%) would have had a favorable response (p less than 0.001). Fourteen group I patients and 17 group II patients in whom VT was initially induced by one or two extrastimuli received chronic therapy with agents predicted effective during acute drug trials. At 18 months, the cumulative percent of patients free of arrhythmia recurrence by actuarial analysis was 79 +/- 14% in group I and 80 +/- 14% in group II (NS). Use of three extrastimuli during drug trials is associated with a lower incidence of acute drug efficacy. Limited data suggest that prophylaxis against VT induction by three, rather than two, extrastimuli may not be a stronger predictor of chronic efficacy in patients whose VT is initially induced by one or two extrastimuli. Further study is needed to identify optimal pacing methods for antiarrhythmic drug assessment.

Anti-Arrhythmia Agents↗
PubMed1982

Programmed ventricular stimulation in predicting vulnerability to ventricular arrhythmias and their response to antiarrhythmic therapy.

In predicting vulnerability to ventricular arrhythmias and their response to antiarrhythmic therapy, several factors and questions need to be considered, including the following. (1) Ventricular tachycardia (VT) can be induced in most patients who have recurrent sustained VT. (2) Because induced VT can often be pace terminated, termination by pacing should be attempted before cardioversion is applied. (3) Acutely effective antiarrhythmic agents are no longer being found for the majority of patients undergoing electrophysiologic-pharmacologic study in our series. (4) Specific VT-induction programs affect both the inducibility of VT and acute efficacy of drugs at electrophysiologic study; this point requires examination. (5) Arrhythmia-induction studies may not product high yield in patients with clinical ventricular fibrillation or unsustained VT. (6) It is as yet unclear whether some drugs, such as amiodarone, can be accurately evaluated by using arrhythmia-induction techniques. (7) Induction of the repetitive ventricular response by V2 stimulation is not a useful method for antiarrhythmic drug selection in patients with recurrent ventricular tachyarrhythmias. (8) Adequate data do not yet exist to identify either the ECG-monitoring technique or the arrhythmia-induction technique as the preferred method for selecting antiarrhythmic drugs for chronic therapy of patients with recurrent ventricular tachyarrhythmias. A study to compare the accuracies of the two techniques is both feasible and needed.

Amiodarone↗
PubMed1982

Intracardiac electrophysiologic study of intravenous diltiazem and combined diltiazem-digoxin in patients.

Fifteen patients without sinoatrial (SA) or atrioventricular (AV) node dysfunction underwent electrophysiologic study (EPS) before and after intravenous diltiazem: 0.20 mg/kg bolus followed by 0.0007 mg/kg/min infusion (seven patients) or 0.25 mg/kg bolus followed by 0.0012 mg/kg/min infusion (eight patients). In six patients intravenous digoxin (0.018 mg/kg) was given and 45 minutes later EPS was repeated while the diltiazem infusion continued. Diltiazem prolonged sinus cycle length (+7%, p less than 0.01), lengthened AH conduction time (+22% in constant rate atrial paced rhythm, p less than 0.001), prolonged AV node functional and effective refractory periods (+6%, p less than 0.01 and +16%, p less than 0.05, respectively), lengthened AV node Wenckebach cycle length (+13%, p less than 0.001), shortened atrial functional refractory period (-3%, p less than 0.05), and reduced mean arterial pressure (-8%, p less than 0.005 in constant rate atrial paced rhythm). Subsequently, intravenous digoxin further prolonged sinus cycle length (+12%, p less than 0.05), AH conduction time (+17%, p less than 0.05), AV node Wenckebach cycle length (+9%, p less than 0.05), and AV node functional refractory period (+7%, p less than 0.05), shortened atrial effective refractory period (-7%, p less than 0.05) and ventricular effective refractory period (-6%, p less than 0.05), and increased systolic arterial pressure (+6%, p less than 0.05). Diltiazem and digoxin have additive depressant effects on SA and AV node function without significant adverse effects.

Adult↗
PubMed1982

Relative efficacy of blind left ventricular aneurysm resection for the treatment of recurrent ventricular tachycardia.

Coronary arterial bypass grafting and left ventricular aneurysm resection and the two combined have been reported effective in control of refractory ventricular tachyarrhythmias; 82 percent of a pool of 127 patients (from 22 reports) survived after surgery. However, the follow-up period in this group is short and the extent of medical therapy is not well defined. Actuarial analysis of results of conventional left ventricular aneurysm resection in 32 Stanford patients with well documented ventricular tachyarrhythmias shows an arrhythmia recurrence rate of 50 +/- 9 percent (mean +/- standard error of the mean) during the postoperative hospitalization. In contrast, after 10 months only 11 +/- 9 percent of 18 patients who underwent myocardial resection guided by intraoperative electrical activation sequence mapping experienced arrhythmia recurrence. These data demonstrate that simple left ventricular aneurysm resection is less effective in preventing ventricular tachyarrhythmias than originally believed. Preliminary data suggest that surgery of the left ventricle guided by intraoperative mapping may provide more effective control of ventricular tachyarrhythmias. However, intraoperative mapping has many technical and interpretive problems. Investigations are needed to determine the roles of conventional and new operative approaches to treatment of medically refractory ventricular tachyarrhythmias.

Aged↗
PubMed1982

Prolongation of the human cardiac monophasic action potential by sotalol.

Sotalol and propranolol are nonselective beta-adrenergic blocking agents. Sotalol at low concentration, unlike propranolol, prolongs the duration of the transmembrane action potential. In a double-blind study, the electrophysiologic effects of intravenous sotalol (0.30 or 0.60 mg/kg; n = 9) were compared with intravenous propranolol (0.15 or 0.20 mg/kg; n = 8) in 17 patients with use of bipolar suction electrodes in the right atrium and right ventricle to determine whether sotalol prolongs the monophasic action potential duration in man. After administration of sotalol, there were significant increases (paired t test) in the Q-T interval (p less than 0.001), right atrial effective refractory period (p less than 0.05), right ventricular effective refractory period (p less than 0.005), right atrial monophasic action potential duration at 90% repolarization (p less than 0.01), and right ventricular monophasic action potential duration at 90% repolarization (p less than 0.005). Prolongation of the monophasic action potential duration was dependent on plasma sotalol concentration. There were no significant changes in these variables after propranolol. The spontaneous cycle length and Wenckebach cycle length increased significantly in both groups, and the mean blood pressure decreased in both, although not significantly after propranolol. In summary, sotalol but not propranolol prolonged atrial and ventricular effective refractory periods and lengthened the monophasic action potential and the Q-T interval of human myocardium after intravenous infusion. The ability to acutely prolong repolarization at therapeutic plasma concentration is unique among known competitive beta-adrenergic receptor antagonists.

Action Potentials↗
PubMed1982

Surgical exclusion of focal paroxysmal atrial tachycardia.

A 37 year old man with no evidence of structural heart disease presented with paroxysmal atrial tachycardia that could not be induced in the electrophysiology laboratory. Epicardial and endocardial mapping of the tachycardia performed in the operating room showed earliest activation at the junction of the right superior pulmonary vein and left atrium. An encircling incision excluded the portion of the left atrium containing the earliest point of activation and both right pulmonary veins from the remainder of the left atrium. The edges of the incision were then reapproximated. The patient is free of arrhythmias 6 months later. This technique should prove useful for the management of arhythmias arising from parts of the atria that are difficult to excise.

Adult↗
PubMed1982

Recurrent ventricular tachycardia induced by an atrial synchronous ventricular-inhibited pacemaker.

Atrial synchronous pacemakers have been known to cause a variety of cardiac arrhythmias. Of particular concern are those arrhythmias involving a pacemaker stimulus occurring on a T wave, because these may lead to ventricular tachycardia. The Medtronic 2409 ASVIP pacemaker is an atrial synchronous pacemaker with several features designed to decrease the likelihood of such arrhythmias. We report a patient in whom a normally functioning Medtronic 2409 ASVIP pacemaker, despite these features, induced recurrent ventricular tachycardia. Conditions which predisposed this patient to pacemaker-induced re-entrant arrhythmias are discussed.

Digoxin↗