Search PubMed⌕ Search

Biomedical subjects

D T Mason

Publications and source records attributed to D T Mason.

At least 307 records · Page 17Linked to original sources
PubMed1976

Arrhythmias in the mitral valve prolapse syndrome. Prevalence, nature, and frequency.

Ambulatory monitoring and maximal treadmill exercise were compared in 40 normal subjects and 31 patients with mitral prolapse. A variable arrhythmia spectrum was observed in prolapse during monitoring: premature ventricular contractions in 18 (58%), supraventricular arrhythmias in 11 (35%), and bradyarrhythmias in 9 (29%). Significantly less arrhythmias occurred in normal subjects during monitoring: 10 (25%, P greater than 0.001), 3 (8%, P less than 0.001), 4 (10%, P less than 0.05), and 2 (5%, P less than 0.02), respectively. In patients with prolapse, arrhythmias occurred on resting electrocardiogram (ECG), 35% premature ventricular contractons, 6% supraventricular arrhythmias, and 10% bradyarrhythmias, and on treadmill exercise, 45%, 10%, and 3%; therefore, ambulatory monitoring was the most sensitive method of arrhythmia detection. No correlation existed between clinical features of prolapse and arrhythmias. Thus, arrhythmias occur in most patients with mitral prolapse, are not predictable by clinical characteristics, comprise a spectrum of ventricular and supraventricular tachyarrhythmias and bradyarrhythmias, and are best detected by ambulatory ECG monitoring.

Adult↗
PubMed1976

Prevention of lower extremity venous thrombosis by early mobilization. Confirmation in patients with acute myocardial infarction by 125I-fibrinogen uptake and venography.

To determine the effects of early ambulation on peripheral venous thrombosis in the coronary care unit, 29 patients with acute myocardial infarction had daily 125I-fibrinogen point counting of both legs using a standard portable technique in the first 3 to 7 days after admission. Twenty-one patients underwent early ambulation during the initial 3 days, while 8 remained at complete bed rest for 5 days. Only 2 of 21 early ambulated patients had positive fibrinogen point counts, in contrast to 5 of 8 nonambulated patients (P less than 0.01). With heart failure, only 2 of 9 ambulated patients had positive point counts, compared with 4 of 5 nonambulated patients (P less than 0.05). In 16 patients undergoing venography, point counts were confirmed in 6 positive and 10 negative findings. These results show that the high frequency of peripheral venous thrombosis in immobilized acute myocardial infarction patients, particularly those with heart failure, can be effectively reduced by early ambulation.

Acute Disease↗
PubMed1976

Determination of improved myocardial perfusion after aortocoronary bypass surgery by exercise rubidium-81 scintigraphy.

Practical and noninvasive means are needed for evaluating efficacy of coronary bypass surgery (CBS) in improving blood flow (CBF) to ischemic myocardium in coronary patients. Revascularization was assessed in 15 patients by pre- and post-CBS rest and exercise rubidium-81 myocardial images with a scintillation camera equipped with pinhole collimator and high-energy shield. Ischemic areas were detected by decreased 81Rb activity after exercise compared to rest. Before CBS all patients had exercise angina (EA), positive treadmill ECG (TECG), and abnormal exercise 81Rb scans. After CBS all 15 patients had increased physical activity before angina or completion of treadmill exercise with increased heart rate-blood pressure product (HRBP) (+ 63 +/- 3.2 X 10(2) bpm - mm Hg) in 14 of 15 patients indicating increased CBF; four had positive TECG, and five had EA. The increased HRBP in 14 patients was associated with improved post-CBS exercise 81Rb scans: six had normal patterns while nine were improved with less ischemic patterns. Further, lack of angina and increased exercise tolerance correlated closely with increased 81Rb myocardial perfusion. Thus pre- and postoperative rest and exercise 81Rb scintigraphy gives an accurate, noninvasive, objective approach for evaluation of CBF following CBS and demonstrates the usefulness of this revascularization procedure in coronary patients.

Coronary Artery Bypass↗
PubMed1976

Rapid overdrive pacing of refractory tachyarrhythmias in patients after open-heart surgery.

The efficacy of rapid ventricular pacemaker overdrive in the treatment of supraventricular and ventricular tachyarrhythmias is presented as a new approach to the management of these rhythm disorders inpatients after cardiac surgery. This mode of therapy is exemplified in the control of heart rate and return of normal sinus rhythm in patients with both types of tachyarrhythmias refractory to conventional antiarrhythmic agents. In addition, the pathogenesis and mechanisms of pacemaker overdrive in termination these rhythm disturbances are delineated.

Bundle-Branch Block↗
PubMed1975

Isosorbide dinitrate. Effect on the vasodilator response to nitroglycerin.

To evaluate whether there is cross-tolerance to the circulatory effects of isosorbide dinitrate and nitroglycerin, six subjects were given 120 mg/day of sustained-action isosorbide dinitrate in three divided doses for six to eight weeks. Prior to and during the last week of long-term isosorbide dinitrate administration, the effects of sublingually given nitroglycerin (0.9 mg) on plethysmographically measured calf blood flow and venous volume at 30 mm Hg (VV[30]) were measured on three occasions and averaged. Although the arteriolar dilation produced by nitroglycerin was unaltered by isosorbide dinitrate, the venodilation was significantly attenuated. The VV[30] increased from 3.00 to 3.28 ml/100 ml (P less than .02) with nitroglycerin prior to isosorbide dinitrate administration, but failed to increase with nitroglycerin during the long-term administration of isosorbide dinitrate (2.95 to 2.95 ml/100 ml, P greater than .5).

Administration, Oral↗
PubMed1975

Propranolol-withdrawal rebound phenomenon. Exacerbation of coronary events after abrupt cessation of antianginal therapy.

Effects on anginal symptoms of sudden withdrawal of large doses of propranolol or placebo were evaluated in 20 patients in a double-blind crossover efficacy trial requiring sudden cessation of the agent. With propranolol, 160 to 320 mg per day for six and 12 weeks, no patients had increased angina or nitroglycerin use, and there were no hospitalizations or deaths. However, within two weeks of discontinuance of propranolol, untoward ischemic events developed in 10 patients. Six had serious withdrawal complications: intermediate coronary syndrome in three, and ventricular tachycardia, fatal myocardial infarction, and sudden death in one each. In four patients discontinuance of placebo increased anginal symptoms; in the remaining 10, ischemic symptoms were not provoked. The rebound phenomenon was related to degree of pre-propranolol angina and relief of pain by the agent. Thus, chronically administered propranolol should be gradually reduced, and activity restricted during its withdrawal.

Adult↗
PubMed1975

Comparative analyses of the kinetics and subunits of myosins from canine skeletal muscle and cardiac tissue.

Two types of canine cardiac myosins, myosin from the free wall of the right ventricle and the free wall of the left ventricle, were compared with canine skeletal muscle myosin from the gastrocnemius. The Vmax values for the ATPase reaction catalyzed by myosin were significantly different among the three types of tissues. For K+-activated myosin the Vmax values in micromoles of Pi per mg per min were: right ventricle, 0.57; left ventricle, 0.72; and gastrocnemius, 0.95. For Ca-2+ -activated myosin the Vmax values were: right ventricle, 0.32; left ventricle, 0.42; gastrocnemius, 0.50. All differences were significant (p smaller than 0.001). For all three types of tissues the Vmax values for NH4+ -activated myosin were the same (2.30). Light chains among all three types of tissues were immunologically identical, whereas the heavy chains of the two cardiac ventricles were immunologically identical with each other; however both were immunologically nonidentical with those of the gastrocnemius. The proportion of myosin light chains to heavy chains was different in the three types of tissue. Of the total protein present in each of the myosins, there was 18% in the light chains of right ventricle myosin, 10% in the light chains of left ventricle myosin, and 13% in the light chains of gastrocnemius. Both left ventricle myosin and myosin from gastrocnemius had significantly less C1d light chain, as compared to myosin from the right ventricle.

Adenosine Triphosphatases↗
PubMed1975

Comparative effects of tolamolol and propranolol on cardiac and peripheral circulatory function in patients with coronary artery disease.

In a clinical study comparing the cardiocirculatroy effects of intravenous tolamolol to those of propranolol, tolamolol, 16 mg, induced similar reduction in resting heart rate as 8 mg propranolol in 16 coronary patients. Tolamolol did not disturb cardiac pump performance and exerted less negative inotropic action than propranolol as assessed by mechanical contractility indices. Myocardial beta-one chronotropic and inotropic stimulation by exogenous epinephrine was blocked equally by tolamolol and propranolol. Tolamolol exerted less systemic vascular beta-two blockade than propranolol as assessed by the peripheral resistance and vasopressor responses to epinephrine infusion. Tolamolction than propranolol and is thereby suitable for careful extension of beta blockade therapy to certain patients with pulmonary and ventricular dysfunction.

Adult↗
PubMed1975

Efficacy of beta adrenergic blockade in coronary heart disease: propranolol in angina pectoris.

Despite widespread clinical application of propranolol (P) in angina pectoris, convincing evidence of its efficacy has been incomplete, thereby resulting in continued controversy. Its antianginal effectivess was investigated in 20 patients with documented coronary heart disease in a 44-wk study incorporating a prolonged 12-wk lead-in period, individualization of P dosage in a 6-wk dose-finding period, and a 24-wk doule-blind crossover phase. On double-blind placebo, patients had 10.5 +/- 2.1 anginal attacks and consumed 12.8 +/- 3.0 nitroglycerin tablets (NTG) each week compared to 6.6 +/- 1.5 anginal episodes (- 37%, p less than 0.001) and 8.0 +/- 1.7 NTG (-38%, p less than 0.001) when on P. No patient experienced more angina with P than with placebo. In addition, time to onset of chest pain during treadmill exercise was prolonged by P from 190 +/- 16 to 248 +/- 22 sec (+31%, p less than 0.02) and ST depression was reduced from 1.7 +/- 0.21 to 0.99 +/- 0.18 mm (-42%, p less than 0.05). There was correlation (r = 0.64 p less than 0.01) between per cent declines in anginal frequency and resting double product with P. Thus, propranolol favorably altered several indices of myocardial ischemia in severe coronary heart disease. This investigation clearly documents the clinical efficacy of optimal beta adrenergic blockade in coronary disease and provides objective justification for the judicious application of propranolol in treatment of angina pectoris.

Adult↗
PubMed1975

Electrophysiologic properties of perhexiline.

Perhexiline maleate (Pexid), a promising clinical antiarrhythmic and antianginal drug, was evaluated for its electrophysiologic effects on the entire conduction system of the intact canine heart throughout a wide range of therapeutic and potentially toxic doses. Intracardiac conduction times were measured by bipolar intramyocardial and transvenous endocardial electrodes before and following the intravenous administration of each dose of perhexiline maleate, 3 mg/kg every 30 min for a total of 4 doses in 7 open-chest anesthetized dogs. Eight animals served as controls in which similar operative technique and electrophysiologic variables were recorded after infusion of the maleate diluent. In addition, the effects of perhexiline on atrial and ventricular thresholds to electrical stimulation were recorded, as well as the QRS and QT intervals, sinus rate, and rhythm disorders. It was observed that perhexiline did not significantly (p greater than .05) alter sinus rate, QT interval, QRS duration, PR interval, intra-atrial conduction time, atrioventricular nodal conduction time, and His-Purkinje conduction velocity. The drug did not affect the cardiac threshold to electrical stimulation of less than 0.1 ma. No ectopic atrial or ventricular activity emerged during the accumulated influence of the agent. From this study, it is concluded that perhexiline does not exert deleterious actions on the conduction system of the intact canine heart. In view of the negligible toxic effects and its efficacy in treating ventricular tachyarrhythmias in patients, the drug deserves further clinical evaluation.

Animals↗
PubMed1975

Improvement of reduced left ventricular diastolic compliance in ischemic heart disease after successful coronary artery bypass surgery.

To determine the effects of myocardial revascularization on decreased left ventricular diastolic compliance consequent to chronic stable coronary artery disease, 15 patients with patent coronary artery bypass grafts (Group I) were compared with 8 patients with occluded grafts (Group II) studied before and after operation. In addition, eight normal patients served as controls. Left ventricular diastolic compliance was assessed by: (1) total observed diastolic compliance: stroke volume (V) related to left ventricular diastolic pressure (P) change (deltaV/deltaP) normalized for end-systolic volume; (2) left ventricular stiffness index of passive elastic modulus (a equals slope of deltaP/deltaV related to mean left ventricular diastolic pressure); and (3) fractional pattern of left ventricular filling. All patients had normal sinus rhythm and none had preoperative or postoperative mitral regurgitation. The two groups with coronary disease were well matched preoperatively for ventricular function, volumes, mass, segmental contraction and compliance. Ejection fraction increased in Group I (0.56 preoperatively to 0.65 postoperatively, P less than 0.05) but was unchanged in Group II (0.63 To 0.61, P greater 0.05). Postoperative indexes of left ventricular compliance improved in Group I: (1) 0.110 to 0.150 (P less 0.05); (2) 0.030 TO 0.019 (P less 0.05); and (3) 37 to 30 percent filling during last one third of diastole (P less 0.05). These indexes were unchanged postoperatively in Group II: (1) 0.109 to 0.102 (P greater 0.05); (2) 0.033 to 0.039 (P greater than 0.05); and (3) 36 to 41 percent (P greater 0.05). Compliance indexes were not altered (P greater 0.05) in a subset of seven patients in Group I with preoperative or intercurrent myocardial infarction. Thus, this investigation demonstrates the relatively reversible nature of abnormal left ventricular compliance after successful coronary artery bypass surgery in certain patients with ischemic heart disease.

Angiocardiography↗
PubMed1975

Unusual echographic manifestations of right and left heart myxomas.

Although echocardiography has provided a useful noninvasive means for detecting cardiac myxomas, the ultrasound manifestations of these tumors may be variable. We describe our experiences with unusual echographic features encountered in left and right heart myxomas. Thus the left atrial tumor may be manifested predominantly by multiple, discrete, linear echoes behind the mitral valve, the anterior leaflet of which may exhibit an abrupt mid-systolic posterior movement. In right heat myxomatous tumor arising from the septal tricupsid leaflet and adjacent interventricular septum, the echographic characteristics include a cloud of echoes throughout the cardiac cycle in the right ventricular outflow tract which are present in the right ventricle body only during relaxation and are anterior to the tricuspid valve in early diastole. Therefore, discrete linear echoes may be the principal echographic presentation of left atrial myxoma, and special attention should be focused on all areas of the tricuspid valve and right ventricle by ultrasound in patients in whom diagnosis of myxoma is suspected.

Adolescent↗
PubMed1975

Relation of ventricular arrhythmias in the late hospital phase of acute myocardial infarction to sudden death after hospital discharge.

To determine the prognostic significance of ventricular arrhythmias persisting during the hospital ambulatory phase of acute myocardial infarction, 64 patients with acute myocardial infarction underwent continuous 10-hour Holter monitoring an average of 11 days after discharge from the coronary care unit (CCU). Patients were categorized according to the results of ambulatory monitoring: 27 patients had ventricular extrasystoles, which were complicated (multifocal, R on T, paired, more than 5/min), or ventricular tachycardia; 22 had uncomplicated premature ventricular contractions; and 15 exhibited no ventricular arrhythmias. The 64 patients were followed prospectively for an average course of 25.8 months; 12 died suddenly; 8 died of other causes, and 44 survived. In all patients who died suddenly, ventricular ectopy was recorded on Holter monitoring before their discharge from the hospital (complicated premature ventricular contractions, eight patients; uncomplicated premature ventricular contractions, four patients); there were no sudden deaths in the patients without ventricular arrhythmias. Patients who died suddenly and those survived were similar in respect to age (60, 62 years), sex, location of infarction, presence of coronary risk factors, severity of acute myocardial infarction (Q waves, cardiac enzymes), serum cholesterol levels, evidence of cardiomegaly on roentgenograms, presence of ventricular gallop and drug therapy received. The occurrence of acute arrhythmias in the CCU did not separate patients who died suddenly from those who survived; there were no differences in ventricular tachycardia or ventricular fibrillation (3 or 12 patients who died suddenly, 6 of 44 patients who survived) or complicated premature ventricular contractions (4 or 12 patients who died suddenly, 18 of 44 patients who survived). Electrocardiograms obtained late in the hospital course revealed no differences in the extent of Q or T wave changes between these two groups. However, the extent of S-T segment abnormality was greater in patients who died suddenly than in patients who survived (5.6 compared to 1.8 leads/standard tracing, p smaller than 0.02) suggesting that the arrhythmias in the former were related to persistent ischemia or segmental ventricular dyssynergy. Thus, in this relatively small number of patients, ventricular arrhythmias persisting late in the hospital course of patients admitted for acute myocardial infarction are shown to predispose to subsequent sudden death.

Acute Disease↗