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Biomedical subjects

D H Bennett

Publications and source records attributed to D H Bennett.

At least 73 records · Page 4Linked to original sources
PubMed1985

Effect of transvenous atrioventricular nodal ablation on the function of implanted pacemakers.

We report on seven patients with implanted pacemakers who underwent transvenous ablation of the atrioventricular junction using direct current shocks of 200 to 350 joules. Pacemaker impulse duration and rate were unaffected, but one rate responsive (TX) pacemaker was reprogrammed by a 300-joule shock. Transient increases in stimulation threshold did occur in two patients, and exit block for 2-15 seconds developed on four occasions. Chronic stimulation thresholds were unaffected. We conclude that it is preferable to carry out ablation before pacemaker implantation, but it is possible to perform transvenous ablation of the atrioventricular junction without damage to an implanted pacemaker; however, a transient rise in stimulation threshold or even exit block may occur, and pacemaker function should be carefully assessed after the procedure.

Adult↗
PubMed1985

Effect of xamoterol (ICI 118587), a new beta1 adrenoceptor partial agonist, on resting haemodynamic variables and exercise tolerance in patients with left ventricular dysfunction.

The effect of xamoterol, a beta1 adrenoceptor partial agonist, on resting haemodynamic measurements and exercise tolerance was studied in 10 patients with dyspnoea of effort. All patients had poor left ventricular function due to myocardial infarction with ejection fractions ranging from 15% to 35% (mean 28%). The cardiac index and stroke work index both rose significantly. The mean pulmonary artery pressure fell from 20(2) mm Hg to 16(2) mm Hg and pulmonary artery wedge pressure from 14(2) mm Hg to 10(2) mm Hg within the first four hours. Exercise tolerance, measured on the treadmill, increased significantly in seven patients but was unchanged in the three who had the lowest left ventricular ejection fractions. Exercise heart rate response was attenuated by the drug in all patients. It is concluded that xamoterol may be beneficial in patients with poor left ventricular function but can be harmful in extremely poor left ventricular function where high sympathetic drive may be important.

Adrenergic beta-Agonists↗
PubMed1985

Effect of percutaneous transluminal coronary angioplasty on arrhythmias complicating angina.

Four patients who had stenosis of a single major coronary artery which was treated by percutaneous transluminal coronary angioplasty are described. Three had exercise induced myocardial ischaemia complicated by ventricular tachycardia, fibrillation, and sinus bradycardia, respectively. Asystole developed in a fourth patient who had spontaneous chest pain. After successful percutaneous transluminal coronary angioplasty these arrhythmias did not recur spontaneously or on treadmill exercise testing. Percutaneous coronary angioplasty can be effective in preventing arrhythmias complicating acute myocardial ischaemia secondary to stenosis of a single major coronary artery.

Adult↗
PubMed1984

Catheter ablation of atrioventricular conduction.

35 patients with refractory supraventricular arrhythmias were treated in three centres by high-energy shocks delivered to the atrioventricular conduction system from a conventional transvenous pacing catheter. After a mean interval of ten months, 26 patients (74%) had persistent complete heart block, 2 (6%) had intermittent complete heart block, and 3(9%) had first-degree heart block. 3 patients continued to have conducted atrial fibrillation, but with slower ventricular rates than previously, and 1 had normalisation of dual atrio-His conduction. In 1 patient a septal accessory pathway was ablated. 30 patients (86%) are completely symptom-free without additional therapy. There were no important long-term complications. Transvenous ablation of atrioventricular conduction is a safe and effective technique for treating a wide range of refractory atrial and junctional arrhythmias.

Adolescent↗
PubMed1984

Angina, coronary risk factors and coronary artery disease in patients with valvular disease. A prospective study.

The relationship between coronary risk factors and coronary artery disease in patients with valvular heart disease was studied prospectively in 387 consecutive patients undergoing routine coronary arteriography prior to valve replacement. Coronary artery disease was as common in patients with mitral valve disease (31.9%) as in those with aortic valve disease (26.8%). Although it occurs more frequently in patients with angina (45.7%) significant coronary artery disease is found in 19.2% (47 of 245) of those without angina (P less than 0.001), suggesting that the presence of angina alone is an unreliable indicator of significant coronary disease. The prevalence and severity of significant coronary artery disease increases progressively as the number of coronary risk factors also increase (P less than 0.001) but the prevalence is low (3%) in patients in whom both angina and coronary risk factors are absent. These findings suggest that preoperative coronary arteriography might be omitted in this latter group of patients.

Adolescent↗
PubMed1984

Experience with 407 transvenous, finned pacing leads with a sintered porous-surfaced electrode.

Experience with 407 transvenous ventricular finned pacing leads with a sintered porous-surfaced electrode is reported. A low complication rate was encountered: 97% of patients were free from lead-related complications. Four patients (1%) required re-operation: two for lead displacement, one for failure to sense spontaneous ventricular activity and one for exit block. A further patient developed exit block which resolved spontaneously. The vast majority of patients had low chronic stimulation thresholds; for example at six months after implantation, the mean threshold for a group of pacemakers with a pulse duration of 0.5 ms was 1.4 +/- 0.7 V and for another group with a pulse duration of 0.8 ms it was 1.9 +/- 0.7 mA. However, six patients developed a transient high stimulation threshold during the month after implantation, and a high threshold developed in another patient at five months and persisted. Mean acute stimulation and sensing thresholds were satisfactory: 0.7 +/- 0.2 V at 0.5 ms pulse duration and 7.6 +/- 2.4 mV, respectively.

Adolescent↗
PubMed1984

Mechanisms of junctional tachycardia showing ventricular pre-excitation.

Over a period of five years 12 patients underwent electrophysiological studies for the investigation of recurrent tachycardias which showed ventricular pre-excitation. Nine patients had a type B pattern and two a type A. One patient had episodes of both types. Dual atrioventricular nodal pathways were found in six of seven patients with atrioventricular nodal re-entrant tachycardia mechanisms. Single direct atrioventricular accessory pathways were present in four patients, single nodoventricular pathways in five, and multiple pathways in three. Twenty one tachycardias were induced, of which 13 showed ventricular pre-excitation. Five patients had nodoventricular pathway conduction during atrioventricular nodal tachycardia and one during atrioventricular re-entrant tachycardia. Only three patients had simple antidromic tachycardia and one additional atrioventricular nodal tachycardia with bystander atrioventricular accessory conduction. Three patients had three different tachycardias, three had two types, and six had one type. Thus junctional tachycardias showing ventricular pre-excitation are often associated with multiple mechanisms and complex anatomical and functional substrates. An accessory pathway was an essential component in only six of 13 tachycardias showing ventricular pre-excitation. Determination of the tachycardia mechanism requires detailed study and analysis.

Adolescent↗
PubMed1984

Effect of Corwin (ICI 118587) on resting and exercise heart rate and exercise tolerance in digitalised patients with chronic atrial fibrillation.

The effect of Corwin, a new oral beta, partial agonist, on the ventricular response to atrial fibrillation was studied in digitalised patients during 24 hour ambulatory electrocardiography and during exercise on a treadmill in a double blind placebo controlled crossover trial. Corwin reduced the maximum heart rate during exercise from 162(16) beats/min to 120(9) beats/min and reduced the peak heart rate during ambulatory electrocardiography from 113(11) to 90(6) beats/min consistent with a beta adrenoreceptor antagonist action at higher levels of sympathetic nervous system activity. Minimum heart rate during ambulatory electrocardiography was increased from 62(5) to 70(5) beats/min indicating that at lower levels of sympathetic activity the drug acts as a beta agonist. The drug increased exercise tolerance significantly. Serum digoxin concentrations were not affected by the drug. Thus Corwin appears to be effective in stabilising heart rate during atrial fibrillation both at rest and during exercise in digitalised patients.

Adrenergic beta-Agonists↗
PubMed1983

Contribution of heart rate to QT interval shortening during exercise.

The contributions of the intrinsic effect of heart rate and factors other than heart rate, to exercise-induced QT interval shortening were assessed by studying a group of 24 patients with implanted, programmable P wave synchronised pacemakers and a group of 10 patients undergoing atrial and ventricular pacing at rest. In each patient with an implanted pacemaker, the relation between atrial rate and QT interval was studied during exercise in both atrial synchronised and asynchronous (fixed-rate) ventricular pacing modes. In three patients the exercise tests were repeated after beta-adrenergic blockade. There was a close linear correlation between atrial rate and QT interval reduction in each exercise test. With asynchronous ventricular pacing, QT shortening did occur but to a lesser extent than during atrial synchronised pacing and could be abolished by beta-adrenergic blockade. When the heart rate was increased at rest by either atrial or ventricular pacing QT interval shortening did occur but again to a lesser degree than with atrial synchronised ventricular pacing during exercise. The results suggest that the heart rate is only one of the determinants of the QT interval duration, and other factors, presumably associated with sympathetic activity, also contribute to QT interval shortening during exercise. By comparing the QT interval changes during atrial synchronised and asynchronous ventricular pacing on a within-patient basis, we determined that the contribution of the intrinsic effect of heart rate to QT interval shortening during exercise varied from 26 to 75%.

Adult↗
PubMed1983

Comparison of resting hemodynamic indices and exercise performance during atrial synchronized and asynchronous ventricular pacing.

Resting hemodynamic indices and exercise tolerance were measured during atrial synchronized (VAT) and asynchronous ventricular pacing (VOO) in 35 patients with implanted pacemakers which could be externally programmed to function in either pacing mode. Cardiac output and mean systemic arterial pressure were significantly greater during VAT pacing (VAT: 4.5 +/- 1.2 1/min, 115 +/- 28 mmHg; VOO: 3.7 +/- 0.8 1/min 105 +/- 25 mmHg respectively), although there was no difference in pulmonary artery end-diastolic pressure. Maximal exercise performance was assessed using the Bruce protocol in both pacing modes. Neither the patient nor the supervising physician was aware of the preselected pacing mode; a second physician monitored the electrocardiogram and blood pressure but influenced the point of exercise termination only if a potentially dangerous arrhythmia or hypotension occurred. Blood pressure responses were superior and atrial rates lower during VAT pacing. In all but five patients, exercise tolerance was improved by VAT pacing. This amounted to 33 percent or more in 23/35 patients. This improvement was shown to be maintained in the 20 patients who had repeat exercise tests several weeks later. Ventricular arrhythmias, hypotension, and lightheadedness frequently complicated exercise during asynchronous pacing but occurred rarely with atrial synchronized pacing. Resting hemodynamic indices did not predict the extent of improvement gained by physiological pacing.

Adult↗
PubMed1983

Atrial synchronized ventricular pacing: contribution of the chronotropic response to improved exercise performance.

In contrast to asynchronous ventricular pacing (VOO, VVI), atrial synchronized ventricular pacing (VAT, VDD, DDD) maintains the normal sequence of cardiac chamber activation and permits a chronotropic response to exercise, thereby improving exercise performance. To assess the separate contributions of these two factors to improved work capacity, 14 patients with implanted programmable VAT pacemakers were exercised according to the Bruce protocol, in three different pacing modes, selected in a random order and on a double blind basis: (a) VAT; (b) chest wall stimulation triggered ventricular (V-CWS-T) pacing, during which the pacemaker was programmed to VAT mode but driven externally using chest wall stimulation at rates fractionally above the patients' atrial rate, thereby providing a chronotropic response to exercise without atrioventricular synchronization; and (c) VOO mode at 70 beats per minute. There was a significant improvement in exercise performance in all patients during both VAT and V-CWS-T pacing as compared to VOO mode; the average increase in work capacity being similar: VAT: 44 +/- 31, (range, 12 to 140) percent and V-CWS-T; 40 +/- 24 (range, 5 to 85) percent. It is concluded that in patients with adaptive pacing systems, the chronotropic response is the major determinant of any improvement in exercise performance.

Aged↗
PubMed1982

Preoperative prediction of significant coronary artery disease in patients with valvular heart disease.

A prognostic index for predicting significant coronary artery disease was established using multiple logistic regression analysis of clinical data from 643 patients with valvular heart disease who had undergone routine coronary arteriography before valve replacement. The index or equation obtained incorporated the presence of angina, a family history of ischaemic heart disease, age, cigarette smoking habits, mitral valve disease, sex, and electrocardiographic evidence of myocardial infarction. The equation was validated using prospective data from 387 patients with valvular disease and shown to enable almost a third of routine coronary arteriograms to be omitted while maintaining 95% sensitivity for patients with coronary artery disease. Similar analysis of the more detailed prospective data produced a second discriminant function incorporating diastolic blood pressure, total cigarettes smoked in life, the severity of angina, family history of ischaemic heart disease, age, current cigarette smoking habits, and the ratio of total to high density lipoprotein cholesterol. This method improved the discrimination between patients with and without coronary artery disease, allowing omission of 30% of routine coronary arteriograms with 100% sensitivity for patients with coronary disease and omission of 41% with a 96% sensitivity level.

Coronary Angiography↗
PubMed1982

Ischemic pain relief in patients with acute myocardial infarction by intravenous atenolol.

Pain relief in acute myocardial infarction (AMI) by the beta-adrenoceptor antagonist, atenolol, was demonstrated by three separate studies. First, 18 patients were randomized to double-blind intravenous atenolol (5 mg) or saline immediately after admission, followed by oral atenolol (50 mg) or placebo 10 minutes later. In patients receiving atenolol, pain relief coincided with reduction in heart rate (HR), systolic blood pressure (SBP), and HR X SBP product (p less than 0.05); however, pain and these parameters were unchanged by placebo. The degree of pain relief was related to the reduction in cardiac work achieved (r = 0.725; p less than 0.001). A second open study involving 22 patients receiving intravenous atenolol (5 to 15 mg) early after AMI showed ischemic pain relief in 17 patients. They achieved a more significant reduction in HR X SBP product than those whose pain remained unchanged (p = 0.004). Finally, a retrospective study of 163 patients randomized to either atenolol or no beta blockade early after AMI revealed that patients receiving atenolol needed less opiate analgesia after admission (p less than 0.001). The safety of this therapy was illustrated by a decreased incidence of left heart failure and atrial fibrillation and no tendency to second- and third-degree heart block.

Adrenergic beta-Antagonists↗
PubMed1982

Acute prolongation of myocardial refractoriness by sotalol.

Sotalol, a beta adrenoceptor antagonist, was given intravenously to 15 patients with accessory atrioventricular pathways during intracardiac electrophysiological studies. Eleven patients had the Wolff-Parkinson-White syndrome and four patients had concealed left sided accessory pathways. Four patients were restudied while receiving oral sotalol. In contrast to the actions typical of beta blocking agents, intravenous sotalol prolonged the effective refractory periods of the ventricles and accessory pathways and reduced the ventricular response to atrial fibrillation in the patients with the Wolff-Parkinson-White syndrome. Similar results were obtained with oral administration. These findings support the observation that sotalol, unlike other beta blocking agents. causes acute prolongation of the myocardial action potential and suggest that this action might be of therapeutic use.

Action Potentials↗