Search PubMed⌕ Search

Biomedical subjects

D E Ward

Publications and source records attributed to D E Ward.

At least 127 records · Page 7Linked to original sources
PubMed1990

Prospective evaluation of a protocol for induction of sustained ventricular tachycardia in patients referred to a tertiary centre.

All eight stages of a stimulation protocol that used one then two extrastimuli from the right ventricular apex in sinus rhythm and three ventricular drive rates (100, 120, and 140 beats/min) were performed in 24 patients with recurrent spontaneous sustained ventricular tachycardia despite drug treatment. Twenty two of the patients had sustained a previous myocardial infarct and 18 were on long term treatment with amiodarone. Sustained (greater than 30 s) ventricular tachycardia was induced in all patients. Two extrastimuli were significantly more likely to induce sustained ventricular tachycardia than one extrastimulus, both overall and individually for the three ventricular drive rates. A ventricular drive rate of 140 beats/min was significantly more likely to induce ventricular tachycardia than ventricular drive rates of 100 and 120 beats/min which were significantly more effective than sinus rhythm. A ventricular drive rate of 140 beats/min with one or two extrastimuli induced ventricular tachycardia in 23/24 (95%) of the patients in this study. The full eight stage protocol was progressive separately for both extrastimuli and ventricular drive rate but the last two stages (ventricular drive rate of 140 beats/min with one or two extrastimuli) were as effective as the entire protocol in inducing ventricular tachycardia.

Aged↗
PubMed1989

Prediction of serious post-infarction cardiac arrhythmias.

Simple clinical findings suggestive of a large myocardial infarction identify most patients at risk from serious post-infarction arrhythmias (defined as sustained ventricular tachycardia and sudden death not associated with reinfarction). However, similar findings are seen in many other patients who remain free of complications. The presence of late potentials and frequent ventricular ectopics on long-term electrocardiographic monitoring add to prognostic accuracy in patients with clinical complications, with a predictive accuracy of nearly 90% when all three features are present.

Electrocardiography↗
PubMed1989

Adjuvant xamoterol or metoprolol in patients with malignant ventricular arrhythmia resistant to amiodarone.

In a randomised cross-over study, six patients with recurrent sustained ventricular tachycardia (VT) were treated with 3 regimens--amiodarone, amiodarone plus metoprolol, and amiodarone plus xamoterol. All patients had poor left ventricular function and were resistant to multiple drugs. Xamoterol (a partial beta-agonist) was more effective than metoprolol as adjuvant therapy to amiodarone in the control of recurrent sustained ventricular arrhythmias and was not associated with any clinical deterioration of ventricular function. Xamoterol was also more effective than metoprolol for suppression of VT at programmed stimulation and as effective as metoprolol for suppression of VT on exercise. Exercise tolerance was significantly greater during treatment with xamoterol/amiodarone than during treatment with metoprolol/amiodarone or with amiodarone alone.

Adrenergic beta-Agonists↗
PubMed1989

Efficacy of flecainide acetate for atrial arrhythmias following coronary artery bypass grafting.

The antiarrhythmic efficacy of intravenous flecainide and intravenous digoxin was assessed in 29 patients (26 men), aged 43 to 73 (63 +/- 7) years who developed atrial arrhythmias in the first 96 hours after coronary artery bypass grafting. Twenty-seven had atrial fibrillation and 2 had atrial flutter. Patients were entered into the study if the arrhythmia persisted for at least 15 minutes with a ventricular rate greater than 120 beats/min. Fifteen patients were randomized to flecainide (group 1) and 14 to digoxin (group 2). Flecainide was given as a bolus of 1 mg/kg over 10 minutes followed by an infusion of 1.5 mg/kg/hr for 1 hour and then 0.25 mg/kg/hr for the rest of the study period (24 hours). Digoxin was given as 3 bolus doses (0.5 mg followed after 6 and 12 hours by 0.25 mg). In both groups, 10 mg of verapamil was given intravenously after 45 minutes if the arrhythmia persisted with a mean ventricular rate greater than 100 beats/min. The antiarrhythmic efficacy was assessed by 24-hour Holter monitoring and frequent 15-second rhythm strips. Within 45 minutes control of arrhythmia, which was maintained for the rest of the study period, was achieved in 10 of 15 patients in group 1 and 2 of 14 in group 2 (p less than 0.01). Nine of 15 reverted to sinus rhythm in group 1 compared to 0 of 14 in group 2 and 1 of 15 remained in arrhythmia with a controlled ventricular rate in group 1 compared to 2 of 14 in group 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Echocardiographic and histologic evaluation of the right ventricle in ventricular tachycardias of left bundle branch block morphology without overt cardiac abnormality.

The right ventricle was investigated by multiple biopsies and detailed echocardiographic evaluation, including measurement of cavity dimensions at the level of the inflow, body and outflow tract, in 27 patients with right ventricular tachycardia who had no clinical evidence of an underlying morphologic abnormality. Nine (33%) patients had abnormal biopsy results, with a quantifiable increase in interstitial fibrosis. Abnormal echocardiograms, defined as an increase in greater than or equal to 2 dimensions of the right ventricular cavity or wall motion abnormalities or both, were seen in 9 patients. There was a strong association between abnormal myocardial histologies and abnormal right ventricular echocardiograms (p less than 0.001). An abnormal echocardiogram was 94% specific and 80% sensitive for an abnormal biopsy. The findings of echocardiography and biopsy were correlated with the electrocardiographic features of the tachycardia. Evidence of right ventricular disease was seen in all 6 patients with superior frontal plane axis of clinical tachycardia as compared with 4 of 21 with inferior axis (p less than 0.001). Thus, 2-dimensional echocardiography is a sensitive means of diagnosing right ventricular disease in patients with nonischemic tachycardias of left bundle branch block morphology. A superior frontal plane axis of ventricular tachycardia in this group strongly suggests right ventricular disease, whereas an inferior frontal plane axis is frequently not associated with any morphologic or histologic abnormality of the right ventricle.

Adult↗
PubMed1989

Comparison of exercise performance of six rate-adaptive right ventricular cardiac pacemakers.

Single chamber cardiac pacemakers capable of automatically adjusting the rate according to body requirements have become an important means of physiologic pacing in patients with bradycardias. Such pacemakers are dependent on a nonatrial sensor of physiologic needs to optimize the rate response. Fifty rate-adaptive right ventricular pacemakers were implanted in 46 patients with a mean age of 60 +/- 4 years (mean +/- standard error of the mean). There were 2 types of activity-sensing pacemakers (Activitrax and Sensolog 702), the QT-sensing pacemakers (TX2 and Quintech), 2 types of respiratory-sensing pacemakers (Biorate [RDP3 and MB1] and Meta) and a rate-adaptive pacemaker that senses right ventricular dP/dt (Deltatrax). The rate responses of a group of 9 volunteers of similar age (62 +/- 2 years) were also included for comparison. Improvement in exercise duration in the rate-adaptive mode compared to the constant-rate ventricular pacing (VVI) mode was achieved during randomized symptom-limited treadmill exercise (from 26 to 49%). Compared with the sinus responses, the activity-sensing pacemakers responded most appropriately in speed. However, their rate responses were not related to workload and had lower correlations with estimated oxygen consumption (r = 0.7 and 0.47 for Activitrax and Sensolog, respectively). Respiratory-sensing pacemakers responded more appropriately in magnitude (r greater than 0.8) although their rate responses were slower. All pacemakers studied either showed no response or a reverse-rate response to the Valsalva maneuver. It is concluded that the currently available rate-adaptive ventricular pacemakers improve exercise performance compared with VVI pacemakers in patients with bradycardias.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise Test↗
PubMed1989

The effects of adenosine on sinus node reentrant tachycardia.

The effects of adenosine given during sinus node reentrant tachycardia were investigated in two patients. Both patients received intravenous bolus doses of 0.1 mg/kg and 0.15 mg/kg. Adenosine slowed the atrial rate in both patients and terminated the tachycardia in one. These effects of adenosine on sinus node reentrant tachycardia suggest that sinus nodal tissue (as opposed to perinodal atrial tissue) is involved in the tachycardia circuit and that these effects should be considered when adenosine is used as a diagnostic agent in narrow-complex tachycardia.

Adenosine↗
PubMed1989

Inducibility of sustained monomorphic ventricular tachycardia as a prognostic indicator in survivors of recent myocardial infarction: a prospective evaluation in relation to other prognostic variables.

The prognostic significance of sustained monomorphic ventricular tachycardia inducible with up to three extrastimuli was assessed in relation to other prognostic markers, including clinical assessment, signal-average electrocardiogram (ECG), Holter monitoring, ejection fraction measurement and exercise testing, in 75 patients after recent myocardial infarction. Among eight patients with inducible sustained monomorphic ventricular tachycardia, six suffered arrhythmic events during a median follow-up period of 16 months. No patient without inducible sustained monomorphic ventricular tachycardia suffered an arrhythmic event. Multivariate analysis showed that of all the variables examined, inducible sustained monomorphic ventricular tachycardia was the only independent predictor of arrhythmic events during the follow-up period. The sensitivity for predicting arrhythmic events by this response was 100%, the specificity 97% and the positive predictive accuracy 75%. Individually, the other prognostic variables were less sensitive and much less accurate predictors of arrhythmic events, but the combination of the occurrence of acute phase complications or frequent ectopic activity with an abnormal signal-averaged ECG approached the sensitivity and accuracy of inducible sustained monomorphic ventricular tachycardia. The prognostic utility of programmed ventricular stimulation in patients with recent myocardial infarction is limited because comparable information can be obtained less invasively. However, the test may have a role in selecting therapy in patients judged to be at risk from arrhythmias on the basis of noninvasive assessment.

Adult↗
PubMed1989

Significance of signal-averaged electrocardiography in relation to endomyocardial biopsy and ventricular stimulation studies in patients with ventricular tachycardia without clinically apparent heart disease.

Signal-averaged electrocardiography (ECG) was performed in 38 patients (mean age 38 years, range 15 to 70) with ventricular tachycardia who had no clinical evidence of structural heart disease. Spontaneous ventricular tachycardia was nonsustained in 23 patients and sustained in 15. None of the patients had symptoms of heart failure or ischemic heart disease, and at cardiac catheterization none had significant coronary artery disease or left ventricular wall motion abnormalities. In addition, all patients underwent left and right ventricular endomyocardial biopsy and ventricular stimulation studies. Signal-averaged ECG was performed and late QRS potentials were defined with use of Simson's method. Late QRS potentials were detected in a minority (18%) of patients including 2 of 23 with nonsustained and 5 of 15 with sustained (p = NS) ventricular tachycardia. Fifteen patients (40%) had abnormal endomyocardial biopsy results and these findings were more common in patients with sustained than in those with nonsustained ventricular tachycardia (9 of 15 versus 6 of 23, p less than 0.05). Late potentials were associated with abnormal endomyocardial biopsy findings (6 of 15 versus 1 of 23, p less than 0.01). An increase in fibrous tissue was the most frequent histopathologic abnormality; this increase was quantified by morphometric methods and compared with biopsy findings in normal control subjects. In the control group the proportion of collagen in relation to myocytes was less than 10%. All patients with both late potentials and abnormal biopsy findings had a greater than 15% ratio of collagen to myocytes in at least one specimen and the biopsies revealed marked interstitial fibrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Electrical ablation of junctional tachycardias showing a long RP interval.

Transvenous catheter ablation of the anomalous pathway was attempted in seven patients with drug-resistant repetitive long RP tachycardias. The patients were aged 5.5-65 years (median 20 years) and had received from four to seven antiarrhythmic agents without effect. Electrophysiological studies confirmed the anomalous substrate for tachycardia in five patients but in two patients an intranodal mechanism could not be excluded. Discharges were delivered to the coronary sinus ostium or low right atrium close to the ostium using conventional defibrillators (three patients) or a modified device (four patients). Transient AV block was seen after six attempts progressing to permanent block in one patient. In no patient could enduring block in the retrograde limb of tachycardia be achieved, and tachycardia recurred in all patients in whom anterograde conduction remained intact. The failure of selective ablation techniques in long RP tachycardia may reflect the diversity of substrate anatomy or particular properties (anatomical or functional) of the pathway compared with the usual types of anomalous pathway.

Adolescent↗
PubMed1989

Closed loop control of rate adaptive pacing: clinical assessment of a system analyzing the ventricular depolarization gradient.

Closed loop control of rate adaptive pacing has theoretical advantages over current rate responsive pacemakers. The first available system (which senses the ventricular depolarization gradient) has been evaluated in ten patients. The pacing response to a variety of exercise and nonexercise stimuli was assessed. Response to isotonic exercise was prompt and proportional to the exertion involved while isometric exercise and mental stress produced obvious but more gradual increases in pacing rate. In seven patients, comparison between the intrinsic P wave and pacing rate showed a high correlation during exercise (r = 0.91) and mental activity (r = 0.87). Postural changes induced a paradoxical response. Closed loop rate responsive pacing based upon analysis of the ventricular depolarization gradient produces a fast and appropriate rate response to most physiological stimuli.

Adult↗
PubMed1989

Reliability of minute ventilation as a parameter for rate responsive pacing.

A minute ventilation sensing rate responsive pacemaker was implanted in 11 patients with bradycardias. Their mean age was 59 +/- 4 years (mean +/- SEM). The pacemaker measures minute ventilation by sensing intravascular impedance using a standard bipolar electrode. The rate responsive programming was simple: apart from ascribing an upper and lower rate, the only programmable parameter was the slope of rate response. This could be derived approximately by assessing the suggested slope value during an exercise test in the 'adaptive VVI' mode. Compared with exercise in the VVI mode, symptom limited treadmill tests in the rate responsive mode showed a 33% improvement of exercise capacity and a 44% improvement of cardiac output as determined noninvasively by continuous wave Doppler measurements of the ascending aortic blood flow. The pacing rate was appropriately increased during a variety of daily activities such as walking at different speeds and gradients, and ascending and descending stairs. Voluntary interference of the respiratory pattern such as during coughing and hyperventilation increased the pacing rate from a resting rate of 70 bpm to 111 +/- 10 and 86 +/- 4 bpm respectively. Continuous talking during exercise attenuated the expected rate response. The pacemaker can sense activity induced by arm swinging. In conclusion, the Meta pacemaker improved cardiac output and exercise capacity in patients with bradycardias. Its rate response was related to workload. Although voluntary interference affected the pacing rate, excessive rate acceleration was not encountered.

Adult↗
PubMed1989

Myopotential interference in unipolar rate responsive pacemakers.

The effects of myopotential interference on unipolar rate responsive pacemakers were assessed in 22 patients. Six types of pacemakers (from four manufacturers) were studied: five TX2 (QT sensing), seven Biorate (five RDP3 and two MB-1, respiratory rate sensing), seven Activitrax (activity sensing), two Medtronic 2503 (dP/dt sensing), and one Sensolog P703 (activity sensing). Provocative tests using arm exercises were performed in both VVI and rate responsive modes. At nominal sensitivity settings (1.8-2.5 mV), 55% of these patients were myopotential positive for at least 1 provocative test. Pressing the palms together was found to be the most sensitive provocative test. Rate response was achieved with treadmill exercise (all patients), hyperventilation (RDP3 and MB-1) and tapping (Activitrax) or wobbling the pacemaker in its pocket (Sensolog). During continued rate acceleration, myopotential interference was induced by arm exercises. The duration of inhibition was shorter when the provocative tests were performed during rate response compared to that occurred at rest. Short periods of myopotential interference resulted in temporary inhibition of pacing but rate response continued immediately on removal of the interference. In one patient with a RDP3 pacemaker, a prolonged episode of myopotential interference during treadmill exercise resulted in reversion of the pacemaker to the interference mode. Appropriate adjustment of the sensitivity setting effectively controlled the symptoms in most patients. However, one patient with a QT sensing pacemaker and symptomatic myopotential interference required programming to the VVT pacing mode. Two out of five patients with RDP3 required pacemaker replacement because of uncontrolled myopotential interference.(ABSTRACT TRUNCATED AT 250 WORDS)

Equipment Design↗
PubMed1989

Optimal atrioventricular delay at rest and during exercise in patients with dual chamber pacemakers: a non-invasive assessment by continuous wave Doppler.

The optimal atrioventricular delay at rest and during exercise was investigated in nine patients with heart block and implanted dual chamber pacemakers. All patients studied had normal left ventricular function and a normal sinus node rate response to exercise. Cardiac output was measured by continuous wave Doppler and was calculated as the product of stroke distance measured by Doppler at the left ventricular outflow, aortic root area measured by M mode echocardiography, and heart rate. Pacemakers were programmed in the DDD mode. Cardiac output was measured with the patient at rest while supine and while erect and at the peak of submaximal exercise (the end of stage 1 of the Bruce protocol) with the pacemakers programmed to the following atrioventricular intervals: 75-80 ms, 100-110 ms, 140-150 ms, and 200 ms. During exercise the basic pacing rate was programmed to 70 beats/min. Cardiac output at rest while supine and erect was greatest with an atrioventricular delay of 140-150 ms and it was significantly higher than that with an atrioventricular delay of 75-80 ms. On average there was a 31% decrease in cardiac output when patients stood up. During treadmill exercise, however, cardiac output was greatest when the atrioventricular delay was 75-80 ms, and this was significantly higher than the cardiac output with atrioventricular delays of 150 and 200 ms. During exercise 1:1 atrioventricular relations were maintained in patients at all atrioventricular intervals. In patients with atrioventricular sequential pacemakers cardiac output at rest is greatest with an atrioventricular delay of 140-150 ms but during exercise the optimal atrioventricular delay is shorter. Rate modulation of the atrioventricular interval may improve the haemodynamic response and possibly exercise tolerance in patients with dual chamber pacemakers.

Adult↗