Biomedical subjects

E Sowton

Publications and source records attributed to E Sowton.

At least 19 recordsLinked to original sources

PubMed1992

The Hatle orifice area formula tested in normal bileaflet mechanical mitral prostheses.

The Hatle formula was derived empirically in native mitral stenosis and may not be valid for normal prosthetic valves. Bileaflet mechanical prostheses open fully at low flows and have minimal interindividual variation in orifice area. In these valves effective area and measured manufacturer's area should be similar. We studied 60 patients aged 58 +/- 12 yr at a mean of 5 months after implantation with a CarboMedics prosthesis. There was a coexistent aortic prosthesis in 21. All diastolic measurements were averaged over 5 beats and stroke volume was calculated from the integral of the subaortic velocity trace and the cross-sectional area of the left ventricular outflow tract. For the whole group, area by the Hatle formula was 3.1 +/- 0.7 cm2 and measured area was 2.8 +/- 0.4 cm2. There was no significant correlation between these values (p = 0.329). Pressure half-time was more closely correlated with peak transmitral velocity (p = 0.012), RR interval (p = 0.015), diastolic time interval (p = 0.062) and stroke volume (p = 0.074). We conclude that the Hatle formula should not be applied to normal bileaflet mitral prostheses where pressure half-time reflects nonprosthetic factors more closely than orifice area.

Aged↗

PubMed1992

The effect of atrio-ventricular delay programming in patients with DDDR pacemakers.

Modern DDDR (dual chamber universal, rate responsive) pacemakers are complex, hugely capable devices incorporating new features that theoretically should enhance haemodynamics and therefore quality of life. Ten patients (mean age 48 years) with chronotropic incompetence and high grade A-V block had activity sensing DDDR devices implanted and underwent a randomized double-blind crossover assessment of rate responsive and different fixed atrio-ventricular delay (AVD) settings during 2 weeks of out-of-hospital activity in DDDR mode. Subjective assessment showed improved 'general wellbeing' and preference for 175 ms rate responsive AVD (P less than 0.01) or 125 ms fixed AVD (P less than 0.05). The longest fixed AVD setting (250 ms) was least acceptable and had increased symptom prevalence (P less than 0.02). Perceived exercise capacity and exercise treadmill tolerance was not significantly different at any setting in DDDR mode but was less in DDD mode. Echocardiographically derived stroke distance was greater at 125 ms AVD than 250 ms at 100 b.min-1 (P less than 0.05) but did not differ at slower heart rates at any AVD. Colour Doppler assessed mitral and tricuspid regurgitation was greatest at 250 ms AVD at all heart rates but did not correlate with increased symptomatology. Stroke distance evaluated from the mitral inflow velocity profile allows improved AVD programming during DDDR pacing. Rate adaptive A-V delay is a useful feature during DDDR pacing.

Adolescent↗

PubMed1992

Comparative long-term results of coronary angioplasty in single and multivessel disease.

The comparative long-term clinical results of coronary angioplasty in 448 patients with single-vessel and 451 patients with multivessel disease are reported. Clinical status was determined at census for 898 patients (99.9%). Actuarial survival at 5 years was 92.7% for single-vessel and 85.6% for multivessel disease patients (relative risk 2.1). Patients with multivessel disease had higher rates of cardiac death and non-fatal myocardial infarction (relative risk 1.8), and coronary artery bypass surgery (relative risk 2.5) than patients with single-vessel disease. At follow-up 72.6% of single-vessel and 61.3% of multivessel disease patients had no angina and 43.3% and 35.8%, respectively, were taking no regular anti-anginal medication. Treatment by coronary angioplasty is associated with a good long-term prognosis, but survival and event-free survival rates are lower in patients with multivessel disease than in patients with single-vessel disease, even after correction for differences in other baseline characteristics.

Angioplasty, Balloon, Coronary↗

PubMed1992

"Subclinical" pacemaker syndrome: a randomised study of symptom free patients with ventricular demand (VVI) pacemakers upgraded to dual chamber devices.

OBJECTIVE: To determine whether symptom free patients with single chamber pacemakers benefit from dual chamber pacing. DESIGN: A randomised double blind crossover comparison of ventricular demand (VVI), dual chamber demand (DDI), and dual chamber universal (DDD) modes after upgrading from a VVI device. SETTING: Cardiology outpatient department. PATIENTS: Sixteen patients aged 41-84 years who were symptom free during VVI mode pacing for three or more years. INTERVENTION: Pacemaker upgrade during routine generator change. MAIN OUTCOME MEASURES: Change in subjective (general health perception, symptoms) and objective (clinical assessment, treadmill exercise, and radiological and echocardiographic indices) results between pacing modes before and after upgrading. RESULTS: 75% preferred DDD, 68% found VVI least acceptable with 12% expressing no preference. Perceived general well-being and exercise capacity (p less than 0.01) and treadmill times (p less than 0.05) were improved in DDD mode but VVI and DDI modes were similar. Clinical, echocardiographic, radiological, and electrophysiological indices confirmed the absence of overt pacemaker syndrome, although mitral and tricuspid regurgitation was greatest in VVI mode (p less than 0.01). CONCLUSIONS: Most patients who were satisfied with long term pacing in VVI mode benefited from upgrading to DDD mode pacing suggesting the existence of "subclinical" pacemaker syndrome in up to 75% of such patients. The DDI mode offered little subjective or objective benefit over VVI mode in this population and should be reserved for patients with paroxysmal atrial arrhythmias. VVI mode pacing should be used only for patients with very intermittent symptomatic bradycardia or atrial fibrillation with a good chronotropic response during exercise.

Adult↗

PubMed1991

The continuity equation tested in a bileaflet aortic prosthesis.

The continuity equation is valid for a population of aortic valves, but its accuracy in individual valves is uncertain. In bileaflet prostheses, obstruction to forward flow is small and individual variability in opening behaviour is minimal. In these valves, the area of the effective orifice should be close to that measured by the manufacturer. A total of 57 patients aged 58 +/- 11 years were studied at a mean of 3.6 months after implantation with a CarboMedics aortic prosthesis. Nine had additional implants in the mitral position and all prostheses were clinically normal. Peak subaortic and transaortic velocities were averaged over 5 beats. The area of the effective orifice was significantly different between the four diameters (P less than 0.00001), and the correlation between the effective and measured area of the orifice was moderate (rs = 0.73, P less than 0.00003). The 95% range for the differences between individual pairs of values, however, was 0.16 +/- 0.61 cm2. Discrepancies probably arose in the estimation of subaortic cross-sectional area and subaortic velocity. Thus, the continuity equation may be inaccurate in an individual prosthetic valve when functioning normally.

Aged↗

PubMed1991

Long-term results of coronary angioplasty for single vessel, proximal, left anterior descending disease.

The acute and long-term results of coronary angioplasty in 295 patients with isolated, proximal left anterior descending coronary stenosis are reported. The angiographic success rate was 83.4% overall, but 90.5% for non-occluded arteries treated since 1985. Clinical success at hospital discharge was achieved in 79.7%. The median duration of follow-up was 2.9 years and vital status was established in 99.7% at census. Cumulative 5-year cardiac survival was 96.2% after successful angioplasty and 95.6% for all patients. Five-year freedom from all cardiac events including cardiac death, myocardial infarction and repeat intervention was 73.8% amongst successfully treated patients, and 63.0% for all patients. After angioplasty, patients had less angina, required less anti-anginal medication and were more likely to be in gainful employment. Our data indicate that coronary angioplasty is an effective long-term treatment for selected patients with single vessel disease involving the proximal left anterior descending coronary artery.

Adult↗

PubMed1991

Hemodynamic consequences of arrhythmias.

Hemodynamic effects during arrhythmias may be caused by underlying pathology (i.e., infarction) as well as disturbance of rate or conduction pattern. In all arrhythmias, compensatory mechanisms tend to restore normal hemodynamics, and with good left ventricular function this can be achieved despite wide disturbance of rhythm. Hemodynamic effects of ectopic beats can result in dramatic fall of stroke volume and reduction in cardiac output, which is greater for ventricular than for atrial ectopics. Prolonged tachycardias are also tolerated up to far higher rates (180/min) if they are atrial, not ventricular, in origin. Mean blood pressure is often maintained even when systolic pressure and cardiac output are reduced. Even in healthy young subjects it is possible for cardiac ischemia to be induced by excessive heart rates. Some of the most deleterious effects are produced by simultaneous atrial and ventricular contraction, which results in continued suppression of cardiac output, both during tachycardias and at normal heart rates. Such situations are often highly symptomatic. Few measurements are available during external chest compression, and these suggest only marginal improvement in hemodynamics, with low pressures and output.

Animals↗

PubMed1990

Quantitative analysis of contribution of rate response in three different ventricular rate responsive pacemakers during out of hospital activity.

The contribution of rate response provided by three different types of rate responsive pacemaker (Sensolog, Meta, and Vitatron TX) was assessed in 25 patients during out of hospital activity. Pacemakers were optimally programmed and full disclosure 24-hour Holter ECG recordings were obtained during everyday activities. Close visual analysis of these tracings revealed that rate response is active for less than 15% of the 24-hour study period with high rate response (paced rate above 100 beats/min) for just 5% of the day showing peak activation between 1600 and 2000 hours. Low rate response (paced rate below 100 beats/min but 5 beats above base rate) was maximal between 0800 hours and midday and comprised 10% of all heart beats during the study period. Thirty percent of study patients were nonpacemaker dependent and rate response in these subjects was significantly (P less than 0.001) less active between 0800 hours and midday than in pacemaker dependent patients though it was equivalent at all other times. Nonpacemaker dependent patients achieved natural sinus response in the morning and tended to rely on pacemaker supplied rate response in the latter part of the day.

Activities of Daily Living↗

PubMed1990

Is accurate rate response programming necessary?

Exercise capacity and general well-being are improved by appropriately programmed rate responsive pacemakers when compared to fixed rate units. Ten patients had activity sensing DDDR units implanted for combined AV block and sinus node incompetence. Ten patients had Sensolog activity sensing VVIR units implanted for complete heart block. The effects of over and under programming of rate response in both dual and single chamber activity sensor rate adaptive pacemakers has been assessed subjectively by visual analog scales and specific activity questionnaires and objectively by graded treadmill testing and the performance of standardized daily activities. Patients were randomly programmed to absent rate response (VVI in the Sensolog group), hyporesponsive (DDD in the dual chamber group), appropriate response (VVIR, DDDR according to Manufacturer's instructions) and over responsive (VVIR+, DDDR+) in a double-blind crossover design. Thirty percent of patients demanded early crossover from VVI, 30% from DDDR+ and 50% from VVIR+. Perception of Exercise Capability was similar to objective exercise treadmill times which were shorter in VVI than in VVIR or VVIR+ (P less than 0.05) or control subjects (P less than 0.001). There was no difference between any dual chamber mode or control subjects. General well-being was poorest in DDDR+ and VVIR+ modes despite objective improvement in exercise capacity. Symptoms were least in VVIR and DDDR and all but one patient chose appropriate programming as their overall preferred mode. Thus, even inaccurate rate response programming results in similar and improved exercise capacity compared to absent rate response but overprogramming is unacceptable to most patients, confirming that appropriate programming and sensor specificity is critical in rate responsive pacing.

Arrhythmia, Sinus↗

PubMed1990

Inappropriate discharges by the implantable cardioverter defibrillator during postoperative testing: implications for intraoperative assessment.

Inappropriate shocks were delivered to a patient while in sinus rhythm by an implantable cardioverter defibrillator (ICD) during routine prehospital discharge testing. This was induced by the standard programmer when the "read" telemetry sequence was initiated. The ICD was removed and found to suffer from electrical artifact that was sensed as ventricular tachycardia during telemetry. To avoid inadvertent telemetry-induced shocks during routine testing, all ICDs should be interrogated, using a standard programmer, intraoperatively, with the unit in "defibrillation on" mode.

Aged↗

PubMed1990

Supraventricular tachycardia control with Tachylog II: long-term follow-up.

Ten patients aged 16-63 years (mean 36.3) had the Siemens P56T "Tachylog II" pacemaker implanted for treatment of drug refractory supraventricular tachycardia. The pacemaker incorporates a noninvasive electrophysiological study (EPS) facility and a sophisticated Holter function combined with a unique "learning" self-search antitachycardia algorithm. The Holter reveals that new tachycardias arise that are not previously detected at conventional EPS. The number of stimuli in the initiation sequences during noninvasive EPS proved highly variable, however, termination sequences remained constant in the long term. There was variability of timing of stimuli in the long term that was significantly greater for "new" tachycardias than for "original" arrhythmias. Long-term follow-up (at 1 month, 6 months, and 1 year) have shown that 90% of patients have good tachycardia control without the need for drugs. All patients confirm the acceptability of this pacemaker for control of their arrhythmias in the long term.

Adolescent↗

PubMed1979

Cold-pressor test.

Explore the source record for details and available documents.

Cold Temperature↗

PubMed1979

[Method for long-term pacemaker treatment of refractory reentry tachycardias].

A new method for pacemaker treatment of refractory reentry tachycardias has been developed which in 5 patients proved effective over a period of up to ten months. The system consists of a modified QRS-synchronous pacemaker and an external trigger unit. During tachycardia the external unit senses pacemaker spikes and by timed skin stimulation activates the implanted pacemaker to provoke the ventricular premature beats necessary for interruption of the tachycardia. The system also allows repetitive non-invasive programmed stimulation of the heart.

Adult↗

PubMed1979

Cold pressor test in detection of coronary heart-disease and cardiomyopathy using technetium-99m gated blood-pool imaging.

50 normotensive subjects (22 controls with no cardiac disease, 24 patients with coronary heart-disease, and 4 with early cardiomyopathy) were investigated with gated cardiac blood-pool scintigraphy before and during cold pressor stimulation. The controls had no change or a significant rise (p less than 0.005) in left ventricular ejection fraction and preserved normal myocardial-wall motion, whereas patients with coronary-artery disease or cardiomyopathy had a significant fall (p less than 0.001) in left ventricular ejection fraction and many developed abnormal regional wall motion despite the absence of angina pectoris. Cold pressor gated cardiac blood-pool studies were more sensitive than single-lead exercise electrocardiography (p = 0.03) in the detection of patients with severe coronary-artery disease without previous myocardial infarction.

Adolescent↗

PubMed1979