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Biomedical subjects

P M Holt

Publications and source records attributed to P M Holt.

13 recordsLinked to original sources
PubMed2002

The electromechanical effects of pacing at different sites within the right atrium.

AIMS: To compare high right atrium (HRA) with right atrial appendage (RAA) pacing with respect to atrial electromechanical function. METHODS: Eleven patients undergoing elective electrophysiological studies were studied in order directly to compare atrial conduction acutely associated with HRA and RAA pacing. Twenty-five patients with chronically implanted, active fixation leads in the HRA were compared with an age and sex matched group of 25 patients with chronically implanted, passive fixation leads in the RAA. For both studies recordings were taken in sinus rhythm then repeated when paced. Measured time intervals were intra- and interatrial activation times. P wave duration and time to onset of atrial systolic blood flow. RESULTS: Right atrial pacing, when compared with sinus rhythm, significantly prolongs the interatrial activation time, the P wave duration and the time to onset of right and left atrial blood flow irrespective of site paced. Comparing the RAA group with the HRA group, there were no statistical differences for any of the measured parameters. CONCLUSION: High right atrial free wall or the right atrial appendage pacing, when compared with sinus rhythm, is significantly detrimental to atrial electromechanical function. There is, however, no demonstrable difference between the two sites.

Adult↗
PubMed1995

Electrophysiology in a district general hospital.

OBJECTIVE: To investigate the feasibility of performing electrophysiological studies at a district general hospital and to evaluate the importance of such studies in the management of patients with suspected arrhythmias. DESIGN: Retrospective study of patients having had electrophysiological studies during a three year period. SETTING: District general hospital. SUBJECTS: 93 patients (50 men, 43 women, mean age 45.9 years) with suspected arrhythmias. RESULTS: The patients were divided into two groups according to symptoms. Group 1 (34 patients) presented with syncope. Group 2 (59 patients) presented with palpitation. All had previously undergone non-invasive investigations. All had had multiple hospital admissions and outpatient attendances. In group 1 nine patients with no documented arrhythmias had inducible ventricular tachycardia and three of six with suspected bradyarrhythmias had ventricular tachycardia. Fourteen patients had suspected ventricular arrhythmias before electrophysiological studies, which were confirmed in all, four receiving automatic implantable cardioverter defibrillators. Electrophysiological studies were used to guide drug treatment in all patients. Group 2 consisted of 32 patients with reentrant supraventricular tachycardia and 15 with ventricular tachycardia; 12 had no documented arrhythmias. In those with supraventricular tachycardia, accessory pathways were identified in all. In 23 patients drug treatment (guided by electrophysiological studies) was successful. In nine, drug treatment guided by electrophysiological studies were ineffective and radiofrequency ablation was successful. In 15 patients with ventricular tachycardia and palpitations, 10 had their drugs changed after electrophysiological studies and their ventricular tachycardia was suppressed. In five patients electrophysiological studies showed that ventricular tachycardia was unsuppressed and they were referred for an operation or implantation of an automatic cardioverter defibrillator. In 12 patients with no documented arrhythmias electrophysiological studies identified significant arrhythmias in six. There were no complications. CONCLUSIONS: Diagnostic electrophysiological studies can safely and effectively be performed in a district general hospital. These studies are especially effective in investigating patients with syncope, and also provide a strategy for future arrhythmia management.

Adolescent↗
PubMed1993

Correction of myocardial ischaemia after transcatheter embolisation of a small left coronary artery venous fistula.

A 50 year old woman presented with a history of angina and palpitation. She had a positive exercise test and thallium scintigraphy showed reversible ischaemia in the territory of the left anterior descending coronary artery. Coronary angiography showed a small coronary arteriovenous fistula arising from the bifurcation of the left main stem--that is, the origin of the left anterior descending and circumflex coronary arteries--with no evidence of coronary stenosis. The aberrant coronary artery was embolised with platinum microcoils delivered by a percutaneous, transcatheter, coaxial technique. The patient was subsequently symptom free with no evidence of ischaemia on exercise testing or thallium scintigraphy. This case suggests that when there is clear evidence of myocardial ischaemia even small coronary arteriovenous fistulas should be treated by embolisation.

Arteriovenous Fistula↗
PubMed1986

Right ventricular outflow tract tachycardias in patients without apparent structural heart disease.

We have investigated 13 patients with monomorphic ventricular tachycardia which originated from the right ventricular outflow tract. No patient had evidence of organic heart disease. There were 3 males and 10 females, aged 13-53 years. All had non-invasive investigations including an exercise electrocardiogram, chest radiography, echocardiograms and gated blood pool scintigraphy. Ten patients underwent cardiac catheterisation. Five patients had a prolonged QTc on their resting electrocardiogram. The remaining investigations showed no evidence of organic heart disease. Ten patients had ventricular arrhythmias which were completely suppressed during maximal exercise but which recurred in the immediate post-exercise period. A further 2 patients with no arrhythmias before exercise had ventricular tachycardia in the post-exercise period. Electrophysiology studies were performed in 5 patients with syncopal episodes, suggesting an automatic focus in 4. Four patients required specific antiarrhythmic surgery for symptoms refractory to medical therapy. Pace-mapping at operation confirmed the origin to be within the right ventricular outflow tract in all. Thus, we have identified a group of patients who have ventricular tachycardia originating from the right ventricular outflow tract in whom there is no apparent structural heart disease. Their arrhythmias are influenced by exercise and are probably due to an automatic focus. Four patients required surgery for ventricular tachycardias and recurrent syncopal episodes refractory to medical therapy.

Adolescent↗
PubMed1986

Hematologic effects of the high-energy endocardial ablation technique.

Ablation of atrioventricular conduction is now widely accepted in the management of supraventricular arrhythmias. Reports of high temperatures, high pressures, and gas production suggest that there may be adverse effects on the blood, the electrode, and the cardiovascular system. In this investigation, using samples of fresh, heparinized pig blood, we measured hemolytic damage, the liberated gas volume and composition, and electrode erosion associated with high-energy electrical ablation. The blood was tested in a 10 liter tank at room temperature. Impulses of 10 to 400 J were applied to new USCI No. 6F bipolar pacing electrodes using both positive and negative polarities. Voltage and current waveforms were recorded. The volume of gas liberated with cathodal electrodes was 0.50 microliter/J up to 50 J and 0.29 microliter/J above 100 J. It was composed predominantly of hydrogen and nitrogen, with carbon dioxide and oxygen. With positive electrodes, the gas volume was linearly related to energy at 4.34 microliter/J up to 200 J and also contained carbon monoxide. The hemolysis was directly proportional to impulse energy for both cathodal and anodal electrodes, being 1.37 microliter/J and 4.48 microliters/J, respectively. Electrode erosion was substantial but clinically acceptable. We conclude that there are marked differences in the energy conversion processes and, where the same energy can achieve a comparable clinical effectiveness, there are advantages in using a cathodal electrode polarity. It is also advisable to use lower energies.

Animals↗
PubMed1985

Low energies and Helifix electrodes in the successful ablation of atrioventricular conduction.

High energies delivered via standard pacing catheter electrodes produce permanent atrioventricular conduction block and generate high pressures. We investigate the use of lower energies and an active fixation electrode. Ten patients with refractory supraventricular tachycardias (six with paroxysmal atrial fibrillation, three with dual AV nodal pathways, and one with a concealed accessory atrioventricular pathway) were treated. A 6F Vitatron Helifix electrode was positioned to give the maximum His bundle deflection. Four shocks of only 50 joules each were delivered at 1-minute intervals. Long-term follow-up showed that seven patients (70%) had persistent complete heart block and two had atrial fibrillation with slower ventricular rates. Nine patients (90%) were symptom-free without antiarrhythmic therapy. Permanent pacemakers were implanted in eight patients. There were no complications resulting from the procedure. Transvenous ablation of atrioventricular conduction can be safely achieved using a Vitatron Helifix electrode and much lower energy values than have been previously employed.

Adult↗
PubMed1985

An investigation into the electrical ablation technique and a method of electrode assessment.

Ablative techniques, using standard defibrillators and commonly available cardiac catheters, have been applied to the His bundle and bypass tracts for the management of arrhythmias. We have done in vitro studies of the physical effects of these high energy electrical impulses delivered via different pacing electrodes. Unipolar impulses of 10 to 400 joules were delivered via three U.S.C.I. bipolar electrodes and three Vitatron Helifix electrodes immersed in Ringer's solution. The effects were recorded on 35 mm still film, video tape, and high speed cine film. Pressure, voltage, and current were measured. The U.S.C.I. bipolar electrodes and the Vitatron Helifix electrodes safely withstood repeated delivery of 400-joule impulses which produced similar flash shapes. Each took the form of an incandescent, spherical "fire-ball" centered around the exposed electrode surface. The mean diameters of the "fire-ball" for 10 to 400 J using the U.S.C.I. electrodes were 5-24 mm and 3-20 mm for the Helifix catheter electrodes. Peak pressure excursions of over an atmosphere were observed 3 cm from the electrode tips. Higher pressures, lower voltages, and larger currents occurred using the U.S.C.I. pacing lead. The simple, 35 mm time exposure technique showed that at low energies the flashes appeared to emerge in a retrograde manner from the U.S.C.I. catheters and more distally from the Helifix electrode. This suggested that the latter might be more effective with lower energy impulses. It is concluded that lower energies should be used to take full advantage of the active fixation electrode.

Arrhythmias, Cardiac↗
PubMed1985

Ventricular arrhythmias. A guide to their localisation.

An electrocardiographic atlas of ventricular tachycardias was produced by pacing 27 epicardial sections of the heart and the mitral papillary muscles to simulate focal ventricular arrhythmias and simultaneously recording their 12 lead electrocardiographic appearances. One hundred and twenty nine patients undergoing cardiac surgery were studied. In five patients all 27 epicardial sites were paced at operation and in 124 individual sections were paced postoperatively with temporary epicardial wires and the electrocardiograms analysed in terms of frontal and horizontal plan QRS axis, maximum limb lead QRS amplitude, and QRS duration. Each ventricular region paced produced a distinctive 12 lead electrocardiographic pattern. Simulated right ventricular arrhythmias had either inferior frontal plane QRS axes (from the anterobasal region) or superior frontal plane QRS axes (from the apical and posterior right ventricular sections). Horizontal plane QRS axes were directed leftwards, with some posterior shift in the anteroapical regions. Simulated arrhythmias from the base of the left ventricle (anteriorly and laterally) had inferior frontal plane QRS and anterorightward horizontal plane QRS axes. Left ventricular arrhythmias with a superior frontal plane QRS axis were readily distinguished by their horizontal plane QRS axes: posterorightwards from the anterior and anterorightwards from the posterior left ventricular sections. Standard errors of the paced QRS axes for the various epicardial sections paced postoperatively ranged from 3.0 degrees to 6.0 degrees using the frontal plane axis. The electrocardiogram was most accurate in localising ventricular arrhythmias from the anterior left ventricle and least accurate for those arising from the inferior right ventricle. The appearance of the paced electrocardiograms was slightly modified by underlying disease such as myocardial infarction and left ventricular hypertrophy. This atlas may be useful in comparing the localisation of ventricular tachycardia with the site of underlying cardiac disease and may facilitate mapping in patients with refractory ventricular tachycardia requiring ablation (either surgical or by high energy impulses).

Adolescent↗
PubMed1980

Effectiveness of amiodarone in resistant arrhythmias.

Amiodarone is used in the treatment of previously drug-resistant supraventricular and ventricular arrhythmias. We report our experience with amiodarone in 8 patients. Five patients had paroxysmal atrial flutter, one had paroxysmal atrial fibrillation, one had supraventricular tachycardia, and one ventricular tachycardia. Considerable improvement, both objectively and subjectively, was observed in all patients. Side effects were as follows: all patients had corneal microdeposits, one developed left bundle branch block which resolved on stopping amiodarone, and one reported constipation and abdominal pains. Six patients have been treated for 10-28 months; 3 developed tolerance at 4-14 months after the introduction of amiodarone therapy, but symptoms improved with increased dosage. It is important to watch for the development of tolerance to this drug.

Adult↗