P.V.L. Curry

High-Performance Liquid Chromatographic Measurement of Amiodarone and Its Desethyl Metabolite: Methodology and Preliminary Observations

A high-performance liquid chromatographic technique is described for the measurement of amiodarone and its desethyl metabolite in plasma. Preliminary observations are presented on the concentrations of metabolite found during the early stages of chronic amiodarone therapy. A case history is outlined in which noncompliance during treatment with amiodarone was confirmed by measurement of the ratio of desethylamiodarone to amiodarone concentrations.

SINGLE LEAD FOR PERMANENT PHYSIOLOGICAL CARDIAC PACING

A method of achieving permanent pacing by the use of a single bipolar transvenous lead is described, the atrial and ventricular electrodes being located on the same lead 14--17 cm apart. The new leads have been implanted successfully in two patients.

Intravenous amiodarone in the acute termination of supraventricular arrhythmias

This study was performed to ascertain whether intravenous amiodarone would revert supraventricular tachycardias to sinus rhythm, and if so, whether this effect depended upon the underlying mechanism of the arrhythmia. Fourteen patients were studied. Seven had Wolff-Parkinson-White (WPW) syndrome, 1 had dual atrioventricular nodal pathways and 1 an ectopic atrial tachycardia. Five patients had atrial fibrillation without accessory pathways. An atrial electrode was inserted to initiate tachycardias and record the electrogram. If tachycardias were stable for more than 5 min, amiodarone (5 mg/kg) diluted with dextrose saline was infused intravenously over 5 min. Two electrocardiographic leads and the right atrial electrogram were monitored. In 7 patients with atrial fibrillation (2 with accessory pathways), 6 did not revert to sinus rhythm, 1 reverted only after 1 hr. In 5 cases without accessory pathways the ventricular rate fell 5-10 min after commencing amiodarone. Four of the 5 patients with WPW syndrome and re-entrant tachycardias returned to sinus rhythm within 6 min of commencing the infusion (atrioventricular and ventriculoatrial times increased by 0-38% and 0-14% respectively). (Tachycardias terminated in the anterograde limb.) Three patients underwent intermittent right atrial stimulation for 1 hr. No tachycardias could be initiated for 30 min post amiodarone. The ectopic atrial tachycardia and that due to dual atrioventricular nodal pathways terminated within 7 and 2 min, respectively, of commencing intravenous amiodarone. Thus the use of intravenous amiodarone would be appropriate in the acute management of sustained supraventricular tachycardias.

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.

Coronary artery thermal damage during percutaneous “hot tip” laser-assisted angioplasty

Abstract A major postulated advantage of laser angioplasty as an alternative treatment for occlusive vascular disease is its ability to vaporize obstructive atheroma. 1,2 The bare fiber systems used initially in the peripheral vasculature were able to traverse occlusions but the channels produced were small, subsequent balloon dilatation was always necessary and a high perforation rate was noted. 3 The “hot tip” laser thermal probe produced by encasing the bare fiber tip in a metal cap 4 overcame some of these limitations. The relatively large, smooth and oval metal cap enhanced coaxial placement while localization of all the laser energy (by heat conversion) at the tip made perforations infrequent. 5,6 In the periphery this device recanalized lesions previously impassable to a guidewire and balloon system. 7 For intracoronary use the smaller peripheral artery probes (1.5 to 1.7 mm tips) were modified to include an eccentric guidewire channel through the tip to facilitate coaxial advancement and subsequent balloon exchange. Percutaneous use of this probe in coronary artery disease has produced mixed results. 8–10 In this report we present experience using a more flexible laser thermal device.

Measurement of plasma disopyramide as a guide to paediatric use

We have studied the relationship between age, daily dose, plasma concentration and clinical efficacy of disopyramide in a group of paediatric patients. Twelve children with ventricular and 3 with supraventricular arrhythmias were treated with oral disopyramide. The initial dose was 3-6 mg/kg per day. This was adjusted until a pre-dose plasma concentration greater than 2 mg/I was achieved. Seven patients were judged to have responded to the treatment on clinical criteria. No symptoms or signs of toxicity were observed. In some of the children the dose of disopyramide required to achieve a plasma concentration greater than 2 mg/l was greatly in excess of the normal adult dose. Generally the youngest children required the highest dose, but the variation was wide. The dose could not be predicted from the age, the body weight or the surface area of the patient. In children high doses of disopyramide may be needed to achieve effective plasma concentrations of the drug; such doses are not associated with adverse effects. Measurement of the plasma concentration is necessary to guard against premature termination of therapy.

His Bundle Ablation with the Laser Thermal Probe (“Hot Tip”): A Feasibility Study

Successful percutaneous ablation of the bundle of His requires accurale localization together with delivery of the minimum effective energy to avoid unwanted effects. The energy output from laser sources can be controlled very precisely but is not easily directed to the bundle of His using conventional fiber optics. The laser thermal probe (“hot tip”) consists of an optical fiber and a terminal metal cap that is rapidly heated during energy delivery. When applied to cadaver hearts at energies of 100–150 joules (10 watts for 10–15 seconds) the 2.0‐mm diameter peripheral artery probe was able to damage the bundle of His without extensive surrounding damage. The right ventricular free wall and interventricular septum were perforated during some applications at these energies leaving a tract with a diameter of less than 2.0 mm. The atrioventricular (AV) membranous septum, Foramen Ovale, right atrial appendage, and septal leaflet of the tricuspid valve were more resistant at these energy levels and perforations were always less than 1.0 mm in diameter. The probe was modified for use during electrophysiological studies and good quality unipolar electrograms were recorded from the metal cap confirming that the probe could be accurately positioned adjacent to the bundle of His. The laser thermal probe deserves further study as a “self directing” ablation tool.

Atrial permanent pacing for sinus node dysfunction with absent right superior vena cava

In patients with sinus node dysfunction and normal atrioventricular conduction, single chamber atrial pacing (AAI or AAIR mode) represents the most physiological treatment. Sinus node dysfunction is recognised in association with an absent right superior vena cava, and we present a case in which complete resolution of symptoms was achieved with endocardial atrial permanent pacing.

Doppler echocardiography of double orifice of the left atrioventricular valve in atrioventricular septal defect

A left atrioventricular valve having a double orifice is a rare congenital abnormality, and is most commonly described in association with atrioventricular septal defect. We report the Doppler echocardiographic findings of this abnormality and present a case where limited surgical repair has resulted in a favourable outcome.

Can the site of origin of ventricular extrasystoles enhance the localisation of exercise-induced ischaemia?☆

Previous work from the Departments of Cardiology and Nuclear Medicine, Guys Hospital, London, has enabled an atlas of the electrocardiographic appearances of ectopics from individual ventricular sites to be compiled. This has been used to investigate the relationship between regions of myocardial ischaemia and the site of origin of exercise-induced ventricular arrhythmias. Two hundred and ten patients underwent maximal exercise testing on a bicycle ergometer, prior to thallium scintigraphy. All 12 leads of the electrocardiogram were recorded simultaneously at rest, immediately post-exercise and then for several minutes afterwards. Thallium scintigraphy was performed immediately and 4 hours post-exercise. Twenty-nine patients of the 210 had ventricular arrhythmias on exercise. Two had dilated (congestive) cardiomyopathy, 1 had hypertrophic cardiomyopathy and 26 were subsequently proven to have ischaemic heart disease. Fifteen of those patients with coronary artery disease and ventricular arrhythmias had otherwise negative exercise tests. Patients with reversible posterior (circumflex) defects had right bundle branch block extrasystoles with a limb lead QRS axis of -60 degrees to -150 degrees. Reversible inferior defects demonstrated ectopic activity with left bundle branch block and a superior axis. Ectopics of septal origin could present with either right or left bundle branch block and an inferior axis from the upper septum, or superior axis from the lower septum. In patients with ischaemic heart disease the 12-lead electrocardiographic appearance of ventricular arrhythmias enables their site of origin to be localised thus suggesting ischaemia in a particular coronary artery territory.