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Biomedical subjects

R A Spurrell

Publications and source records attributed to R A Spurrell.

At least 37 records · Page 2Linked to original sources
PubMed1983

A comparison of the antiarrhythmic effects on AV junctional re-entrant tachycardia of oral and intravenous flecainide acetate.

Both the electrophysiological and antiarrhythmic effects of some antiarrhythmic agents may differ markedly depending on their route of administration. Flecainide acetate, a new class 1 agent, was therefore administered both intravenously and orally to 13 patients with recurrent paroxysmal tachycardia to assess whether the acute response to intravenous flecainide accurately predicts the response to oral therapy. Eight patients had atrioventricular re-entrant tachycardia (AVRT) and five patients intra AV nodal re-entrant tachycardia (AVNRT). When administered by either route, flecainide markedly prolonged both the anterograde and retrograde conduction intervals during constant rate pacing and the anterograde and retrograde Wenckebach cycle lengths during incremental pacing. Five of the 13 patients developed complete retrograde block after both routes of administration of the drug. All 13 patients received intravenous flecainide during tachycardia with successful reversion to sinus rhythm in all cases. Tachycardia could be reinitiated in five of the patients with AVRT after intravenous flecainide and in one further patient after oral administration. It was not possible to reinitiate tachycardia in any of the five patients with AVNRT after either intravenous or oral flecainide. The size of the tachycardia initiation windows, by either atrial or ventricular premature stimuli, were significantly reduced by both intravenous and oral flecainide. In those patients in whom tachycardia could be reinitiated, tachycardia cycle length was significantly increased, and to a similar degree, by both routes of administration of the drug. This increase in cycle length was predominantly due to prolongation in retrograde conduction. It is concluded that flecainide acetate is a potent antiarrhythmic agent for use in patients with junctional tachycardia. The intravenous administration of flecainide reliably predicts the subsequent response to oral therapy.

Administration, Oral↗
PubMed1983

Ambulatory monitoring of pulmonary artery pressure. A preliminary clinical evaluation.

Traditional measurement and recording methods are inadequate for continuous monitoring of ambulatory pulmonary artery pressure. Therefore a new miniaturised solid state system has been developed and assessed. A manometer tipped catheter, inserted via a subclavian or cephalic vein, was used together with an isolated amplifier and peak detectors to determine systolic and diastolic pressures. Pressures were averaged over 30 seconds and stored in digital memory. After a 24 hour recording period data were rapidly transferred to a microcomputer for numerical or graphical display. Thirteen patients had continuous ambulatory monitoring performed for between 24 and 96 hours, in seven to evaluate symptoms of dyspnoea in subjects with valvular or coronary disease (group 1), and in six to achieve optimal oral treatment for left heart failure (group 2). The catheter was calibrated before insertion and was rechecked after removal. There was less than 1% zero level drift and similar gain stability. Systolic pressures ranged from 10 to 97 (mean 39.5) mmHg, and diastolic from 1 to 46 (mean 15.3) mmHg. Four patients in group 1 had symptoms of dyspnoea associated with normal pressures, while three had raised pressures. Four of the six patients monitored in group 2 had major alterations in their treatment based on data obtained during monitoring. There were no complications. This system, which allows safe, reliable, and prolonged recording of ambulatory pulmonary artery pressure, represents a considerable advance in the ability to assess the cause of dyspnoea and to manage left heart failure.

Adult↗
PubMed1983

Electrophysiological abnormalities in the transplanted human heart.

Fourteen relatively long term survivors of cardiac transplantation underwent systematic electrophysiological evaluation and ambulatory electrocardiographic monitoring. Six patients had prolonged conduction intervals during sinus rhythm. Sinus node function could be assessed in all donor atria and in 10 recipient atria. Sinus node recovery times were prolonged in four of the donor atria and in six recipient atria. In the donor atria abnormalities of sinus node automaticity were invariably associated with abnormalities of sinoatrial conduction. Four patients showed functional duality of atrioventricular nodal conduction during programmed extrastimulation, but no patient developed re-entrant arrhythmia. During ambulatory electrocardiographic monitoring no pronounced tachyarrhythmias were recorded. Three patients showed abnormalities of sinus node impulse formation. All three patients had abnormal sinus node recovery times during their electrophysiological study. Long term survivors of cardiac transplantation have a high incidence of electrophysiological abnormalities. Abnormalities of donor sinus node function are probably of clinical significance. The clinical significance of abnormalities detected within the atrioventricular conduction system of the denervated heart remains to be elucidated.

Adult↗
PubMed1983

The direct electrophysiologic effects of disopyramide phosphate in the transplanted human heart.

To evaluate the direct electrophysiologic effects of i.v. disopyramide phosphate and to differentiate these effects from its autonomically mediated actions, we administered the drug (2 mg/kg over 5 minutes) during electrophysiologic study to eight cardiac transplant recipients who had documented functional cardiac denervation. After disopyramide, the cycle length of the denervated donor right atrium increased from 626 +/- 129 to 716 +/- 148 msec (mean +/- SD, p less than 0.001), whereas that of the innervated recipient atrium decreased from 846 +/- 195 to 659 +/- 99 msec (p less than 0.02). There were small increases in both the sinus node recovery time (1128 +/- 616 to 1198 +/- 592 msec, p less than 0.05) and corrected sinus node recovery time (440 +/- 418 to 489 +/- 409 msec, p less than 0.02) of the donor atrium, whereas the recovery times of the recipient atrium shortened (sinus node recovery time, 1298 +/- 218 to 1218 +/- 196 msec; corrected sinus node recovery time, 464 +/- 108 to 410 +/- 115 msec). Disopyramide markedly prolonged all conduction intervals. The PA interval increased from 47 +/- 16 to 54 +/- 17 msec (p less than 0.01), the AH interval from 55 +/- 12 to 78 +/- 12 msec (p less than 0.001), the HV interval from 38 +/- 9 to 58 +/- 13 msec (p less than 0.001), the QRS duration from 93 +/- 18 to 129 +/- 34 msec (p less than 0.001) and the QT interval from 339 +/- 23 to 403 +/- 39 msec (p less than 0.001). There was no significant change in the effective refractory period of the atrium, ventricular or atrioventricular node. The functional refractory period of the atrioventricular node increased from 369 +/- 34 to 395 +/- 31 msec (p less than 0.001). The electrophysiologic effects of disopyramide in the denervated heart are markedly depressant. In the innervated normal heart, the majority of these effects are counteracted by the drug's autonomically mediated anticholinergic actions.

Adult↗
PubMed1982

Initial experience with a fully implantable, programmable, scanning, extrastimulus pacemaker for tachycardia termination.

A fully implantable automatic scanning pacemaker designed for tachycardia termination has been used in three patients with regular paroxysmal supraventricular tachycardia. The pacemaker recognizes tachycardia and delivers one or two extrastimuli which automatically scan inwards if tachycardia continues. A memory is incorporated to retain and immediately reuse a successful pacing sequence if tachycardia recurs. Ventricular pacing has been used in two patients and atrial stimulation in one. Although all had suffered frequent attacks of tachycardia after implantation no sustained episodes of tachycardia have been appreciated. No unwanted arrhythmias have been induced and drug treatment has been stopped in all three patients. Fully implantable scanning pacemakers which automatically recognize and revert tachycardia offer an effective and versatile form of treatment of recurrent paroxysmal tachycardias.

Aged↗
PubMed1982

The long QT syndrome; effects of drugs and left stellate ganglion block.

Four patients, two with congenital QT prolongation (Romano-Ward syndrome) and two with acquired idiopathic QT prolongation not related to bradycardia, drug toxicity, electrolyte imbalance, or neurological disorder were investigated for the onset of recurrent palpitations and/or syncope. The effects on the measured QT interval of intravenously administered propranolol (QTp), an infusion of isoproterenol (QTi) and left stellate ganglion block (QTs) were assessed at identical atrial paced rates and during sinus rhythm, corrected for rate change (QTc). Propranolol shortened the QTc in all patients. The QTp shortened only in those with congenital QT prolongation. Isoproterenol lengthened the QTc in the three patients studied. However, the QTi lengthened in the congenital syndrome whereas it shortened in the acquired syndrome. The QTs was uninfluenced by left stellate ganglion block in all patients. It is suggested that the congenital and acquired forms can be differentiated by pharmacological interventions and that the efficacy of propranolol in the former may result from its ability not only to increase the threshold for ventricular fibrillation, but also its ability to shorten the QT interval.

Adult↗
PubMed1982

Combined exercise radionuclide and hemodynamic evaluation of left ventricular aneurysmectomy.

Twelve patients were studied by rest and exercise radionuclide ventriculography following left ventricular aneurysmectomy (LVA). Left ventricular filling pressure (LVFP) was also measured. Nine patients had been studied pre-LVA at rest and exercise before and after isosorbide dinitrate (ISDN). Resting ejection fraction (LVEF) improved after LVA (p less than 0.25), but exercise LVEF did not. End-diastolic volume (EDV) and resting LVFP also fell after LVA (p less than 0.25 for EDV, p less than 0.05 for LVFP) and although exercise LVFP fell (p less than 0.02), the values were abnormal in all patients. Ejection fraction of contractile segment (EFCS) from the resting radionuclide study pre-LVA was related to resting LVEF post-LVA (r = 0.71 p less than 0.02), although postoperative LVEF could not be predicted from preoperative EFCS in individual patients. Deterioration in LVEF and LVFP from rest to exercise post-LVA occurred both in patients with single-vessel occlusion and in those with multivessel coronary disease, irrespective of whether or not revascularization had been performed. Thus LVA is effective in improving resting ventricular function; exercise performance may remain abnormal even in patients without residual coronary disease.

Adult↗
PubMed1982

Implantable automatic scanning pacemaker for termination of supraventricular tachycardia.

Thirteen patients suffering from reentrant supraventricular tachycardia have undergone implantation of a scanning extrastimulus pacemaker. This pacemaker is fully implanted and automatic, and it requires no external control device to activate or control it. The pacemaker is activated when tachycardia occurs. After four cycles an extrastimulus is induced with a preset coupling time from a sensed intracardiac potential, and every four cycles thereafter a further extrastimulus occurs, but on each occasion there is a decrement in coupling cycle by 6 ms until 90 ms of the cardiac cycle has been scanned by extrastimuli. When necessary, two extrastimuli can be introduced with a fixed but preset coupling time between them. Every four beats two extrastimuli are induced but the coupling time between the spontaneous cardiac potential and the first stimulus is decreased by 6 ms until 90 ms of the cardiac cycle has been scanned. The coupling time between the two stimuli is fixed throughout the scan. When termination of tachycardia occurs the successful timing variables are retained in the pacemaker memory so that at the onset of the next episode of tachycardia these settings are used first. Pacemaker pulse width, sensitivity, tachycardia trigger rate, coupling intervals for both stimuli and the use of single or double extrastimuli are all programmable transcutaneously. Three patients required single, and seven patients double ventricular premature stimuli; three patients required double atrial premature stimuli for termination of tachycardia. Despite frequent attacks of tachycardia before implantation, only two patients had a sustained attack of tachycardia after pacemaker implantation.

Adolescent↗
PubMed1982

The ventricular paced QT interval--the effects of rate and exercise.

Changes in the QT and QTc intervals in 19 patients were studied at a ventricular paced rate difference of 50 beats/min. In all patients the measured QT interval shortened as the pacing rate was increased, from a mean value of 441 ms to 380 ms (p less than 0.001), but when corrected for heart rate the QTc lengthened from a mean value of 518 ms to 575 ms. In 11 patients the QT interval was measured at rest and immediately following exercise sufficient to increase the atrial rate by approximately 50 beats/min at identical ventricular paced rates. In all patients exercise-induced QT interval shortening from a mean value of 433 ms to 399 ms (p less than 0.001). These results show first that Bazett's formula is unsuitable for correction of QT interval induced by ventricular pacing, and second that heart rate and changes in sympathetic tone independently influence the duration of the QT interval. It is suggested that these results are relevant to the design of physiological pacemakers in which the duration of the QT interval influences the discharge frequency of the pacemaker and to the consideration of ventricular pacing for the treatment of abnormal repolarization syndromes.

Adolescent↗
PubMed1982

Electrophysiological effects of sotalol--just another beta blocker?

The electrophysiological effects of intravenous sotalol hydrochloride (0.4 mg/kg) were assessed in 24 patients, including 13 with the Wolff-Parkinson-White syndrome, undergoing routine electrophysiological study. Fifteen to 30 minutes after sotalol administration there was a significant increase in sinus cycle length and in sinus node recovery time. There was a small increase in the AH interval, but the HV interval was unchanged. The QT and JT intervals, measured during sinus rhythm, were both increased. The atrial, ventricular, and atrioventricular nodal effective refractory periods were all prolonged, as was the atrioventricular nodal functional refractory period. In 13 patients with ventricular pre-excitation there was an increase of the accessory pathway anterograde and retrograde effective refractory periods. In 12 of these 13 sotalol was given during atrioventricular re-entrant tachycardia, resulting in termination in five. Tachycardia cycle length increased in all patients, with the major effect being in the atrioventricular direction. Though some of the effects seen in these patients are consistent with the beta adrenergic antagonist properties of sotalol, the effect on atrial, ventricular, and accessory pathway effective refractory periods and on ventricular repolarisation is not typical of that observed with other beta blockers but may be the result of lengthening of the action potential duration. These findings suggest that sotalol may be a more versatile antiarrhythmic agent than other beta receptor antagonists.

Adolescent↗
PubMed1982

Acute electrophysiological effects of flecainide acetate on cardiac conduction and refractoriness in man.

The electrophysiological effects of flecainide acetate (2 mg/kg as an intravenous infusion over five minutes) were assessed in 47 patients undergoing electrophysiological study. Seven patients had normal electrophysiology, 16 had a direct accessory atrioventricular pathway, 12 had dual atrioventricular nodal (AH) pathways, five had paroxysmal ventricular tachycardia, six had conduction system disease, and one patient had a left atrial tachycardia. No significant change occurred in sinus cycle length. The PA interval, AH interval, and HV interval were all significantly prolonged. The QRS complex duration increased significantly. The QT interval showed slight prolongation due entirely to the increase in QRS duration. Refractoriness of the atrial and ventricular myocardium was slightly prolonged, but was significant only at ventricular level. No significant change occurred in refractoriness of the normal atrioventricular node. Pronounced prolongation of retrograde "fast" AH pathway refractoriness was observed in those patients with dual AH pathways. Anterograde and retrograde accessory pathway refractoriness were both greatly increased. These electrophysiological properties strongly suggest that flecainide will be useful in the management of a wide variety of cardiac arrhythmias. It should be administered, however, with caution to patients with pre-existing conduction system disease. Because repolarization is not delayed flecainide is unlikely to induce ventricular arrhythmias related to prolongation of the QT interval.

Adolescent↗
PubMed1980

Suppression of long-standing incessant ventricular tachycardia by amiodarone.

A 25 year old man had experienced virtually incessant ventricular tachycardia since the age of 16 years, and complained of increasing lethargy and shortness of breath over the past 5 years. Despite medical therapy with numerous conventional antiarrhythmic agents, no single drug or combination of drugs had successfully controlled the tachycardia. Isotope and contrast angiography revealed an enlarged left ventricle with poor function. Electrophysiological studies demonstrate earliest endocardial activation at the left ventricular apex. No electrical procedure terminated tachycardia. Following institution of amiodarone, continuous ECG monitoring revealed periods of sinus rhythm alternating with periods of ventricular bigeminy. Repeat isotope angiography indicated a considerable improvement in L.V. function. There was a corresponding reduction in heart size on the chest radiograph. Clinical improvement was evidenced by disappearance of lethargy and shortness of breath. This report demonstrates that amiodarone, a new antiarrhythmic agent, may suppress long standing incessant ventricular tachycardia resistant to other antiarrhythmic agents. The marked reduction in heart size on amiodarone may suggest that the associated cardiomegaly is secondary to tachycardia.

Adult↗
PubMed1980

Autodecremental pacing--a microprocessor based modality for the termination of paroxysmal tachycardias.

Five patients aged between 27 and 48 years were referred for investigation of recurrent paroxysmal tachycardias. Electrophysiological studies revealed concealed ventriculoatrial accessory pathways in two patients, possible atrionodal pathways in two patients and dual intranodal pathways in one patient. During electrophysiological study, particular attention was paid to methods of terminating tachycardia by pacing techniques including single or double atrial and ventricular extrastimuli, atrial or ventricular underdrive, atrial overdrive pacing, and in two patients, rapid ventricular pacing. 'Autodecremental' atrial pacing was employed in all five patients and autodecremental ventricular pacing in two patients. This system is controlled by a microprocessor interfaced with a stimulator. When tachycardia of a cycle length less than 375 ms is sensed the system initiates pacing sequences. The initial stimulus is introduced at an interval less than the tachycardia cycle determined by a preset decremental value D. Each subsequent pacing interval is reduced by the value of D resulting in a gradual acceleration of pacing. The total duration of pacing is limited by the value of the pacing period (P). The final pacing rate is determined by P but cannot exceed 275 bpm (cycle length of 218 ms). Both P and D are operator programmable variables. Tachycardias of a cycle length less than 218 ms do not activate the pacemaker. The postpacing sensing deadtime of the system is set at 50 ms. In three patients, double atrial extrastimuli or atrial overdrive initiated atrial flutter or fibrillation. Autodecremental atrial pacing was successful in converting tachycardia to sinus rhythm in all five patients without initiation of other tachyarrhythmias. Autodecremental ventricular pacing was successful in one of the two patients in which it was used. This new modality of pacing has several theoretical advantages over conventional methods: the decremental mode may avoid stimulation in the vulnerable period and minimizes the risk of initiating other tachyarrhythmias; gradual acceleration of pacing over a short period results in stimulation at different phases of the tachycardia cycle length; and the operator variables D and P provide a flexible system which may be adjusted to suit a particular patient and tachycardia. The development of a fully implantable programmable system is made attractive by the simplicity and adaptability of this technique.

Adult↗
PubMed1980

Effect of intravenous propranolol on QT interval. A new method of assessment.

Changes in the QT and QTc intervals were studied in 16 patients by atrial pacing at rates of 100, 130, and 150 beats/minute. In all patients the measured QT shortened when the atrial paced rate was increased, but when corrected for heart rate the QTc lengthened. Intravenously administered propranolol produced a bradycardia and a lengthening of the QT interval in 15 of the 16 patients studied. When the QT interval was corrected for heart rate using Bazett's formula the QTc was shortened in 13 patients, unchanged in one, and lengthened in two. However, when the QT interval was measured at identical atrial paced rates the QT of the 15 patients studied was lengthened in 10 and unchanged in five. In none was the QT interval shortened. These results show firstly that Bazett's formula is unsuitable for correction of QT interval changes induced by atrial pacing, and secondly that, though intravenously administered propranolol usally produces a shortening of the QTc, when its effect is assessed directly by using an identical atrial paced rate the QT interval usually lengthens, or may remain unchanged, but never shortens. It is suggested that the formal assessment of drug induced QT interval changes should be made at identical atrial paced rates.

Adult↗
PubMed1980

Assessment of function of contractile segments in patients with left ventricular aneurysms by quantitative first pass radionuclide ventriculography. Haemodynamic correlation at rest and exercise.

Thirteen patients with left ventricular aneurysms complicating myocardial infarction were studied by contrast angiography and by first pass radionuclide ventriculography. The ejection fraction of the contractile segment (EFCS) was measured from both studies using a double hemishperoid model, and the values correlated closely. There was a monotonic relation between EFCS and stroke volume index measured from thermodilution cardiac outputs carried out simultaneously with the radionuclide study. When radionuclide ventriculography was performed at submaximal supine exercise, changes in EFCS paralleled changes in the total left ventricular ejection fraction in 10 of the 13 cases. In nine patients, changes in EFCS paralleled changes in stroke volume index and the relation between EFCS and stroke volume index was maintained at exercise. After administration of the vasodilator isosorbide dinitrate to 12 patients, repeat exercise radionuclide ventriculography showed an improvement in left ventricular ejection fraction and in eight patients EFCS improved. First pass radionuclide ventriculography can accurately estimate EFCS, which may be an important factor in predicting the likely response to aneurysmectomy. Changes in EFCS on exercise are reflected in changes in total left ventricular ejection fraction and stroke volume index. Isosorbide dinitrate may improve contractile segment function on exercise.

Adult↗