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Biomedical subjects

D G Benditt

Publications and source records attributed to D G Benditt.

At least 145 records · Page 8Linked to original sources
PubMed1983

A combined atrial/ventricular lead for permanent dual-chamber cardiac pacing applications.

A new urethane insulated dual unipolar atrial/ventricular transvenous lead has been developed to facilitate implantation of permanent dual-chamber cardiac pacing systems in man. The atrial portion of the lead has tines and is designed to retain a permanent J configuration, while the coaxially situated ventricular lead is freely and independently adjustable and incorporates a ring tip electrode with four urethane tines. Our initial experience with the dual lead in one patient is reported herein and suggests that combined atrial/ventricular pacing leads are feasible and may obviate need for implantation of two separate pacing electrodes in patients being considered for permanent dual-chamber pacing.

Electrodes, Implanted↗
PubMed1982

Onset of atrial fibrillation during antidromic tachycardia: association with sudden cardiac arrest and ventricular fibrillation in a patient with Wolff-Parkinson-White syndrome.

Electrophysiologic evaluation in an 18 year old youth with the Wolff-Parkinson-White syndrome who had a sudden cardiac arrest while playing racquetball revealed two types of paroxysmal reciprocating tachycardia: (1) A normal QRS tachycardia with a short ventriculoatrial (V-A) interval fulfilled the criteria for reentry within the atrioventricular (A-V) node; and (2) a wide QRS tachycardia with a QRS configuration of maximal preexcitation was demonstrated to be the result of an antidromic mechanism. During laboratory study, the wide QRS tachycardia spontaneously degenerated into atrial fibrillation. In the basal state, the shortest R-R interval between preexcited QRS complexes was 270 ms, but after infusion of isoproterenol (1.6 microgram/min intravenously), the shortest R-R interval became 180 ms. Consequently, this electrophysiologic study suggested that evolution of antidromic reciprocating tachycardia into atrial fibrillation with a rapid ventricular response during exercise-induced catecholamine release may have been the mechanism for ventricular fibrillation in this patient.

Adolescent↗
PubMed1982

Antiarrhythmic, antifibrillatory, and hemodynamic actions of bethanidine sulfate: an orally effective analog of bretylium for suppression of ventricular tachyarrhythmias.

Bethanidine sulfate is a chemical and pharmacologic analog of bretylium tosylate that has virtually identical antifibrillatory and inotropic actions on the heart. Bretylium is the only drug approved by the Food and Drug Administration specifically for the "prophylaxis and treatment of ventricular fibrillation." Unlike bretylium, which is poorly absorbed from the gut and limited to parenteral use, oral bethanidine is absorbed rapidly. Bethanidine was given to 23 patients with recurrent multiple drug refractory ventricular tachycardia and fibrillation. Eighteen patients (78%) had complete suppression of spontaneous or electrophysiologically inducible tachyarrhythmias; 3 were improved and 2 had no benefit. In 6 of a 9 patient subgroup studied by programmed electrophysiologic drug testing, bethanidine completely prevented previously inducible ventricular tachyarrhythmias at the maximal stimulus tested (including 4 extrastimuli and burst-pacing at 10 times threshold). Cardiac output measured in 6 patients 1 to 2 hours after bethanidine was increased in 4, unchanged in 2, and decreased in 1. Ten patients on long-term therapy with bethanidine and protriptylene (to prevent orthostatic hypotension) have been free of arrhythmias from 2 to 26 (average 13) months.

Adult↗
PubMed1982

Effects of reduced PO2 on rapid-drive-induced hyperpolarization of diastolic transmembrane potential in feline cardiac Purkinje strands.

Using standard microelectrode techniques, we evaluated effects of diminished oxygen tension on the magnitude and time course of frequency dependent changes in maximum diastolic transmembrane potential (MDP) and on alteration of action potential duration (APD) in feline Purkinje fibers. MDP was recorded continuously during a control period (cycle length (CL) = 1000 ms), during a 5-min period of rapid drive (CL = 400 ms) and following return to pacing CL = 1000 ms. Rapid drive resulted in hyperpolarization of MDP from control value; and after return to pacing CL = 1000 ms. MDP gradually depolarized, eventually attaining a steady state value within +/- 0.5 mV of the control value. The difference between hyperpolarized MDP value and final steady-state value was designated VH, and the decline of MDP towards steady-state value approximated an exponential function (time constant = tau VH). Exposure to reduced PO2 (75 +/- 2.1 mmHg vs. control 473 +/- 39.1 mmHg) (1 mmHg = 133.322 Pa) resulted in reduction in the magnitude of VH (6.2 +/- 3.43 mV vs. 7.8 +/- 2.73 mV, mean +/- SD, p less than 0.005) and shortening of APD within 0-24 min, while measurable prolongation of tau VH (75 +/- 18.5 vs. 54 +/- 9.0 s, p less than 0.005) began at 25-49 min following onset of reduced PO2. These observations suggest that rate-related changes of MDP in cardiac tissues are oxygen dependent, and they support previously reported analagous observations in nerve which suggested that frequency dependent potential changes may in part reflect alterations of electrogenic Na-K pump activity.

Action Potentials↗
PubMed1982

Enhanced atrioventricular conduction in patients without preexcitation syndrome: relation to heart rate in paroxysmal reciprocating tachycardia.

We studied the electrophysiologic characteristics of atrioventricular (AV) nodal conduction in patients with reciprocating tachycardia (RT) without ventricular preexcitation, and the relation of these characteristics to RT cycle length (CL). Thirty-five symptomatic patients who had a normal PR interval (0.13-0.20 second) during sinus rhythm underwent detailed intracardiac electrophysiologic study during which ventricular preexcitation was excluded, and the RT mechanism was determined. RT was due to reentry using an accessory AV pathway capable of conduction only in the retrograde direction (concealed AP) in 13 patients (37%) and to reentry within the AV node in 22 (63%). Dynamic properties of AV conduction (assessed by degree of AH prolongation during progressive increase in atrial pacing rate) were normally distributed (p less then 0.005); 12 patients (34%) fulfilled the criteria for enhanced AV conduction (EAVC). The patients with EAVC had a shorter RT CL than did patients without EAVC (294 +/- 43.3 msec vs 360 +/- 68.1 msec, p less than 0.01). However, CL differences were primarily due to the influence of EAVC in the subgroup of patients with RT using a concealed AP (EAVC CL, 274 +/- 35.1 msec; without EAVC, 326 +/- 15.7 msec, p less than 0.005). The RT CL in patients with reentry within AV node was not measureable influenced by concomitant EAVC (EAVC, 314 +/- 43.8 msec; without EAVC, 376 +/- 76.8 msec) (NS). This study suggests that despite the presence of a normal PR interval during sinus rhythm, dynamic AV conduction responses can vary widely in patients with RT. In patients with RT using a concealed AP, but not in those with reentry within the AV node, coexisting diminished physiologic AV conduction slowing may be associated with more rapid tachycardia rates.

Adult↗
PubMed1981

Long-term evaluation of persistent supraventricular tachycardia in children: clinical and electrocardiographic features.

Although the long-term prognosis of children with persistent supraventricular tachycardia (SVT) has been generally considered benign, recent reports have suggested that some of these patients may develop cardiac dysfunction secondary to their persistent SVT. The clinical course of six children demonstrating ECG criteria of persistent SVT are presented herein with follow-up data for 5 to 20 years. Persistent SVT was present in each patient from 2 to 19 years. Two patients had transient congestive heart failure early in their course of persistent SVT, and two others demonstrated continued roentgenographic evidence of mild cardiomegaly without associated symptomatology. Conventional antiarrhythmics administered briefly in five patients and chronically in two were without effect on their arrhythmias. Persistent SVT remains in three patients and a fourth continues to exhibit intermittent episodes of SVT; however, all six patients are currently asymptomatic with two in stable normal sinus rhythm. This investigation indicates that the persistent form of SVT (lasting more than 1 year) is uncommon among children with paroxysmal SVT, and long-term observation of the consequences of persistent SVT supports the view that this rhythm disturbance is generally well tolerated in such patients.

Adolescent↗
PubMed1981

Cellular electrophysiological changes in "round heart disease" of turkeys: a potential basis for dysrhythmias in myopathic ventricles.

Arrhythmias are commonly recorded in "round heart disease", a presumed viral, congestive cardiomyopathy of turkeys. To assess whether cellular electrophysiological changes may be associated with arrhythmia susceptibility, we compared transmembrane action potential characteristics in left and right ventricular endocardial muscle fibres from 19 inbred myopathic turkeys with findings in 13 normal control turkeys (age 1 to 74 days). In left ventricular tissue, as a group, action potential duration at 50% repolarisation (APD50) was reduced in myopathic hearts (201+/-6(SEM) vs 228+/-9 ms in controls. P less than 0.01), while the maximum rate of phase 0 (dV/dtmax) action potential amplitude, diastolic resting membrane potential and action potential duration at 90% repolarisation (APD90) did not differ from control turkeys. By contrast, in myopathic right ventricular tissue, as a group, both APD50 (186+/-5 vs 206+/-4 ms in controls) and APD90 (208+/-4 vs 228+/-3 ms in controls) were shorter (P less than 0.01). The plateau potential in both right and left ventricular tissue was significantly higher in inbred turkeys. Since a spectrum of cardiac dilatation and hypertrophy is present in myopathic turkeys, we examined the effect of hypertrophy on action potential characteristics. In "round heart disease" turkeys, left ventricular hypertrophy was characterised by reduced dV/dtmax (98+/- vs 274+/-26 V.s-1, P less than 0.01) and right ventricular hypertrophy by further shortening of both APD50 (174+/-7 vs 202+/-6 ms, P less than 0.01) and APD90 (193+/- vs 224+/-5 ms, P less than 0.01), but no change in dV/dtmax (105+/-13 vs 120+/-9 V.s-1, P = NS). These results indicate that certain electrophysiological differences (eg reduced action potential duration), may, in part, contribute to dysrhythmia susceptibility in this presumed viral cardiomyopathy model.

Action Potentials↗
PubMed1980

'Dual atrioventricular nodal pathways" in patients with Wolff-Parkinson-White syndrome.

'Dual atrioventricular nodal pathways" were found in five patients who also had the Wolff-Parkinson-White syndrome. All five patients had a re-entrant tachycardia that used the atrioventricular node for conduction in the anterograde direction and an accessory atrioventricular pathway for conduction in the retrograde direction. One of the patients also had a re-entrant tachycardia that originated within the atrium or the atrioventricular node. Dual atrioventricular nodal pathways were identified in three of the five patients during their first electrophysiological study because the effective refractory period of the accessory atrioventricular pathway in the anterograde direction was longer than the effective refractory period of the fast atrioventricular nodal pathway. In the other two patients the dual atrioventricular nodal pathways were found only after operative division of an accessory atrioventricular pathway. Re-entrant tachycardia that uses an accessory pathway may be cured by operative division of the accessory pathway. Tachycardia resulting from re-entry within the atrioventricular node cannot be cured by an operation unless the normal conduction system is divided and a permanent pacemaker implanted. These five patients indicate the importance of determining the aetiology of tachycardia by studying the tachycardia itself and not only the type of atrioventricular conduction present.

Atrioventricular Node↗
PubMed1979

Incessant atrial tachycardia in childhood: association with rate-dependent conduction in an accessory atrioventricular pathway.

A detailed electrophysiologic study in a 7 year old boy with incessant atrial tachycardia revealed the presence of an atrioventricular pathway conducting only in the ventriculoatrial direction. The results indicate a reentrant mechanism with the retrograde limb of the circuit entering the atrium in the region of the proximal to mid coronary sinus. The accessory pathway exhibited relatively long conduction times and conduction properties suggesting decremental conduction. Thus, an electrophysiologically atypical anomalous conduction pathway may be responsible for the occurrence of incessant atrial tachycardial in some children.

Atrioventricular Node↗
PubMed1979

Reentry within the atrioventricular node: surgical cure with preservation of atrioventricular conduction.

Paroxysmal supraventricular tachycardia (PSVT) is commonly caused by reentry within the atrioventricular (AV) node. This arrhythmia was abolished by operative dissection of the AV junction in a patient with disabling tachycardia that was not controlled by drugs. The operation was intended to create complete AV block, but AV conduction persisted after surgery. An electrophysiologic study 1 year after the operation revealed that the operation changed AV conduction in both the antegrade and retrograde directions, which may explain the absence of tachycardia. The patient has been free of arrhythmias for 18 months.

Atrioventricular Node↗
PubMed1979

The estimation of sinoatrial conduction time in rabbit heart by the constant atrial pacing technique.

This study compared estimates of sinoatrial conduction time (SACT) obtained by constant atrial pacing (CAP) and premature atrial stimulation (PAS) with measured SACT in isolated rabbit right atrial preparations. Transmembrane potentials and surface electrograms were recorded from the sinus node and crista terminalis, respectively. The crista terminalis was paced 5, 10 and 15 beats/min faster than the spontaneous sinus rate with a train of eight pulses. Estimate of SACT by CAP was taken as the difference between the first atrial return cycle and the mean spontaneous cycle length. SACTs at 5, 10 and 15 beats/min faster were 76 +/- 10, 86 +/- 10 and 96 +/- 10 msec (mean +/- SEM; n = 12), respectively; correlation coefficients with the true SACT were 0.7, 0.54 and 0.4. Consecutive determinations of SACT by PAS and CAP in the same preparation (n = 6) at 10 beats/min faster gave SACTs of 86 +/- 13 and 79 +/- 14 msec, respectively, compared with true SACTs of 79 +/- 10 msec. Shortening of sinus node action potential, depression of automaticity and shifts in the site of the primary pacemaker contributed to the errors in both techniques. Estimation of SACT by CAP may be further complicated by failure of sinus node capture. Principles to minimize some of these errors are also presented.

Animals↗
PubMed1979

Ventriculoatrial intervals: diagnostic use in paroxysmal supraventricular tachycardia.

Reciprocating tachycardias due to reentry either within the atrioventricular (AV) node or using an accessory AV pathway are a common cause of paroxysmal supraventricular tachycardia in humans. Unfortunately, although of potential therapeutic value, differentiation of these forms of reciprocating tachycardia may be difficult and require detailed electrophysiologic study. To develop diagnostic criteria that permit exclusion of participation of an accessory AV pathway in reciprocating tachycardia without extensive laboratory testing, results of electrophysiologic studies were examined in 50 patients with Wolff-Parkinson-White syndrome, 15 patients with accessory AV pathways that conducted only in the ventriculoatrial direction, and 15 patients with reentry within the AV node. The interval between onset of ventricular activation and both earliest recorded atrial activity (V-Amin) and high lateral right atrial electrogram (V-HRA) was measured during tachycardia. A V-Amin of 61 ms or less or V-HRA of 95 ms or less did not occur in patients with accessory AV pathways, but occurred frequently (12 of 15 and seven or eight, respectively) in patients with reentry within the AV node. Therefore, in patients with paroxysmal reciprocating tachycardias, V-A interval measurements provide a screening test capable of excluding participation of an accessory AV pathway.

Adolescent↗
PubMed1978

Effect of catheter position on the initiation of atrial echoes with atrial pacing and premature stimulation in patients with accessory pathways.

Eleven patients with an accessory pathway and reciprocating tachycardia were studied using both fixed rate atrial pacing and the atrial extrastimulus technique. Six of the patients had an accessory pathway that conducted in both the anterograde and retrograde direction; but the effective refractory period of their accessory pathway in the anterograde direction was relatively long and was greater than the longest coupling intervals that initiated atrial echoes. Five patients had an accessory pathway that conducted only in the retrograde direction. The extrastimulus technique could be used with stimulation sites near to and remote from the accessory pathway in 10 of the 11 patients. Atrial echoes were initiated by a single atrial extrastimulus at both sites in 7 of the 10 patients, and in each patient the upper limit of the echo zone was longer with stimulation at the site near the accessory pathway. In the other three patients atrial echoes were initiated only during stimulation at the site near the accessory pathway because either atrial refractoriness or atrioventricular nodal refractoriness was encountered before the echo zone was entered during stimulation at the site remote from the accessory pathway. Differences in the longest cycle length that initiated an atrial echo during fixed rate atrial pacing were similarly demonstrated in three patients. In these three patients, pacing at the site near the accessory pathway initiated echoes at a longer cycle length than pacing at the site remote from the accessory pathway. In three other patients the electrophysiologic characteristics of atrioventricular conduction prevented a demonstration of these differences. Catheter position is an important variable in the initiation of atrial echoes in patients with accessory pathways.

Arrhythmias, Cardiac↗