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Biomedical subjects

D G Benditt

Publications and source records attributed to D G Benditt.

At least 91 records · Page 5Linked to original sources
PubMed1989

Provocation of bradycardia and hypotension by isoproterenol and upright posture in patients with unexplained syncope.

Neurally mediated hypotension and bradycardia are believed to be common causes of syncope. We used the "upright-tilt test" (duration, less than or equal to 10 minutes) with or without an infusion of exogenous catecholamine (isoproterenol [1 to 5 micrograms per minute], given intravenously) to elicit bradycardia, hypotension, or both in 24 patients with recurrent syncope and in 18 control subjects. A conventional electrophysiologic test performed before the tilt test was positive in 9 of the 24 patients, revealing arrhythmias that may have caused recurrent syncope, but was negative and thus nondiagnostic in 15 patients. The tilt test alone (i.e., without isoproterenol) induced symptomatic bradycardia or hypotension in 1 of the 9 patients with positive electrophysiologic tests (11 percent), 4 of the 15 patients with negative electrophysiologic tests (27 percent), and none of the controls. When the isoproterenol infusion was administered during the tilt test, 9 of the 11 patients with negative electrophysiologic and tilt tests had syncope, marked slowing of the heart rate, and hypotension. In contrast, isoproterenol was associated with tachycardia and only a slight decline in arterial pressure in the 8 remaining patients with positive electrophysiologic tests and the 18 control subjects, and syncope developed in only 1 of the 8 patients with positive electrophysiologic tests and negative tilt tests (13 percent) and 2 of the 18 control subjects (11 percent). We conclude that an isoproterenol infusion administered in conjunction with the upright-tilt test may be useful for identifying susceptibility to neurally mediated recurrent syncope.

Adolescent↗
PubMed1989

Cardiac electrophysiologic and hemodynamic correlates of neurally mediated syncope.

This study assessed the temporal relation of RR interval, AH interval and systemic blood pressure changes during induced symptomatic bradycardia-hypotension episodes in 14 patients with recurrent syncope suspected of being neurally mediated. Upright tilt with isoproterenol reproduced symptoms in 9 of 14 patients (positive response) and was negative in 5 of 14 (negative response). Isoproterenol alone shortened supine RR intervals in all patients. With tilt, however, isoproterenol prolonged RR intervals in those with positive results (supine 519 +/- 124 ms vs tilt 845 +/- 212 ms, p less than 0.005) while further shortening RR intervals among negative responders (supine 436 +/- 90 ms vs tilt 377 +/- 82 ms, p less than 0.05). Similarly, tilt with isoproterenol prolonged AH intervals in patients with positive responses despite RR prolongation, while shortening AH in negative responders. Additionally, with combined tilt and isoproterenol, systemic arterial pressure decreased significantly in patients with positive responses (systolic 99 +/- 13 vs 57 +/- 13 mm Hg, p less than 0.001, diastolic 62 +/- 17 vs 28 +/- 9 mm Hg, p less than 0.001) but not in patients with negative responses. Further, onset of hypotension (42 +/- 14 seconds after tilt) preceded onset of RR interval prolongation (52 +/- 23 seconds after tilt). Syncope (142 +/- 72 seconds after tilt) coincided closely with nadir of systemic pressure (136 +/- 74 seconds) and both tended to precede maximum RR prolongation (152 +/- 87 seconds). Thus, the bradycardia and hypotension associated with neurally mediated syncope exhibit characteristic but distinctly different time courses, with arterial pressure changes developing earlier and coinciding more closely with symptom development.

Adult↗
PubMed1989

Cellular electrophysiologic effects of dexamethasone sodium phosphate: implications for cardiac stimulation with steroid-eluting electrodes.

Impregnation of implantable cardiac pacemaker electrodes with dexamethasone sodium phosphate dexamethasone) has been associated with reduced energy requirements for both atrial and ventricular stimulation. To determine whether cardiac cellular electrophysiologic effects of dexamethasone could in part account for lower stimulation thresholds, conventional microelectrode recording and stimulation techniques were used to assess both the immediate (acute) effects of dexamethasone (10(-6) and 10(-4) M) in superfused isolated rabbit right atrial and right ventricular preparations, and chronic effects in rabbit right ventricular tissue following 2 weeks of either daily parenteral dexamethasone (5 mg/kg, plasma concentration approximately 1 to 5 x 10(-5) M) or saline placebo injections. In acute superfusion studies, dexamethasone resulted in a concentration dependent prolongation of spontaneous right atrial cycle length, but did not significantly affect right atrial transmembrane action potential characteristics or refractoriness. However, acute dexamethasone superfusion tended to increase right ventricular resting membrane potential and diminish stimulation threshold. On the other hand, compared to findings in saline-injected control rabbits, chronic dexamethasone injection had little effect on right ventricular stimulation threshold transmembrane action potential characteristics, or right ventricular refractoriness. Thus, the acute direct electrophysiologic effects of high-dose dexamethasone are compatible with the early reduction of cardiac stimulation thresholds associated with dexamethasone impregnated pacing electrodes. On the other hand, electrophysiologic findings in the presence of chronic dexamethasone exposure do not fully account for long-term reduction of stimulation energy requirements.

Animals↗
PubMed1989

Accelerated idioventricular rhythm complicating atrioventricular junction ablation for automatic atrial tachycardia.

A 13-year-old male with histologic evidence of cardiomyopathy, drug-refractory primary atrial tachycardias, and deteriorating left ventricular function underwent transcatheter His bundle ablation to control ventricular rate. Following an initial successful ablation at the level of the atrioventricular node, the patient exhibited an accelerated escape rhythm of apparent junctional origin (ventricular cycle length = 470 msec, HV = 100 msec) with complete heart block. A second ablation procedure was undertaken, following which an accelerated idioventricular rhythm (cycle length = 500 msec) became apparent and has persisted (follow-up 15 months). Thus, findings in this patient suggest that attempts to control refractory rapid ventricular responses in cardiomyopathy patients with primary atrial tachycardias may be complicated by the potential for junctional and idioventricular sites to exhibit similar abnormally accelerated subsidiary pacemaker function.

Adolescent↗
PubMed1989

Cardiac asystole: a manifestation of neurally mediated hypotension-bradycardia.

It has been proposed that prolonged cardiac asystole mimicking an episode of sudden cardiac death may occur as a manifestation of neurally mediated hypotension-bradycardia syndrome. To assess this possibility, electrocardiographic and hemodynamic findings during upright tilt testing were evaluated in six survivors of suspected asystolic sudden cardiac arrest with normal conventional electrophysiologic evaluation (Group I). These observations were compared with findings in two control groups: six patients with syncope but without evident asystole and with normal conventional electrophysiologic evaluation but demonstrable neurally mediated hypotension-bradycardia (Group II), and six patients with syncope in whom conventional electrophysiologic evaluation provided a presumptive diagnosis (Group III). Patients in all three groups ranged in age from 16 to 59 years. During head-up tilt testing (either alone or with isoproterenol infusion), patients in both Groups I and II developed syncope in less than or equal to 5 min, whereas patients in Group III remained asymptomatic. Patients in Groups I and II exhibited a similar tilt-induced decrease in mean arterial pressure (-46 +/- 9 and -40 +/- 9 mm Hg, respectively, p = NS) and heart rate (-44 +/- 28 and -49 +/- 12 beats/min, respectively, p = NS). In contrast, patients in Group III manifested only a moderate decrease in mean arterial pressure (-14 +/- 5 mm Hg) and had an increase in heart rate (+14 +/- 8 beats/min). Both mean arterial pressure and heart rate changes in Group I and Group II patients differed significantly (p less than 0.001) from values in Group III patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Cardiac electrophysiologic effects of orally administered DPI 201-106 in conscious canines: effects of pharmacologic autonomic blockade or cardiac transplantation.

This study assessed the cardiac electrophysiologic effects of DPI 201-106 (DPI), a novel orally absorbable positive inotropic agent, the administration of which has been associated with electrocardiographic (ECG) QT and T-wave changes. In the intact conscious dog, oral administration of both 8 and 16 mg/kg DPI produced marked sinus cycle length prolongation (8 mg/kg, + 11%; 16 mg/kg, + 9%) within 60 min of DPI administration (p less than 0.05 vs. baseline). DPI also tended to prolong right atrial refractory periods, and increase sinus node recovery time. In addition, DPI exhibited a negative dromotropic effect on the atrioventricular (AV) node, prolonging both AV node effective and functional refractory periods and tending to increase the minimum atrial paced cycle length at which AV conduction of 1:1 was maintained. DPI also significantly increased right ventricular effective refractory period (ERP) at both doses studied and increased ventricular functional refractory period (FRP) at the 16-mg/kg dose. Finally, although DPI administration was associated with QT interval prolongation, this effect was slight when corrected for sinus cycle length (SCL) (QTc, +3%). When administered concomitantly with propranolol and atropine or after surgical cardiac denervation, DPI-induced electrophysiologic changes were largely attenuated or abolished. Thus, findings in this study indicate that the apparent cardiac electrophysiologic effects of DPI are predominantly of neurally mediated origin in this animal model.

Administration, Oral↗
PubMed1989

Electrophysiological effects of left ventricular free wall traction in intact hearts.

Transmural multipolar electrodes, sonomicrometers implanted within the left ventricular wall, and cardiac electrical stimulation techniques were used to examine the effect of transient mechanically applied traction to the left ventricular free wall on local electrophysiological properties. Twenty-five open-chest dogs were atrially paced (cycle length 400 ms) followed by insertion of timed premature extrastimuli at left ventricular epicardial pacing sites either in the vicinity of (traction zone) or remote from (nontraction-control zone) the site of left ventricular free wall traction. Electrophysiological recordings were made before and during intermittent left ventricular free wall traction applied in late diastole (rate 25 cm/s; duration 170 ms). In 22 of 25 dogs, application of traction resulted in early local ventricular activation (mean activation advancement 64 +/- 15 ms), altered QRS morphology of the last conducted atrial drive train beat, and a relative prolongation of ventricular refractoriness in the traction zone. Conversely, in the nontraction-control zone, early activation did not occur and refractoriness was unchanged. Alterations in regional myocardial blood flow (assessed by microsphere technique) did not appear responsible for the observed changes. Furthermore, phenol interruption of local sympathetic or combined sympathetic and parasympathetic innervation or verapamil pretreatment had no impact on the mechanically induced electrophysiological changes. Thus, in normal myocardium in situ, regional abnormalities in wall motion may be associated with alterations of local ventricular activation and refractoriness, factors that in the diseased heart could lead to increased susceptibility to arrhythmias.

Animals↗
PubMed1988

Usefulness of transcutaneous triggering of conventional implanted pulse generators by an activity-sensing pacemaker for predicting effectiveness of rate response pacing.

A noninvasive procedure has been developed to assess effectiveness of activity-sensing rate response ventricular (VVIR) pacing systems in patients with implanted conventional fixed-rate ventricular (VVI) pacemakers capable of triggered mode operation (VVT). A VVIR pacemaker (activity threshold medium or low, rate response 6 to 10, upper rate 125 or 150 beats/min) was strapped to the chest wall (prepectoral area) of patients with previously implanted fixed-rate VVI pacemakers. In 17 of the 18 patients included in the study, the implanted pacemaker was capable of triggered mode operation (VVT). Triggering of the conventional pacemaker was achieved by reprogramming it to the VVT mode (high sensitivity, short refractory) and connecting the output of the "strapped-on" VVIR pacemaker (5 volts, 1.5-ms pulse width) to 2 standard cutaneous electrodes positioned so as to be in proximity to the implanted intracardiac electrode system. Patients underwent symptom-limited treadmill exercise tests during both VVI and VVIR pacing. Triggering conventional VVI pulse generators by a "strapped-on" VVIR pacing system proved feasible in 16 of 17 cases and improved overall heart rate response (fixed rate 86 +/- 22 vs VVIR 118 +/- 7 beats/min) and exercise duration (fixed rate 6.6 +/- 4.9 vs VVIR 10.1 +/- 4.8 minutes) (mean values for all patients studied during exercise testing). Triggering of a previously implanted permanent pacemaker by a strapped-on activity-triggered device may be useful to assess rate response pacing before implantation of a VVIR device in patients in whom elective pulse generator replacement is planned.

Adolescent↗
PubMed1988

Contribution of atrioventricular synchrony to left ventricular systolic function in a closed-chest canine model of complete heart block: implications for single-chamber rate-variable cardiac pacing.

This study assessed the impact of atrioventricular (AV) synchrony on characteristics of left ventricular (LV) systolic function during ventricular pacing over a wide heart rate range in a conscious closed-chest canine model of complete AV block. Ten healthy adult dogs underwent thoracotomy during which complete AV block was created by formaldehyde injection, and paired ultrasonic sonomicrometers were positioned on the LV anterior-posterior minor axis. Following recovery from surgery, peak and end-diastolic LV transmural pressure, maximum dP/dt, stroke work, end-diastolic minor axis dimension, and maximum velocity of shortening, were quantitated at heart rates of 80, 100, 120, 140, and 160 beats per minute (bpm) during both ventricular pacing alone and AV sequential pacing with increasing AV intervals (0, 50, 100, 150, 200, 250, and 300 ms). Over the heart rate range tested, parameters of LV systolic function did not differ significantly during ventricular pacing with or without AV synchrony. For example, during ventricular pacing alone maximum LV dP/dt varied from 2110 +/- 70 mmHg/s to 2463 +/- 567 mmHg/s, a range essentially identical to that observed in the presence of AV synchrony. On the other hand, although the impact on LV performance of varying AV interval from 0 to 300 ms was small, differences tended to become more pronounced at higher pacing rates. At 80 bpm, neither stroke work nor maximum LV dP/dt were affected by change in AV interval, while at heart rates greater than or equal to 120 bpm both stroke work and LV dP/dt tended to maximize at AV intervals of 50 and 100 ms and thereafter declined.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Success of re-use of cardiac electrode catheters.

The feasibility of cardiac electrode catheter re-use was prospectively evaluated over a 5-year period (1981 to 1986), during which time 178 catheters were used 1,526 times for 847 electrophysiologic procedures. Detailed records of catheter testing and use were maintained. No complications were encountered during the study period. All re-used catheters functioned for cardiac pacing and electrographic recording. Surveillance cultures and biologic indicators revealed that adequate sterilization procedures were used. Thus, electrode catheters may be safely re-used provided a thorough cleaning, testing and record-keeping system is instituted. This may result in lower patient cost (approximately $30 per re-use vs [200 per single use) for electrophysiologic catheterization.

Cardiac Catheterization↗
PubMed1987

Role of extrastimulus site and tachycardia cycle length in inducibility of atrial preexcitation by premature ventricular stimulation during reciprocating tachycardia.

Preexcitation of the atria during reciprocating tachycardia (RT) by a premature ventricular complex occurring when the His bundle is refractory provides direct evidence of the presence of accessory atrioventricular (AV) connection. The impact of ventricular stimulation site and RT cycle length on inducibility of atrial preexcitation was assessed in 38 patients with RT utilizing a single accessory AV connection (right free wall in 5 patients, left free wall in 21 and posterior septal/paraseptal in 12). Extrastimuli were inserted at right ventricular (RV) apical, left ventricular (LV) septal and LV free wall sites. Inducibility of and magnitude of atrial preexcitation increased as stimulation site approached accessory AV connection site. Thus, for RV free wall connections, RV extrastimuli preexcited the atria in 5 of 5 patients, LV septal in 1 of 5 and LV free wall in 0 of 4. For LV free wall accessory connections, RV extrastimuli preexcited the atria in only 3 of 21 patients, compared with 12 of 17 with LV septal and 20 of 21 with LV free wall stimulation. Additionally, the magnitude of atrial preexcitation achieved was related to RT cycle length, diminishing as cycle length shortened. Finally, in a few instances both RV apical and LV free wall extrastimuli failed to elicit preexcitation in patients with a posterior septal connection. Thus, ventricular pacing site and RT cycle length contribute importantly to induction of atrial preexcitation by ventricular extrastimulation technique and should be considered during evaluation of patients with RT in whom accessory AV connections may be present.

Adolescent↗
PubMed1987

Cardiac and skeletal muscle abnormalities in cardiomyopathy: comparison of patients with ventricular tachycardia or congestive heart failure.

Results of cardiac muscle and skeletal muscle biopsies were compared in 22 patients with cardiomyopathy; 11 patients presented with symptoms secondary to ventricular tachycardia (Group 1) and 11 had symptoms of severe congestive heart failure (Group 2). No patient had structural or ischemic cardiac disease. In Group 1 patients, hemodynamic abnormalities were subtle, but invasive study demonstrated dilated cardiomyopathy in two patients and restrictive cardiomyopathy in nine. In Group 2, eight patients had dilated cardiomyopathy and three had restrictive cardiomyopathy. Cardiac biopsy results were abnormal in all 22 patients and the abnormalities were similar for the two groups. Cardiac histologic study revealed a spectrum of abnormalities including fibrosis, dilated sarcoplasmic reticulum, increased numbers of intercalated discs and mitochondrial abnormalities. Histologic abnormalities of skeletal muscle were similar in each group, consisting of endomysial fibrosis and increased lipid deposits. Slightly more than half of the Group 1 and Group 2 patients also had a low concentration of skeletal muscle long chain acylcarnitine. These data demonstrate that abnormalities of both cardiac and skeletal muscle are common in patients with cardiomyopathy; abnormalities are similar whether initial symptoms are due to ventricular tachycardia or congestive heart failure. It is suggested that these patients with cardiomyopathy may have a generalized myopathy.

Adolescent↗