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Biomedical subjects

A D Sharma

Publications and source records attributed to A D Sharma.

At least 55 records · Page 3Linked to original sources
PubMed1989

Longitudinal electrophysiologic assessment of asymptomatic patients with the Wolff-Parkinson-White electrocardiographic pattern.

Although most asymptomatic patients with the Wolff-Parkinson-White electrocardiographic pattern have a good prognosis, some die suddenly. The mechanism of sudden death is usually ventricular fibrillation, which is triggered by atrial fibrillation with a rapid ventricular response rate. Electrophysiologic testing has been proposed to identify asymptomatic patients who may be at risk for sudden death. Meaningful application of such testing requires a knowledge of whether the electrophysiologic measurements are reproducible over time. Consequently, we performed electrophysiologic studies on two occasions at least 36 months apart (mean +/- SD, 54.7 +/- 14) in 29 asymptomatic patients with the pattern. Twenty-seven patients remained asymptomatic, and sustained supraventricular tachycardia developed in two during the follow-up period. Nine patients (31 percent) lost the capacity for preexcitation and anterograde conduction over the accessory pathway, which produces the Wolff-Parkinson-White pattern. The others had little change in measurements of conduction over the accessory pathway. Patients who lost conduction over the accessory pathway tended to be older (mean +/- SD, 50 +/- 18 vs. 39 +/- 11 years; P = 0.06) than patients who retained preexcitation, and they had longer anterograde effective refractory periods at the first assessment (414 +/- 158 vs. 295 +/- 27 msec; P = 0.003). We conclude that a considerable number of asymptomatic patients with the Wolff-Parkinson-White pattern lose their capacity for anterograde conduction over the accessory pathway. This loss of capacity probably contributes to the low mortality among asymptomatic patients.

Atrial Fibrillation↗
PubMed1989

Results of operative therapy in the permanent form of junctional reciprocating tachycardia.

To assess the results of operative therapy for permanent junctional reciprocating tachycardia, a type of incessant tachycardia, the clinical and electrophysiologic data of 8 such patients referred for management of tachycardia were reviewed. The duration of incessant tachycardia was 14 +/- 10 years (range 2 to 30). The heart rate at rest during tachycardia ranged from 120 to 150 beats/min. Four of 8 patients had cardiomegaly or depressed ejection fraction (16 +/- 10%, range 5 to 27) at presentation and, of these, 2 had symptoms of congestive heart failure. Exertional dyspnea despite normal left ventricular function was noted in 1 patient, 2 had chronic palpitations and 3 were asymptomatic. Electrophysiologic data confirmed the presence of a posteroseptal pathway with atrioventricular node-like properties conducting slowly in the retrograde direction only. Seven patients underwent successful surgical ablation of the accessory pathway. Hypothermic cardiopulmonary bypass was used in 2 and a closed heart technique without cardiopulmonary bypass in the other 5. Three of 4 patients with reduced left ventricular function showed an improvement in ejection fraction to 34 +/- 20% (range 16 to 63) after control of dysrhythmia. Three patients had no evidence of cardiomegaly despite equivalent periods of incessant tachycardia. Another patient with normal left ventricular function despite incessant tachycardia for over 30 years underwent spontaneous remission to sinus rhythm and did not undergo surgery. These data suggest that permanent junctional reciprocating tachycardia has a variable presentation and that congestive heart failure is not an infrequent presenting symptom. The substrate is invariably an accessory atrioventricular pathway with a long conduction time and decremental properties conducting only in the retrograde direction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Efficacy of empirical cardiac pacing in syncope of unknown cause.

Cardiac pacing is often considered in patients with recurrent syncope after repeated attempts to document the cause have failed. To assess the results of this tactic we reviewed the records of 104 patients who had received pacemakers for known or suspected bradycardia between September 1973 and March 1985. The patients were classified retrospectively into three groups: group 1 (31 patients with a mean age of 73 years) had unequivocal documentation of bradycardia during syncope, group 2 (42 patients with a mean age of 71 years) had electrocardiographic or electrophysiologic evidence of potential bradycardia but no documentation during spontaneous syncope, and group 3 (31 patients with a mean age of 69 years) had a history "suggestive of" bradycardia-related syncope but no other evidence to support the diagnosis. The rates of recurrence of syncope during follow-up were 6.3%, 7.3% and 32.2% in groups 1, 2 and 3 respectively (p less than 0.01). In group 3 recurrence was more probable in patients with loss of consciousness for more than 2 minutes than in those who were unconscious for 2 minutes or less (p less than 0.05). The results suggest that pacemaker implantation is justified for recurrent syncope after extensive attempts to document a spell have failed if abnormal diagnostic test results suggest bradycardia as a possible cause. Empirical pacing is less satisfactory in patients with normal results of evaluation but may arguably be justified when patients have recurrent syncope with injury.

Aged↗
PubMed1989

Usefulness of isoproterenol during atrial fibrillation in evaluation of asymptomatic Wolff-Parkinson-White pattern.

The asymptomatic individual with a Wolff-Parkinson-White (WPW) pattern is considered at risk for ventricular fibrillation if a rapid ventricular response (shortest RR interval less than or equal to 250 ms) is observed during induced atrial fibrillation (AF) in the laboratory. It has been suggested that isoproterenol administration during AF may more accurately define the patient at risk. Consequently, the effect of isoproterenol on ventricular response during AF was studied in 21 asymptomatic individuals with WPW pattern to assess the potential of isoproterenol to identify patients at risk for sudden death. An electrophysiologic study that included elective induction of AF was performed. The shortest and mean RR intervals between 2 consecutive preexcited and normal QRS complexes, the average RR interval and the proportion of preexcited QRS complexes were measured in the control state and after bolus injections of isoproterenol (0.5, 1.0, 2.0 and 4.0 micrograms) during AF. Both atrioventricular nodal and accessory pathway conductions were enhanced proportional to isoproterenol dose. Isoproterenol had a greater effect on the atrioventricular node, as reflected by significantly greater changes in the shortest RR between normal complexes (339 +/- 70 vs 255 +/- 21 ms, mean +/- standard deviation, p less than 0.001) than the shortest RR between preexcited complexes (264 +/- 39 vs 219 +/- 34 ms, p less than 0.001) and a decrease in percentage of preexcited complexes (65 +/- 37 vs 50 +/- 33%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Acute effect of disopyramide on atrial fibrillation in the Wolff-Parkinson-White syndrome.

Disopyramide was administered intravenously to 54 patients during atrial fibrillation and predominantly pre-excited QRS configuration at the time of electrophysiologic study. All patients had Wolff-Parkinson-White syndrome and no patient had coexistent heart disease. The drug was given during sustained atrial fibrillation (n = 45) or during sinus rhythm before induction of atrial fibrillation for patients whose atrial fibrillation was self-terminating in the control state (n = 9). Atrial fibrillation converted to sinus rhythm within 15 min after disopyramide in 37 (82%) of the 45 patients. The shortest RR intervals between two pre-excited cycles increased from 208 +/- 42 to 293 +/- 117 ms (p less than 0.0001). The average RR interval of all cycles prolonged from 332 +/- 60 to 396 +/- 117 ms(n = 45, p less than 0.0001). The 9 patients in whom pre-excitation was abolished after the drug had a significantly longer initial shortest RR interval than that of the 36 patients in whom pre-excitation persisted (246 +/- 47 versus 199 +/- 36 ms, p = 0.0022). No patients developed significant hemodynamic or other adverse effects after disopyramide. These data support the intravenous use of disopyramide in patients with normal ventricular function who have atrial fibrillation and a predominant ventricular response over an accessory atrioventricular pathway.

Adolescent↗
PubMed1989

Surgical therapy for arrhythmogenic right ventricular adiposis.

Arrhythmogenic right ventricular adiposis, formerly dysplasia, was identified when the first patients underwent map-guided surgery for treatment of their ventricular tachycardia. We report our experience with 12 patients operated on using a conservative approach between 1973 and 1981 (Paris). Subsequently, we used a more comprehensive approach in five patients (London, Canada); the right ventricular free wall disconnection was used to confine all potential right ventricular tachycardias within the excluded right ventricular wall.

Adipose Tissue↗
PubMed1989

Cross-talk in bipolar pacemakers.

Investigation of dual chamber pacing and sensing interactions at high rates is becoming increasingly important with the advent of sensor driven dual chamber pacemakers. The present study was designed to investigate the pacemaker and lead interactions that will affect cross-talk during high rate atrial and ventricular pacing. The study was divided into two phases, phase one investigated the mechanisms of cross-talk using standard pacemaker circuitry and various electrode types in a canine model. In six dogs with complete heart block, dual chamber pacing was carried out with four lead types at increasing pacing rates, while output of the ventricular sense amplifier of a pacemaker breadboard was monitored. Ventricular sense amplifier output signals (n = 332) progressively increased from 31.5 +/- 18.3 mV at 100 ppm to 102 +/- 55 mV at 160 ppm. Smooth platinum-iridium and platinized leads were statistically different at higher pacing rates (P less than 0.05). This signal level is sufficient to lead to a ventricular sensing event. In a second phase of the study, the incidence of cross-talk at high pacing rates was studied in patients with implantable dual chamber bipolar pacemakers. In 166 clinical trials on 106 patients with the same pacemaker, there was evidence of cross-talk in 1/59 cases at 110 ppm and 3/47 at 130 ppm, but none at higher rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Localization of accessory pathways in the Wolff-Parkinson-White syndrome.

Operative and ablative therapy in the Wolff-Parkinson-White syndrome requires accurate localization of accessory atrioventricular pathways. A reasonable first approximation to pathway location can be obtained by noninvasive techniques, the 12-lead electrocardiogram being the most readily available of these. Accurate characterization of the number and anatomic localization of accessory pathways still requires invasive electrophysiological assessment. The most useful technique for accessory pathway localization remains endocardial atrial mapping of the tricuspid and mitral (via the coronary sinus) ring during atrioventricular reciprocating tachycardia and ventricular pacing. Other techniques provide important confirmatory evidence and may be the only guides to accessory pathway location in selected individuals.

Algorithms↗
PubMed1989

Sequential pulse countershock between two transvenous catheters: feasibility, safety, and efficacy.

We evaluated the feasibility, safety, and efficacy of sequential pulse countershock (SqCS) delivered solely through two endocardial catheters for the termination of ventricular tachycardia (VT) and fibrillation (VF) in patients undergoing electrophysiology studies (EPS). Thirty-four patients (31 men, 3 women) with a mean age of 56.8 +/- 10.1 years were studied. Etiology of VT/VF was ischemic heart disease (n = 26), cardiomyopathy (4) repaired tetralogy of Fallot (n = 1), heart transplant (n = 1), and no identifiable heart disease (n = 2). Catheters were positioned successfully in 29 patients. These were positioned in the right ventricular apex (RVA) and the coronary sinus (CS), respectively. The RVA electrode served as the common cathode for both pulses. The two electrodes located near the right atrium/superior vena cava junction served as anode for pulse 1 while the distal CS electrodes served as anode for pulse 2. Twenty-nine induced VT episodes with cycle length (CL) 220-370 msec were treated. SqCS successfully terminated 15 VT (100-500V) while 14 were accelerated or degenerated to VF. VTCL was longer in successful SqCS episodes than in those that were accelerated (285 +/- 17.3 vs 245 +/- 30.8 msec, P less than .003). Of 26 VF episodes, 21 were terminated with SqCS (500-900V) and 5 were terminated by transthoracic rescue shocks. On 2 occasions, failure to defibrillate was attributable to poor catheter position at the time of shock. No complications occurred. We conclude that SqCS delivered solely between endocardial catheter electrodes is feasible and effective using energy doses within the range of existing implantable cardioverter defibrillators.

Adult↗
PubMed1989

The protective effect of vagus nerve stimulation on catecholamine-halothane-induced ventricular fibrillation in dogs.

Parasympathetic neural activity modulates some ventricular arrhythmias in man. Therefore, a canine model of arrhythmias produced by the interaction of halothane and catecholamines was used to study the effects of vagal stimulation on the induction of ventricular fibrillation. The dose of catecholamine required to induce ventricular fibrillation was determined during a constant heart rate. Vagal stimulation reversibly raised the norepinephrine dose that produced ventricular fibrillation from 16.4 +/- 2.4 to 30.0 +/- 3.8 micrograms (p less than 0.001, n = 10), and the epinephrine dose from 15.5 +/- 2.0 to 22.5 +/- 2.6 micrograms (p less than 0.001, n = 5). Following atropine, vagal stimulation failed to raise the threshold dose of norepinephrine (16.8 +/- 2.4 vs. 18.3 +/- 3.3 micrograms, nonsignificant, n = 6) or epinephrine (15.5 +/- 2.0 vs. 16.0 +/- 2.3 micrograms, nonsignificant, n = 5). Ligation of the cervical vagus nerves did not affect the epinephrine threshold dose (16.3 +/- 3.3 vs. 17.5 +/- 2.7 micrograms, nonsignificant, n = 5). Following elevation of basal vagal tone by morphine premedication, the norepinephrine threshold of 53.0 +/- 9.2 micrograms declined by a nonsignificant amount to 46.5 +/- 11.5 micrograms after vagotomy (nonsignificant, n = 5). Thus resting vagal tone does not prevent catecholamine-halothane-induced ventricular fibrillation, whereas increasing vagal tone by electrical stimulation substantially protects against this arrhythmia. The protection is mediated through a muscarinic cholinergic receptor.

Animals↗
PubMed1989

Atrioventricular nodal tachycardia in the absence of retrograde conduction.

A patient with atrioventricular (AV) nodal reentrant tachycardia assessed by electrocardiographic and electrophysiological criteria is described. During ventricular pacing, retrograde conduction was absent at the longest cycle length tested with the site of block determined to be the AV node by concealed conduction criteria. These findings localize the tachycardia circuit above the His bundle and exclude a His-atrial bypass tract as the retrograde limb of the tachycardia circuit in this patient.

Adult↗
PubMed1988

The coronary sinus diverticulum: a pathologic entity associated with the Wolff-Parkinson-White syndrome.

Of 65 patients with posterior septal accessory pathways, 6 were found intraoperatively to have a previously unrecognized pathologic entity: a coronary sinus (CS) diverticulum in the posterior septal region. The CS diverticulum is a venous pouch within the left ventricular wall, with a neck opening into the CS. The pouch, 2 to 5 cm in diameter, has a deep wall corresponding to the left ventricular wall, with venous channel openings and a thin superficial wall made of myocardium. The CS diverticulum neck is 5 to 10-mm wide, opens into the CS and is proximal to the midcardiac vein. Using an epicardial approach during normothermic bypass, the neck of the CS diverticulum was identified, separated from the left ventricle and then closed. Accessory pathway conduction disappeared only after separation of the CS diverticulum neck. The accessory pathway is intimately related to the diverticulum. The latter is a bridge between the left ventricle and the right or left atrium. The accessory pathways associated with CS diverticula had short anterograde refractory periods and were associated with potentially malignant arrhythmias. An epicardial operative approach with division of the neck of the diverticulum is recommended when surgery is indicated.

Adult↗
PubMed1988

Elevation of serum total cholesterol and triglyceride levels during amiodarone therapy.

Over the last decade there has been increasing awareness that some cardiovascular medications may adversely affect serum cholesterol concentrations. It has been suggested previously that amiodarone may alter serum cholesterol, triglyceride and glucose concentrations, but no substantive data support this observation. During the course of a 1-year study of adverse effects in patients taking amiodarone, 21 patients with normal total serum cholesterol before entry in the study were prospectively investigated for changes in lipid metabolism. A statistically significant sustained rise of 17% in total serum cholesterol occurred from a baseline of 178 +/- 7 mg/dl (4.6 +/- 0.2 mmol/liter) to 208 +/- 9 mg/dl (5.4 +/- 0.2 mmol/liter). Ten of the patients developed elevations of cholesterol above the 75th percentile for their age and sex. This group experienced a sustained rise of 20% in mean cholesterol concentration from baseline, had statistically significant elevations of triglyceride concentrations and had higher glucose and desethylamiodarone concentrations than patients who did not develop elevations in cholesterol greater than the 75th percentile. It may be possible to predict these differences in response as early as 4 to 8 weeks after starting therapy. Because amiodarone is increasingly used in patients without ischemic heart disease or life-threatening arrhythmias, the potential atherogenic risk of these metabolic abnormalities merits further investigation.

Amiodarone↗
PubMed1988

Comparative quantitative electrophysiologic effects of adenosine triphosphate on the sinus node and atrioventricular node.

A pharmacologic approach was used to characterize the sinus node (SN) and atrioventricular (AV) node responses to intravenous adenosine triphosphate (ATP) in 21 patients during electrophysiologic testing. ATP produced dose-dependent prolongation of spontaneous sinus cycle length. The mean maximal increase in sinus cycle length was 294 +/- 60 ms (n = 10). The mean dose of ATP required to produce this maximal sinus cycle length prolongation was 3.5 +/- 1.0 mg. The dose-response curve for sinus cycle length prolongation was sigmoid in shape with an EC50 of 0.39 mg derived from a median effect plot. There was a negative correlation between the control sinus cycle length and the dose of ATP required to produce the maximal prolongation of cycle length (p less than 0.05). In contrast, the mean dose of ATP producing AV block was 4.4 +/- 0.97 mg and the EC50 was 2.98 mg. There was a positive correlation between the AV nodal functional refractory period and the prolongation of the AH interval with a 2 mg dose (p less than 0.05). Consistent with the AV nodal dose-response curves, 8 mg ATP terminated paroxysmal reentrant supraventricular tachycardia at the AV node in 8 of 9 patients. Thus, SN and AV node responses to ATP have differences in their electrophysiologic correlates and EC50. These findings suggest that ATP has potentially different mechanisms of action on SN automaticity and AV nodal conduction that requires further investigation.

Adenosine Triphosphate↗
PubMed1988

An approach to therapy for paroxysmal supraventricular tachycardia.

A variety of options are available for managing recurrent paroxysmal supraventricular tachycardia. These options include empirical drug therapy on a trial and error basis, drug therapy based on the results of electrophysiologic testing and nonpharmacologic treatment including operative therapy, catheter ablation and antitachycardia devices. Empirical drug therapy is appropriate when the tachycardia is relatively well tolerated and the patient has access to a medical facility. Therapy guided by electrophysiologic testing is more appropriate for patients with severe symptoms during tachycardia, patients with a potential for more serious arrhythmias such as atrial fibrillation in the Wolff-Parkinson-White syndrome and in patients who have failed to respond to empirical trials of drug therapy. Electrophysiologic testing usually provides information about the precise mechanism responsible for the tachycardia and allows verification of drug efficacy. It is a strict prerequisite for operative, ablative or antitachycardia device therapy. The choice of therapy depends a great deal on local expertise, patient preference and individual considerations. Operative therapy is very successful in patients with supraventricular tachycardia associated with the Wolff-Parkinson-White syndrome and should be given high priority as an option in younger patients facing a lifelong commitment to antiarrhythmic drugs.

Cardiac Pacing, Artificial↗
PubMed1988

Comparative effects of adenosine triphosphate on accessory pathway and atrioventricular nodal conduction.

Adenosine triphosphate (ATP) has potent negative dromotropic effects on the atrioventricular (AV) node, but variable effects on accessory pathway conduction have been described. The effects of an intravenous bolus injection of 8 mg ATP on accessory pathway and AV nodal conduction were determined during electrophysiologic testing with controlled atrial and ventricular rates. AV conduction was monitored during atrial or ventricular pacing at a constant cycle length, 30 msec longer than the cycle length at which block occurred. During atrial pacing antegrade block after administration of ATP occurred in 1 of 30 (3.2%) patients with accessory pathway conduction and 12 of 13 (92%) patients with AV nodal conduction (p less than 0.001). During ventricular pacing only 5 of 26 (16%) patients had accessory pathways blocked, whereas 25 of 35 (71%) patients with AV nodal conduction had block (p less than 0.001). Thus, failure of ATP to produce ventriculoatrial block identified the presence of an accessory pathway with a sensitivity of 84%, specificity of 71%, and predictive value of 72%. There was no correlation between accessory pathway properties and the effects of ATP. The effects of ATP on the AV node were concordant with the effects of a combination of verapamil and propranolol in 21 of 23 patients, suggesting that this dose ATP is an equipotent AV nodal blocker with a short duration of action. Thus, although the effects of ATP on accessory pathways and the AV node differ, block in ventriculoatrial conduction after administration of ATP cannot be used as the sole criterion to distinguish the mechanism of conduction.

Adenosine Triphosphate↗