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Biomedical subjects

M M Scheinman

Publications and source records attributed to M M Scheinman.

At least 271 records · Page 15Linked to original sources
PubMed1979

Electrophysiologic effects of disopyramide phosphate on sinus node function in patients with sinus node dysfunction.

The electrophysiologic effects of intravenously administered disopyramide (2 mg/kg) on three parameters of sinus node function were examined in 16 symptomatic patients with sinus node dysfunction. Based on their ECG data before study, patients were subdivided into group A (n = 8), those with sinus pauses and/or sinoatrial (SA) exit block; and group B (n = 8), those with sinus bradycardia. Disopyramide shortened spontaneous cycle length in 10 of 16 patients and lengthened it in six--markedly so (91%) in one patient. Estimated SA conduction time decreased in seven of 14 patients and increased in seven. Two patients developed second degree SA exit block after disopyramide. Maximum sinus node recovery time was prolonged by disopyramide in 11 of 16 patients and markedly so in four. For the group as a whole there was no significant difference in spontaneous cycle length, maximum sinus node recovery time or estimated SA conduction time. P-wave and QRS durations and H-V intervals were significantly lengthened by disopyramide. Marked depression of the three parameters of sinus node function occurred in three group A patients and in one group B patient who had persistent severe sinus bradycardia. These four patients also had secondary pauses after termination of rapid atrial pacing under control conditions. Disopyramide should be administered cautiously to patients with sinus node dysfunction, particularly those with sinus pauses, SA exit block or secondary pauses.

Adult↗
PubMed1979

Determination of His-Purkinje refractoriness in man with His bundle pacing.

Consistent His bundle pacing was accomplished in one of 60 consecutive patients. Intracardiac electrophysiologic studies in this patient revealed rapid atrioventricular nodal conduction (AH = 55 msec). While the relative refractory period of the His-Purkinje system as a whole determined by His bundle pacing (using the extrastimulus technique) was identical to that determined by atrial pacing, changes in right bundle branch refractoriness differed. An atrial extrasystolic interval of 370 msec resulted in right bundle branch block, whereas direct His pacing at a shorter extrasystolic interval (360 msec) failed to produce a bundle branch block pattern. The effective refractory period of the His-Purkinje system could not be determined by atrial pacing because of atrial refractoriness, but was obtained by His bundle pacing. Theoretically, direct His bundle pacing may be of value in determining His-Purkinje system refractoriness when this parameter is unobtainable due to either atrial or atrioventricular nodal refractoriness. This technique appears to have limited clinical usefulness, however, because of the very small success rates. Finally, His-Purkinje system refractoriness may differ, depending on site of stimulation, presumably due to differing inputs into the His-Purkinje system.

Adult↗
PubMed1978

Clinical and electrophysiologic findings in patients with paroxysmal slowing of the sinus rate and apparent Mobitz type II atrioventricular block.

Over five years, 13 patients with episodic apparent type II atrioventricular (AV) block associated with sinus slowing were seen. This phenomenon occurred only transiently during an acute illness in eight patients (group I) but recurred chronically in five (groupII). For the group as a whole, the mean spontaneous cycle length was 42% longer during the period of AV block compared with periods of 1:1 AV conduction (800 +/- 116 msec to 1138 +/- 489 msec) (P less than 0.05). Electrophysiologic studies in four group I patients showed no abnormalities, whereas abnormalities in AV nodal conduction and refractoriness or provocation of intranodal Mobitz type II AV block (during carotid massage) were observed in three patients in group II and were totally abolished by atropine. In group I patients, apparent type II AV block was self-limited. In the chronic group, recurrent symptoms required insertion of permanent pacemakers in two patients. Simultaneous type II block and sinus slowing appeared to be related to the effects of increased vagal tone on both nodal structures. Intracardiac pacing is not indicated for patients with transient episodes associated with an acute illness, but may be required for symptomatic patients with recurrent episodes.

Adult↗
PubMed1978

The clinical significance of bundle branch block complicating acute myocardial infarction. 1. Clinical characteristics, hospital mortality, and one-year follow-up.

To provide an understanding of the clinical characteristics of patients with acute myocardial infarction (MI) and bundle branch block, experience from five centers was accumulated. Patients in whom bundle branch block first appeared after the onset of cardiogenic shock were excluded. In 432 patients, the most common types of block were left (38%) and right with left anterior fascicular block (34%). In 42% of the patients, bundle branch block was new. Progression to high degree (second or third degree) atrioventricular (AV) block via a Type II pattern occurred in 22% of the patients. Hospital and first year follow-up mortality rates were 28% and 28%, respectively. Only 46% of the patients developed pulmonary edema or shock (Killip Class III or IV), and hospital mortality was related to the amount of heart failure (8%, 7%, 27%, 83% for Killip Classes I-IV, respectively). Patients with progression to second degree or third degree AV block via a Type II pattern had increased hospital mortality compared with patients without this complication (47% vs 23%, P less than 0.001). In the absence of pulmonary edema or shock, patients with Type II second degree or third degree AV block still had a higher mortality rate than patients without advanced AV block (31% vs 2%, P less than 0.005), with nearly all the deaths due to abrupt development of AV block. Thus, in many patients MI with bundle branch block is associated with severe heart failure. However, this was not true for a majority of the patients, in whom therapy aimed at preventing morbidity and mortality due to the bradyarrhythmia of advanced AV block might be beneficial.

Acute Disease↗
PubMed1978

The clinical significance of bundle branch block complicating acute myocardial infarction. 2. Indications for temporary and permanent pacemaker insertion.

The indication for prophylactic temporary and permanent pacing during acute myocardial infarction (MI) complicated by bundle branch block is high risk of progression via a Type II pattern to second or third degree (high degree) AV block during hospitalization or follow-up. In this study, determinants of high degree AV block during hospitalization and sudden death or recurrent high degree block during the first year of follow-up were examined in 432 patients with MI and bundle branch block. Timing of onset of bundle branch block, the involved fascicles, and the PR interval were examined as determinants of risk of progression to high degree AV block during MI. At highest risk were 186 patients with blocks involving the right bundle and at least one fascicle of the left bundle which were not documented on prior electrocardiograms. Risk was similar with (38%) or without (31%) accompanying first degree AV block. Patients with transient high degree AV block during MI had a 28% incidence of sudden death or recurrent high degree block during the first year of follow-up. Patients not continuously paced had a higher incidence of sudden death or recurrent high degree block than patients continuously paced (65% vs 10%, P less than 0.001). Sudden death during follow-up also occurred in 13% of patients without high degree block during MI. A subgroup with 1) documented prior MI, 2) anterior or indeterminant acute MI, and 3) no symptoms of cardiac failure had a 35% risk of sudden death. The role of permanent pacing in this group is unknown. Thus, patients at high risk of high degree AV block should receive prophylactic temporary pacing. Patients who survive high degree block with MI should receive temporary and then permanent pacing. Patients without high degree AV block during MI who nervertheless have a high risk of sudden death may benefit from permanent pacing.

Adult↗
PubMed1978

Effect of therapy with methylprednisolone on the size of myocardial infarcts in man.

The use of steroids to decrease the size of the infarct and the mortality in patients with acute myocardial infarction has long been the subject of controversy. In the present study, two large doses of methylprednisolone were administered intravenously to 14 patients with relatively uncomplicated myocardial infarction within 17 hours after the onset of symptoms, whereas a comparable group of 15 patients with myocardial infarction served as controls. The size of the infarct was assessed utilizing serial measurements of serum levels of creatine phosphokinase and its myocardial isoenzyme, the MB form of creatine phosphokinase. There was no significant difference between the two groups of patients with regard to peak cumulative levels of total creatine phosphokinase and the MB form of creatine phosphokinase. Similarly, there was no difference between the two groups in mortality or in the incidence of malignant ventricular arrhythmias, atrioventricular block, congestive heart failure, or extensions of the infarct. We conclude that high intravenous doses of steroids given early in the course of myocardial infarction have neither deleterious nor beneficial effects.

Adrenal Cortex Hormones↗
PubMed1978

Radiofrequency-triggered pacemakers: uses and limitations. A long-term study.

Seven patients with either recurrent paroxysmal supraventricular tachycardia (five), alternatinng bradycardiatachycardia (one), or ventricular tachycardia (one) underwent insertion of permanent radiofrequency-triggered pacemakers. Follow-up evaluation (36 +/- 24 months, mean +/- SD) revealed that arrhythmias were well controlled in five of seven patients, although three of the five required medication to decrease frequency of arrhythmias. Overdrive pacing was ineffective in one patient with Wolff-Parkinson-White syndrome who had recurrent bouts of atrial fibrillation or atrial flutter. One additional patient with ventricular tachycardia became refractory to overdrive atrial pacing. These studies document the long-term effectiveness of radiofrequency pacemakers in some patients with recurrent refractory arrhythmias. Careful patient selection and electrophysiologic studies are mandatory before implantation of a permanent radiofrequency pacemaker. Physicians must be aware of both the benefits and possible limitations of radiofrequency pacemakers in order to choose between pacemaker versus surgical intervention in patients with cardiac arrhythmias refractory to standard drug therapy.

Adult↗
PubMed1978

Electrophysiologic testing in patients with sinus pauses and/or sinoatrial exit block.

28 symptomatic patients with documented episodes of sinus pauses and/or sinoatrial exit block underwent electrophysiologic study. Abnormal responses to electrophysiologic testing were observed in 23/28 patients (82%). Abnormal prolongation of the maximum sinus node recovery time (SNRT max) occurred in 17/28 (61%) patients, of postpacing cycles 2.10 (secondary pauses) occurred in 21/28 (75%), and of estimated sinoatrial conduction time occured in 15/28 (54%). The incidence of abnormal responses to rapid atrial pacing (prolonged SNRT max or secondary pauses) (22/28, 79%) was higher than the incidence of abnormal responses to premature atrial stimulation (15/28, 54%) (P less than 0.005). Life-threatening cardiac arrhythmias were observed, prior to electrophysiologic study, in 5 out of 28 (18%) patients. Symptomatic patients with sinus pauses and/or sinoatrial exit block frequently (23/28, 82%) showed abnormal responses to electrophysiologic testing and have a relatively high incidence of life-threatening arrhythmias.

Adult↗
PubMed1977

Graded exercise testing in patients with sinus node dysfunction.

Serial measurements of heart rate and oxygen uptake were obtained before and during maximal upright graded bicycle stress testing in 16 patients, 10 to 77 years old (mean 46 years), with sinus node dysfunction; five had permanent and two had temporary demand ventricular pacemakers. In 15 patients, including those with pacemakers, maximal exercise was performed before and after the intravenous administration of 1 mg atropine. Maximal exercise was terminated because of cerebral symptoms in seven (three had effort-induced tachyarrhythmias and one had autonomic insufficiency), fatigue in five (one had effort-induced heart block), heart failure in three and angina pectoris in one. With maximal exercise, patients with sinus node dysfunction were unable to obtain maximal heart rates or oxygen uptakes comparable to age- and sex-matched control subjects. Additionally, maximal oxygen uptake did not differ significantly between patients with or without pacemakers even when ventricular pacing rates were increased (two instances). The administration of atropine increased the resting heart rate, but the maximal heart rate and oxygen uptake achieved during maximal exercise did not differ significantly from those obtained before the administration of atropine in the patient and control groups. Physically active patients with sinus node dysfunction have diminished exercise capacity due in part to cardiac arrhythmia, latent or overt cardiac failure, or autonomic dysfunction.

Adolescent↗
PubMed1977

Clinical and electrophysiological effects of intravenous quinidine in man.

Quinidine gluconate (total dose 4-4 to 9-1 mg/kg) was infused intravenously over 22 minutes in 20 patients with either frequent premature ventricular contractions or supraventricular arrhythmias, 16 of whom had bundle-branch block. Therapeutic plasma quinidine levels (3 to 7 mg/l) were achieved in 15. Heart rate, atrioventricular nodal, and infranodal conduction times did not change significantly. The QRS duration increased significantly from 128+/-30 to 134+/-29 ms at peak plasma quinidine levels (P less than 0.01). Mild hypotension occurred during infusion in most patients. Two patients had a severe but transient toxic response characterised by hypotension, nausea, vomiting, and diaphoresis. Atrioventricular dissociation with escape His bundle or fascicular rhythm occurred in 1 patient with sinus bradycardia. Bundle-branch block does not contraindicate administration of quinidine. Quinidine gluconate administered intravenously (0-3 to 0-4 mg/kg per min) is frequently associated with hypotenstion and should be used only in an intensive care setting and with careful monitoring of blood pressure.

Arrhythmias, Cardiac↗
PubMed1977

Prognostic value of infranodal conduction time in patients with chronic bundle branch block.

His bundle recordings were obtained in 121 patients with chronic bundle branch block and the patients were followed for a mean period of 18 months. Seventy-nine patients had an infranodal conduction time (H-Q) less than 70 msec while 42 had H-Q greater than or equal to 70 msec. There was no significant difference in mean age, smoking history, diabetes, syncope, dizziness, blood pressure, and serum cholesterol or triglyceride levels between the two groups. There was a significantly greater incidence of progresssion to second degree or third degree atrioventricular block (9/42, 21%), and of severe congestive heart failure (16/42, 38%) in patients with H-Q greater than or equal to 70 compared with those with H-Q less than 70 (1/79, 1.3%; and 13/79, 16%, respectively). The risk of sudden death was significantly greater only in the group with H-Q greater than or equal to 70 and severe congestive heart failure. There was no correlation between the presence of first degree atrioventricular block and/or any particular type of bundle branch block pattern with sudden death and/or progression to second degree or third degree atrioventricular block. Analysis of the surface electrocardiogram is only of limited value in predicting high risk patients with chronic bundle branch block. Electrophysiologic studies are of greatest value in patients with bundle branch block with transient neurologic symptoms in whom no cause for the symptoms is evident.

Bundle-Branch Block↗