The American journal of cardiology
-
In an attempt to prevent recurrent reentrant supraventricular tachycardia, an experimentally designed new pacemaker has been developed. The pacemaker, when connected to both atrial and ventricular electrodes, is capable of sensing either an atrial or ventricular signal and, in turn, triggers simultaneous atrioventricular A-V) stimulation. ⋯ Consequently, the reentrant tachycardia zone was completely abolished in all patients. This study has thus demonstrated the clinical feasibility of simultaneous A-V pacing to abolish the supraventricular tachycardia zone in man.
-
The hemodynamic effects of the cardioselective beta adrenergic blocking agent metoprolol, at a dose of 0.1 mg/kg body weight administered intravenously, were studied in 10 patients undergoing routine cardiac catheterization. The beta adrenergic blocking effect of the drug was confirmed by a highly significant reduction (53 percent, P less than 0.001) in the mean heart rate response to a challenge with isoproterenol, and by a mean heart rate rssponse to a challenge with isoproterenol, and by a highly significant reduction (73 percent, P less than 0.001) in the isoproterenol-induced increase in the first derivative of left ventricular pressure (dP/dt). An intrinsic negative inotropic effect was shown by a 43 percent reduction (P less than 0.05) in the response of mean left ventricular dP/dt when the heart rate was fixed by atrial pacing alone. ⋯ There was no significant change in right atrial, femoral arterial or left ventricular end-diastolic pressure; analysis of left ventricular angiograms performed during atrial pacing before and after metoprolol revealed no significant effect on angiographic ejection fraction, pressure-volume loops or diastolic compliance. In two patients improvement in segmental wall motion was noted, and no deterioration was seen in any patient. Metoprolol is an effective cardioselective beta adrenergic blocking agent that, under these conditions, reduces catecholamine-induced increases in heart rate and left ventricular dP/dt without significant alteration in ejection fraction, preload or afterload.
-
Mitral valve replacement is considered when there is severe mitral stenosis, severe mitral insufficiency or a combination of the two. Ordinarily, surgical replacement is considered only for patients who are in functional classes III or IV and do not respond to medical management. Patients with symptomatic mitral stenosis should be treated with mitral commissurotomy whenever possible. ⋯ In infective endocarditis, operation is more often needed because of congestive heart failure than because of refractory infection. Evidence of mitral stenosis or insufficiency in a patient with a previously implanted prosthetic valve usually indicates an urgent need for study and early operation. Uncommon causes of mitral incompetence that may require valve replacement are endocardial fibroelastosis, Marfan's syndrome, calcified mitral anulus, osteogenesis imperfecta, methysergide-induced heart disease and carcinoid heart disease.
-
Case Reports
Paroxysmal nonreentrant tachycardias due to simultaneous conduction in dual atrioventricular nodal pathways.
Electrophysiologic studies were performed in a 41 year old man for analysis of paroxysmal tachycardias appearing in various electrocardiographic patterns of supraventricular and ventricular bigeminy, junctional and ventricular tachycardia and atrial fibrillation, among others. All these arrhythmias were due to dual atrioventricular (A-V) nodal pathways with simultaneous dual fast and slow conduction of single atrial beats at a normal basic sinus rate. Moderate changes in sinus rate and in fast or slow pathway conduction times, or both, changed the position of the slowly conducted beats between the neighboring two fast conducted beats and resulted in various electrocardiographic manifestations of the conduction disturbance. ⋯ After intravenous injection of 25 mg of ajmaline, unexpected lengthening and shortening of the A-H interval occurred, suggesting variable shifts between fast and slow pathway conduction. The incidence of dual A-V nodal pathways is discussed; it was documented in 17 (4.2 percent) of 405 patients studied. A theoretical model of A-V nodal conduction is proposed to explain its normal properties and abnormal patterns.