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SUMMARY The role of simultaneous and sequential atrioventricular (AV) stimulation in prevention of tachyeardia induction, and the underlying electrophysiologic mechanisms involved, were studied in 10 patients with documented paroxysmal reentrant supraventricular tachycardia (PSVT). Reentry circuit was localized to the AV node in seven of 10. The remaining three cases had Wolff-Parkinson-White (WPW) syndrome patients with recurrent PSVT, seven of whom had reentry localized to the AV node, while the other three cases had reentry circuit involving an accessory pathway of the Kent bundle type. We present initial observations in these patients and discuss the possible electrophysiologic mechanisms. In addition, clinical implications of the electrophysiologic findings in these patients are discussed. Materials and MethodsElectrophysiologic studies were performed in a postabsorptive, nonsedated state. The nature of the procedure was explained to all patients and signed consents were obtained. Quadripolar electrode catheters were percutaneously introduced into peripheral veins, fluoroscopically guided and positioned in the region of the tricuspid valve, high right atrium (HRA), coronary sinus and right ventricle. The catheters were used for local intracardiac electrogram recordings and/or stimulation using techniques previously described.'8 All intracardiac electrograms, surface ECG leads I, II, V, and time lines were simultaneously displayed on a multichannel oscilloscope and recorded on an FM tape recorder. The records were subsequently retrieved for analysis on a paper at a speed of 100-250 mm/sec. The intracardiac stimulation was performed with a digital stimulator capable of delivering rectangular impulses of 10-V amplitude and < 2-msec duration. During these studies patients were isolated and all electrical equipment was grounded to a common point free of any ground loops.

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The purpose of this investigation was to compare data on early exercise testing for variables known to be of diagnostic/prognostic value following myocardial infarction in post-myocardial revascularization surgery patients. 70 patients were evaluated soon after surgery, by cardiac catheterization, moderate-intensity treadmill exercise testing, and rest and exercise radionuclide angiography. The results indicated no significant differences among groups with satisfactory and unsatisfactory results by catheterization compared for METs, peak heart rate, double product, ST-segment change, angina pectoris, and dysrhythmias. Significant differences were found among groups when rest and exercise ejection fraction and exercise-induced regional wall motion abnormality were taken into account. It was concluded that the moderate-intensity treadmill exercise test was ineffective in differentiating current cardiac function and arterial/graft status among postmyocardial revascularization surgery patients. Exercise radionuclide angiographyc studies were able to identify groups of patients with adequate or inadequate postoperative cardiac catheterization results.

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