No abstract

The acute and long-term hemodynamic benefit from atrial synchronization in ventricular (VAT) pacing has been investigated at rest and during exercise in 10 patients undergoing pacemaker implantation for complete A-V block. The results were compared to conventional (VOO) ventricular stimulation at rates of 70 BPM and 96 BPM. Cardiac index (CI) in VAT-pacing increased at rest by 8% and during exercise by 15% more than with VOO pacing (p less than 0.01). No significant change between the two different rates of asynchronous pacing was observed. CI at rest and during exercise was unchanged after 10 weeks of VAT-pacing. CI is regulated by change of stroke volume in VOO-pacing and by heart rate only with VAT-pacing. In contrast to earlier results with asynchronous ventricular pacing, the hemodynamic benefit of pacing in an atrial synchronized mode is long-lasting. Physiologic mechanisms regulate hemodynamics during exercise and in heart failure.

No abstract

AUTHORS' SYNOPSIS. Total heart block was produced in dogs without thoracotomy by means of a formaldehyde injection into the bundle of His. The method was successful in 22 out of 24 experiments. It is a useful model for haemodynamic studies in the intact animal.Experimental atrioventricular (AV) block in dogs is a versatile research model and numerous methods for its production have been devised. With only two exceptions (Williams and Lambert, 1964;Fisher, Lee, Christianson, and Kavaler, 1966) all these methods use thoracotomy, with or without atriotomy, as the operative approach. Thoracotomy, however, produces important cardiovascular changes, for left ventricular volume and cardiac output decline, and heart rate, pulmonary vascular resistance, and ventricular ejection fraction all rise upon opening the chest ((Rushmere, Finlayson, and Nash, 1954;Fermoso, Richardson, and Guyton, 1964;Coles, Buttigliero, and Gergely, 1965). All these facts make exact cardiological evaluation of acute experimental AV block difficult, since immediate and late effects of thoracotomy become superimposed on the primary change in cardiac dynamics.These observations have prompted us to develop a new method of block production in dogs. This method does not require thoracotomy, produces only a small myocardial lesion, and results in a permanent AV block. In this paper, which represents a further extension of our first report about experimental AV block (Turina and Babotai, 1967), we describe percutaneous production of chronic AV block in dogs. Stability of the block is confirmed by long-term observations, and the histological changes in the acute and chronic phases of experimental heart block are reported. MethodsTwenty-two mongrel dogs, weighing between 17 and 33 kg were used. In 11 dogs, the block was produced in an acute experiment under non-sterile conditions. Thirteen dogs were operated upon under sterile conditions and allowed to recover; duration of the block and long-term histological changes were studied in these animals.Anaesthesia was induced with sodium pentobarbital (Pentothal) 1&15 mg/kg. Each animal was placed on its left side with the neck slightly elevated, and the right external jugular vein was exposed through a small incision. A stainless-steel cannula, 35 cm long (Fig. 1) was introduced into the right atrium under fluoroscopic guidance, until its tip rested slightly superior to the septa1 tricuspid leaflet, anterior to the coronary sinus.

Authors' synopsis Experimental permanent total atrioventricular block was produced by a simplijed method, without thoracotomy, by one person, and without the aid of x-ray apparatus. For this purpose, a newly designed cannula for the injection of 40% formalin into the bundle of His was made.