Sintered platinum for cardiac pacing.

Platinum electrodes for cardiac stimulation having a surface porosity in the range of 40 micrometers have been prepared with a sintering process. These electrodes showed excellent in vitro characteristics (low polarization and sensing impedance). Animal testing proved good tissue acceptance and clinical trials in 31 patients gave the following results: threshold at implant 0,375 microJ (SD: 0.174 microJ), chronic threshold 1.15 microJ (SD: 1.05 microJ). The longest observation period was 7 months and the mean observation period was 17.1 weeks. These results indicate that this type of electrode allows safe stimulation of the heart with low energy pulses; in particular a reliable safety margin could be obtained with pulses having the amplitude of the existing lithium batteries, avoiding the need for a voltage doubler. This would improve the battery utilization and the pulse generator longevity.

Activation of the hypertrophic right ventricle in the dog.

Right ventricular hypertrophy (RVH) of mild, moderate, or severe degree was produced in six dogs following systolic overload of the right ventricle by surgical banding of the pulmonary trunk. Activation of the myocardium and specialized conducting tissue of the right ventricle was studied using intramural multi-electrodes or an exploring electrode, first with the heart in situ and then with the heart in a modified Langendorff perfusion circuit. Normal epicardial and intramural activation patterns were found in RVH, and the prolonged excitation time was found to be due to the increased muscle mass. No delay in activation was found in any part of the specialized conducting tissue of the right ventricle. Late activated Purkinje fibres were found in the outflow tract of the right ventricle in the dogs with hypertrophy and in a control series of normal dogs. The present electrocardiographic criteria for complete and incomplete right bundle branch block (RBBB) are based on widening of the QRS complex and the rSR pattern. This type of change can occur also in RVH. Because it has been shown here that no delay occurs in the specialized conducting system of the right ventricle in RVH secondary to systolic loading; the application of criteria to electrocardiograms that also fulfil the criteria for RVH may be misleading. It is suggested that in such cases the diagnosis of a conduction disturbance must also depend upon other methods, and that the terms "incomplete' and "complete' RBBB should be handled with care in this context.

Multiple measurement of intranural myocardial oxygen tension.

A method was developed for measuring the intramural oxygen tension in the ventricular wall (MpO2). The 10 electrodes of intramural needles are employed simultaneously for measurement of MpO2, and, by means of the same amplifiers and registration system, of the electrogram. In this way information could be obtained about the local MpO2 and the local electrical activity obtained from over 100 points in the ventricular wall. In the normal in situ dog heart we found an MpO2 of 5-90 mm Hg (mean 32 mm Hg). When the arterial pO2 was raised, the mean value of MpO2 was decreased. Directly after the start of a period of severe hypoxia a marked fall in MpO2 could be observed, which was reversible after return to the normoxic situation, provided that the hypoxic period was short. Changes in heart rate had only transient effects on the MpO2. Heart massage of the fibrillating heart in the open-chested dog was effective in restoring the arterial pO2, but gave no significant rise in MpO2 which did not exceed 5 mm Hg.