[Thoracic transcutaneous cardiac pacing]. / La stimulation cardiaque transcutanée thoracique.

Transcutaneous cardiac pacing was abandoned when endocardial pacing was developed, but it has now come back, with a new methodology, in cardiological intensive care. Its safety and efficacy have been improved by 50 to 100 sq. cm electrodes, impulses of 20 to 40 ms duration and programmed energy. A perfect electrocardiographic analysis can be obtained by specific treatment of the pacing signal. New research work has begun concerning the sequence of activation. The hypothesis of simultaneous atrial and ventricular pacing, which has been put forward after the first experimental studies, is seldom confirmed by clinical data: it has been demonstrated that pacing is exclusively ventricular and that its influence on haemodynamics is equivalent to that of endocardial ventricular pacing. Transcutaneous pacing is the only technique that can be used in non-hospital extensive care, and this leads to the concept of mobile units performing defibrillation, ensuring electrophysiological monitoring and capable to treat circulatory arrests due to pause or ventricular tachyarrhythmias. Transcutaneous pacing is being reconsidered in cardiology units, where it can be used to reduce ventricular tachycardias, since it has the advantage over endocardial pacing or being immediately applicable and completely safe.

[Then hemodynamic efficacy of transcutaneous cardiac stimulation]. / Efficacité hémodynamique de la stimulation cardiaque transcutanée.

Bradyarrhythmia or asystole is the most common rhythm disturbance with ventricular fibrillation and tachycardia, for 30-40% of patients admitted in intensive coronary care units. Already use in the therapy of bradyarrhythmia or asystole, as a method of emergency, immediately in place, the external pacing is very useful in an out of hospital therapy with personnel skilled in its use until the initiation of support therapy in coronary care units. Actually, with less significant side effects (no severe pain, no strong muscular contractions, no skin burns) and a best innocuity and tolerance based on the employment of larger adhesive pre-gelled patches, temporary transcutaneous cardiac stimulation is not only confined to unconscious patients but also in case of severe bradycardia, complete AV block in conscious patients. Our hemodynamic study shows a good level of systemic pressure and of cardiac index to permit the transport of patients in coronary care units in good conditions. Furthermore, the experimental study demonstrates the importance of the polarity of the electrodes and of the duration of the stimulus (more than 10 ms) to minimize the threshold (mA/cm2) so as to increase the tolerance in clinical application. Transcutaneous cardiac pacing is a simple and rapid pacing procedure with effective hemodynamic results for victims of out-of-hospital cardiac arrest and can be easily used in conscious patients without any complication.

Directional variability of stimulation threshold measurements in isolated guinea pig cardiomyocytes: relationship with orthogonal sequential defibrillating pulses.

Reports on delivery of separated orthogonal pulses markedly improving cardiac defibrillation have suggested that the stimulation threshold of heart fibers varies in accordance with their orientation within the electric field. The present work was aimed at investigating the directional variability of stimulation thresholds in isolated guinea pig cardiomyocytes. This variability was measured in 48 single myocytes by rotating each one through a theta (theta) angle between two-fixed parallel electrodes 1.1 cm apart, thus making theta vary between the electric field and the myocyte axis. For theta = 0 degrees, the mean longitudinal current stimulation threshold was 16.92 +/- 4.20 mA (n = 48). When theta was increased by increments of 10 degrees up to 90 degrees, the stimulation threshold increased in an exponential way. For theta = 90 degrees, the mean transverse stimulation threshold was 63.13 +/- 13.30 mA. These results clearly demonstrate the dependence of isolated cardiomyocyte stimulation thresholds on their orientation within the electric field and may account for the improved efficacy of defibrillation previously observed after delivery of orthogonal pulses.

Reduction of energy required for defibrillation by delivering shocks in orthogonal directions in the dog.

Reduction of energy required to defibrillate (ERD) seems to represent a necessary condition for intensive development of implantable defibrillator, so as for minimization of cardiac and pulmonary damages provoked by high energy transthoracic defibrillation electric shocks. The present work describes a defibrillation method using shocks delivered in orthogonal directions and separated by a 100 ms delay. Defibrillation threshold measured with classical unidirectional shocks on 30 dogs has been found to be 286.8 +/- 22.2 joules. In the same animals, defibrillation threshold measured by use of orthogonal shocks has been found to be 101.4 +/- 14.9 joules. We conclude that this crossed shocks method leads to a substantial reduction of ERD (64%).

[A new method for studying uterine contraction. Impedance measurement]. / Une nouvelle méthode d' etude de la contraction utérine. La mesure d'impédance.

PIP: These are preliminary results of a new method of tracing uterine contractions by impedance recorded with 2 electrodes placed 15 cm from the midline slightly below the umbilicus. A high-frequency electric current of constant intensity was the source of the signal. Results from 2 primiparae in term labor are presented: 1 was spontaneous and uncomplicated; the second had first contractions of low amplitude, then periods of permanent contracture treated with a spasmolytic (Buscopan), and finally a normal delivery. Tracings of typical contractions, confirmed by tocography, resembled a rapidly rising curve (1-3 seconds) associated with beginning of labor pain, a rounded peak, an exponential descent, a brief horizontal pause at the isoelectric line whose duration varied with the length of the contraction, a rapid fall (1-3 seconds), a rounded nadir, and finally an exponential return to the isoelectric line. The return to base line was preceded 10-15 seconds by a slight dip. This type of tracing was associated with normal contractions and was not influenced by fetal movements. The method delineated contractions, relaxations, and the effect of medication instantly.^ieng