Atrial Repolarization in Healthy Males

Monophasic action potentials: concepts to practical applications

Monophasic action potential (MAP) recordings reproduce the repolarization time course of intracellular action potentials with high accuracy and provide precise information on the local activation time. With the advantage of in vivo application and the development of the safer and simpler contact catheter technique, MAP recording has become the method of choice for evaluating myocardial repolarization changes. This review aims to provide information on practical application of MAP recording in the clinical setting. MAPs can easily be recorded from the endocardium with the contact catheter technique in the electrophysiology laboratory and from the epicardium with electrode probes during open heart surgery. The technical aspects are described in detail. The rate dependence of myocardial excitability and repolarization and the effect of antiarrhythmic drugs on MAP duration and effective refractory period are thoroughly reviewed. The use of MAPs in detecting myocardial ischemia, in studying early afterdepolarization and triggered arrhythmias, in measuring dispersion of repolarization, in identifying intracardiac conduction and the development of the T wave, and in verifying the arrhythmogenic effect of mechanoelectric feedback are presented. Computerized automatic analysis of MAPs and the limitations of the MAP technique are also discussed.

The vulnerability of the right atrium. III. Electrophysiologic correlates of atrial vulnerability

70 patients were investigated by means of the atrial extrastimulus method at three different driving rates: 80, 100 and 120/min. At each rate the effective, the relative, the total and the functional refractory periods were measured. 30 patients who showed signs of atrial vulnerability at least one of the tested rates were included in the so called vulnerability group. The remaining 40 patients, who did not fulfill the criteria for atrial vulnerability, were included in the nonvulnerability group. When the two groups were compared to each other there were significant larger P waves (p less than 0.005), shorter effective refractory periods (p less than 0.001) and longer relative refractory periods (p less than 0.001) in the vulnerability group. With increasing driving rate there was an increased tendency to repletitive firing in the vulnerability group. The phenomenon of vulnerability correlated well with the rate-induced shortening of the effective and the lengthening of the relative refractory period. The above described phenomena are compatible with the concept of re-entry as the electrophysiologic mechanism of atrial vulnerability in man.

Right atrial monophasic action potential in patients with paroxysmal supraventricular tachyarrhythmias

Thirteen patients with paroxysmal atrial tachyaarhthmias (six atrial supraventricular tachycardia, six atrial fibrillation, and one atrial flutter) have been investigated by recording of monophasic action potentials (MAP) during a period free from arrhythmias. None of the patients differed from healthy individuals with respect to any of the MAP variables. Occasional recordings showed values not found in healthy individuals, such as prolonged duration of the MAP or slow phase 4 depolarization. The atrial effective refractory period (AERP) was determined in two patients. One AERP was short compared with values found in healthy individuals. Thus some MAP recordings gave a possible explanation for the mechanism behind the arrhythmias, while other recordings showed no differences from results in healthy individuals.

Human atrial conduction with reference to heart rate and refractory periods

Atrial conduction time (ACT) between a stimulating pacemaker electrode and an "impulse-detecting" monophasic action potential (MAP) electrode has been determined in 20 healthy males. A small increase in ACT was found with increasing paced heart rates. Using the extra stimulus technique, ACT was found to increase when the early ectopics approached the atrial effective refractory period (AERP). The degree of ACT prolongation was similar at long and short basic ACTs, indicating that the slowing of impulse propagation probably occurred near the simulating electrode and presumably within 1/2-1 cm from that electrode. The increase in ACT close to the AERP was of importance when determining the atrioventricular refractory period. In three recordings a supernormal phase of conduction was found. The small errors of the MAP recordings in detecting the time of excitation make the method sensitive enough to detect small differences in ACT.