His bundle electrogram in P mitrale

Epicardial His bundle recordings in the guinea pig in vivo

In small animals, His bundle activity is commonly registered using intracavitary electrodes in Langendorff-perfused hearts. The present study evaluates the feasibility of epicardial registration of His bundle activity in 30 guinea pigs in vivo, anesthetized with 60 mg/kg sodium pentobarbital i.p. Following median sternotomy, a bipolar electrode, mounted on a flexible stand, was placed into the aortic-right atrial groove. His bundle activity was easily detected in all animals. Mean PA, AH, and HV intervals were 16.7 +/- 1.4 msec (range: 6.0-34.0 ms), 36.4 +/- 1.5 ms (range: 22.0-54.0 msec) and 14.4 +/- 0.4 msec (range: 9.0-20 msec), respectively. Administration of verapamil and vagal stimulation induced significant prolongations of AH intervals without affecting HV intervals; lidocaine prolonged both AH and HV intervals. Both at baseline and following drug administration there was excellent agreement between the AH and HV intervals assessed from simultaneously registered epicardial and endocardial His bundle electrograms (n = 12). The presented model provides reproducible values for atrioventricular (AV) nodal and His-to-ventricular conduction intervals in the guinea-pig in vivo and will, thus, be a valuable tool in electrophysiologic drug evaluation.

Transesophageal versus intracardiac atrial stimulation in assessing electrophysiologic parameters of the sinus and AV nodes and of the atrial myocardium

Electrophysiological parameters of the sinus and AV nodes and of the atrial myocardium were assessed with both transesophageal atrial stimulation (TAS) and intracardiac atrial stimulation (ICS) in the same patient during the same study. The study group was comprised of nine men and seven women, aged 45 to 79 years, referred for the evaluation of syncope of possible arrhythmogenic origin. Twelve patients were included for analysis. Autonomic inhibition (AI) was obtained in five patients. The most striking result was the significantly longer AERP with TAS (mean 286 +/- 9 ms) than with ICS (mean 244 +/- 12 ms; p than 0.02). After AI, the AERP was even more prolonged with TAS (mean 332 +/- 20 ms) than with ICS (mean 237 +/- 8 ms; p less than 0.01). Intraatrial and AV nodal conduction times assessed at multiple paced cycle lengths were significantly shorter with TAS than with ICS. There was no difference between TAS and ICS with regard to AVERP, Wenckebach periodicity and H-V intervals. Although a tendency towards shorter sinus node recovery time (SNRT) and sinoatrial conduction time (SACT) was observed with TAS, the difference was not statistically significant. Possible mechanisms of the differences are discussed. It seemed clear that the site of origin of an atrial impulse can have definite effects upon excitability and conduction properties of atrial and AV nodal fibers. Enhanced sympathetic activity during TAS was also suggested. The electrophysiological properties inherent in the TAS technique warrant further elucidation.

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.

Bradycardia-dependent interatrial block with retrograde left atrial activation

A patient with a peculiar interatrial block is reported. The electrocardiogram showed a short PR interval and negative P waves in II, III, and aVF, which were preceded, 0-07 s earlier, by another positive P wave present in the right praecordial leads which were absent in the limb leads. From the study with His bundle electrograms, high right atrial electrograms, and bipolar oesophageal electrocardiograms, it could be proved that atrioventricular, His-Purkinje, and right intra-atrial conduction were normal, and that P waves recorded in limb leads represented left atrial depolarization; whereas the ones in the right praecordial leads corresponded to right atrial activation. The vectorial analysis from both P waves and atrial potentials showed that the left atrium was activated in a retrograde fashion, because of an interatrial block. This block was bradycardia dependent and it disappeared in the cycles shorter than 800 ms.

P-A interval: lack of clinical, electrocardiographic and electrophysiologic correlations

P-A interval is measured from the onset of the P wave to the onset of the low right atrial electrogram during His bundle recording. The significance of this interval was evaluated in 214 patients with intact A-V conduction and bundle branch block. One hundred fifty-eight patients had normal P-A (NPA) 27 +/- 9, mean +/- SD, and 56 had prolonged P-A (PPA). The NPA and PPA patients were similar (P greater than .10) in regard to sex, age, cardiac functional class, and P-R. PPA patients had significantly (P less than .05) greater P duration (mean +/- SEM, PPA vs NPA) 106 +/- 2 msec vs 100 +/- 1 msec), slower heart rates (72 +/- 2 vs 79 +/- 1), and longer sinus recovery times (1104 +/- 44 msec vs 980 +/- 38 msec). A-H was slightly shorter in PPA than in NPA patients suggesting that a systematic error in measruement of PA due to a relatively distal recording site may have been responsible for PA prolongation in some patients. Patients were prospectively followed for 16-56 months (mean 21.9 +/- 0.8 months). PPA was associated with only minor increase in P wave duration and decrease in sinus automaticity. PPA did not predict future occurrence of significant atrial dysrhythmia.