Significance of pacing cycle lengths in manifest entrainment of orthodromic circus movement tachycardia by ventricular pacing.

The physiology of entrainment of orthodromic circus movement tachycardia (CMT) was studied using ventricular pacing during 18 episodes of induced CMT in 7 patients with atrioventricular (AV) accessory pathways. The first paced impulse was delivered as late as possible in the tachycardia cycle (mean 88 +/- 5% of the spontaneous cycle length [CL]). Entrainment was demonstrated by the following criteria: 1:1 retrograde conduction via the accessory pathway; capture of atrial, ventricular and His bundle electrograms at the pacing rate; and resumption of tachycardia at its previous rate after cessation of pacing. The number of ventricular paced impulses ranged from 5 to 14 (mean 8 +/- 3), and entrainment occurred in 2 to 7 paced cycles (mean 4 +/- 2). Orthodromic activation of a major part of the reentry circuit (manifest entrainment) was demonstrated during 9 episodes by the occurrence of His bundle electrogram preceding the first CMT QRS at the time anticipated from the last paced beat. In the 9 other episodes, persistent retrograde His bundle activation and AV nodal penetration by each paced impulse caused a delay (mean 79 +/- 25 ms) in activation of the His bundle preceding the first CMT QRS after the last paced beat. The mean pacing CL achieving manifest entrainment was 92 +/- 3% of the tachycardia CL, compared with 84 +/- 3% for retrograde AV nodal penetration (p less than 0.01). In conclusion, manifest entrainment of orthodromic CMT can be demonstrated by ventricular pacing at very long CLs; shorter CLs may cause CMT termination due to retrograde AV nodal penetration.

Cellular electrophysiologic changes and "arrhythmias" during experimental ischemia and reperfusion in isolated cat ventricular myocardium.

The cellular electrophysiologic consequences of both regional and global experimental ischemia and reperfusion were studied in the isolated cat myocardium, using conventional microelectrode techniques. Oxygenated Tyrode's solution was perfused through the left anterior descending and circumflex coronary arteries, while the preparation was superfused with Tyrode's solution gassed with 95% nitrogen and 5% carbon dioxide. Electrophysiologic characteristics of endocardial muscle cells were normal during coronary perfusion. When perfusion was discontinued for 30 minutes, resting membrane potential was decreased by 21.6 +/- 4.1%, action potential amplitude was decreased by 29.1 +/- 8.6% and action potential duration was decreased by 54.1 +/- 12.5% (p less than 0.001). Ectopic activity occurred after 5 to 10 minutes of ischemia and was more frequent in regional than in global ischemia (p less than 0.05). Rapid ventricular activity was observed in only 5 (17%) of 29 preparations during ischemia, whereas it occurred in 24 (83%) of 29 preparations during reperfusion. Rapid ventricular activity began 5 to 40 seconds (mean 19) after the start of reperfusion, stopped spontaneously after a mean of 113 +/- 211 seconds and occurred after both regional and global ischemia. The cellular electrophysiologic changes induced by ischemia returned to baseline values within the next 5 minutes. Repeated ischemia and reperfusion runs reproduced the same electrophysiologic changes and rapid ventricular activity. Coronary perfusion with procainamide (20 mg/liter) aggravated the ischemic depressions of action potential amplitude and action potential duration and increased conduction delay during ischemia, but it did not prevent rapid ventricular activity induced by reperfusion. In contrast, verapamil (1 mg/liter) perfusion did not affect the changes in action potential variables during ischemia but prevented reperfusion-induced rapid ventricular activity. Perfusion with calcium ion (Ca2+)-free Tyrode's solution just before ischemia and during reperfusion slowed or prevented reperfusion-induced rapid ventricular activity, without affecting the action potential changes during ischemia. It is concluded that, in these isolated perfused ventricular muscle preparations, different mechanisms may be operative in ischemic and reperfusion arrhythmias and Ca2+ may play an important role in the development of arrhythmias during the reperfusion phase of ischemia/reperfusion sequences.

Attempted entrainment of circus movement tachycardias by ventricular stimulation.

Entrainment was attempted while pacing the right ventricle in 12 patients with circus movement tachycardias. At the onset of stimulation eight patients had short episodes of intraventricular and atrioventricular dissociation during which the paced impulses activated the various ventricular recording sites (right and left), but did not reach the atria. The latter occurred because the ventricular electrograms were recorded from parts of the ventricles which were not essential components of the reentry circuit. Relatively long (greater than 5 s) runs of entrainment were not possible in any case because of the relatively prompt termination of the tachycardias. Whereas in three patients this was due to the abrupt appearance of retrograde block in the accessory pathway, in nine patients it happened when the sequential, anterograde and retrograde, penetration of the AV node resulted in AV nodal block of the subsequent, reentering atrial impulse. The findings in this study showed that, with the methodology used, entrainment of circus movement tachycardias by ventricular stimulation had to be defined conceptually, by the fulfillment of requirements which did not include its occurrence for at least 5 seconds. Furthermore, the results also suggested that entrainment and tachycardia termination were best demonstrated by a technique which allowed the emission of the first stimulus in a constant (late) moment of the cycle, with deliverance of one additional stimulus at the same cycle length in successive pacing runs.

Entrainment of circus movement tachycardia utilizing an accessory pathway with long retrograde conduction times during ventricular and atrial stimulation.

An unusual case is presented in which a circus movement tachycardia incorporating an accessory pathway with long retrograde conduction time was transiently entrained. Overdrive high right atrial stimulation produced entrainment without atrial fusion since collision of anterograde and retrograde impulses took place within the accessory pathway. Tachycardia termination occurred when, at a faster pacing rate, an atrial impulse that collided in the accessory pathway was blocked at the atrioventricular (AV) node. In contrast, the entrainment seen during right ventricular apical stimulation was characterized by the occurrence of both fusion and collision within the ventricles. The tachycardia was terminated when a pure paced impulse that collided in the normal pathway was blocked in a retrograde direction in the accessory pathway. These data indicate that: 1) transient entrainment of this arrhythmia (circus movement tachycardia) can be identified by the classical criteria used to diagnose it, provided that fusion and collision occur within the ventricles; and 2) the accessory pathway is the weak link for tachycardia termination only during ventricular pacing since the AV node is the weak link during atrial stimulation.

[Pacing and right atrial ventricular dissociation in auricular stimulation in reciprocal tachycardia using an accessory pathway]. / Entraînement et dissociation oreillette droite-ventricule lors de la stimulation auriculaire au cours des tachycardies réciproques utilisant une voie accessoire.

The effects of right atrial (RA) and coronary sinus (CS) stimulation have been studied in 13 patients with circus movement tachycardia (CMT). Tachycardia entrainment has occurred in all patients during RA pacing and in 11/13 during CS pacing, for a pacing rate 10 to 31 beats faster than the tachycardia rate. During RA pacing, short episodes of right atrial ventricular dissociation (6/13 patients) occurred but not during CS pacing. This can be explained by the anatomical proximity of the CS to the AV node (AVN) or by postulating two separate lateral inputs in the upper part of the AVN. Tachycardia entrainment is a criteria in favor of a reentry mechanism. It delineates a ranges of frequency between tachycardia rate and the slowest possible atrial stimulation rate capable of tachycardia termination which may be benefit for patients with drug resistant CMT, for whom antitachycardia pacemaker is envisaged.

[Aortic stenosis with low preoperative ejection fraction. Long-term postoperative hemodynamic and angiographic studies]. / Rétrécissement aortique à fraction d'éjection pré-opératoire basse. Etude hémodynamique et angiographique à distance de l'intervention.

Twenty-two patients underwent aortic valve replacement for aortic stenosis with a preoperative ejection fraction less than 45%. Three patients died peroperatively and a fourth patient died 18 months later before the haemodynamic control. The other 18 patients were systematically reinvestigated, on average 16 months after surgery. Sixteen had a remarkable functional improvement and a significant increase in ejection fraction at haemodynamic control: 32 +/- 6% to 61 +/- 8%, p less than 0.001. They were surgical successes (Group I). In this group, the 7 patients with the most severe alteration of ventricular function and an average ejection fraction of: 26 +/- 3%, also improved to near normal function with a postoperative fraction of 62 +/- 11%. There was no significant improvement of the ejection fraction in 2 patients, and they were classified with the fatalities as surgical failures (Group II). The clinical, electrocardiographic, radiological, haemodynamic and angiographic data of these two populations were compared to try and identify preoperative indices of prognostic value. Only the angiographic left ventricular myocardial mass index (LVMI) was significantly higher in Group II (253 +/- 98 g/m2) than in Group I (156 +/- 56 g/m2, p less than 0.05). A discriminating analysis showed that the most important parameters to separate the 2 groups of patients were the LVMI and the thickness of the left ventricular wall. The marked increase of the postoperative ejection fraction in 3/4 of our patients confirmed the clinical value of valvular replacement justifying the indication for surgery in patients with severe aortic stenosis in spite of a severe alteration of left ventricular function.

Electrocardiographic patterns resulting from improper connections of the right leg (ground) cable.

The patterns resulting from improper connections of the right leg (ground) cable to the right arm, left arm, and left leg electrodes (hardly ever discussed in books dealing with electrocardiography) are presented and their genesis is explained. Knowledge about this technical error is important because it: (1) may be misinterpreted as resulting from switching the right arm and left arm cables; and, worse, (2) may not be recognized, which, in patients with abnormal electrocardiograms, can lead to clinically significant errors in interpretation.