Studies in P wave synchronization

Interpretation of cardiac pathophysiology from pressure waveform analysis: pacemaker hemodynamics

The abnormal sequence of A-V contraction produces alteration of right and left heart hemodynamics reflecting the inappropriate timing of atrial contraction to ventricular filling. Some symptomatic patients may require A-V sequential pacing to improve cardiac output. The clinical effects of the atrial contribution to left ventricular function can be demonstrated by careful review of hemodynamic tracings in these individuals.

Current physiologic pacemakers: a serious problem with a new device

Twenty adults underwent implantation of an automatic (DDD) pacemaker (Medtronic model 7000, Versatrax I) for treatment of symptomatic bradyarrhythmias. Only 9 patients had optimal DDD mode pacing during 78 paced months. In 3 patients, the DDD mode was changed to atrioventricular (AV) sequential (DVI) early because of risk imposed by sustained tachycardia upon underlying myocardial ischemia. The remaining 8 had had tachycardia due to pacemaker reentry, and 7 had neurologic and cardiovascular symptoms. DDD pacing was abandoned in 5 when reentry could not be interrupted by digitalis administration or reprogramming. Three continue to be paced in DDD mode despite intermittent reentrant tachycardias, with digitalis diminishing episodes of reentry in only 1. Mean ventriculoatrial conduction time was 229 +/- 34 ms. Reentrant pacemaker tachycardia developed in 7 of 12 with normal or nearly normal AV conduction, but in only 1 of 5 with complete heart block. Preimplantation electrophysiologic study did not reliably detect and initial postoperative Holter monitoring did not predict reentrant tachycardia. The risk of reentry caused by a short, fixed atrial refractory period combined with the high occurrence of slow retrograde AV conduction, particularly in patients with normal or nearly normal anterograde conduction, renders the Versatrax I and other similar pacemakers unsuitable for DDD mode pacing in many patients.

Catheter mapping of retrograde atrial activation. Observations during ventricular pacing and AV nodal re-entrant paroxysmal tachycardia

A systematic study of retrograde atrial sequence at commonly used electrode catheter recording sites in 8 patients without, and in 4 patients with AV nodal re-entrant paroxysmal tachycardia was made. During right ventricular pacing, the retrograde atrial activation sequence was low septal right atrium--proximal coronary sinus--distal coronary sinus--high right atrium. During the episodes of paroxysmal tachycardia, a similar pattern was observed. This information should be helpful in the understanding of abnormal activation sequences in patients with paroxysmal supraventricular tachycardia in whom retrogradely conducting anomalous pathways are suspected.

Verapamil induced premature ventricular beats before reversion of supraventricular tachycardia

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Patterns of ventriculo-atrial conduction in the Wolff-Parkinson-White syndrome

In 36 patients with the Wolff-Parkinson-White syndrome, ventriculo-atrial (VA) conduction was studied using the single test stimulus method. In 22 patients no significant change in VA conduction time occurred following test stimuli with increasing prematurity suggesting exclusive VA conduction by way of the accessory pathway, an accessory pathway with a shorter refractory period than the His-AV node pathway, or identical refractory periods in both pathways. In 14 patients showing this VA conduction pattern tachycardias could be initiated by a single early ventricular premature beat. This finding lends credence to the hypothesis that the accessory pathway is an essential link in the tachycardia circuit. In two of the five patients showing exclusive VA conduction over the His-AV node pathway single re-entrant beats with antegrade conduction over the accessory pathway could be elicited by appropriately timed ventricular premature beats. In one patient showing this pattern a sustained tachycardia with AV conduction over the accessory pathway could be initiated. A total of eight patients did not show VA conduction over the accessory pathway.

Ventriculo-atrial conduction in man

Transvenous electrodes were placed in the right atrium and ventricle of 50 patients with heart disease and arrhythmias. The ventricles were paced at several rates, each in excess of the sino-atrial rate. An atrial electrogram and surface electrocardiogram were recorded simultaneously in each patient; utilizing strict criteria, the incidence with which 1:1 ventriculo-atrial conduction (VAC) could be elicited in these patients was assessed. These patients were divided into two groups-26 patients with normal A-V conduction comprised group 1, and 24 patients with prolonged A-V conduction, group 2. VAC was demonstrated in 89% of group 1 patients but in only 8% of the group 2 patients. The difference in the incidence of 1:1 VAC between the two groups was statistically significant ( P < 0.01). The presence or absence of 1:1 VAC could not be related to type of heart disease, medication, presence of acute myocardial infarction, or presence of intraventricular conduction defect.

Altering the paced ventricular rate or introducing stimulated ventricular premature depolarization in group 1 patients could produce any degree of VAC impairment. During such maneuvers, ventricular reciprocal beats (ventricular echoes) and ventricular reciprocal rhythms were observed.

Significance of right bundle-branch block patterns during pervenous ventricular pacing

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Reciprocal beating induced by ventricular pacing

Ventricular pacing is frequently associated with retrograde ventriculo-atrial conduction. In the absence of atrioventricular (A-V) block, the relatively intact antegrade A-V conduction system supplies the necessary pathway for a re-entry mechanism that may become operative in the presence of delayed retrograde conduction.

Two patients with bradycardia and unimpaired antegrade A-V conduction exhibited reciprocal (echo) beating following nodal beats before ventricular pacing was instituted. After the introduction of an artificial ventricular pacemaker, reciprocal beats followed the paced ventricular beats in both patients.

These observations suggest that a similar mechanism is involved in the production of reciprocal beats linked to impulses originating from the A-V node and the ventricles.

When ventricular pacing is indicated for the treatment of bradycardia in the presence of intact antegrade A-V conduction, a situation which may produce echo beats, demand pacing is considered preferable to fixed-rate pacing as the latter may deliver a stimulus into the vulnerable phase following an echo beat.