Anthony N. Damato

Catheter Technique for Recording His Bundle Activity in Man

A technique for the routine recording of His bundle (H) activity in man using a bipolar or multipolar catheter is described. The recording catheter is inserted percutaneously, via the Seldinger method, into the right femoral vein and advanced fluoroscopically into the right atrium. Placement of the pre-formed curve at the catheter tip across the tricuspid valve in nine patients resulted in stable recordings of His bundle activity in successive cardiac cycles. Right atrial pacing resulted in progressive lengthening of the P-H interval with increasing frequency but the H to S-wave interval remained constant at all rates. Similar lengthening of the P-H interval was produced during atrial pacing when pressure was applied to the carotid sinus. The use of this recording technique in man will facilitate diagnostic interpretation of the electrocardiogram and can be used in various investigations of atrioventricular and intraventricular conduction in man.

Patterns of Atrioventricular Conduction in the Human Heart

Atrial, His bundle (H), and ventricular electrograms were recorded by an electrode catheter in unanesthetized man. Conduction time through the atrioventricular (A-V) conduction system was subdivided into A-V nodal (A-H interval) and ventricular specialized conduction system (H-V interval). The right atrium was driven at a constant rate and the pattern of A-V conduction of premature atrial test impulses was determined as they occurred progressively earlier in the cardiac cycle. In the type 1 response, conduction delay and block were limited to the A-V node only. The type 2 response was characterized by progressive conduction delay in both the A-V node and ventricular specialized conduction system with block occurring in several instances in the latter. In the type 3 response there was also a progressive delay in A-V nodal conduction time, and a sudden marked delay in conduction in the ventricular specialized conduction system. Conduction block occurred distal to the His bundle depolarization. The relevance of conduction delay and block in the different regions of the A-V conduction system to the full recovery time and the relative, functional, and effective refractory periods of A-V conduction are indicated.

The Essential Role of Atrioventricular Conduction Delay in the Initiation of Paroxysmal Supraventricular Tachycardia

Studies have shown that in patients with paroxysmal supraventricular tachycardia (SVT), spontaneous or stimulated atrial premature depolarizations (APD) falling within a specific portion of the relative refractory period of the atrioventricular (A-V) conduction system initiate SVT. The present study was designed to determine whether the A-V nodal conduction delay these APDs exhibit, or their coupling interval, is essential for the initiation of SVT. Multiple episodes of SVT were initiated and terminated by single APDs in four patients with a history of paroxysmal SVT. The atria were then paced at numerous fixed rates in excess of the spontaneous sinus rate. In each patient, at atrial rates where progressive A-V nodal conduction delay occurred from beat to beat (Wenckebach cycles), a specific degree of A-V nodal conduction delay always resulted in atrial reentry or SVT. Although the atrial coupling interval was considerably longer during Wenckebach cycles initiating SVT than for single APDs resulting in the arrhythmia, the prolongation of A-V nodal conduction was identical. Independent of atrial coupling interval, a requisite degree of A-V nodal conduction delay always resulted in atrial echoes or SVT. This supports the conclusion that SVT results from atrial reentry via the A-V node.

Demonstration of Re-entry within the His-Purkinje System in Man

Re-entry within the His-Purkinje system (HPS) was consistently observed in 15/24 consecutive patients in whom retrograde refractory period studies were performed using His bundle electrograms and the ventricular extrastimulus method. Within a narrow range of ventricular coupling intervals (V1V2), V2 retrogradely conducted to the bundle of His (H2) with significant infra-His bundle conduction delay (V2H2 interval). At critical V2H2 delays another beat of ventricular origin (V3) followed V2 and was associated with H2V3 intervals greater than the H-V intervals of sinus beat. It is postulated that V2 retrogradely blocked within the right bundle branch and activated the bundle of His via the left bundle branch after which antegrade conduction occurred along the right bundle branch producing the V3 response. In support of re-entry within the HPS are the following: 1) V3 occurred in a narrow range of V1V2 intervals and critical V2H2 delays, 2) V3 did not occur when V2 retrogradely blocked below the bundle of His, 3) V3 was independent of retrograde A-V nodal delay, 4) V3 rarely occurred in patients with pre-existing complete right bundle branch block pattern. These results reasonably exclude local re-entry near the site of stimulation.

A Study of Heart Block in Man Using His Bundle Recordings

The technique of recording His bundle electrograms in man by a tripolar electrode catheter was applied in a study of patients with first, second, and third-degree heart block. In all patients with first-degree heart block (congenital, acquired, or induced by atrial pacing), the delay in A-V conduction occurred proximal to the His bundle as evidenced by a prolonged P-H interval. The enhancement of A-V conduction (shortening the P-H interval) due to isoproterenol was qualitatively similar in the three forms of first-degree block. In cases of Wenckebach phenomenon the P-H interval progressively increased until a dropped beat occurred. The nonconducted P wave was not followed by a His deflection, indicating block proximal to the His bundle. Cases of 2:1 and 3:1 block occurring proximal to the His bundle were also studied. The usefulness of His-bundle recordings in the diagnosis of cases of complete and incomplete bilateral bundle-branch block is also demonstrated.

Study of atrioventricular conduction in man using electrode catheter recordings of His bundle activity.

The technique of recording electrograms of the His bundle, using a tripolar electrode catheter positioned across the tricuspid valve, was applied in a physiological study of atrioventricular conduction in man. Increasing the heart rate to 160 beats/min by right atrial pacing produced progressive prolongation of the P-H interval while the H-Q interval remained constant. At any given paced heart rate, digitalis caused a prolongation of the P-H interval. Isoproterenol and atropine markedly shortened the P-H interval at any given heart rate. Neither drug had any significant effect on the H-Q interval. Coupled premature atrial stimulation produced prolongation of the P-H interval alone when the resultant ventricular depolarization was normal, and prolongation of both the P-H and H-Q intervals when the resultant ventricular depolarization was aberrant.

The electrophysiologic demonstration of atrial ectopic tachycardia in man

Abstract Three patients with almost continuous atrial tachycardia were studied in an attempt to delineate the mechanism responsible for their cardiac arrhythmia. During cardiac catheterization intracardiac electrograms and specific atrial stimulation sequences revealed: (1) episodes of tachycardia were initiated by atrial premature depolarizations (APDs) which exhibited no increased delay in AV nodal conduction, (2) during tachycardia atrial cycle length was not a direct function of AV nodal conduction, (3) initial cycles of tachycardia showed progressive shortening in cycle length, (4) APDs introduced during tachycardia resulted in resetting of the atrial cycle, and (5) single APDs and atrial overdrive during tachycardia failed to interrupt it. The electrophysiologic behavior of the arrhythmia was consistent with the hypothesis that it was initiated and was sustained by an ectopic rapidly firing automatic atrial pacemaker.

The electrophysiology of propranolol in man

Abstract The effects of intravenous propranolol (0.1 mg. per kilogram) on the electrophysiologic properties of the A-V conducting system were studied in 16 patients using His-bundle electrograms and the extrastimulus method. The drug was infused at a rate of 1 mg. per minute without significant side effects. Sinus cycle length was slowed in 15 out of 16 patients (average, 128 msec.). AVN conduction time was increased in 13 out of 16 patients (average, 10 msec.) during sinus rhythm and in all patients during atrial pacing. AVN Wenckebach block occurred at slower paced rates in 14 patients. Corrected QT interval was shortened in 9 out of 16 patients (average, 24 msec.). The functional and effective refractory periods (ERP) of the AVN were prolonged in 14 out of 14 patients (average, 29 msec.) and 9 out of 9 patients (average, 24 msec.), respectively. No significant changes were seen in His-Purkinje system (HPS) conduction time, ERP of the atrium, relative refractory period or ERP of the HPS, or ERP of the ventricle in all patients in whom these variables could be muasured. Mean end-study blood level was 13.6 ng. per milliliter. Effects on the AVN explain the efficacy of propranolol in (1) controlling the ventricular rate in atrial fibrillation and flutter and (2) the treatment and prophylaxis of re-entrant supraventricular tachycardias. Its lack of effects on the HPS make its use relatively safe in patients with infra-His conduction disturbances.

Recording of Specialized Conducting Fibers (A-V Nodal, His Bundle, and Right Bundle Branch) in Man Using an Electrode Catheter Technic

Extracellular action potentials of the A-V node (N), His bundle (H), and right bundle branch (RB) were recorded in subjects with an electrode cardiac catheter which was fluoroscopically positioned across the tricuspid valve. The N potential is a slow diphasic wave occurring between the atrial electrogram (P) and the H potential. It is characterized by slurring or notching on the upstroke. The H potential, as previously described, is a biphasic or triphasic wave of 15 to 20-msec duration. The RB potential is a fast biphasic wave of 10 to 20-msec duration occurring between the H potential and the Q wave. During single atrial pacing and premature atrial stimulation, the A-V conduction delay could be localized to the N-H interval. Evidence suggests that during aberrant ventricular conduction of the right bundle-branch block type the impulse was blocked proximally in the right bundle. During concealed conduction the nonconducted impulse was completely blocked within the A-V node or the N-H interval.

Antegrade and retrograde conduction characteristics in three patterns of paroxysmal atrioventricular junctional reentrant tachycardia.

Abstract In 20 patients with PSVT without ventricular pre-excitation, the site of reentry and functional characteristics of Ant. and Ret. pathways were studied. Three distinct patterns of PSVT were observed. In 13 patients (group I) in whom A-V node was the site of reentry, the interval between the Ant. H bundle deflection and the following atrial echo response (H-Ae) measured 30 to 85 msec. and the Ae was partially or completely obscured by ventricular electrogram. The ratio between the H-Ae and the subsequent Ae-H interval ranged 1:3.1–17.3. In a majority of Group I patients (eight out of 13) the Ret. conduction was better than Ant. conduction, as the VACS sustained a 1:1 response at faster paced rates than AVCS. The FRP of the AVCS in Group I was determined by the A-V node in all patients and significantly exceeded the FRP of the VACS; the latter was determined by the HPS in 12 out of 13 patients. In four patients (Group II) a V-A AP silent antegradely was operative during PSVT. The H-Ae in Group II valued 145 to 200 msec. and the Ae clearly followed the ventricular electrogram, the H-Ae: Ae-H being 1:0.5–1.7. The V-A conduction in all Group II patients was better than the A-V conduction. A-V node determined the FRP of the AVCS, whereas AP determined the FRP of the VACS in Group II patients, and the former significantly exceeded the latter. Good correlation existed between PSVT, Ant. and Ret. conduction patterns in Group I and Group II patients. In three patients (Group III) the H-Ae measured 270 to 470 msec. with an H-Ae:Ae-H of 1:0.2–0.4, a relationship quite the opposite of Group I patients. No definite relationship existed between PSVT, Ant. and Ret. conduction patterns in Group III patients. The data in Group III patients were compatible with (1) A-V nodal reentry with reversal of conduction balance compared to Group I, (2) intra-atrial reentry, and (3) enhanced atrail automaticity. It is concluded (1) the site of reentry in patients with PSVT is variable, (2) a fair estimation of reentry site can be made from H-Ae and Ae-H relationship, (3) all patients with PSVT have intact V-A conduction and in most the V-A conduction is better than A-V conduction, and (4) in the majority of patients with PSVT refractoriness of the AVCS exceeds that of the VACS.