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.

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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. ADDITIONAL KEY WORDS premature atrial impulses functional refractory period effective refractory periodHis bundle electrogram conduction block conduction delay full recovery time relative refractory period • Conduction of impulses from the atria to the ventricles involves propagation through a series of elements known as the atrioventricular (A-V) conduction system. This system includes the A-V node and the ventricular specialized conduction system (VSCS), which includes the bundle of His, the bundle branches and peripheral Purkinje network (1).Previous investigations in dogs have shown some of the physiological properties of A-V conduction by studying the propagation of premature atrial impulses (2-5). The characteristic types of A-V delay differed in different

SUMMARYPatterns of antegrade and retrograde conduction and refractory periods were studied using His bundle electrogram recordings, incremental atrial and ventricular pacing and the extrastimulus technique. In 36/50 patients antegrade conduction was "better" than retrograde conduction (group I), as evidenced by a) onset of retrograde atrioventricular (A-V) 766 Materials and MethodsRight heart catheterization was performed in the nonsedated postabsorptive state using local anesthesia. Fifty patients were studied for basic electrophysiological characteristics; in 40 of these patients, antegrade and retrograde refractory periods were determined. The experimental nature of the procedure was explained to all patients and signed consents were obtained. Electrode catheters were percutaneously introduced and fluoroscopically positioned in the region of 1) the lateral wall of the right atrium near its junction with the superior vena cava, to record from and stimulate the region of the high right atrium; 2) the tricuspid valve, to record bundle of His and low atrial activity;'4 3) the right ventricular apex or outflow tract, for ventricular pacing. Standard ECG leads and intracardiac electrograms (filter frequency settings 40-500 Hz) and timelines generated at 10, 100 and 1000 msec were displayed on a multichannel oscilloscope and recorded on magnetic tape. The records were subsequently replayed and recorded on photographic paper at a speed of 150 mm/sec.Atrial and ventricular pacing were accomplished using a programmed digital stimulator capable of delivering rectangular impulses of 1.5 msec duration at an adjustable milliamperage. Minimum milliamperage which allowed reliable capture for atrial (less than 2 ma) and ventricular pacing (less than 1 ma) was used. Starting at a rate slightly faster than sinus rhythm, the rate of stimulation was

SUMMARYRe-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 (V,V2), V, 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 reentry within the HPS are the following: 1) V3 occurred in a narrow range of V,V2 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. Additional Indexing Words:Refractory periods THE SUGGESTED mechanisms of ventricular arrhythmias include ectopic impulse formation and re-entry within the ventricular specialized conduction system. -15 In the animal heart, re-entry within the His-Purkinje system (HPS) has been frequently demonstrated in the setting of depressed conduction brought about by a variety of factors, most notably a high extracellular concentration of potassium'0"12 and acute myocardial ischemia.3 13,15 This report deals with observations made in a group of 24 patients in whom unsustained re-entry within the HPS was observed during the performance of ventricular refractory period studies. In 15 patients reentry was consistently observed within a relatively narrow range of ventricular coupling intervals and appeared to be entirely dependent upon retrograde conduction delay within the HPS and totally independent of retrograde A-V nodal conduction time. In this study, re-entry within the HPS and the A-V node