A Comparative Analysis of Antegrade and Retrograde Conduction Patterns in Man By MASOOD AKHTAR, M.D., ANTHONY N. DAMATO, M.D., WILLIAM P. BATSFORD, M.D., JEREMY N. RUSKIN, M.D., AND J. BIMBOLA OGUNKELU, M.D. SUMMARY Patterns 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) nodal Wenckebach phenomenon at a slower rate compared to the antegrade counterpart (25 patients: group IA) or b) no ventriculo-atrial conduction at all ventricular paced rates (11 pts: group IB). The site of retrograde block in group IB patients was the A-V node. In eight patients (group II), antegrade and retrograde conduction appeared to be equal up to maximum paced rates of 160 beats/min. In six patients (group III) retrograde conduction was "better" than antegrade conduction, as indicated by onset of antegrade A-V nodal Wenckebach periods at slower rates than retrograde Wenckebach periods. During antegrade refractory period studies the area of maximum refractoriness was the A-V node in 19/40 patients, the His-Purkinje system (HPS) 6/40, and the atrial muscle in 15/40. During retrograde refractory period studies the A-V node was the area of maximum refractoriness in 12/36 pts (4/40 patients had A-V dissociation during ventricular pacing), the HPS in 12/36, and the ventricular muscle in 10/36. In 2/36 patients the site of maximum refractoriness retrogradely could not be determined: The area of maximum refractoriness during both antegrade and retrograde refractory period studies was the same in 11 patients (A-V node in seven and HPS in four), was different (i.e., A-V node or HPS) in 18 patients, and was the atrial or ventricular muscle in six patients. In five patients, including four patients in whom V-A conduction failed to occur, the above comparisons were not made. It is concluded that 1) antegrade conduction is better than retrograde conduction in most patients; 2) it is not always possible to predict area of maximum refractoriness during premature stimulation (both atrium and ventricle) from observations made during incremental pacing; 3) it is equally difficult to extrapolate patterns of retrograde tory period studies.

conduction and refractory periods from results of antegrade conduction and refrac-

Materials and Methods was performed in the nonheart catheterization Right sedated 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

THE FUNCTIONAL BEHAVIOR of the cardiac conduction system during conduction in the antegrade direction has been extensively studied.' 8 In contrast, few systematic studies are available dealing with patterns of retrograde conduction in a significant number of human subjects,9"' other than patients with Wolff-Parkinson-White (WPW) syndrome.'2 13 This report deals with findings in 50 patients in whom antegrade and retrograde conduction and refractory period measurements were made at comparable cycle lengths.

From the Cardiopulmonary Laboratory, U. S. Public Health Service Hospital, Staten Island, New York. Supported in part by the Bureau of Medical Services, USPHS Project Py 75-1 and the National Heart and Lung Institute Project HE 12536-05. Presented in part at the 24th Annual Scientific Session of the American College of Cardiology, Houston, Texas. Address for reprints: Masood Akhtar, M.D., Cardiopulmonary Laboratory, USPHS Hospital, Staten Island, N.Y. 10304 Received March 6, 1975; revision accepted for publication May 22, 1975.

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RETROGRADE AND ANTEGRADE CONDUCTION gradually increased (by 10 beats/min) up to a maximum of 200 beats/min for atrial and 160 beats/min for ventricular pacing. Antegrade and retrograde refractory period studies were performed using the extrastimulus method (A2 or V2), at comparable basic cycle length (A1A1 or V1V1).15 The coupling interval (A1A2 or V1V2) was progressively decreased (by 5-20 msec) up to the point of atrial or ventricular refractoriness. Stimuli were delivered through an isolation unit and care was taken to insure proper grounding of all equipment. No instance of untoward effects occurred.

trogram and was taken to approximate retrograde conduction time within the HPS and the A-V node. During ventricular pacing when the retrograde His bundle depolarization was recognized within the local ventricular electrogram, the V-H interval was measured from the corresponding stimulus artifact to the end of retrograde His bundle deflection, and the H-A interval was measured from the end of retrograde His bundle potential to the onset of low atrial electrogram. Retrograde Refractory Periods

Definition of Terms' 16 Antegrade Conduction Times

A-H interval was measured, as is routinely done, from the onset of low atrial electrogram to the onset of His bundle deflection and was taken as an approximation of A-V nodal conduction (normal values for our laboratory:60-140 msec). A-H interval was also measured from the end of low atrial electrogram to the beginning of the His bundle potential. This was done mainly to compare the A-H values with the retrograde counterpart (H-A interval). A-V interval was measured from the end of low atrial electrogram to the beginning of ventricular activity (on ECG or HBE). This parameter of antegrade conduction was measured in order to compare antegrade conduction time with retrograde conduction time (SA or VA interval, see below). H-V interval represents HPS conduction time and was measured from the beginning of the His bundle electrogram to the earliest onset of ventricular activation, as observed on the standard ECG recording or local ventricular electrogram (normal values for our laboratory:30-55 msec). Antegrade Refractory Periods

S1, A1, H1, and V1 represent stimulus artifact, atrial, His bundle, and ventricular electrograms of the basic atrial drive beats, respectively. S2, A2, H2, and V2 represent the stimulus artifact, atrial, His bundle, and ventricular electrograms of the atrial premature beats, respectively. Effective Refractory Period (ERP) of the Atrioventricular Conduction System (AVCS) is the longest A1A2 interval at which A2 fails to conduct to the ventricles. ERP of the A-V node is the longest A1A2 interval at which A2 fails to depolarize the bundle of His. ERP of the His-Purkinje System (HPS) is the longest H1H2 interval at which H2 does not propagate to the ventricles. ERP of the atrium is the longest S1S2 interval at which S2 does not evoke an atrial response. Functional Refractory Periods (FRP) of the AVCS is the shortest V1V2 response resulting from any A1A2 interval. FRP of the A-V node is the shortest H1H2 interval in response to any A1A2. This parameter can only be determined if it is not limited by atrial refractoriness. FRP of the HPS is the shortest V1V2 interval in response to any range of H1H2 intervals. The FRP of the HPS can only be determined when it exceeds the FRP of the A-V node. Therefore at a certain range of H1H2 intervals H2 was associated with longer H2V2 intervals than those of the basic drive beats (H1V1). Retrograde Conduction Times V-A or S-A interval was measured from the corresponding stimulus artifact to the beginning of the low atrial elec-

S1, V1, H1, and A1 represent the stimulus artifact, ventricular, His bundle, and atrial electrograms of the basic ventricular drive beats, respectively. S2, V2, H2, and A2 represent the stimulus artifact, ventricular, His bundle, and atrial electrogram of the premature ventricular beats, respectively. The retrograde His bundle deflection for the basic ventricular drive beats (H1) was in most patients obscured by the ventricular electrogram; it could be identified in only eight patients. Data from animal experiments indicate that for the basic ventricular drive beats the interval between the stimulus artifact and the retrograde His deflection (SH, or

V,Hj) is constant.17 During ventricular premature stimulation, the retrograde His deflection emerged from the ventricular electrogram and was identified by morphology and expected physiologic behavior. For practical purposes S1H2 (V1H2) can be equated with H1H2 intervals when the latter value cannot be determined, as is the case with most patients, realizing that the latter value is less than the former by a constant amount. ERP of the ventriculo-atrial conduction system (VACS) is the longest V1V2 interval at which V2 fails to evoke an A2 response. ERP of the A-V node is the longest V1H2 or H1H2 interval at which the retrograde His deflection of the premature ventricular beat (H2) is not followed by A2. ERP of the HPS is the longest V1V2 at which V2 blocks below the bundle of His. This parameter can be determined only if the H2 is clearly identifiable prior to the occurrence of retrograde block. ERP of the Ventricular Myocardium is the longest S1S2 interval when S2 does not evoke a ventricular response. FRP of the VACS is the shortest A1A2 interval which results from any V1V2. FRP of the A-V node is the shortest A1A2 interval in response to two successive retrograde impulses both propagated from the bundle of His. FRP of the HPS is the shortest V1H2 or H1H2 interval in response to any range of V1V2 intervals. The foregoing definitions of refractory periods apply to conduction along the normal pathways at a given basic cycle length and in the absence of antegrade or retrograde bypass tracts. Results All patients were in sinus rhythm and were taking no medications. Patients who had historical or electrocardiographic evidence of supraventricular tachycardia, WPW syndrome, or ventricular arrhythmias were excluded from this study. Also, none of the patients had clinical evidence of electrolyte imbalance or acute myocardial ischemia at the time of the study. Since ventricular pacing was not performed

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at rates faster than 160 beats/min (at a cycle length (CL) of 375 msec), only atrial rates up to 160 beats/min were compared to corresponding ventricular rates. The essential clinical and electrophysiologic data are summarized in tables 1-3. The

numerical designation for individual patients in the tables does not necessarily correspond to the chronological order in which they were studied. The patients are divided into three groups (I, II, III) based primarily upon behavior of antegrade and

Table 1 Clinical Data Pt. no. Age

Sex

61 46 63 25 51 21 51 50 63 60 65 60 64 19 48 47 65 60 19 60 35 65 74 65 65 19 49 69 67 75 65 50 60 66 56 66 74 57 52 73 25

M m M M M M

1 2 3 4 5 6 7 8 9 10 11 1]2 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

61

67 18 62 61 56 69 58 17

MI M M M M M M M M M M WM F M F M M M M M M M M M M M M m F M M M M M M M M M m M M M M F

Resting ECG

Diagnosis

NHD NHD NHI) NHD NHD NHD NHD NHD Hyp NHD HDUEJ NHD ASHD MVP NHD ASHD ASHD ASHD NHD NHD NHD ASHD, Hyp Hyp Hyp ASHD NHD NHD ASHD NHD ASHD NHD ASHD ASHI) ASHD NHD ASHD ASHD RHD NHD Hyp NHD HDUE ASHD NHD ASHD, COPD NHD Hyp ASHD MVP MVP

CL

SB Normal RBBB SB RBBB + LAD

1050

8.50 900 1150 900 900 800 740 850 900 950 1150 800 820 900 640 700 1040

Normal Normal Normal Normal Normal SB; LVII SB LVH; ST-T Normal RBBB (inc) Old inf MI, RBBB; short Pr LBBB Old inf MI, short PR; Normal QRS Normal SB Normal IVCD LVH

Normal RBBB and LAD Normal RBBB + LAD

Normal SB, RBBB + LAD LBBB LAD

Short PR, normal QRS Old inf MI, short PR; Normal QRS RBBB + LAD Normal Sinus bradyeardia, 10 A-V block, RBBB, LAD LBBB LVH RBBB RBBB, LAD Short PR, normal QRS RBBB, LAD Old ant MI 1° A-V block LBBB

Normal LAD, LVH Old inf MI APCs, ST-T APCs

675 1240 620 800 800 900 800 900 1070 700 1150 590 790 800 770 900 760 1050

750 1000 800 900 670 800 900 1100 700 670 800 760 960 800

Sinus rhythm A-H H-V

85 85 65 115 80 120 656 90 95 120 80 105 90 70 65 60 70 65 90 95 80 70 90 120 100 80 120 125 145 80 85

)55 50

75 90 210 80 100

65 80 70 80 80 230 105 100 115 90 90 120

40 40 45 40 55 45 40 50 40 40 40 50 40 40 40 45 60 50 50 50 50 55 45 56 50 55 50 50 50 50 50 35 50 50 45 60 65 40 35 45 40 60 55 45 75 40 50

55 45

55

All electrophysiologic values are in milliseconds. Abbreviations: CL = cycle length; NHD = no heart disease; ASHD = arteriosclerotic heart disease; HDUE = heart disease, unknown etiology; RBBB = right bundle branch block; LBBB = left bundle branch block; LVH = left ventricular hypertrophy; APCs = atrial premature contractions; Hyp = hypertension; COPD = chronic obstructive pulmonary disease; SB = sinus bradyeardia; ST-T = ST and T wave abnormalities; inf = inferior; MI = myocardial infarction; ant = anterior. Circulation, Volume 52, November 1975 Downloaded from http://circ.ahajournals.org/ at UNIVERSITY OF TEXAS on June 8, 2015

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RETROGRADE AND ANTEGRADE CONDUCTION Group I A

Table 2

Conduction Studies (table 2, 25 pt)

Conduction Times (Ave value in msec) Group

V-A

A-V (Onset of LAE)

A-V (End of LAE)

IA II III

183 166 159

139 150 167

89 93 117

All patients in this group demonstrated retrograde Wenckebach periods at a ventricular CL of 375 msec or greater. The average ventricular CL at which retrograde WP occurred was 505 msec (range 750-400 msec). In comparison only ten of 25 patients demonstrated antegrade Wenckebach periods at an average atrial CL of 403 msec (range 550-375 msec, table 2). The remaining 15 patients had 1:1 A-V responses up to an atrial CL of 375 msec. Retrograde Wenckebach periods were characterized by progressive increases in V-A interval in all except three patients (2, 20 and 23) in whom very insignificant increases in V-A interval, i.e., < 5 msec, preceded the blocked beat. In only five patients (2, 12, 19, 20, and 23) was a retrograde His bundle potential recognizable during ventricular pacing, and thus establishing the location of the retrograde Wenckebach period in the A-V node (fig. 1). For the following reasons, it can be reasonably inferred that in the remaining 20 patients the A-V node was also the site of retrograde Wenckebach period: 1) The well-known relationship between decreases in basic CL and increases in refractoriness and conduction within the A-V node.2'3 2) Data from animal experiments and from a limited number of patients in this study indicate that during continuous ventricular pacing the interval from the site of stimulation of the His

LAE = low atrial electrogram.

retrograde conduction patterns during continuous atrial or ventricular pacing at comparable heart rates. Group I (36) showed evidence of "better" A-V than V-A conduction. In group II patients (8) A-V and V-A conduction appeared to be equal, whereas in group III (6), V-A conduction appeared to be "better" than A-V conduction. Group I

All 36 patients (#1-27, 41-49) in this group demonstrated "better" A-V conduction than V-A conduction. This group was further subdivided into two subgroups based upon the evidence for "better" A-V conduction. Group IA consisted of 25 patients (nos. 1-23, 41, 42, tables 1 and 2) in whom the onset of retrograde Wenkebach periods occurred at longer paced ventricular CL than did antegrade Wenkebach periods at paced atrial CL. Group IB consisted of 11 patients (nos. 24-27 and 43-49, tables 1 and 2) in whom V-A conduction never occurred at any paced ventricular CL.

2

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430

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Figure 1 Antegrade and retrograde conduction (pt. no. 12). Tracings in each panel are ECG leads 1, 2, 3 and V1, high right atrial electrogram (HRA), His bundle electrogram (HBE), and time lines (T). S denotes stimulus artifact. The same abbreviations are used in subsequent tracings. Panel A shows sinus rhythm; the A-H and H-V measure 105 and 50 msec respectively. Note the high-to-low atrial activation sequence and upright P waves in leads 1-3. Panel B shows 1:1 A-V response at a paced atrial cycle length (CL) of 375. Panel C demonstrates 1:1 V-A conduction during right ventricular apical pacing at a ventricular CL of 750 msec. Retrograde His bundle activation (H) is recognizable during ventricular pacing and the S-H and H-A interval measure 95 and 145 msec, respectively. Panel D shows retrograde A-V nodal Wenckebach periods at a ventricular CL of 665 msec. The S-H interval stays constant at 95 msec and the H-A interval increases and results in A-V nodal re-entry in the form of ventricular echo beat (Ve), which terminates the Wenckebach cycle. The QRS morphology and H-V interval of Ve are similar to the sinus beats (panel A). Note the low-to-high atrial activation sequence and inverted P wave in ECG leads 1-3 during ventricular pacing.

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Table 3

Refractory Period Data Pt.

1 2 3 4

5 6 7 8 9 10 11

12 13 14 15 16

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

35 36 37 38 39 40

Basic paced CL

Al Ai or Vl Vl

ATR

900 700 700 1000 600 900 800 800 700 700 800 800 700 700 600 900 600 600 700 600 500 600 700 600 1000 800 550 600 700 600 500 500 600 600 600 500 700 700 600 750 600 600 900 600 700 700 600 800 600

280 270 270 260 250 300 280 310 240 280 240 320 320 260 270 280 270 250 260 260 260 250 260 230 330 290 240 280 310 290 270 220 300 270 290 260 280 290 280 280 250 300 320 270 300 250 240 280 300

Antegrade refractory periods FRP ERP HPS AVCS AVN AVN

350 300

510 385 280 420 500 350 380 490 340 470 360 490 680 420 290 - 365 430 490 360 445 480 515 -350 320 430 445 365 375 360 435 365 37,5 370 400 -- 395 475 415 395 380 440 450 350 300 350 300 390 400 520 330 510 400 440 - 340 350 430 455415 470 360 __ 380 365 390 465 600 770 320 540 415 310 450 330 440 500 330 380 470 -

510 385 400 480 490 470 490 680 355 490 445 480 515 340 320 425 365 355 355 365 375 345 400 380 430 410 395

355 360 350 350 390 520 510 440 330 370 400 355 365 360 465 770 540

405 450 440 500 470

HPS