Retrograde ventriculoatrial conduction in complete heart block

DIAGNOSTIC SHELF

Retrograde Ventriculoatrial Conduction in Complete Heart Block Studies with His Bundle Electrography PREM K. GUPTA, MD JACOB I. HAFT, MD

In a patient with complete heart block and retrograde ventriculoatrial conduction, His bundle electrography demonstrated (1) orthograde block beyond the bundle of His, (2) retrograde conduction through the atriovehtricular (A-V) node as evidenced by retrograde P’ waves with His bundle echoes, and by the effect of idioventricular beats on subsequent sinus P wave to His bundle intervals, even in the absence of retrograde P’ waves. It is concluded that retrograde conduction can occur in complete heart block if the block is beyond the bundle of His and the A-V node is intact. The retrograde pathway around the block to the A-V node may be by muscular conduction.

Bronx, New York

Retrograde conduction from the ventricles to the atria in the presence of complete atrioventricular (A-V) block is not seen frequently. The retrograde P waves are inverted in leads II, III and aVF and upright in lead aVR, thus suggesting a reverse activation of the atria. According to Scherf et a1.l retrograde P waves of this type appear only after automatic ventricular complexes or ventricular premature beats. They occur in late atria1 diastole, just before the next sinus P wave is due. Occasionally fusion P waves are seen. Since failure of orthograde conduction is complete, the phenomenon of retrograde conduction in complete heart block seems paradoxical. Scherf and Cohen2 in 1964 collected 81 reported cases of ventriculoatrial (V-A) conduction in A-V block. In this communication we present the electrophysiologic events recorded during bundle of His electrography in a patient with complete heart block and retrograde V-A conduction. Case Report An 82 year old white man was admitted with a history of dizziness on exertion of 6 to 7 weeks’ duration. He also complained of shortness of breath and chest pain on exertion. There was no history of syncopal episodes or convulsions. He had taken no medications. On physical examination he was not in acute distress. Pulse rate was 42/min and regular, blood pressure was 220/90 mm Hg. Cardiac auscultation revealed a first heart sound of various degrees of intensity, splitting of the second heart sound at the pulmonic area, and a short ejection systolic murmur at the mitral area. The electrocardiogram showed complete A-V block with an idioventricular rhythm of IO/min and sinus P waves at 65/min. Retrograde P waves following QRS complexes were seen (Fig. 1). Roentgenogram of the chest showed slight cardiomegaly with clear lung fields. From the Cardiac Section of the Bronx Veterans Administration Hospital and Mount Sinai School of Medicine, New York, N.Y. Manuscript received July 9, 1971, accepted October I, 1971. Address for reprints: Jacob I. Haft, MD, Cardiac Section, Veterans Administration Hospital, 130 W. Kingsbridge Rd., Bronx, N.Y. 10468.

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Studies

During the insertion of a temporary transvenous pacemaker, bundle of His electrograms were recorded by means of a modification of the method of Damato et a1.3 Under fluoroscopic control a no. 4F bipolar electrode catheter was passed up to the right atrium by way of the right femoral vein through a no. 14 Jelco sheath introduced percutaneously. The 2 poles of the catheter were positioned near the tri-

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electrocarFigure 1. Admission diogram showing complete heart block with inverted retrograde P waves evident in lead II a.nd the rhythm strip.

His bundle electrogram (bottom tracing) and simultaneous lead II electrocardiogram (top tracing). H = His bundle deflecFigure 2. tion; P = atrial deflection; QRS = ventricular depolarization. Time lines = 1 second. A and Bare sections of the same tracing.

cuspid valve so that the electrodes were close to the bundle of His. The leads of the catheter were connetted to an EEP 8 channel of an Electronics for Medicine oscilloscopic photographic recorder with the frequency response limits set at 40 to 500 cycles/ sec. His bundle electrograms and a simultaneous lead II electrocardiogram were recorded at a paper speed of 100 mm/set.

Analysis of His Bundle Electrograms Analysis of His bundle electrograms showed the following: (1) Complete A--V heart block with the area of block distal to the area of recording of the His bundle po-

tential. (2) P waves conducted retrograde from the ventricles. (3) Retrograde conduction from the ventricles to the His bundle and to the A-V node even in the absence of retrograde P waves. The retrograde conduction was recognized either by absence of a His bundle potential or prolongation of the P wave to His bundle interval following a sinus P wave that came soon after an idioventricular complex. (4) P waves conducted in retrograde fashion with His bundle echoes (blocked distal to the His bundle). (5) Sinoatrial exit and entrance block following retrograde P waves. Figure ZA shows complete A-V dissociation with a His bundle potential following each P wave (except the third), thus suggesting block distal to the bundle of His. The P-P

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Figure 3.

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His bundle electrogram and simultaneous lead II electrocardiogram.

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Figure 4.

His bundle klectrogram k&l sikhtaneous

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interval is constant at 960 msec and originates at the sinus node. The Q-Q interval is constant at 1,530 msec. The P-H interval is 110 msec and is within normal limits. No P’ waves conducted in retrograde fashion are evident on this strip. The third P wave is not conducted in retrograde manner; it occurs 960 msec after the previous P wave (the sinus cycle) and has the same configuration as the other sinus P waves. This P wave is not followed by a His bundle potential, thus suggesting that the A-V node or bundle of His was depolarized in retrograde fashion by the preceding ventricular complex and hence was refractory to antegrade depolarization. Similarly, in Figure 2B, the P-His interval of the third P wave is prolonged, suggesting that the A-V node had been depolarized in retrograde fashion by the preceding idioventricular QRS complex and was partially refractory to antegrade conduction. tion. Figure 3 shows P’ waves conducted in retrograde manner from the ventricles after the first and third ventricular complexes. The sinus P wave cycle remains 960 msec (interval between the third and fourth P waves). The second and the fifth P waves are believed to have been conducted in retrograde fashion because (1) they appear earlier than would be expected if they had originated in the sinus node (810 and 920 msec after the preceding sinus P waves), and (2) they differ in configuration in both the standard lead II and the intracardiac electrogram. The QRS-P’ interval is related to the preceding P-QRS interval in that the longer the P-QRS interval, the shorter will be the QRS-P’ interval. This finding is attributed to the recovery time of the A-V node and junctional tissue; that is, if the conduction tissue is more recently depolarized, the retrograde conduction rate will be slower. An interesting feature in this tracing is the long compensatory pause following the P’ waves conducted in retrograde fashion with the interval from the P wave preceding the retrograde P’ wave to the P wave following the retrograde P’ wave equal to twice the sinus P-P interval. This suggests that the retrograde P’ wave had not reset the sinus node; that is, there is entrance and functional exit block (because the atrium is

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still refractory at the time of sinus nodal firing) in the sinus nodal area.4 Figure 4 shows retrograde P’ waves following the first and third ventricular complexes with compensatory P’-P pauses following each P’ wave, similar to those in Figure 3. The P-QRS interval between the first P wave and the first QRS complex is 480 msec, with the QRS-P’ interval 300 msec. A His spike follows this retrograde P’ wave and is probably a His bundle echo. The P-QRS interval preceding the second retrograde P’ wave is 620 msec. Because the P-QRS interval is longer, the QRS-P’ time is shorter, 240 msec, and there is no echo; that is the second P’ wave is not followed by a His spike. This suggests that the longer the QRS-P’ interval the more likely the appearance of a His bundle echo after a retrograde P’ wave. The last P wave in the tracing is probably a sinus P wave and is followed by a His spike with a P-H interval of 250 msec, which suggests that the preceding QRS complex was conducted in retrograde fashion to the A-V node but not to the atrium and produced a delay in antegrade conduction after the sinus P wave. Alternatively this last P wave may be a fusion between a retrograde and an antegrade P wave, with the resulting prolongation of the subsequent P-H interval due’ to the recent retrograde conduction through the node to the atrium.

Discussion Briggs2 was the first to describe retrograde conduction after production of complete heart block in the perfused rabbit heart. Winternitz and Langendorf4 in 1944 found 19 reported cases of A-V block with normal retrograde conduction and described 6 cases of their own. Scherf and Cohen2 in 1964 collected 81 cases of A-V block with intact retrograde conduction and reported 3 of their own1 Subsequently there have been single case reports.5s Adams7 described a patient with complete heart block and retrograde conduction during ventricular pacing. More recently Castillo and Samet8 showed

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ventriculoatrial conduction during ventricular pacing in 4 or 7 patients with complete heart block and in 1 patient with 2: 1 A-V blodk.

Mechanisms

of V-A conduction

in A-V block:

A number of theories have been postulated to explain retrograde V-A conduction in the presence of complete antegrade A-V block. Scherf and Shookhoffg have suggested the existence of parallel pathways (“functional longitudinal dissociation of the conduction system”); conduction of the impulse is antegrade through one pathway and retrograde through another pathway that might be spared when disease of the conduction system causes antegrade block. Kline et al.1° suggested that a supernormal phase of conductivity is stimulated in the blocked area by the blocked antegrade impulse, and the blocked area is then able to conduct the next ventricular beat in retrograde fashion. Schramm and Korthll suggested that a damaged conduction system might be unable t,o conduct in antegrade fashion, but can be stimulated to conduct in retrograde fashion by a larger impulse that might be generated by depolarization of the ventricle. Scherf12 proposed the possibility that the strength of electrotonic potentials accompanying the wave of ventricular activity allows retrograde conduction. According to this theory atria1 activation is too weak to cross the block in antegrade fashion, whereas ventricular activation is stronger and able to cross the block in retrograde fashion. Other workers have :postulated that the mechanical contraction of the ventricle per se causes depolarization of the conduction system proximal to the block,2 or that the con.traction mechanically stimulates the atria to depolarize and contract.13 Some investigators hold the concept of actual retrograde conduction through a blocked area as yet to be proved.2 Interpretation of His bundle electrograms: As seen in the patient presented here, retrograde conduction does occur and can be demonstrated to exist even in the absence of retrograde P’ waves if the

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bundle of His electrogram is recorded (Fig. 2 and 4). This is evident when a sinus P wave occurring soon after a ventricular complex either does not have a His potential following it or has a prolonged P-H interval. This phenomenon can be explained by retrograde depolarization of the A-V node or the His bundle (or both) by the preceding ventricular complex making it either refractory to the following sinus P wave or producing a conduction delay in the antegrade direction. The phenomenon of His bundle echo beats with a prolonged P’-H interval suggests that the node had recently been depolarized, most likely by the retrograde impulse that stimulated the retrograde P’ wave, and confirms that retrograde conduction through the node had occurred. From our findings we can say that retrograde conduction across the A-V node does occur when block is distal to the bundle of His, and that antegrade and retrograde conduction across the node seem to transverse a single pathway (because the occurrence of retrograde conduction affects the rate of antegrade conduction, that is, prolongs the P-H time). It is not clear if conduction from the ventricles to the node goes through the blocked conduction system distal to the His in a retrograde fashion, or if it goes around the block either through a parallel retrograde pathway or through muscular conduction (as in a right or left bundle branch block). Since most instances of permanent complete heart block are due to block beyond the A-V node in the intraventricular conduction system,14 the occurrence of retrograde activation of the atria can be understood since the node is intact. In the same way that the right ventricle is eventually depolarized in the presence of right bundle branch block, areas of the ventricular musculature proximal to the block might be depolarized and the impulse might get into the intact proximal portion of the intraventricular conduction system and be conducted in retrograde fashion to the atria. It would be interesting to see if retrograde conduction to the atria occurs when block at the A-V node is the cause of complete heart block.

References 1. Scherf D, Cohen J, Orphanos RP: Retrograde activation of atria in atrioventricular block. Amer J Cardiol 13:219-225, 1964 2. Scherf D, Cohen J: The Atrio-ventricular Node and Selected Arrhythmias. Grune & Stratton, New York, 1964, p 208225 3. Damato AN, Lau SH, Helfant RH, et al: Study of atrioventricular conduction in m#an using electrode catheter recording of His bundle activity. Circulation 39:287-296, 1969 4. Winternitz M, Langend& R: Auriculo-ventricular block with ventriculoauricular response. Report of six cases and critical review of the literature. Amer Heart J 27:301-321, 1944 5. Louvros N, Costeas F: Retrograde activation of atria in auriculo-ventricular block. Arch Intern Med (Chicago) 116:778-779.1965 6. Gubbay ER, Mora CA: Retrograde conduction and isorhythmic dissociation in heart block. Amer Heart J 68:166-172. 1964 Retrograde atrial conduction with complete 7. Adams CW: heart block following implantation of an internal ventricular pacemaker. Dis Chest 4:3:544-545, 1963

8. Castillo C, Samet P: Retrograde conduction in complete heart block. Brit Heart J 29:553-558, 1967 Experimentelle Untersuchungen 9. Scherf D, Shookhoff C: Wien Arch Inn Med ueber die “Umkehr-extrasystole”. 12:501, 1926. Quoted in Ref 2, p 220 10. Kline EM, Conn JW, Rosenbaum FF: Variations in A-V and V-A conduction dependent upon the time relations of auricular and ventricular systole: the supernormal phase. Amer Heart J 17:524-535.1939 11. Schramm E, Korth C: Ueber die Rueckleitung automatischer AV-Reize aum Vorhof bei komplettem AV Block. Klin Wschr 16:771, 1937 12. Scherf D: Retrograde conduction in complete heart block. Dis Chest 35: 320-327, 1959 13. Cohn AE, Frazer FR: The occurrence of auricular contraction in a case of incomplete and complete heart block due to stimuli received from the contracting ventricles. Heart 5:141-156,1919 14. Narula OS, Scherlag BJ, Javier RP, et al: Analysis of the A-V conduction defect in complete heart block utilizing His bundle electrograms. Circulation 41:437-448, 1970

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