British Journal, 1975, 37, 583-592. Atrioventricular conduction in patients with clinical indications for transvenous cardiac pacing1

Stafford I. Cohen, L. Kent Smith, Julian M. Aoresty, Panagiotis Voukydis, and Eugene Morkin From the Cardiac Unit, Department of Medicine, Beth Israel Hospital and Harvard Medical School, Boston, Massachusetts, U.S.A.

Eighty patients with clinical indications for cardiac pacing had atrioventricular conduction analysed by His bundle study. The indicationsfor cardiac pacing included high grade , sick sinus node syndrome without , -tachycardia syndrome, unstable bilateral bundle-branch block, and uncontrolled ventricular irritability. Complete , Wenckebach block (Mobitz I), and 2:i block were notedproximal and distal to the His bundle. Mobitz II block only occurred distal to the His bundle. Ofspecial interest were the high incidence ofdistal conduction abnormalities by His bundle analysis (40/80, 5o%), the re-establishment ofnormal atrio- ventricular conduction in acutely ill patients with recent evidence of heart block, and the high incidence of intraventricular conduction disturbances on standard electrocardiogram (48/8o, 60%).

Intensive study of atrioventricular conduction by occurring electrophysiological data in this large His bundle analysis has been performed in a variety group of patients in clinical need of pacemakers of patient populations. In many instances studies constitutes the substance of this report. The data were electively undertaken in patients who had should be representative of the cardiac conduction never been threatened by a compromising cardiac abnormalities which present in a general hospital. . In addition, abnormalities of atrio- ventricular conduction were frequently achieved by Subjects and methods pacemaker-induced acceleration of the atrial rate. Atrioventricular conduction was studied in 8o patients The purpose of this study was to characterize atrio- referred for temporary or permanent cardiac pacing. ventricular conduction in a group of patients who Temporary transvenous pacing was performed via the had clinical indications for a cardiac pacemaker. transfemoral route with a No. 5 bipolar catheter. The ring electrodes were 2 mm in width and spaced I cm Atrioventricular conduction was analysed by His apart. His bundle electrograms were obtained by stan- bundle electrogram in 80 patients who were referred dard methods and were recorded on an 8-channel for transvenous cardiac pacing. The clinical indi- Electronics for Medicine oscilloscope recorder. Acutely cations for cardiac pacing included third degree ill patients had temporary pacemakers inserted and block, second degree block, sick sinus node syn- electrophysiological study conducted in the cardiac drome without tachycardia, bradycardia-tachycardia catheterization laboratory or the intensive care unit. syndrome, unstable bilateral bundle-branch block, Study in the latter area was facilitated by the use of a and uncontrolled ventricular irritability. Data per- fluoroscopic bed and image intensifier. All permanent taining to atrioventricular conduction were obtained pacemakers were implanted in the cardiac catheteriza- during the course of transfemoral venous pace- tion laboratory. Patients who required permanent pace- maker revision or replacement had a No. 5 bipolar maker insertion. The characteristics of atrioven- temporary transfemoral catheter positioned for electrical tricular conduction were noted as well as standard control during the procedure. electrocardiographic evidence of remote or current Bipolar electrograms were obtained by standard intraventricular conduction disturbances. methods which defined atrial excitation (A), His bundle The presentation of the analysis of the naturally excitation (H), and ventricular excitation (V) (Scherlag et al., I969, I970; Damato et al., I969; Damato and Received 28 October I974. Lau, 1970; Scherlag, Samet, and Helfant, I972). His ISupported in part by a training grant from the National bundle electrograms were validated either by an increase Heart and Lung Institute. in the AH interval during spontaneous or induced atrial 584 Cohen, Smith, Aoresty, Voukydis, and Morkin

TABLE I TABLE I (Cont'd)

Case Sex Age His bundle electrogram Case Sex Age His bundle electrogram No. AH (ms) HV (ms) No. AH (ms) HV (ms) Third degree block: absent at study Sick sinus syndrome: without tachycardia-cont'd I M 55 55 95 55 F 79 II2 56 2 F 84 IIO 45 56 M 83 I50 55 3 F 84 I30 35 57 F 78 170 46 4 F 74 250 47 58 M 76 I85 47 5 M 8i 93 IOO, Mobitz I 59 M 8o II5 40 6 F 75 66 5i, Mobitz I 60 M 86 I26 43 7 F 7I I50 35 6i F 73 i60 58 8 M 63 I22 II4 62 F 8i I73 62 9 F 85 I25 40 63 M 70 88 45 IO M 56 62 47 II M 69 I50 38 Bradycardia-tachycardia syndrome 12 F 74 70 68 64 F 70 82 34 I3 M 65 I35 65 65 F 72 120 57 66 F 72 I60 38 Third degree block: present at study 67 M 8i 80 35 I4 F 8i 95 68 F 73 134 66 I5 F 84 100 i6 M 8i 200 Bilateral bundle-branch block 17 M 83 - 69 M 86 258 66 i8 M 74 87 70 M 78 I40 80 I9 F 75 66 7I M 75 I97 54 20 M 77 72 M 83 I05 42 2I M 80 I30 73 M 85 IOO 46 22 M 76 I27 74 F 63 94 35 23 M 73 II5 75 M 72 98 49 24 M 76 88 76 M 6i I06 40 25 F 77 130 77 M 6i 95 54 26 M 70 27 F 75 Control of ventricular ectopia 28 F 74 78 F 78 io8 58 29 M 68 92 79 M 76 i6o 35 30 M 86 80 M 78 I05 40 31 M 6i 145

Second degree block: absent at study 32 M 60 125 70 premature beats (Scherlag et al., I969) or by His bundle 33 F 86 I05 I40 pacing (Scherlag et al., 1972; Narula, Scherlag, and 34 F 79 120 40 Samet, 1970b). The AH interval generally delineated F 35 84 125 conduction time, the normal range Second degree block: present at study of which is 50 to 120 ms. Measurements were made 36 M 68 ioi 67, 2:I from the onset of the A wave to the first clear deflection 37 M 86 253, Mobitz I 49 of the H wave. Prolongation of atrioventricular node 38 F 80 232, Mobitz I 45 conduction time was defined as first degree block of the 39 F 83 145,2:1 4I atrioventricular node. 40 M 77 102 75, 2:1 The HV interval delineated His-Purkinje conduction 41 F 80 87 87, 2:I time, the normal range of which was taken as 35 to 54 ms 42 F 8o 148 53, 2:I (Kuppersmith, Krongrad, and Waldo, I973). Measure- 43 F 79 I20,2:I 53 44 M 7I 62 57, Mobitz II ments were made from the first clear deflection of the H 45 M 6i 66 77, Mobitz I wave to the earliest onset of ventricular excitation pre- 46 F 84 88 75, Mobitz I senting in one of several sampled standard electro- 47 F 84 99 80, Mobitz I cardiographic leads or the bipolar electrograms (V 48 F 65 ioi IIO, Mobitz I wave). The HV interval is one measurement of con- 49 M 43 120, Mobitz I 58 duction through the distal specialized conduction system. 50 M 66 375, Mobitz I 47 Prolongation of the HV interval was defined as first Sick sinus syndrome: without tachycardia degree block of the intraventricular conduction system. were 5I M 64 87 34 All available electrocardiograms reviewed for 52 M 72 150 40 evidence of intraventricular conduction abnormality in 53 F 73 94 35 the bundle-branch system. Abnormal conduction in the 54 F 69 123 38 right bundle-branch, left bundle-branch, anterior divi- sion of the left bundle-branch, and posterior division of Atrioventricular conduction in patients with clinical indications for transvenous cardiac pacing 585

TABLE 2

Group No. of Normal I0 block 20 block 30 block patients atrioven- tricular AVN IVC AVN IVC AVN IVC conduction Mobitz I 30 block absent at study I3 2 5 2 2 2) (2 30 block present at study i8 6 7 5) (5 Sick sinus syndrome I3 4 5 I 3) (3 Bradycardia-tachycardia 5 2 I I syndrome Bilateral bundle-branch block 9 6 I 23 -(2 Suppression of ventricular 3 I I I ectopia

Group No of Normal I° block 2° block 2:I block patients atrioven- tricular AVN IVC AVN IVC AVN IVC conduction Mobitz Mobitz Mobitz Mobitz I II I II 2° block absent at study 4 I I 2) (2 20 block present at study 15 3 4 I 2 3 I) (

)-( This symbol indicates more than one abnormality. The number of patients with the combined abnormality are noted by the number on the open ends of the symbol. AVN = Atrioventricular node, IVC = Intraventricular conduction. the left bundle-branch, respectively, result in right study (Fig. I and 2). First degree block of the atrio- bundle-branch block, left bundle-branch block, left axis ventricular node was present in 5 patients. First deviation, and (Rosenbaum, Elizari, degree block in the distal conduction system was and Lazzari, I970; Cohen et al., I968). Combined dis- present in 2 patients. Combined first degree block turbances in more than one conducting pathway can be in the atrioventricular node as well as in the distal recognized by combinations ofthese features. was 2 The 80 patients had an average age of 75 years, with specialized conduction system present in the 44 men averaging 72 years and the 36 women aver- patients. Wenckebach phenomenon (Mobitz I block) aging 77 years. The patients were grouped as follows: was present in the distal conducting system in 2 transient third degree block absent at study (I3), third patients. degree block during study (i8), second degree block Fixed third degree block during study was present absent at study (4), second degree block during study in I8 patients, of whom 6 had block at the atrio- (I5), unstable bilateral bundle-branch block (9), ven- ventricular node (failure to demonstrate a His tricular irritability (3), sick sinus syndrome (without deflection) and I2 had block in the distal specialized tachycardia) (I3), and bradycardia-tachycardia syn- conducting system. Among the I2 patients who had drome (5). distal block, 5 had associated first degree block in the atrioventricular node. Results Transient second degree block was present before study in 4 patients. One patient had normal Atrioventricular conduction conduction at the time of study, i patient had first The results ofatrioventricular conduction studies are degree block in the distal conducting system, and 2 detailed in Table i and summarized in Table 2. Of I3 patients had first degree block of both the atrio- patients with transient third degree block before ventricular node and distal conducting system. study, only 2 had normal conduction at the time of Second degree block was present during study in 586 Cohen, Smith, Aoresty, Vouhydis, and Morhin

MONITOR LEAD ..... DAY I

..

LEAD II DAY 3 7 r .

FIG. Third degree heart bloch with acute . Top panel: this patient entered hospital with complete heart bloch. Though a temporary pacemaher was promptly in- serted, atrioventricular conduction had returned to normnal at the time of study (Fig. 2). Bottom panel: third degree bloch intermittently recurred during the stay in hospital. S=pacemaher stimulus induced ventricular excitation.

A rate g2 min

BE ~~AHVA V A V

A+i(msec) 62 62 62 H-V(msec) 47 47 47

B rate. 133 min Isec _p.1

A V A V A V A V A V BE

A-H 66767 67 67 H-V 47 47 47 47 47

FIG. 2 Normal atrioventricular conduction shortly after third degree heart bloch (Fig. s). Toppanel: normnal atrioventricular conduction at a rate of90/minute. Bottompanel: atrioventric- ular conduction remains normal with acceleration of rate to 133/min by atrial pacing. Abbrevia- dions in this and other figures: A = atrial excitation. H= His bundle excitation, V = ventricular excitation, BE = bipolar electrogram, B = atrial pacing stimulus. Atrioventricular conduction in patients with clinical indications for transvenous cardiac pacing 587

I5 patients. Wenckebach block (Mobitz I) occurred during the tachycardia. Two patients had normal at the atrioventricular node in 4 patients (Fig. 3) atrioventricular conduction, and there was one in- and also was noted in the distal conducting system stance each of first degree block of the atrioventric- in 4 other patients (Fig. 4). One patient had Mobitz ular node and of the distal conduction system. The II block in the distal conducting system (Fig. 5). remaining patient had first degree block of both Three patients had 2: I block which occurred in the the atrioventricular node and of the distal conduc- distal conduction system (Fig. 6). Two patients had tion system. 2: i block of the atrioventricular node (Fig. 7). An Nine patients had unstable bilateral bundle- additional patient had 2: i block in the distal con- branch block. Six of this group had normal atrio- ducting system and first degree block at the atrio- ventricular conduction, I had first degree block of ventricular node. the atrioventricular node, and 2 had combined first Sick sinus node syndrome without tachycardia degree block of the atrioventricular node and distal occurred in I3 patients. The ventricular response conducting system. was correspondingly too slow to sustain a haemo- Implantation of a permanent pacemaker for con- dynamic compensation. Four patients had normal trol of ventricular irritability was performed in atrioventricular conduction, 5 had first degree block three patients. One patient had prolonged His- of the atrioventricular node, 3 had combined first Purkinje conduction time. Another had prolonged degree block of the atrioventricular node and distal atrioventricular node conduction. The remaining conducting system (Fig. 8), and i had first degree patient had normal atrioventricular conduction. block of the distal conducting system. Bradycardia-tachycardia syndrome was present in 5 patients. This syndrome is characterized by sinus Intraventricular conduction on standard bradycardia which is interrupted by a variety of electrocardiogram rapid supraventricular . The patients Review of standard electrocardiograms before the may be symptomatic during the bradycardia or development of heart block during hospitalization

RRnmsec) 1004 1000 I

V S: A-A(msec) A-A(msec) 980 A BE }4A^ HV A H V HV _-_I------_ + >* A-H (msec) 254 320 330 H-V(msec) 49

CONTINUOUS RR -o03

A-A 9a5 I"0 l000 BE A H V A A H V

A-H 360 253

H-V 49

FIG. 3 Mobitz I block of the atrioventricular node. There is a progressive delay ofatrioventric- ular node conduction. AH interval increases from 254 ms to 360 ms during four cardiac cycles until failure of transmission through the atrioventricular node. The first and last beats on the continuous recording have the shortest, though considerably prolonged, atrioventricular nodal conduction times of 254 and 253 ms. 588 Cohen, Smith, Aoresty, Voukydis, and Morkin

PNRh(secl 182 194 /7'7

V 'I,/

AN V A H V A H A H V BE

A Hrsec) 66 66, 6.. H}V, sw,c 82 94

OCINTINULOS ~ ~ ~ ~ ~ ~ ~ ~ ~ -*------s~

P R Onse<: ^ - 21)...... - V~~Ir,V-o~--W_.SW_

A H V AH V ANH AH V BE ^- _ sser > _ ANr(msec) 66 66 66 66 HV(msec) 99 110 77 pt JR FIG. 4 Mobitz I block of the distal conduction system. There is a progressive delay of intra- ventricular conduction (HV interval) from 82 ms to 94 ms and from 77 ms to IO ms during two-beat and three-beat sequences respectively, until transmission through the distal system fails. The abnormally delayed distal conduction in the first beat of each new cycle indicated first degree block of the right bundle-branch in the setting of this patient's left bundle-branch block.

I SEC

AHV AHV BE AHV AN AHV AH

*N1 msec1 62 62 62 H-V (msec) 57 5?o7 57

FIG. 5; Mobitz II block of distal system. There is first degree block of the distal system. The first two beats are conducted normally. Without warning, the third and fifth atrial excitations (arrows) are not conducted to the ventricles. Atrioventricular node conduction is unchangedfor all beats. Atrioventricular conduction in patients with clinical indications for transvenous cardiac pacing 589

A B CHEST -lHUMP

It DK C

...... - _ S 'e. . .41 v I/

AH AH V AH AH V

..,._ - V Al

A-H(mrSC) 81 57 87 87 HV(mseC) - 87 87

D I

AH AH V AH V AH BE A-Humsec) 87 87 H-V(msec) ,08 FIG. 6 2:I block and Mobitz I block in the His-Purkinje system. This patient presented with a basic 2:I block, rare episodes ofMobitz I block (A), and (B). Intracavitary electrograms demonstrated the 2:I block and the Mobitz I block to be localized distal to the His bundle (C, D). In addition, there is first degree block of the intraventricular conduction system.

5-1-72 1-sec

BEI A HV

BE A M{V A A AHV A r AHFV ,_. P ~~~~~~~~~~ -~~~~~~~~~~~~~~~~~~~~~~~~~~~ -~~~~~~~~~~~~~~~~~

145 145 _ A-H(nc) 1 41 41 H-V(msOc) 41 pt 3F

5/_s.. 1-sec

I

A HV A AV_-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~A HV A HV A H V A 8-~~~~~~~~~~~~~~~'\ ~1, BE- A-H (rnsec)l55 155 155 155 155 HM-V(mec)41 41 41 41 41pt B FIG. 7 2:I block at the atrioventricular node in acute inferior myocardial infarction. Top panel demonstrates 2: i block of the atrioventricular node on thefirst day of acute inferior myo- cardial infarction. On the sixth day the atrioventricular node has recovered enough topermit I: I conduction. Note a persistentfirst degree block at the atrioventricular node. 590 Cohen, Smith, Aoresty, Voukydis, and Morkin

.., ___ _ -1 SEC

A H v, A H V BE It

A-H (msec) 150 150 H-V (msec) 55 55 pt JL

FIG. 8 First degree block of the atrioventricular node and the intraventricular system. or at the time of study in the presence of atrio- Underlying cardiac disease ventricular conduction, revealed a high frequency of The whole series included a predominance of intraventricular conduction abnormalities such as patients with symptoms of ischaemic heart disease right bundle-branch block, left bundle-branch (72 patients). Other diagnoses included presumed block, right axis deviation (greater than + go9), and idiopathic fibrosis of the conduction system (S), (more leftward than -30°). high with disease (2), Right bundle-branch block with right or left axis and (i). deviation was considered a manifestation of bilateral bundle-branch block. The frequency of intraven- in was tricular conduction abnormalities each group Discussion as follows: third degree block absent at study, 6 of I3 patients; third degree block present at study, ii of His bundle study separates atrioventricular conduc- i8 patients; second degree block absent at study, 2 tion into two major components consisting of atrio- of 4 patients; second degree block present at study, ventricular node conduction and His-Purkinje I2 of I5 patients; sick sinus node syndrome, 4 of intraventricular conduction. The present study I3 patients; bradycardia-tachycardia syndrome, 2 characterized atrioventricular conduction in an of 5 patients; ventricular irritability 2 of 3 patients. elderly population that required cardiac pacing. The specific conduction abnormalities are summar- Standard electrocardiograms revealed a high inci- ized in Table 3. dence of intraventricular conduction delay. Isolated

TABLE 3 Intraventricular conduction disturbances

Group No. of Right bundle- Right bundle- Left axis Left bundle- All intraven- patients branch block branch block+ deviation branch block tricular conduc- left axis deviation tion defects (%) 30 block Absent at study I3 I 2 3 46% Present at study I8 2 5 I 3 6i% 20 block Absent at study 4 I I 50% Present at study I5 I 6 2 3 80% Sick sinus syndrome I3 2 I I 3I% Brady-tachy syndrome 5 I I 40% Bilateral bundle-branch block 9 9 I00% Ventricular irritability 3 I I 37% Totals 80 5 27 5 II 60% Atrioventricular conduction in patients with clinical indications for transvenous cardiac pacing 591 and combined atrioventricular conduction abnor- reference has been made to a pathological process malities were frequently noted during His bundle which extended from the distal conduction system study. The two most common diffuse underlying to the atrioventricular node (Narula et al., 197I; pathological processes causing high degree heart Rosen et al., I97I). The presumption of a process, block are fibrosis ofthe conduction system (Lenegre's such as a diffiuse coronary disease, or more than one disease) and ischaemic heart disease (Lenegre, ageing process, might explain the combined conduc- I962, I964; Davies, I97I). Our population had an tion abnormalities of this study and in other studies average age of 75 years; go per cent of the patients (Rosen et al., 197I). James (I972) has noted that suffered symptoms of cardiac ischaemia and 6o per coronary disease may directly produce abnormalities cent had standard electrocardiographic evidence of of the entire conduction system and may be assoc- abnormal conduction in at least one of the major iated with degenerative disease of the conduction intraventricular conducting pathways. system. In most patients it is likely that an ageing process of the conducting system becomes generalized before the occurrence of a clinical problem which Normal atrioventricular conduction shortly requires pacemaker therapy (James, I972); in spite after atrioventricular block of anatomical observations that pathological ageing Two patients with combined acute anterior and in- processes distinguish between the- atrioventricular ferior infarctions, had intermittent third degree node and remainder of the conducting system block. Though drugs were admin- (Davies and Harris, I969), isolated abnormalities istered, intermittent third degree block occurred of distal conduction as defined by HV time and before and after catheter insertion (Fig. 2) and both isolated abnormalities of atrioventricular node con- patients died from pump failure. duction were found with almost equal frequency. Transient second degree block occurred in There were 23 instances of the former and 24 in- another patient with an acute anterior infarction. stances of the latter. Fifty per cent of all patients Atrioventricular conduction was normal at the (40/80) had an infra-His conduction abnormality time of study. Normal atrioventricular conduction confined to the distal system or combined with a precluded localization of the site of block. However, conduction abnormality of the atrioventricular it is likely that the rapid change from normal to node. Examples of the high frequency of distal abnormal atrioventricular conduction resulted from block were as follows: second degree block of the ischaemia to the conduction pathway(s) (Whiting Mobitz I variety occurred six times in the distal et al., I970; Nevins, I972). Other parameters such system (Fig. 4) and four times in the atrioventricular as and blood pressure have been impli- node (Fig. 3). 2:I block occurred four times in the cated in the development of ischaemic atrioventric- distal system (Fig. 6) and twice in the AV node ular block (Gershengorn and Haft, I972). (Fig. 7). Mobitz II block occurred once and was in the distal system (Fig. 5). Our finding of a high incidence of distal conduction abnormality supports the findings of others in chronic third degree heart Intraventricular conduction disturbances on block (James, I972; Narula et al., I97oa; Steiner et standard electrocardiogram al., I97I), Mobitz II block (Narula and Samet, Abnormality of intraventricular conduction of the I970; Narula et al., I97I; Samet and Narula, I970; electrocardiogram varied from 3I per cent (4/I3) in Gupta, Lichstein, and Chadda, I973), and sick sinus the sick sinus syndrome to I00 per cent (9/9), by node syndrome (Samet and Narula, I970). definition, in unstable bilateral bundle-branch Combined physiological abnormalities of the block (Table 3). We have previously mentioned the atrioventricular node and distal conduction system high incidence of distal conduction abnormality as occurred in 17 of our patients (2I%), which corre- defined by HV time in third degree block (James, sponds with anatomical observations, such as Lene- 1972; Narula et al., I97oa; Steiner et al., I97i) and gre's (I964) that combined atrioventricular node and sick sinus node syndrome (Samet and Narula, I970). distal pathology was present in I6 per cent of 62 It is not surprising, therefore, to find a respective cases of complete heart block. Combined first 6i per cent and 3I per cent abnormality of intra- degree block was documented in 10 patients (Fig. ventricular conduction in standard electrocardio- 8). First degree block of the atrioventricular node grams of patients in these categories. Patients in occurred in combination with second degree block other categories uniformly had a high incidence of of the distal system in i patient and in combination electrocardiographic intraventricular conduction ab- with third degree block of the distal system in 5 normality. Bilateral bundle-branch block in associa- patients. On the basis of repeated His bundle study, tion with third degree block has been noted by 592 Cohen, Smith, Aoresty, Voukydis, and Morkin

many observers (Friedberg, Donoso, and Stein, axis deviation (with left parietal and peri-infarction block) I964; Lasser, Haft, and Friedberg, I968; Scanlon, to complete heart block and syncope. Circulation, 37, 429. LenAgre, J. (i962). Les blocs auriculo-ventriculaires complets Pryor, and Blount, 1970; Ehsani et al., I972). There chroniques: etude des causes et des lesions a propos de 37 is a well-recognized relation between Mobitz II cas. Malattie Cardiovascolari, 3, 3II. block and third degree block. Narula et al. (I97oa) Len6gre, J. (I964). Etiology and pathology of bilateral bundle described I3 patients with Mobitz II block, io of branch block in relation to complete heart block. Progress in Cardiovascular Diseases, 6, 409. whom had electrocardiographic evidence of abnor- Narula, 0. S., and Samet, P. (I970). Wenckebach and Mobitz mal intraventricular conduction. Four of these type II A-V block due to block within the His bundle and patients had complete heart block. 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