The Significance of Second Degree Atrioventricular …circ.ahajournals.org/content/circulationaha/49/4/638.full.pdf · The Significance of Second Degree Atrioventricular Block and

The Significance of Second Degree Atrioventricular Blockand Bundle Branch Block

Observations Regarding Site and Type of Block

By RAMESH C. DHINGRA, M.D., PABLO DENES, M.D., DELON WU, M.D.,RUBEN CHUQUIMIA, M.D., AND KENNETH M. ROSEN, M.D.

SUMMARYHis bundle (H) electrograms were recorded in 15 patients with second degree atrioventric-

ular (A-V) block and bundle branch block and these patients were prospectively followed. Site ofblock was proximal to H in four (BPH), distal to H in nine (BDH), and undetermined in two(studied during 1:1 conduction). Surface electrocardiographic features were retrospectively ex-amined to determine the value of these recordings in predicting the site of block. Patients withtype I block, with or without type II or 2:1 block, had BPH. Patients with type II block, 2:1block, or type II combined with 2:1 block had BDH. Heart failure was more common in thosewith BPH (three of four patients as compared to three of nine patients with BDH). Syncopedeveloped more commonly in patients with BDH (six of nine patients) as compared to those withBPH (one of four patients). Permanent pacing was indicated in three of four patients with BPH,nine of nine patients with BDH, and one of two patients with block at undetermined site be-cause of syncope or heart failure. Five of nine patients with BDH required pacemakers within tendays of initial admission.

Most patients with second degree A-V block and bundle branch block will need permanentpacing. In patients with 20 BDH, pacemakers are indicated whether or not symptoms are pres-ent because of high risk of syncope and potential risk of sudden death. In asymptomatic patientswith 2° BPH, careful observation is indicated.

Additional Indexing Words:His bundle electrogram Conduction diseaseLev's disease Lenegre's disease Mobitz blo(

JT HAS BEEN SUGGESTED that type I seconddegree block usually occurs in the atrioventricu-

lar (A-V) node, reflects a functional disturbance ofconduction, and has a benign clinical course.1 2 Incontrast, type II block, is said to reflect bilateralbundle branch block, represents structural disease

From the Cardiology Section, Abraham Lincoln School ofMedicine, University of Illinois College of Medicine; WestSide Veterans Administration Hospital; and Department ofAdult Cardiology, Cook County Hospital, Chicago, Illi-nois.

Supported in part by NIH contract 71-2478 under theMyocardial Infarction Program, National Heart and LungInstitutes, National Institutes of Health, Department ofHealth, Education and Welfare, and West Side VeteransAdministration Hospital, Chicago Basic InstitutionalSupport.

Address for reprints: Kenneth M. Rosen, M.D., Cardi-ology Section, University of Illinois Hospital, P.O. Box 6998,Chicago, Illinois 60680.

Received July 2, 1973; revision accepted for publicationNovember 30, 1973.

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Wenckebach periods Pacemakers

in the His-Purkinje system, and has a malignantclinical course.Most observations regarding type I block have

been made in patients with narrow QRS and eitherinferior myocardial infarction or digitalis intoxica-tion. Most observations concerning type II blockhave been made in patients with bundle branchblock and massive antero-septal infarction, or inisolated cases with pre-existent bundle branchblock.8-1

The natural history of type I and II block may infact reflect the clinical circumstances in which theseblocks tend to occur, and not the intrinsic behaviorof either the type or site of block.

In this study, we have examined the clinicalcourse of patients with second degree A-V blockand pre-existent bundle branch block. This grouphas been chosen for analysis since the wide QRS isconsistent with a site of block either proximal to ordistal to the His bundle. The group was clinicallyhomogeneous, and thus thie influence that the type

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PROGNOSES FOR 20 A-V BLOCK AND BBB

and site of block had on subsequent course could beevaluated. We have also examined the accuracy ofsurface electrocardiographic criteria in predictingthe site of block in this group of patients withsecond degree block and bundle branch block.

Methods

Definitions

The following electrocardiographic definitions were

utilized. Second degree block was defined as in-complete A-V block with dropped ventricular beats.Type I second degree block was characterized byprogressive prolongation of conduction intervals preced-ing the dropped beat, and type II block by fixedconduction intervals for two or more beats precedingthe dropped beat. Two to one block was not classifiedas to type. Left and right bundle branch block were

diagnosed using standard electrocardiogiiaphic cri-teria.1' Left anterior and posterior fascicular blockwere diagnosed utilizing the criteria of Rosenbaum.12

Patient Selection

During the past two years, all electrocardiograms inthe West Side Medical Center (University of IllinoisHospital, West Side Veterans Hospital, and CookCounty Hospital) have been screened by members ofthe respective cardiology departments for the presenceof conduction disease. This report details our totalexperience with previously undiagnosed second degreeblock and bundle branch block, detected in either themedical clinics or the hospital emergency rooms.

Although a number of the patients were symptomatic atthe time of admission, the presence of this combinationof conduction defects, even without symptoms, was

considered cause for admission. Specifically excludedfrom the study group were patients with acutemyocardial infarction, and patients with bundle branchblock who developed the second degree block patternwhile hospitalized for cardiovascular or other disease.Clinical and electrocardiographic data from the studygroup are summarized in table 1. More detailed analysisof the patients is presented in the appendix.

Electrophysiological Studies

His bundle electrograms were recorded in allpatients, usually at the time of temporary pacemakerinsertion, with previously described catheter tech-niques.13 14 Eleven of the patients were in seconddegree block at the time of study. Four of the patientshad 1:1 A-V conduction at the time of study. In two ofthese, a probable site of second degree block was

established utilizing atrial pacing. In the other twopatients, a probable site of block could not bedelineated.

His bundle electrograms were differentiated fromatrial electrograms by noting typical A-H Wenckebachsequences during either spontaneous or atrial pacedepisodes of type 1 block. His bundle pacing was notutilized for validation.

Patient Follow-up

This study was conducted concomitantly with a largeprospective study of patients with bifascicular blockand intact conduction. The prospective study of seconddegree block and bundle branch block was complicatedby the fact that only three of the 15 patients were

totally asymptomatic when first seen. However, an

attempt was made to judiciously define the naturalhistory of second degree block and bundle branch blockin both asymptomatic and symptomatic patients. In

Table 1

Clinical and Electrocardiographic Data

ElectrocardiogramQRS

Patient Age Sex Clinical diagnosis Type of 20 Block Axis Complex

1 75 M Calcific AS Type I & 2:1 -100 RBBB2 52 M ASHD Type I & II - 300 LBBB3 76 M ASHD Type I & II -150° RBBB4 62 M ASHD, Dig Int Type I +1000 RBBB5 75 M HCVD 2:1 +900 RBBB6 58 m ASHD Type II & 2:1 - 300 LBBB7 78 M ASHD Type II & 2:1 - 600 LBBB8 42 m AS 2:1 +200 LBBB9 41 F ASHD Type II & 2:1 +750 RBBB10 72 M ASHD Type II & 2:1 -100 LBBB11 82 M ASHD Type II & 2:1 - 300 LBBB12 80 F HCVD 2:1 -750 RBBB13 54 M ASHD 2:1 -10° LBBB14 54 m RHD Type II -300 LBBB15 51 M ASIID Type I & II -600 RBBB

Abbreviations: M = male; F = female; ASHD = Arteriosclerotic heart disease; AS = Aortic stenosis;HCVD = Hypertensive cardiovascular disease; RHD = Rheumatic heart disease; RBBB = Right bundlebranch block; LBBB = Left bundle branch block, and Dig Int = I)igitalis intoxication.


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several of the patienits, it xvas obviois, at or soon afteradmiiission, that permanenit pacing was iildicated, basedupon eitlher the severity of l)radycardia, a hiistory ofseveral syncopal episodes, or evidence of significantcongestive failuri.e complicating the bradyarrhythmia.These patienits were treated with permanent pace-miiakers on the initial addmissioni. Those patienits. in vhominiitial symptoms did not appear to niecessitatepermanent pacemaker insertion were discharged afterproloniged inpatient monitoring and were followed atclose intervals in a coniduction disease clinic. Subse-quent recuri-ren-ce of synicope and/ or development ofconigestive failurie ws ere cons-idered cause for rehospital-izationi anid implanitation of permanent paceemakers.Detailed ainalysis of follow-up anid therapy is presenitedin the appeindix.

Results

Electrophysiological Studies

Fouir patients were conisidered to have seconddegree block at the A-V niode (cases 1-4) (table 2).In three of these, sponitaineous 2° block proximal toH was noted during electrophysiological study. Thefourth was conisidered to have 20, A-V niodal blockbecause of prolonged A-IL intervals (greater thani130 msee) and development of type I block proxi-mal to H at an atrial paced rate of 100 beats/min.14All fouir of these patients maniifested type I block

Table 2

Electrophysiological Data

Patient A -i r-v Site ofNo. (msec) (rnser) 2 Btock

50(- P I.()x

2 -- 131o)x3 6.) Prox

4 1:38 48 PrIox

(prba'ble)79 I)ist

(6 91) (65* I)ist7 145) 7.5* )ist8 126 k list9) 84 (6iS* l)isl

l(1 l6t) 80* list-

1 2 1 (5 69* I)isf1 3 93 74 I)ist

(probable)14 88 7:3 UTnikniowni

Ti pe of 2° Block(lutring study

I & III (at pa ed rate

of 10t)/minuitie)II1I & 2:111 & 2:1Ir11 & 2:12:1IT2:1II (at paced rate

of 127 /iIinutte)I Proximal to II

(at paced rate of160/minut.te)

15 12.5) 42 VniJkiioxn I Proximal to IT(at paced rate of16.5/minute)

Abbreviations: Prox = Proximal to the His burndle; Dist- l)istal to the Hlis bun(Ile, and * =- \-V interval of coii-dueted beats.

A

A A H A H' A A H

Figure 1

Case 2. El cti.oairdiographi rhyjrli strip V1 tho big type Isecond dlegree atriovenitricutlar. (A-V) block and left bunidlebranch block. There is progressive prolongation of P-Rintervals prior to the dropped P weave. Panels A and Bare s:imuiltanieouis His buindle clectrogra ins (H-BE) of thesoanic patient. Thec P waves are labeled A (atrial electro-grain), His buindle potentials labeled H, and A-H intervalsare listed. Paper spieed is .100 mc7i/sl,ec anid timielines are atone second or this and allsibsequenit illustrations. Panel A)20 A-V block (type I) p)roxim7al to H. Note there is pro-gressive prolongation of A-H intervals and the fourth P isblocked proximal to H. Panel B) 20 A-V block proximal toH. Here the A-Fl intervals are relatively constant suggestingtype II block.

proximal to H during the electropb .siologicalstudies (figs. 1A and 2A). Two of these patienlts(Cases 2 and 3) had, in additioni, episodes of typeII block proximal to H (figs. lB and 2B).

In eight patienits, spontaneous seconid degreeblock was distal to the His bu-ndle (Cases 5-12).Onie additionial patient (Case 13) was felt to have2 A-V block distal to H because of prolongved H-Vinterval and development of type II block distal toHI at a paced rate of 127/mnin. All had type II blockor 2:1 block during the stuidy (figs. 3 and 4). Seveniof these nine patients with 2° block distal to H hadprololnged H-V intervals (greater than 55 msec).14None of these patients had type I block distalto H.

In txvt) patients, site of second degree block wasconsidered undetermined (Cases 14 and 15)because of normal pacinlg resp5oises at the time ofstudy. Onie of these had a considerably prolongedH-V initerval (73 msec) suggesting bilateral bunidlebranch disease.

Surface Electrocardiogram and Site of Block

Onice the site of block xvas determined, surfaceelectrocardiographic features could be retrospec-tively examined to determine their value in


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Figure 2

Case 3. Rhythm strip V1 showing type II, 2~ A-V block

and right bundle branch block. The PR intervals are con-

stant before a dropped P wave. Panels A and B are His

btundle electrograms (HBE) of the same patient. EGG leads

I, 11, III and V. are also shown. Panel A) 2' block proximal

to H, with gradual prolongation of A-H interval prior to

blocked P wave (type I). Paniel B) 20 block proximal to H,

with fixed A-H interval before the dropped beat (type II).

The long A-H following the dropped P may reflect repeti-

tive concealed conduction.

predicting the site of block (table 3). Several

features are of interest. Left bundle branch block

was more commonly associated with block distal to

H, while right bunidle branch blo.ck was equally

associated with block either proximal or distal

All patients with type block, with or without

type block, and with or without 2:1 block, had a

L.!

Figure 3Case 5. 2:1 block distal to H. Shown are rhythm strip leadII, and HBE of the same patient. Note the H potential fol-lowing each P wave. Every second H impulse is not con-ducted to the ventricles. The QRS morphology is of rightbundle branch block pattern.


F 1. r- 't-n~r---

Figure 4

Case 7. Type II, 2' A-V block distal to H. Rhythm strip V1shows Mobitz type II block with left bundle branch block.Lower panel is HBE from the same patient. Note that thethird P is blocked distal to H.

site of block proximal to H (with the exception ofone patient with undetermined site of block). Inconitrast, the site of the block in all patients withtype II block alone, or type II with 2: 1 block, wasdistal to H (with the exception of one patient withundetermined site of block). All patients with 2:1block alone had block distal to H.

Symptomns and Clinical CourseCongestive heart failure occurred more common-

ly in patients with block proximal to H, with threeof four patients (75%) developing this condition ascompared to three of nine patients (33%) withblock distal to H (P<K 0.01) (table 4). Syncopeoccurred less frequently in patienits with blockproximal to H occurring in one of four patients,(25%) as compared with six of niine patients (66%)with block distal to H who experienced syncope(p <0o.01).The site of block was analyzed with respect to the

patient's clinical course. Two of four patients with2- block proximal to H had a permanent pacemakerinserted. One had congestive heart failure andbradyeardia within one month of diagniosis and theother developed syncope at two and a half monthsafter diagnosis. A third patient with second degreeblock proximal to H developed intermittent com-plete heart block and congestive heart failurewith dizziness one month after diagnosis but hasrefused pacemaker implantation. One patient has20 block proximal to H while receiving digitalis.Second degree block has recurred once in thispatient three mon(ths later while off digitalis. Thispatient has remained asymptomatic without per-manent pacing.

All nine patients with block distal to H requiredpermanent pacemaker implantation. Five requireda pacemaker within ten days of admission, three

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Table 3

Correlation of Electrocardiographic Features with Site of Block

Patients Patients PatientsSurface ECG with block with block wvith unknown

findings proximal to H distal to H site of block

Bundle Branch BlockLBBB (8 pts) 1 (12%) 6 (75%) 1 (12%)RBBB (7 pts) 3 (43%) 3 (43%) 1 (14%)

A-V BlockType I Block with or without Type II or 2:1 (5 pts) 4 (80%) 0 (0%) 1 (20%)Type II Block alone or with 2:1 (6 pts) 0 (0%h) 5 (80%) 1 (20%)2:1 alone (4 pts) 0 (0%) 4 (100%) 0 (0%)

Abbreviations: LBBB = Left bundle branch block;Patients.

with syncope and two with congestive heart failure.Three patients developed syncope at two to fourmonths after diagnosis. The one remaining patientdeveloped congestive heart failure within twomonths following diagnosis and was treated withpermanent pacing.One of the two patients with an unknown site of

block required a pacemaker within three monthsof diagnosis because of syncope; the other patientwho did not need pacemaker implantation hasbeen followed for three months and remainsasymptomatic.

RBBB = Right bundle branch block, and Pts

Discussion

The electrocardiographic classification of seconddegree A-V block into Mobitz types I and II isbased upon the behavior of PR intervals prior to thedropped beat.'5 Type I block is characterized typrogressive prolongation of PR intervals before a

blocked P wave, while in type II PR intervals arefixed. McNally et al. and Langendorf et al.suggested that type II block reflected bilateralbundle branch disease with likelihood of progres-sion to higher degree of block.1 2 These conclusionswere supported by sporadic case reports of patients

Table 4

Correlation Between Site of Block and Clinical Outcome

Days betweendiagnosis and

Patient Site of block Syncope Dizziness CHF PPMR PPMR insertion

1 Prox - - + Yes 262 Prox - + + Ind -

(ref)3 Prox + - - Yes 774 Prox - - + No -

(Probable)5 Dist + - - Yes 86 Dist - - + Yes 37 Dist + + - Yes 498 Dist + - - Yes 869 Dist - + + Yes 6410 Dist - - + Yes 611 Dist + - - Yes 912 Dist + - - Yes 313 Dist + + - Yes 128

(Probable)14 Unk - - - No -

15 Unk + + - Yes 87

Abbreviations: Prox = Proximal; Dist = Distal; Unk = Unknown; CHF = Congestive Heart Failure;PPMR = Permanent Pacemaker Insertion; Ind = Indicated, and Ref = Refused.


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with type II block and bundle branch block, orfrom observations of patients with second degreeblock and acute antero-septal myocardial infarc-tion.7 10 In contract, type I block was said to reflectA-V nodal dysfunction, with much less risk ofprogression of conduction disease. These conclu-sions were supported by observations in patientswith narrow QRS and either digitalis intoxication oracute diaphragmatic infarction. 7 The clinicalcourse associated with type I and II block mayreflect the associated clinical conditions and not theintrinsic behavior of either site or type of block.The His bundle recording technique has provided

a means for delineating the site of block other thanthe surface electrocardiographic criteria.1'-8 Hisbundle recording in patients with type I block (andgenerally narrow QRS) has revealed a site of blockproximal to the His bundle (A-V node). However,several patients with type I block distal to H havebeen reported.'9-22 All of these patients hadantecedent bundle branch block, suggesting thatWenckebach periods were occurring in the contra-lateral bundle branch.

In most patients studied with type II block thesite of block has been distal to the His bundle.16'9Almost all of these patients have had bundle branchblock. Several patients have been described withtype II block and narrow QRS, these patientshaving either block in or proximal to the Hisbundle. 9' 23

Thus, the His bundle recording technique has ingeneral confirmed most previous speculations re-garding the relationship between type of block andsite of block. However, this confirmation dependedprimarily upon comparison of patients with type Iblock and narrow QRS and patients with type IIblock and wide QRS. The results of the presentstudy in patients with bundle branch block andsecond degree block also partially confirm previousspeculations. Patients with type I block, with orwithout type II block or 2:1 block, had a site ofblock proximal to the His bundle. Patients withtype II block alone, 2:1 block alone, or type II and2:1 block had a site of block distal to H.The presence of bundle branch block in all

patients in this series suggested a high risk ofbilateral bundle branch disease. Left bundle branchblock was associated with a very high incidence ofsecond degree block distal to H, e.g., second degreeblock distal to H in six of seven patients withLBBB. In contrast, RBBB was associated with anequal incidence of second degree block proximaland distal to H. These findings are consistent withCirculation, Volume XLIX, April 1974

results of His bundle recording in patients withbundle branch block and intact conduction.21 24,25H-V prolongation suggesting bilateral bundlebranch disease is frequently seen in patients withleft bundle branch block. In addition, pathologicalstudies in patients with left bundle branch blockhave revealed signfficant involvement of bothbundle branches.2.6 However, it should be notedthat A-V nodal disease can be a cause of seconddegree block, despite the presence of a bundlebranch block, as demonstrated in the present study.This also could be inferred from previous studies inpatients with bundle branch block and intactconduction, in that A-H prolongation was frequent-ly found in patients with both right and left bundlebranch block.21

There is little reported data concerning thesubsequent clinical course of patients with chronicsecond degree A-V block where site of block hasbeen delineated with His bundle recording. Narulaet al. noted that three out of eight patients withtype II second degree block distal to H and bundlebranch block had complete heart block at sixmonths follow-up.19 However, no data was present-ed concerning the time of onset of complete blockin these patients or regarding the clinical course inthe other patients studied. Other authors haverecorded His bundle electrograms in selectedpatients with 20 A-V block and syncopal attacks,and demonstrated sites of block in or distal to theHis bundle.27 28 However, there have been nopreviously reported attempts utilizing prospectivefollow-up to determine the natural history of seconddegree block as related to site of block.

Again, our results partially confirm previousspeculations." 2 Our patients with second degreeblock distal to H and bundle branch block had aserious prognosis. All nine needed pacemakers, insix because of syncopal episodes. It should bespecifically noted that absence of syncope at thetime of initial diagnosis did not negate the lateroccurrence of syncope. Our results in patients withbundle branch block and second degree blockproximal to H were somewhat surprising in thatthree of four of these patients also neededpacemakers. The clinical course in the patients withsecond degree block proximal to H was, however,somewhat less hectic than patients with chronicdistal block. Syncope was less common in thisgroup, and heart failure more common. Despite thehigher incidence of heart failure, digitalis intoxica-tion could be implicated in only one of the patientswho has not needed a pacemaker. Even in this

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latter patient, the subsequent development ofasymptomatic second degree block when offdigitalis suggested the presence of chronic A-Vnodal disease.

These results concerning correlation of clinicalfeatures and site of block are in keeping with our

previous observations made in 49 patients withcomplete heart block.29 Congestive heart failurewas found to be more common in patients withcomplete block proximal to or in the His bundle,while syncope was found to be more frequent inpatients with block distal to H.

ConclusionsThe following conclusions are suggested by this

study. Second degree block complicating bundlebranch block may be either proximal or distal to theHis bundle, the latter being more common. Type I

block in any combination with type II block or 2:1block suggests the presence of proximal block. Thepresence of left bundle branch block and type IIblock alone, or in combination with 2:1 block, or

2:1 block alone, suggests block distal to H.The clinical course in most patients with second

degree block and bundle branch block will bemalignant, with most patients needing pacemakerswhether block is proximal or distal to the Hisbundle. Patients with block distal to H will have a

higher incidence of syncope.We would recommend the following regarding

management of patients with second degree blockand bundle branch block. All patients withsymptomatic second degree block and bundlebranch block should be treated with permanentpacemakers, unless there is an obvious reversiblecause of block such as digitalis intoxication. Inasymptomatic patients with bundle branch blockand second degree block, those with a site of blockproximal to H can be followed closely, andpacemakers inserted if symptoms develop. Inpatients with block distal to H, pacemaker insertionis indicated because of the high incidence ofsyncope and potential risk of sudden death.

AcknowledgmentWe would like to thank Mrs. Vicki Leyva and Mrs. Jo

Price for their secretarial help and Mrs. Loretta Kasparas forher technical assistance.

References1. LANGENDORF R, PICK A: Atrioventricular block, type II

(Mobitz)-Its nature and clinical significance. Circu-lation 38: 819, 1969

2. MCNALLY EM, BENCHIMOL A: Medical and physi-

ological considerations in the use of artificial pacing.Part I. Am Heart J 75: 380, 1968

3. FRIEDBERG CK, DoNoso E: Arrhythnmias and conduc-tion disturbances due to digitalis. Progr CardiovascDis 2: 408, 1959

4. FiSCH C, GREENSPAN K, KNOEBEL SB, FEICENBAUM H:Effect of digitalis on conduction of the heart. ProgrCardiovasc Dis 6: 343, 1964

5. COHEN DB, DOCTOR L, PICK A: The significance ofatrioventricular block complicating acute myocardialinfarction. Am Heart J 55: 215, 1958

6. COURTER SR, MOFFAT J, FOWLER NO: Advancedatrioventricular block in acute myocardial infarction.Circulation 27: 1034, 1963

7. NORRIs RM: Heart block in posterior and anteriormyocardial infarction. Br Heart J 31: 352, 1969

8. KAUFMAN JG, WACHTEL FW, ROTHFIELD E, BERNSTEINA: The association of complete heart block andAdams-Stokes Syndrome in two cases of Mobitz typeof block. Circulation 23: 253, 1961

9. DONoso E, ADLER LN, FRIEDBERC CK: Unusual formsof second degree atrioventricular block, includingMobitz type II block, associated with the Morgagni-Adams-Stokes Syndrome. Am Heart J 67: 150, 1964

10. STOCK RJ, MACKEN DL: Observations on heart blockduring continuous electrocardiographic monitoring inmyocardial infarction. Circulation 38: 987, 1968

11. Criteria Committee of the New York Heart Associa-tion: Diseases of the heart and blood vessels, nomen-clature and criteria for diagnosis. Boston, Little,Brown and Co., 1969

12. ROSENBAUMI MB, ELIZAIII MV, LAZZARI JO: Thehemiblocks. Oldsmar, Florida, Tampa Tracings, 1970

13. SCHERLAC BJ, LAU SH, HELFANT RH, BERKOWITZ WD,STEIN E, DAMATO AN: Catheter technique for re-cording His bundle activity in man. Circulation 39:13, 1969

14. DHINGRA RC, ROSEN KM, RAHIMTOOLA SH: Normalconduction intervals and responses in 61 patientsusing His bundle recording and atrial pacing. Chest64: 55, 1973

15. MOBMrz W: Uber die unvollstandige storung derErregungsuberleitung Zwischen vorhof und kammerdes menschilichen herezens. Zeit Ges Exp Med 41:180, 1924

16. DAMATo AN, LAU SH, HELFANT RH, STEIN E, PATTONRD, SCHERiLAG BJ, BEsuOWI1rZ WD: A study of heartblock in man using His bundle recordings. Circula-tion 39: 297, 1969

17. NARULA OS, COHEN LS, SAMET P, LISTER JW,SCHERLAG BJ, HILDNER FJ: Localization of A-Vconduction defects in man by recording of Hisbundle electrogram. Am J Cardiol 25: 228, 1970

18. ROSEN KM: The contribution of His bundle recordingto the understanding of cardiac conduction in man.Circulation 43: 961, 1971

19. NARULA OS, SAMET P: Wenckebach and Mobitz type IIA-V block due to block within the His bundle andbundle branches. Circulation 41: 947, 1970

20. PUECH P, GROLLEAU R, LATOUR H, DUFOIX R, CA-BASSON J, ROBIN J: L'enregistrement de l'activit6electrique du faisceau de His dans les blocs A.-V.spontanes. Arch Mal Coeur 63: 784, 1970


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21. ROSEN KM, RAHIMTOOLA SH, CHUQUIMIA R, LOEBHS, BUNNAR RM: Electrophysiological significance offirst degree atrioventricular block with intraventricu-lar conduction disturbances. Circulation 43: 491, 1971

22. RANGANATHAN N, DHURANDHER R, PHILLIPS JH,WIGLE ED: His bundle electrogram in bundle branchblock. Circulation 45: 282, 1972

23. ROSEN KM, GUNNAR RM, RAH1MTOOLA SH: Mobitztype II block without bundle branch block. Circula-tion 44: 1111, 1971

24. HAFr, JI, WVEINSTOCK M, DEGUIA R, GUPTA PK, FANOA: Assessment of atriGventricular conduction in leftand right bundle branch block using His bundleelectrograms and atrial pacing. Am J Cardiol 27:474, 1971

25. ROSEN KM, EHSANI A, RAHIMTOOLA SH: H-V intervalin left bundle branch block. Clinical and electro-cardiographic correlations. Circulation 46: 717, 1972

26. LEV M: The anatomic basis for disturbances inconduction and cardiac arrhythmias. Progr CardiovascDis 2: 360, 1960

27. HAFT II, WEINSTOCK M, DEQUIA R: Electrophysiologicstudies in Mobitz type II second degree heart block.Am J Cardiol 27: 682, 1971

28. SCHUILENBUJRG RM, DURRER D: Conduction distur-bances located within the His bundle. Circulation45: 612, 1972

29. ROSEN KM, DHINGRA RC, LOEB HS, RAHIMTOOLASH: Chronic heart block in adults: Clinical andelectrophysiological observations. Arch Intern Med131: 663, 1973

AppendixCase 1

The patient was a 75 year old male with calcific aorticstenosis, mild congestive heart failure, and type I and 2:1block with right bundle branch block (RBBB) admitted fromclinic on 7/3/72. Electrophysiological studies on 7/6 re-

vealed second degree block proximal to H. A permanentpacemaker was implanted on 7/29 because of persistentsecond degree block with congestive heart failure. Thepatient expired on 10/5/72 with chronic uremia.

Case 2

The patient was a 52 year old male with arterioscleroticheart disease (ASHD), congestive failure (CHF), type Iand II second degree A-V block with LBBB, admitted on

9/14/72. He had been receiving 0.25 mg of digoxin per dayprior to admission. Electrophysiological studies on admissionrevealed type I and II block proximal to H. Digoxin was dis-continued but 20 block persisted. Permanent pacemaker was

advised because of persistent block with CHF, but refusedby the patient. The patient has been subsequently followedin clinic. In October 1972, he complained of dizziness andcardiogram revealed complete heart block with a ventricularescape rate of 30/min. The patient has still refused a pace-maker.

Case 3

The patient was a 76 year old asymptomatic male witharteriosclerotic heart disease admitted on 2/2/72 becauseof type I & II block with RBBB detected during a routine


clinic visit. Electrophysiological studies on admission re-

vealed 20 block proximal to H. The patient was dischargedon 273/72 and followed in clinic. On 4/20/72, the patienthad a syncopal episode. Similar electrophysiological findingswere demonstrated and permanent pacemaker was im-planted.

Case 4

The patient was a 62 year old male with ASHD, CHF,and type I block with RBBB admitted on 9/25/72. He hadbeen receiving 0.25 mg of digoxin per day prior to admis-sion. Digoxin was discontinued and A-V conduction re-

turned. Electrophysiological studies on 9/28/72 revealed a

prolonged A-H. Type I second degree block proximal to Hwas noted at a paced atrial rate of 100/min, suggesting that20 block had been A-V nodal. The patient was discharged on

10/5/72. Second degree block has been noted only on one

occasion (12/14/72) during a treadmill exercise test. Thepatient has remained asymptomatic.

Case 5

The patient was a 75 year old male with hypertensivecardiovascular disease, recurrent syncope, and 2:1 A-Vblock with right bundle branch block admitted on 7/11/72.Electrophysiological studies on admission revealed type IIblock distal to H. A temporary pacemaker was inserted on

admission and a permanent pacemaker was implanted on

7/19/72.

Case 6

The patient was a 58 year old male with arterioscleroticheart disease, congestive heart failure, and type II and 2:1A-V block with left bundle branch block, admitted on

6/5/72. Electrophysiological studies on admission revealed20 block distal to H. A permanent pacemaker was implantedon 6/8/72 because of congestive heart failure and brady-cardia.

Case 7

The patient was a 78 year old male with ASHD, syncope,

and type II and 2:1 A-V block with left bundle branchblock, admitted on 10/15/71. Electrophysiological studieson admission revealed spontaneous type II and 2:1 A-Vblock distal to H. The patient refused permanent pacemakerand was followed in clinic with persistence of 2° A-Vblock. On 12/3/71, a permanent pacemaker was implantedfor dizziness and syncope.

Case 8

The patient was a 42 year old asymptomatic male with a

prosthetic aortic valve, and 2:1 A-V block with left bundlebranch block, admitted on 7/17/72. Electrophysiologicalstudies on admission revealed type II block distal to H. Thepatient was discharged with stable 2:1 block. On 10/10/72,the patient had a syncopal episode. A permanent pacemakerwas implanted on the same day.

Case 9

The patient was a 41 year old female with ASHD, dizzi-ness, CHF and type II and 2:1 A-V block with right bundlebranch block admitted on 12/2/71. Electrophysiologicalstudies on admission revealed 20 block distal to H. A

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DHINGRA ET AL.

temporary demand pacemaker was inserted at that time.Three days after the pacemaker insertion, electrocardiogramrevealed 1:1 A-V conduction which persisted for severaldays. At the patient's insistence, the pacemaker was removed.Two months later, dizziness recurred and ECG revealedintermittent complete heart block. A permanent pacemakerwas implanted on 2/4/72, with relief of symptoms.

Case 10

'The patient was a 72 year old male with ASHD, con-gestive heart failure, type II and 2:1 A-V block with leftbundle branch block, admitted on 5/2/72. Electrophysi-ological studies on admission revealed 2:1 block distal to Hisbundle. A permanent pacemaker was implanted on 5/8/72because of bradyeardia and congestive failure.

Case 11

The patient was an 82 year old male with ASHD, recur-rent syncope and type II and 2:1 A-V block with leftbundle branch block, admitted on 8/9/72. Electrophysi-ological studies on admission revealed 2' block distal to H.A permanent pacemaker was implanted on 8/18/72.

Case 12

The patient was an 80 year old female with hypertensivecardiovascular disease, recurrent syncope and 2:1 A-Vblock with right bundle branch block, admitted on 3/19/73.Electrophysiological studies revealed a ventricular rate of35 and 2:1 A-V block distal to H. A permanent pacemakerwas implanted on 3/22/73.

Case 13

The patient was a 54 year old male with arterioscleroticdisease, dizziness and 2:1 A-V block with left bundle branchblock admitted on 5/31/72. 1:1 A-V conduction returnedwithin 24 hours. Electrophysiological studies on 6/2/72

revealed intact A-V conduction, with an A-H of 93 msecand a H-V of 74 msec. The patient developed type II blockdistal to H at a paced rate of 127/min. The prolonged H-Vand development of 20 block distal to H with pacing sug-gested that spontaneous 20 block had been distal to H.

Since 1:1 conduction had returned, the patient was dis-charged and remained asymptomatic without recurrence ofA-V block for four months. On 10/8/72, the patient had asyncopal episode. Admission electrocardiogram revealedLBBB with intact conduction. A permanent pacemaker wasimplanted. The patient has subsequently remained asympto-matic.

Case 14

The patient was a 54 year old asymptomatic male withrheumatic heart disease, admitted 1/10/73 for evaluation ofconduction disease. Routine clinic electrocardiogram hadrevealed one episode of type II block with left bundle branchblock. No other episode of 20 block has been noted. Electro-physiological studies revealed 1:1 conduction with an A-Hinterval of 88 msec and an H-V of 73 msec. Type I blockproximal to H was noted at a paced rate of 160/min. Thepatient has remained asymptomatic.

Case 15

The patient was a 51 year old male with ASHD, onesyncopal episode, and right bundle branch block with leftanterior hemiblock, admitted on 12/29/72. Electrophysi-ological studies on admission revealed an A-H interval of125 msec and an H-V of 42 msec. Type I 20 block wasnoted at a paced rate of 165/min. He was discharged andreadmitted again on 3/16/73 for recurrent dizziness andchest pain. ECG was unchanged from the previous admis-sion. The patient exhibited type I and II 2° block withcontinuous tape monitoring (Holter) during hospitalization.A permanent pacemaker was implanted on 3/26/73.


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KENNETH M. ROSENRAMESH C. DHINGRA, PABLO DENES, DELON WU, RUBEN CHUQUIMIA and

Observations Regarding Site and Type of BlockThe Significance of Second Degree Atrioventricular Block and Bundle Branch Block:

Print ISSN: 0009-7322. Online ISSN: 1524-4539 Copyright © 1974 American Heart Association, Inc. All rights reserved.

is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231Circulation doi: 10.1161/01.CIR.49.4.638

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