Exercise-Provoked Distal Atrioventricular Block Saurabh K. Chokshi, MD, Joseph Sarmiento, MD, Jose Nazari, MD, Thomas Mattioni, MD, Terry Zheutlin, MD, and Richard Kehoe, MD

S pontaneous or pacing-induced nonfunctional atrioventricular

(AV) block occurring distal to the His bundle recording site is associ- ated with a high probability of subse- quent syncope or progression to high grade AV block. l Accordingly, a reli- able noninvasive method that could potentially unmask distal His-Pur- kinje block would be helpful in iden- tifying patients in whom invasive conduction system studies should be undertaken. We report 3 patients in whom the occurrence of second-de- gree AV block during exercise test-

ing unmasked serious underlying conduction system disease, which would have otherwise gone undetect- ed by routine ambulatory monitoring and resting electrocardiograms. Sub- sequent evaluation of their conduc- tion systems by electrophysiologic studies revealed marked prolonga- tion of the HV interval and AV block distal to the His bundle in response to rapid atria1 pacing.

CASE 1: A 74-year-old woman had syncope while sitting at the din- ner table. Her previous cardiac his- tory was unremarkable except for a

FIGURE 1. Twelve-lead eketrocardiogramshowingnennal~planeaxisand campleterightbundebranchblockincasel.

FIGURE 2. Exe&e -am (leads II, VI and Vg) at&r 6 minutes of exerdse al an atrial rate 110 beats/mln; 43 AV con&c&m is shown by astehh ink+adV~andarrowinleadVsincasel.

similar episode 2 years ago. The resting electrocardiogram demon- strated sinus rhythm, a PR interval of 0.18 second and a complete right bundle branch block with a normal frontal plane axis (Figure 1). Con- tinuous ambulatory monitoring for 72 hours failed to reveal evidence for AVblock. An exercise stress test was carried out using the modified Bruce protocol. The patient had a resting heart rate of 85 beatslmin. During stage III of exercise testing, with the increase in heart rate up to 110 beatslmin, 4:3 Mobitz type I second- degree AV block appeared. At sinus rates of 130 beatslmin, 3:2 AV block was observed (Figure 2). Normal anterograde conduction resumed at 2 minutes into the recovery period (sinus rate 98 beatslmin). No ST-T changes were provoked during the exercise test. Subsequent electro- physiologic studies demonstrated prolongation of the HV interval (85 ms) at rest (Figure 3A). During rap- id atria1 pacing, 1:I conduction was maintained at rates up to 105 beats/ min. At an atria1 pacing rate of 1 IO beatslmin (cycle length 545 ms), a 3:2 Mobitz type I second-degree AV block distal to the His bundle was observed (Figure 3B). With pacing rate up to 120 beatslmin (cycle length 500 ms), a 3:2 AV block was noted (Figure 3C). The paced rate at which block appeared was identical to the sinus rate at which spontane- ous block occurred during exercise testing. The patient received a per- manent dual chamber (DDD) pace- maker and has remained asymp- tomatic during 36 months offollow- up*

CASE 2: A 53-year-old woman with biopsy-proven polymyositis was evaluated for episodic light- headedness during exertion. The resting electrocardiogram revealed

From the Section of Cardiology (Department of Medicine), Northwestern University Medi- cal School, Chicago, Illinois. Dr. Chokshi is a Research Fellow of the American Heart Asso- ciation, Massachusetts Affiliate, Needham, Massachusetts. His present address and ad- dress for reprints: Department of Cardiology, St. Elizabeth’s Hospital, 736 Cambridge Street, Boston, Massachusetts 02135. Manu- script received January 30,199O; revised man- uscript received and accepted February 26, 1990.

114 THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 66

TABLE I Electrophysiologic Correlation of Exercise-Provoked Distal AtrioventriCUlar Block

EP Evaluatron

Age (yr) AM El-r Atrial Pacing Study & Sex Symptoms RBBB (beats/min) (beats/min) y:s, (beats/min)

Klausche et al7 54, M Dourness, angrna + Type II 2:l AVB (130) 2:l AVB (140) 44 2:l AVB(100) Freeman et ale 55, M Dizziness + 2:l AVB(125) 50 3:2AVB(llO) Woelfel et al9 54, M Palpitations 0 - 3:2 AVB (125) 70 2: 1 AVB (85)

69, M Diuiness + 2:l AVB (140) - 2:l AVB(170) 55, M 0 + No AVB 2:l AVB (140) 65 2:l AVB (120)

Peller et ali0 44, I= Palpitation, dizziness 0 Type II 2:l AVB (148) 2:l AVB (148) 45 3:2AVB(120)

Present study 74, F Syncope + No AVB 4:3AVB(llO) 85 4:3 AVB (110) 53, F Dizziness + No AVB 2:l AVB(130) 90 2:l AVB (120)

69, M Dizziness 0 No AVB 2:l AVB (110) 75 2:1AVB(llO)

AM = ambulatory monltorlng. AVB = atrloventrlcular block, EP = electrophystologlc, E T T = exercw treadmill test, RBBB = right bundle branch b&k: + = present: 0 = absent,

sinus rhythm with first-degree AV block, left anterior divisional block and complete right bundle branch block. Forty-eight-hour ambulatory monitoring failed to reveal sponta- neous second-degree AVblock. Dur- ing an exercise stress test, at a sinus rate of 130 beatslmin, a 2:1 Mobitz type I second-degree AV block oc- curred. During the subsequent inva- sive electrophysiologic study, a 2:l second-degree block distal to the His bundle developed in response to atri- al pacing at a rate of 120 beats/min. Implantation of a permanent pace- maker led to resolution of symp- toms.

CASE 3: A 69-year-old white man was seen for progressive lighthead- edness. On cardiac monitoring, he was found to be in a third-degree heart block with a ventricular rate of 22 beats/min (sinus rate I1 0 beats/ min). A temporary transvenous pacemaker was placed for 72 hours. He evolved a small, anterior wall, non-Q-wave myocardial infarction. Over the next 36 hours, the high grade AVblock completely resolved. Cardiac catheterization revealed to- tal occlusion of the distal right coro- nary artery, 50% stenosis of the left anterior descending artery, 40% ste- nosis of the left circumflex artery and mild apical hypokinesis of the left ventricle. On exercise stress test, a 2:l AV block was demonstrated at sinus rates of 110 beatslmin; how- ever, a thallium scan failed to reveal perfusion defects. The subsequent electrophysiologic studies revealed a prolonged HV interval (90 ms) and 2:l AT/block distal to the His bundle during atria1 pacing at rates of 110 beatslmin. The patient received a

FIGURE 3. Surface and intracadiac electrocanliographic tracings &&ng &w rhythm (A) and atrial pacing at rates of 110 beatdmin (B) and 120 beats/min (C) in~re1.A,duingd~m~,1:lAVconduelion~~.TheHV intewal is con&ant 1SSms. B,~atriatpmhgatcydehgth545ms, S~AVbkdcdstdtooHb~po~isrcen(a~w~ C,ataNgher atrial pacing rate (cycle+ knglh 500),3P AV block (arrow) distal to His is no~.A=rigMabialdatkction;H=Hb~detlection;HBE=H~kndk zmaErsHRA = high rtght atrtal ektrogram; V = dght venbidar deflection .

represent duration in ms.

THE AMERICAN JOURNAL OF CARDIOLOGY JULY 1, 1990 115

dual chamber pacemaker and has remained asymptomatic.

The diagnosis of conduction dis- ease in 1 or 2 of the 3 fascicles sug- gests an impaired safety margin for AV conduction.’ A wealth of ana- tomic and clinical studies supports a relation between intraventricular conduction disturbance and progres- sion to high grade or complete AV block.2,3 Progression to complete AV block may be sudden or may occur episodically and could result in sud- den death or syncope. The ability to recognize patients with intraven- tricular conduction disturbance at high risk for progression to complete AV block is important; they could benefit from prophylactic pacemaker therapy.

Standard 12-lead electrocardiog- raphy has a limited value in identifi- cation of such patients.3 Ambulatory monitoring has also been ineffective in unmasking high grade AV block, especially in the early stage of pro- gression. All 3 patients reported here failed to demonstrate AV block on ambulatory monitoring despite 72 hours of recording. This may be ex- plained by the fact that none of the patients accelerated their heart rates during activities that could have in- duced AV block.

Exercise-induced AV block is un- commonly observed.4,5 When pres- ent, it carries a significant value in identifying patients with a higher risk for progression to complete AV block. Fewer than 25 cases of exer- cise-induced AV block occurring in patients with normal AV conduction have been reported.4-10 Since AV conduction should be enhanced as a result of exercise-related vagal with-

drawal and increased sympathetic drive, AV block has been shown to improve or resolve during exercise. Several investigators have postulated that the site of AV block occurring during exercise is more likely to be localized to the distal His-Purkinje system rather than the AV node be- cause the His-Purkinje system is rel- atively insensitive to autonomic mod- ulation, and it has a relatively fKed effective refractory period that fails to decrease sufficiently with decreas- ing atria1 cycle length to permit 1: 1 AV conduction.

In patients with bifascicular block and syncope, utility of electrophysio- logic studies has been well estab- lished.’ Both prolongation of the HV interval at rest and demonstrable block distal to the His bundle during rapid atria1 stimulation are widely used to stratify patients at a high- er risk of developing complete AV block.7-10 Previously published stud- ies have established the utility of these markers. For example, in the study by Dhingra et al,’ 15 of 496 patients with chronic bifascicular block developed distal block during rapid atria1 pacing; during follow-up, complete AV block developed in 8 of the 15 patients and 2 died suddenly. In addition to the 3 patients reported here, in only 6 other cases have exer- cise-induced findings of AV block been correlated with invasive electro- physiologic data (Table I).7-10

In patients with coronary artery disease, reversible, transient second- degree or high grade AV block may occur due to exercise-induced isch- emia6 or secondary to coronary spasm. It is important to note that clinical or angiographic evidence for

coronary artery disease was present in only 1 of our 3 patients; however, myocardial ischemia, based on ST-T segment changes, was absent in the remaining 2.

In summary, the 3 patients we re- port add to the limited body of pub- lished data regarding the significance of exercise-provoked AV block. Since the patients with symptoms of lightheadedness or syncope and exer- cise-induced AV block are likely to have a block distal to His, permanent pacing seems justified.

1. Dhingra RC, Wyndham C, Bauernfeind R, Swiryn S, Deedwania PC, Smith T, Dews P, Rosen KM. Significance of block distal to the His bundle induced bv atria1 oacine in the oatients with chronic bifascicular bloci C&lotion’1 979,60:1455-1464. 2. Lev M. The normal anatomy of the conduction system and its pathology in atrioventricular block. Ann NY Acad Sci 1964:ll It81 7-821, 3. Lasser RP, Halt JI, Freidberg CK. Relationship of right bundle branch block and marked left axis devi- ation (with left pa&al and per&infarction block) to complete heart block and syncope. Circulation 1968; 37:429-437. 4. Baskt A, Goldberg B, Schamroth L. Significance of exercise-induced second degree atrioventricular block. Br Heart .I 1975;37:984-986. 5. Mouloooulos SD. Darsinos J. Sideris DA. Atrio- ventricular block response to exercise and intraven- tricular conduction at rest. Br Heart J 1972;34:998- 1004. 6. Rozanski JJ, Castellanos A, Sheos D, Pozen R, Myerberg RJ. Paroxysmal second-degree atrioven- tricular block induced by exercise. Heart Lung 1980,9:887-890. 7. Klausche D, Roskamm H. Tachycardia depen- dent second-degree A-V block in a patient with right bundle branch block. / Electrocardiol 1987;20:169- 175. 8. Freeman G, Hwang MW, Danowiz J, Moran JF, Gunnar RM. Exercise-induced “Mobitz type II” sec- ond degree AV block in a patient with chronic bi- fascicular block (right bundle branch block and left anterior hemiblock). J Ekctrocardiol 1984;17:409- 412. 9. Woelfel AK, Simpson RJ, Gettea LS, Foster JR. Exercise-induced distal atrioventricular block. JACC 1983;2:578-581. 10. Peller OG, Moses JW, Kligfield P. Exercise- induced atrioventricular block: report of three cases. Am Heart J 1988:115:1315-1317.

116 THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 66