British I971, 33, 626-628. Heart_Journal, Br Heart J: first published as 10.1136/hrt.33.4.626 on 1 July 1971. Downloaded from Intraventricular trifascicular block Observations on conduction disturbance in bundle-branch system Nabil El-Sherif From the Cardiology Department, Faculty of Medicine, Cairo University, Cairo, Egypt, U.A.R. A case of intraventricular trifascicular block secondary to an inferior myocardial infarction is reported. The case denonstrates instances of 2: I atrioventricular conduction due to alternating block in the right bundle-branch and block in the right bundle and both anterior and posterior divisions of the left bundle (trifascicular block). Instances of I: i A V conduction with grade I block and periods of type I (Mobitz) block are ascribed to a delayed and a Wenckebach type of conduction respectively in the posterior division of the left bundle. Recent recognition of the trifascicular nature but experienced two separate attacks of fainting of the bundle-branch system has changed sensation not mounting to actual syncope within some of the concepts about AV conduction I2 hours and suddenly expired 24 hours later. disturbances and the pathways of impulse Description of cardiogram (Fig.) The record propagation in the ventricular myocardium. reveals two different QRS patterns and three In a recent review by Rosenbaum et al. (I969) types of AV conduction disturbance. no more than 20 cases of intraventricular The first QRS pattern (type A) is always pre- http://heart.bmj.com/ trifascicular block were found while the ceded by a normal PR interval of O-I9 sec and has authors recognized the various combinations a duration of O'i2 sec. The pattern reveals right that may arise secondary to the different bundle-branch block (RBBB) in the chest leads grades of conduction disturbance in the three and a frontal plane axis of -400 with ST-T fascicles of the bundle-branch system. The changes suggestive of inferolateral injury. The second QRS pattern (type B) is always preceded following report deals with a further case of by a prolonged PR interval of at least o025 sec intraventricular trifascicular block and pre- and has practically the same duration of O-I2 sents certain features of interest where differ- sec. The pattern reveals more prominent S on October 1, 2021 by guest. Protected copyright. ent grades of AV conduction disturbance are waves in leads II and III shifting the frontal plane explained on the basis of variable dysfunction axis to -8oo, and significant changes in the of the three fascicles of the bundle-branch praecordial leads especially lead V6 which shows system. loss of the initial Q wave and a more prominent S wave. The ST-T changes of inferolateral injury pattern are less prominent. Case report The three types of AV conduction disturbance A 54-year-old man was admitted to Kasr El-Aini are as follows. Faculty of Medicine of Cairo University on March 1960. The patient, who was known to have I Periods of 2: I AV block occurring at an atrial diabetes and hypertension for some time, began rate of 65-7I beats per minute. The conducted P to complain of anginal attacks one week before wave has a PR interval of O-I9 sec and is always admission. The attacks were frequent, not always followed by type (A) QRS pattern. related to exertion, and lasted from a few up to 2 Periods of I:I AV conduction seen to take I5 minutes. On examination, he was in no appar- place at critical slowing of the atrial rate to 6o-65 ent distress. His pulse showed frequent irregu- beats per minute. These periods always start at a larities and his blood pressure was I5o/Ioo mm P wave followed after a PR interval of O-I9 sec Hg. Cardiac examination revealed no abnormality. by type (A) QRS pattern, while the next P waves Continuous cardiographic monitoring for half an are conducted with constant PR intervals of o 25 hour showed frequent shifts between i: i and 2: I sec and are followed by type (B) QRS pattern. AV response with occasional instances of the 3 Periods of Wenckebach conduction usually in Wenckebach conduction. The patient received the form of 3:2 or 4:3 periods. During instances sublingual tablets of isoprenaline every 3 hours of 3:2 conduction, the first P wave is followed Intraventricular trifascicular block 627 Br Heart J: first published as 10.1136/hrt.33.4.626 on 1 July 1971. Downloaded from *'':+'''--':::X. .}: :.g: .:: .. .~~~~~~~~~~~~......... VI i;-'77; 000 tt0>>, x rirf0 t' 12t<f i 4'6__< _ _ = X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<~~~~~~..... FIG.Intraventriculartrifascicular block. See text for details.~~~~~~~~~~~~~~~E'.41R -H after a PR interval of O-I9 sec by type (A) QRS of the left bundle. On the other hand, during type pattern, while the second P wave is followed after (B) QRS pattern, the impulse is conducted through a PR interval of 0-25 to o04 sec by type (B) QRS the posterior division of the left bundle alone. http://heart.bmj.com/ pattern and the third P wave is blocked. During This pattern is always preceded by prolonged PR 4:3 Wenckebach periods, the second P wave is interval of at least 0-25 sec. This reveals that there always followed by type (B) QRS pattern after a is a conduction delay in the posterior division of PR interval of at least 0-25 sec, while the third P the left bundle which becomes uncovered only by wave reveals further prolongation ofthePRinterval block of the conduction in the anterior division. before block of the fourth P wave (see lead V6). The shorter PR interval of O-I9 sec preceding type (A) QRS pattern can now be explained by Interpretation ofcardiogram Type (A) QRS the relatively faster conduction through the pattern represents right bundle-branch block. anterior division. on October 1, 2021 by guest. Protected copyright. The presence of left axis deviation of -4o0 During periods of 3:2 Wenckebach conduction, in the frontal plane is, however, unusual. This the first atrial impulse is conducted through both can be explained either by involvement of the anterior and posterior divisions of the left bundle diaphragmatic surface of the heart in myo- (though faster through the former division) and cardial infarction or by the presence of an 'in- is blocked in the right bundle-branch alone (a complete' block in the anterior division of the monofascicular block). The second atrial impulse left bundle or both. However, for the rest of the is conducted through the posterior division of the report the pattern will be considered to represent left bundle alone and is blocked in both the right 'pure' RBBB. This will make the discussion bundle and the anterior division of the left bundle easier and will not interfere much with the validity (a bifascicular block). The third atrial impulse of the interpretations. Type (B) QRS pattern re- shows complete AV block which is explained by veals more conspicuous left axis deviation in the failure of conduction in the three fascicles of the frontal plane and represents RBBB +'complete' bundle-branch system (a trifascicular block). block in the anterior division of the left bundle. During periods of 4:3 conduction the second and The recognition of these two QRS patterns facili- third atrial impulses reveal an increasing conduc- tates the interpretation of the AV conduction dis- tion delay through the posterior division of the turbance. Though concomitant disturbance at the left bundle before block of the fourth atrial beat. AV node-His bundle cannot be excluded, yet the Lastly, instances of 2: I block are explained by evidence points to exclusive disturbance at the conduction through the two divisions of the left bundle-branch system. bundle alternating with a trifascicular block. During type (A) QRS pattern, the impulse The observation that both I: i conduction in reaches the ventricles through the two fascicles the posterior division of the left bundle and com- 628 Nabil El-Sherif Br Heart J: first published as 10.1136/hrt.33.4.626 on 1 July 1971. Downloaded from plete block in the anterior division take place at a (Mobitz) block, while anteroseptal infarction critical slowing of the atrial rate to 6o to 65 beats associated with extensive lesion of the bifur- a minute is explained by the presence of a higher cation or bundle-branches or both usually critical rate for conduction in the posterior leads to type II block. Lepeschkin (I964) has division of the left bundle (6o-65 beats per minute) and a slower critical rate for conduction theoretically related this observation to the in the anterior division. The latter probably lies greater difference in velocity between the somewhere between 35 beats a minute (the rate slow conduction through the AV node and of the ventricular response during instances of the rapid conduction through the bundle- 2: I AV block) and 6o beats a minute (the slowest branches. Thus a pathological prolongation rate of ventricular response during I: I conduction of impulse conduction at the AV node will in the posterior division). usually give rise to measurable change in the PR interval, while a constant delay simulating Discussion grade I block or an increasing delay simulating type I (Mobitz) block will not usually lead to One or more of the fundamental patterns of measurable delay in the PR interval. In fact AV conduction disturbance can be observed according to this consideration, Lepeschkin in the three fascicles of the bundle-branch (I964) has suggested that analysis of AV con- system in the present case. The right bundle- duction time may be helpful in locating the branch shows a permanent third degree (com- level of AV block in myocardial infarction.