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Editorial His Bundle Electrograms Editorial Br Heart J: first published as 10.1136/hrt.33.5.633 on 1 September 1971. Downloaded from British HeartJournal, I971, 33, 633-638. His bundle electrograms Charles S. Smithen' and Edgar Sowton Since the recording of the first human electro- base of the atrial septum in the middle of the tri- cardiogram by Wailer in I889 the science of cuspid valve area where a sharp rapid biphasic electrocardiography has developed and ad- or triphasic deflection should appear between the vanced but has been limited the P and QRS complexes of a standard electrocardio- rapidly, by gram recorded simultaneously. The recording of inability to record electrical activity from this His potential is safe and is usually obtained specialized areas of the heart. A significant about 5 minutes after the catheter is placed in the contribution was made by Alanis, Gonzailez, femoral vein. The P-His interval, measured from and L6pez in 1958 when they recorded His the beginning of the P wave to the beginning of bundle potentials in the isolated perfused the His potential, represents conduction through dog heart using fine needle electrodes placed the atrium and atrioventricular node; and the along the atrioventricular groove. The first His-Q interval, measured from the beginning of His potentials to be recorded in humans the His potential to the beginning of the QRS were described by Giraud, Puech, and complex, represents intraventricular conduction copyright. Latour and later (Fig. i). The generally recognized normal values (i960), by Watson, Emslie- for P-His interval are 80 to 140 msec and for Smith, and Lowe (I967). However, it was left His-Q interval are 35 to 55 msec. to Scherlag and associates (I969) to develop a simple and safe electrode catheter technique Validity of measurement for the consistent of electrical recording po- As there are several possible sites for recording tentials from the His bundle site in man. This electrical http://heart.bmj.com/ technique was later extended to the recording activity during the PR interval, proof of atrioventricular nodal and right bundle- that this rapid deflection represents His branch potentials (Damato et al., i969a) and bundle activity is imperative. By performing has resulted in an extensive investigation of several interventions in isolated perfused dog the specialized conduction tissue in normal hearts, Alanis et al. (1958) were able to validate and abnormal circumstances. As a result cer- their measurements. Crushing of the SA node tain age-old concepts have now been proved resulted in His bundle activity followed by correct or have had to be ventricular activity without any correspond- modified, and in par- on September 25, 2021 by guest. Protected ticular the traditional criteria for interpreta- ing atrial potential. Production of complete tion of many dysrhythmias have been shown heart block resulted in atrial activity followed to be inadequate. by a constantly related His potential with an independent ventricular potential. Man- Catheter technique oeuvres such as atrial stimulation, vagal In order to record the His bundle potential a bi- stimulation, acetylcholine and epinephrine polar or multipolar electrode catheter is intro- injection, or the production of asphyxia duced percutaneously into the femoral vein and appropriately modified the P-His interval under fluoroscopic control positioned across the without affecting the His-Q interval. tricuspid valve into the right ventricle. The In man validation of the His bundle poten- proximal terminals of the electrode catheter are tial is more difficult. The position of the re- attached to an electrocardiograph amplifier and cording electrode is at the established ana- used either as a unipolar or bipolar system. His tomical position of the bundle of His. During bundle activity is best recorded at high frequency several successive cardiac cycles the configura- settings of 4O to 5OO cps at a paper speed of ioo or 200 mm/second. The position of the recording tion of the potential should not vary signifi- electrode is then adjusted until it is stable at the cantly, and the distance from the P wave should not vary by more than 5 msec. This 1 Address: Department of Cardiology, Guy's Hospital, configuration and relation to the P wave has London. been validated by direct placement of the 1 634 Smithen and Sowton Br Heart J: first published as 10.1136/hrt.33.5.633 on 1 September 1971. Downloaded from P-right bundle-branch interval is also pro- 801min longed with atrial pacing. The right bundle potential is normally about I0 msec in dura- tion and appears closer to the QRS complex, whereas the His potential is I5 to 20 msec in duration and appears closer to the P wave. However, if only one potential is recorded it H. B. E. *I*$# I is difficult to say for certain where it is re- corded from. Narula, Scherlag, and Samet (I97od), by pacing at the site of the electri- cal activity, were able to distinguish these two potentials. Pacing the right bundle- branch resulted in left bundle-branch block, whereas pacing the bundle of His caused no change in the QRS configuration. The pacing stimulus to QRS interval was the same as the His-Q interval recorded during sinus rhythm. Thus, for absolute separation of the His bundle and right bundle-branch potentials, LEAD 2 pacing at the recording site appears necessary. Atrioventricular block During the past few years it has become apparent largely from histological studies that the aetiology of complete atrioventricular block is usually due to pathology in the main bundle-branches rather than in the atrio- ventricular node (Lenegre, I964; Lepeschkin, copyright. 'HF"<H I S-Q (45m sec) I964). The electrocardiographic criteria for P-H I S (120m sec) precise location of the site of the lesion in complete heart block have hitherto been un- but the of His F I G. i A recording of His bundle activity reliable, recording bundle in a normal subject. H.B.E. = His bundle electrograms now allows the cardiologist to electrogram. Sinus rhythm at 8o beats/min is make an accurate assessment of the site of http://heart.bmj.com/ present. The P-His interval is 120 msec and the block. In 86 per cent of one series (Narula the His-Q interval is 45 msec. Paper speed is et al., I970c) the block was demonstrated to IOO mm/sec. be distal to the bundle of His, the P-His interval being normal in all patients. In all I0 patients studied by Damato and Lau (1970), the block was found to be in His-Purkinje electrode on the His bundle during cardi- system, atrioventricular nodal conduction otomy under experimental conditions (Hoff- being normal. In our own experience acquired man et al., I960). However, in this catheter heart block appears to be almost uniformly on September 25, 2021 by guest. Protected position both atrioventricular nodal and right due to bundle-branch disease though one bundle-branch activity may also be recorded. patient with Ehlers-Danlos syndrome and Atrioventricular nodal activity can be easily congenital heart block was found to have block identified and differentiated from either the proximal to the bundle of His (Smithen and bundle of His or right bundle-branch poten- Sowton, I971). It appears likely that congeni- tials. It is of longer duration (up tO 50 msec), tal heart block is frequently due to a defect in of lower amplitude, inscribed slowly, and the atrioventricular node. often with notching on the upstroke. Increas- His bundle recordings have been particu- ing the heart rate by atrial pacing results in larly useful in identifying mechanisms in the progressive prolongation of the P-His inter- two types of second degree heart block. val, the His-Q interval remaining constant Mobitz Type I block (Wenckebach) is charac- (Damato and Lau, 1970). Though the P-atrio- terized by a progressive prolongation in the ventricular nodal interval also increases with PR interval until there is a non-conducted P atrial pacing, the increase is only a fraction of wave. His bundle records show that this the prolongation in the P-His interval. The dysrhythmia, either spontaneous or produced distinction between right bundle-branch and experimentally by atrial pacing, is usually due His bundle activity is more difficult. The to block in the atrioventricular node and that His bundle electrograms 635 Br Heart J: first published as 10.1136/hrt.33.5.633 on 1 September 1971. Downloaded from intraventricular conduction is normal (Da- artery occlusion, is in the atrioventricular node. matoetal., I969c; Narulaetal., I970a). Mobitz Rosen's findings confirm the view that heart Type II block is characterized by a constant block following acute anterior infarction is PR interval with periodic non-conducted P due to bundle-branch disease. The difference waves. It usually occurs with bundle-branch in clinical behaviour between heart block in block but sometimes with a narrow QRS com- anterior and diaphragmatic infarctions can plex. The clinical observations of Langendorf thus be explained by the different anatomical and Pick (I968), and the experimental obser- site of the lesion. vations of Watanabe and Dreifus (I967), sug- A very fascinating case of what appears to gest that Type II block represents bilateral be second degree atrioventricular block on a bundle-branch disease. His bundle electro- standard electrocardiogram was reported by grams have confirmed that in cases of Mobitz Rosen, Rahimtoola, and Gunnar (1970c). Type II with bundle-branch block, the site His bundle electrograms revealed that the of block is distal to the His bundle, the atrio- apparent block was due to multiple non- ventricular nodal conduction being entirely propagated premature His bundle depolariza- normal (Narula and Samet, I970). In Mo- tions with concealed conduction in the atrio- bitz Type II block with narrow QRS the ventricular junction.
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