Precise “on line” measurement of intracardiac electrograms

J. ELECTROCARDIOLOGY, 9 (4) 1976 329-333

Precise "On Line" Measurement of Intracardiac Electrograms BY ROBERT W. PETERS, M.D., MICHAEL RUBINSTEIN, M . S . E . E . AND MELVIN M. SCHEINMAN, M.D.* W i t h t h e t e c h n i c a l a s s i s t a n c e of GUNNARD MODIN, B.S.

SUMMARY

MATERIALS AND METHODS

Atrioventricular nodal (A-H) and infranodal (H-Q) conduction times were determined in 22 p a t i e n t s u n d e r g o i n g i n t r a c a r d i a c electrophysiologic studies. These measurements were determined independently both on line from a digital oscilloscope and from paper recordings at a rate of 100 mm/sec. There was no significant difference and exc e l l e n t c o r r e l a t i o n b e t w e e n m e a n A-H (91.39 -+ 29 versus 95.44 _+ 32 msec) and H-Q (53.48 _+ 14 versus 50.52 ___ 15 msec) intervals determined by these two methods. The digital oscilloscope enables virtually instantaneous highly accurate (-+ 1 msec) timing of intracardiac events and rapid and more efficient processing of data. Potential applications during electrophysiologic studies include precise monitoring of drug effects on a t r i o v e n t r i c u l a r c o n d u c t i o n and refractoriness, on line analyses of complex rhythm disturbances, and ready storage of data for computer retrieval and analyses.

His bundle electrograms were recorded in 22 patients according to the method of Scherlag et al.4 In brief, a hexapolar electrode catheter was inserted percutaneously into the right femoral vein and positioned across the tricuspid valve. The X, Y, and Z leads of the F r a n k orthogonal lead system were displayed simultaneously with the His bundle electrogram on an Electronics for Medicine DR-12 research recorder and recorded at a paper speed of 100 mm/sec. The surface lead showing earliest ventricular depolarization and the intracardiac electrogram were displayed simultaneously on a digital oscilloscope (Nicolet Model 1090), enabling on line recording of atrioventricular and infranodal conduction times. The A-H intervals were measured from the first high frequency component of the low right atrial electrogram to the onset of the His bundle deflection, while H-Q was measured from the His deflection to the earliest onset of ventricular depolarization as recorded from the surface leads. In our study, two of the three surface leads were displayed on the digital oscilloscope in sequence, enabling determination of the surface lead showing initial depolarization. Measurements of A-H and H-Q were determined by one of the authors (Melvin Scheinman) from the digital oscilloscope at the time of the study, and independent measurements of these intervals were made from the subsequent paper recording by another author (Robert Peters), who was not informed of the measurements from the oscilloscope. The oscilloscope uses digitized analog information, stores it in a computer-type memory bank, and then displays the original input signal, which is recreated from the digital memory on a cathode ray tube (CRT). Thus, simultaneous surface and intracardiac electrograms can be displayed indefinitely on a CRT, enabling accurate on line time measurements. The Model 1090 has the capability of dividing the input signal into 4096 discrete points, each point being measured to an accuracy of 0.25%. In this application only one-quarter of the memory is used for each measurement, so that up to four separate sets of complexes may be stored at one time. The sweep time is adjusted such that the input signal is sampled once every millisecond. This results in the signal being divided into 1024 points, 1 msec apart. Thus, time relationships between two complexes can be measured with a resolution of 1 msec. The frequency response of the instrument in this configuration is then 0 to 200 Hz. If higher frequency response is desired, one-half or all of the

T h e u s e of electrode c a t h e t e r s for r e c o r d i n g i n t r a c a r d i a c e l e c t r o g r a m s h a s g r e a t l y exp a n d e d o u r k n o w l e d g e of cardiac a r r h y t h m i a s and conduction disturbances. 1 3 Described h e r e i n is a m e t h o d for a c c u r a t e i m m e d i a t e " o n line" (at t h e t i m e of study) d e t e r m i n a t i o n of t i m e r e l a t i o n s h i p s d e r i v e d f r o m t h e s e s t u d i e s a n d t h e p o t e n t i a l a p p l i c a t i o n s of t h i s technique.

From the Medical Service, San Francisco General Hospital, and the Department of Medicine and the Cardiovascular Research Institute, University of California, San Francisco, California. *This study was performed during tenure of the American H e a r t Association Teaching Scholar in Cardiology. Reprint requests to: Robert W. Peters, M.D., San Francisco General Hospital, Building 30, Room 3501, 1001 Potrero Avenue, San Francisco, CA 94110. 329

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PETERS ET AL

memory may be used, resulting in a doubling or quadrupling of the frequency response, respectively. The instrument also has the capability of measuring and displaying two different wave forms simultaneously, enabling direct read out of desired time intervals. Other important features of the oscilloscope are the various modes of triggering the sweep. The triggering signal may be initiated either manually by the patient's own R wave or by a pacing artifact. The sweep may be made to start either immediately upon reception of the triggering signal or in the middle of the signal. Thus, in the immediate mode the information stored and displayed will be that occurring immediately after the triggering signal. In the mid-signal mode, however, it is possible to display the input signal both immediately before and after the trigger signal because the instrument is continually storing data. Measurement of A-H and H-Q intervals are made by capturing the beat of interest on the digital oscilloscope and thus displaying both the surface and the intracardiac signals. Either a manual or a triggered sweep may be used to effect the capture. Direct measurements are made by setting the instrument into a numerics mode in which the

exact time of occurrence of a particular point of a wave form can be measured by positioning a cursor over the point of interest and reading the time off the screen of the instrument. For example, if it were desired to measure the H-Q interval, the cursor would first be positioned on the initial deflection of the QRS from the surface leads and the time read off the screen; then the cursor would be positioned over the first high frequency wave of the His bundle deflection and that time would be read off the screen. The difference between the two times would be the H-Q interval. This procedure is illustrated in Fig. 1. The determination of intracardiac refractory p e r i o d s i n v o l v e s t h e use of a s y n c h r o n i z e d stimulator by which premature stimuli may be introduced at various points during the cardiac cycle. Refractory periods are then measured, using the mid-signal triggering mode of the digital oscilloscope. Using the pacing artifact as a trigger in the mid-signal mode, the oscilloscope will display the beat before the pacing spike, the paced beat, and the beat after the spike. Then, using the numerics display as discussed above, measurements of any desired time interval may be made quickly and easily.

Fig. 1A

Fig. 1B Fig. 1. Intracardiac electrogram (top tracing) and surface Z electrocardiographic lead (bottom tracing) from a representative patient displayed on a digital oscilloscope. The numbers at the bottom are the relative times of occurrence of the events marked by the vertical cursor. A shows the cursor at the onset of low right atrial depolarization. B shows the cursor at the onset of the His deflection. The A-H interval is then computed by subtracting the times shown in each picture, i.e., 445 - 230 = 215 msec. C shows the cursor at the onset of the Q wave of the surface electrocardiographic lead. The H-Q interval is computed by subtracting the relative times shown in each picture, i.e., 504 - 445 = 59 msec.

Fig. 1C J. ELECTROCARDIOLOGY, VOL. 9, NO. 4, 1976

M E A S U R E M E N T OF I N T R A C A R D I A C E L E C T R O G R A M S

RESULTS

331

(53.48 -- 14 versus 50.52 +-- 15 msec). Widely discrepant results between methods were observed in three patients (Nos. 5, 11, and 20), and the differences were probably related to observer errors. P a t i e n t #20 was of particular interest because of rapid a t r i o v e n t r i c u l a r nodal conduction times associated with an H-Q time on the oscilloscope t h a t is at the upper limit of

The data for all patients are summarized in Table I. There was close correspondence and no significant difference between the mean A-H t a k e n from the digital oscilloscope and t h a t from the paper recordings (91.39-+ 29 versus 95.44 _+ 32 msec). Similarly, there was excellent correlation between mean H-Q meas u r e m e n t s u s i n g t h e s e two t e c h n i q u e s

TABLE I Comparison of Conduction Times Measured by the Digital Oscilloscopeversus Conduction Times Measured by the Standard Paper Recording A-H Measurement (msec) Patient No.

Digital Oscilloscope

Paper Recording

H-Q Measurement (msec) Digital Paper Oscilloscope Recording

1

105

100

77

77

2

75

75

53

4O

3

81

9O

56

60

39

35

4

Atrial fibrillation

5

161

195

47

35

6

95

94

41

37

6O

6O

7

Atrial fibrillation

8

70

75

48

51

9

88

8O

36

35

10

79

90

58

55

11

114

115

55

35

48

45

12

Atrial fibrillation

13

132

135

85

85

14

80

87

64

62

53

53

15

Mobitz I

16

109

100

32

33

17

68

8O

49

56

18

88

9O

35

4O

19

122

120

81

75

20

37

42

58

43

21

60

70

52

45

22

81

8O

51

55

Mean

91.39

95.44

53.48

50.52

-+SO

29

32

14

15

J. ELECTROCARDIOLOGY, VOL. 9, NO. 4, 1976

332

PETERS ET AL

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Fig. 2A. This is a copy of the high speed oscilloscopic tracing of patient #20: The upper line represents the intracardiac electrogram, while the lower line is the surface lead showing earliest depolarization. At this paper speed, each dot represents 2 msec.

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Fig. 2B. This is a copy of the intracardiac electrogram of patient #20 at a paper speed of 100mm/sec. External Frank leads X,Y, and Z of the orthogonal system are labeled, as are two intracardiac leads. The lead showing the His deflection most clearly is labeled HBE.

J. ELECTROCARDIOLOGY, VOL. 9, NO. 4, 1976

MEASUREMENT OF INTRACARDIAC ELECTROGRAMS

normal for our laboratory, certainly an unu s u a l combination. It is possible t h a t we missed a split His potential or that a symmetric delay in both the right and left bundle branches might produce prolongation of the H-Q interval without altering the QRS complex. Our electrophysiologic study in this pat i e n t excluded v e n t r i c u l a r pre-excitation, although it was suggestive of J a m e s fiber physiology (i.e., an atrioventricular nodal bypass). Figure 2A shows the high speed oscilloscopic tracing of this patient's intracardiac electrogram. We recorded these oscilloscopic tracings to double-check our readings. Similarly, Fig. 2B shows the intracardiac electrogram of patient #20. Note the short A-H interval (60 msec) t h a t is c h a r a c t e r i s t i c of the LownGanong-Levine syndrome.

DISCUSSION Thus, we found that the Nicolet Digital Oscilloscope a l l o w s p r e c i s e and i m m e d i a t e m e a s u r e m e n t of i n t r a c a r d i a c c o n d u c t i o n times. The major advantage of this device over existing methods lies in the fact that accurate measurements are made available at the time of electrophysiologic study. We found several important clinical applications of this technique. It has been demonstrated by Damato et al 5 and Rosen et al 2 that His bundle potentials can be differentiated from right bundle branch potentials by the duration and timing of their respective depolarizations as well as by the relationship of these depolarizations to the atrial electrogram. We found that this technique is extremely helpful in applying these criteria in order to distinguish between these two different types of depolarizations during electrophysiologic studies. The d e t e r m i n a t i o n of refractory periods from the intracardiac electrogram by present methods is a time-consuming, laborious process that cannot be performed at the time of study. As described, the Nicolet Digital Oscilloscope allows us to o b t a i n r e f r a c t o r y periods accurately and immediately. Thus, drug studies are facilitated in that adverse effect on atrioventricular conduction can be detected rapidly so that corrective actions can be carried out. I n addition, the digital storage oscilloscope allows detection of tachycardia induction and precise comparison of conduction times during b o t h n o r m a l c o n d u c t i o n and induced tachycardias. This facility has been helpful to us in designing further studies of patients with supraventricular tachycardias. Furthermore, our ability to determine refractory periods has greatly enhanced our ability to assess the efficacy of various drugs in the J. ELECTROCARDIOLOGY, VOL. 9, NO. 4, 1976

333

t r e a t m e n t and prevention of supraventricular t a c h y c a r d i a s . Finally, the digitized information can be reported quickly to the referring physician and may be stored in a computer terminal for data retrieval or analyses. An a d d i t i o n a l i m p o r t a n t clinical application emerges from the recent observations of Lie et al. 6 They found that the infranodal conduction time in patients with acute anterior myocardial infarction complicated by right bundle b r a n c h block has i m p o r t a n t prognostic implications. For example, higher degrees of atrioventricular block developed in 81% of their patients with H-Q prolongation compared with only 47% in p a t i e n t s with n o r m a l H-Q times. Obviously, r a p i d and a c c u r a t e d e t e r m i n a t i o n s of H-Q i n t e r v a l s m a y identify a subgroup of p a t i e n t s with acute m y o c a r d i a l infarction and b i l a t e r a l branch block who may benefit from insertion of a temporary transvenous pacemaker. This is e s p e c i a l l y i m p o r t a n t b e c a u s e p r e v i o u s s t u d i e s ~ in o u r l a b o r a t o r y s h o w e d t h a t i n s e r t i o n of a t e m p o r a r y v e n t r i c u l a r pacemaker in patients with acute myocardial infarction is associated with 19% incidence of serious ventricular dysrhythmias. Thus, by using the Nicolet Digital Oscilloscope we have been able to m a k e this decision immediately and obviate the necessity of doing a second procedure and keeping a potentially unstable patient in the catheterization laboratory for an unreasonably long period of time. REFERENCES 1. GOLDREYER, B N: I n t r a c a r d i a c electrocardiography in the analysis and understanding of cardiac arrhythmias. Ann Intern Med 77:117, 1972 2. ROSEN,K M, RAHIMTOOLA,S H, SINNO,M Z. AND GUNNAR, R M: Bundle branch and ventricular activation in man. Circulation 43:193, 1971 3. NARULA, O S, SCHERLAG, B J, SAMET, P AND JAVIER, R P: Atrioventricular block. Am J Med 50:146, 1971 4. SCHERLAG, B J, LAU, S H, HELFANT, R H, BERKOWITZ,W D, STEIN, E AND DAMATO,A N: Catheter technique for recording His bundle activity in man. Circulation 39:13, 1969 5. DAMATO, A N, LAU, S H, BERKOWITZ, W D, ROSEN, K M AND LISI, K R: Recording of specialized conducting fibers (A-V nodal, His bundle, and right bundle branch) in man using an electrode catheter technique. Circulation 39:435, 1969 6. LIE, K I, WELLENS,H J, SCHUILENBURG,R M, BECKER,A E AND DURRER,D: Factors influencing prognosis of bundle branch block complicating acute antero-septal infarction. Circulation 50:935, 1974 7. SCHEINMAN,M M ANDBRENMAN,B: Clinical and anatomic implications of intraventricular conduction blocks in acute myocardial infarction. Circulation 46:753, 1972