Measurement of ventricular electrogram amplitude during intraoperative induction of ventricular tachyarrhythmias

ARRHYTHMIAS AND CDNDUClIDN DlSTURBANCES

Measurement of Ventricular Electrogram Amplitude During lntraoperative Induction of Ventricular Tachyarrhythmias Kenneth A. Ellenbogen, MD, Mark A. Wood, MD, Bruce S. Stambler, MD, William J. Welch, MD, and Ralph J. Damiano, MD Adequate sensing of ventricular tachycardla (VT) and ventricular fibrillation (VP) is necessary for proper functlonlng of an implantable cardioverter deflbrlllator (ICD). Several ICDs currently undergolng investlgation have programmable fixed gain sensltivfty for tachycardia detection. If intracardiac electrogram amplitude decreases below the programmed sensltivlty during VT or VF, detection of a ventricular arrhythmia may be delayed or missed. The mean amplitude of intracardiac electrograms (ICEGM) recorded wlth bipolar epicardial or transvenous senslng leads was measured in 63 patlents durlng induced VT and VP recorded In the operating room at the time of ICD implantation. The mean amplitude of the ICEGM during 41 episodes of VF in 15 patients decreased from 14.9 f 0.9 mV during slnus rhythm to 8.8 f 0.7 mV at 1 second, 9.7 f 0.7 mV at 5 seconds, and 9.4 f 0.7 mV at 10 seconds (p CO.0001 vs slnus rhythm ICEGM) wlth endocardlal leads. The mean amplitude of the ICEGM recorded during 173 episodes of VF in 43 patients with eplcardlal leads decreased from 10.4 f 0.3 mV in sinus rhythm to 7.8 f 0.3 mV at 1 second, 8.3 f 0.3 mV at 5 seconds and 8 mV at 10 seconds (p
to be superior to epicardial leads in providing higher amplitude signals during VF, but not during VT. (Am J Cardid 1992;70:1017-1022)

heimplantablecardioverter defibrillator (ICD) delivers therapy after a ventricular tachyarrhythmia is sensed.Reliable detection of ventricular tachyarrhythmias currently requires that the ventricular electrogram be of adequateamplitude within the given frequency range measured by the sensing amplifier of the ICD. Newer ICDs undergoing clinical investigation, such as the Guardian 4202/4203 and 4210 (Telectronits Inc., Denver, Colorado) and the PCD (Medtronic, Minneapolis, Minnesota) have programmable fRed gain sensing. If intracardiac electrogram amplitude is less than the programmed sensitivity, delayed or complete lack of detection of ventricular tachyarrhythmias may occur. To assessthe relation between ventricular electrogram amplitude throughout the duration of ventricular tachycardia (VT) and ventricular fibrillation (VF), we measuredthe amplitude of the ventricular intracardiac eltxtrograms (ICEGM) at ICD implantation after induction of VF and VT at 1,5 and 10 secondsfollowing arrhythmia induction and during sinus rhythm. We also assessedthe relation between ventricular electrogram amplitude during sinus rhythm to that measuredduring VT and VF. Finally, ICEGM amplitude during ventricular tachyarrhythmias was analyzed with respect to lead configuration (i.e., epicardial vs transvenous).

T

METHGDS We studied 63 consecutivepatients undergoing ICD implantation at the Medical College of Virginia or the M&tire Veterans Affairs Medical Center from 1990 to 1991. All patients underwent implantation of a CPI Ventak 1550 or 1600 (Cardiac Pacemakers,Inc., St. Paul, Minnesota) or a Guardian 4202/4203 or Guardian ATP 4210. All patients gave written informed consent for intraoperative testing at the time of implantation. Our standard intraoperative testing includes testing for termination of VF at 120 J on 3 of 3 consecutive trials. The defibrillation shock was delivered after From the Division of Cardiology and Cardiothoracic Surgery, Medical 11 to 13 secondsof VF. When the patients were cliniCollegeof Virginia and the McGuire VeteransAdministration Medical cally stable, VF was repeatedly induced and defibrillaCenter, Richmond, Virginia. Manuscript received March 26, 1992; tion thresholds were determined at lower energies. A revisedmanuscript receivedand acceptedJune 15,1992. Address for reprints: Kemeth A. Ellenbogen, MD, MCV Station, minimal 2-minute rest period was interspersedbetween Box 53, Richmond, Virginia 23298. each episodeof VF. VENTRICULAR ELECTROGRAM AMPLITUDE DURING VENTRICULAR FIBRILLATION

1017

TABLE I Clinical Characteristics of Patient Population No. 6013 60 f 12 (21-85) 32 2 11 (10-55)

Men/women Age (years) Ejection fraction f%) Underlying heart disease Coronary artery disease Coronary artery bypass surgery Previous acute myocardial infarction Dilated cardiomyopathy (nonischemic) Hypertrophic cardiomyopathy Mitral valve prolapse No structural heart disease Clinical indications Cardiac arrest Syncope Refractory to antiarrhythmic

50 35 40 8

1 2 2 17

33 medications

Induced arrhythmias Monomorphic VT Polymorphic VT or VF VT and VF Valuesare mean 5 SEM. Numbers in parentheses are range. VF = ventricular fibrillation; VT = ventricular

13

Epicardial (mV)

Seconds

Transvenous (mV)

P Value

Ventricular Tachycardia Normal sinus rhythm

1 5 10

18.5 + 1.8 mV

14.4 f 2.0

0.14

15.7 + 1.8 18.0 + 1.8 16.0 + 1.7

12.3 r 1.9 14.1 + 1.9 13.7 + 1.9

0.20 0.13 0.37

14.9 8.8 9.7 9.4

0.001 0.20 0.05 0.07

Ventricular Fibrillation Normal sinus rhythm

1 5 10 pvalue:

10.4 + 0.3

7.8 + 0.3 8.3 f 0.3 8.0 f 0.3 epicardial

k + 2 2

0.9 0.7 0.7 0.7

versus transvenous.

14

35 14

tachycardla.

Rate sensingelectrodesconsistedof either a transvenous active fmation lead (Gscor Medical Corporation PY 1OOBVor Telectronics Accufii, OF 040-113) placed in the right ventricular apex or a pair of bipolar epicardial screw-in electrodes (Possis model 052572, Medtronic model 6917-35T or Daig model 030-223) placed over the right ventricular outflow tract or apex. The screw-in electrodeswere repositionedif the amplitude of the ventricular electrogram in sinus rhythm was <6 mV. In patients who had undergone cardiac surgery or were not undergoing additional procedures, an active fmtion transvenoussensinglead (e.g., Gscor lead) was always used. In patients undergoing concomitant valve or bypasssurgery, epicardial sensingleads were always used. VF was induced by delivering 2 to 5 secondsof alternating current applied through the epicardial patchesor ratesensing leads. The mean ventricular electrogram amplitude was measured 1 secondafter alternating current was terminated, and again at 5 and 10 secondsafter induction of VF. Electrograms were recorded and filtered through either the External Cardioverter De& brillator II (CPI model 2806) or the External Testing Device (Telectronics model 4510). Electrograms were displayed on a VR-16 (Electronics for Medicine, Pleasantville, New York) and recorded at a paper speedof 50 to 100 mm/s. Calibration signals (5 mV amplitude) were delivered before induction of each episodeof VF and after restoration of sinus rhythm. The amplitude of sinus rhythm electrograms was determined by averaging 5 consecutive beats, and the amplitude of electrograms during VF was measuredby averaging the amplitude of 4 to 7 electrogramsrecorded during a l-second interval at 1, 5 and 10 secondsafter induction of VF or VT. When electrograms were fragmented, the portion of the electrogram with the greatest magnitude and greatest slopewas measured.In general, a period of 120 to 150 ms was chosen before measuring the next 1018

TABLE II Epicardial and Transvenous Intracardiac Electrogram Amplitude

THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70

electrogram to avoid measuring multiple peaks of the sameelectrograms. S&&tksr The relation between the intracardiac electrogram amplitude in sinus rhythm, VT and VF at 1, 5 and 10 secondswas compared with baselinevalues by repeated-measuresanalysis of variance for normally distributed data. Testing of epicardial versus transvenous amplitudes of ICEGMs and comparison between ICEGM amplitudes at 1, 5 and 10 secondswere done with a paired t test. A Bonferonni correction was made for multiple comparisonsto the baseline.A probability level of <0.05 was consideredsignificant. Linear regression (Pearson’scorrelation coefficient) was used to assessthe correlation betweenelectrogram amplitude during sinus rhythm and ventricular tachyarrhythmias. Continuous data were reported as mean f standard error of the mean. RESULTS We studied 60 consecutivepatients undergoing implantation of patches and epicardial or transvenous sensingleads at the time of initial intraoperative place ment and 3 patients at the time of generator replace ment. The clinical characteristics of our patient group are summarized in Table I. Venbhdar tachycardia There were a total of 34 episodesof monomorphic VT observedin 14 patients. Each patient had a mean of 2.4 episodes(range 1 to 4). The cycle length of VT ranged from 240 to 360 ms (mean 288 f 8). During 3 episodes,VF organized into monomorphic VT after 1 to 3 seconds,and ICEGM amplitudes of tachycardia were only measuredat 5 and 10 seconds.Seventeenepisodesof VT were recorded through epicardial leads,and the other 17 episodeswith a transvenoussensinglead. The mean amplitude of the ICEGMs during VT are reported at 1,5 and 10 seconds with both lead configurations (Table II). The mean amplitude of ICEGMs during VT showed no significant change with time for either epicardial and transvenousleads. Most patients tended to have a 125% change in intracardiac electrogram amplitude over 10 seconds.The change in intracardiac electrogram amplitude from sinus rhythm to onset of VT was OCTOBER 15, 1992

VF and

Mean

epicardial

4 rJ3 2.

15

5

10

NSR for

characterized by a 125% decreasein amplitude during 11 episodes,an increase or decrease in amplitude of I1 0% in 9 episodes,and an increase in amplitude of L 10%for 11 additional episodes.These patterns had no relation to the sensinglead configuration (e.g., epicardial vs transvenous). VanMeular fibrillatias~: There were a total of 173 episodesof VF recorded with epicardial leads and 41 episodesof VF with transvenousleads. There were 4 f 1 episodesin patients with transvenousleads (range 3 to 7), and 4.3 f 1 episodesin patients with epicardial leads (range 3 to 9). The mean amplitude of ICEGMs at 1, 5 and 10 secondsfor epicardial and transvenous leads is listed in Table II and Figure 1. The mean ICEGM amplitude at baseline was 10.4 f 0.3 mV for epicardial leads and 14.9 f 0.9 mV for transvenous leads (p = 0.001). The mean ICEGM amplitude for epicardial leads was 7.8 f 0.3 mV, and for transvenous leads was 8.8 f 0.7 mV at 1 second (p = 0.2). At 5 seconds,the epicardial ICEGM amplitude was 8.3 f 0.3 and 9.7 f 0.7 mV for the transvenousleads (p = 0.05). At 10 seconds,the mean ICEGM amplitude was 8.0 f 0.3 mV for the epicardial leads and 9.4 f 0.7 mV for the transvenous leads (p = 0.07). The change in

all,

and transvenous

= 214

n = 173

E s r” i% s! F

a

5

0 Epi

Trbns

TABLE Ill

(Cont’d) 1 Second

TABLE III Time-Dependent Changes in Ventricular Electrogram Amplitude During Ventricular Fibrillation 1 Second Pt. No. 1

Sensing (NSR-mV*) Epi. (8) Epi. (8)

3

Epi. (7)

4

Epi. (14)

Max.

Min.

Max.

Min.

Max.

2

5 5 2 6 4 9 6 8 3 3 12 8 10 8

3 2 3 2 3 2 6 2 4 5 3 5 10 8 6 7 6 7

5 5 3 3 3 6 4 8 5 6 9 7 15 18 10 8 8 10 20

2 2 2 3 3 3 4 7 2 3 4 6 5 4 6 8 4 4 7

6 5 4 6 5 5 8 9 7 7 6 10 15 10 8 8 14 8

18 10 15

22 25 20

18 15

25 25

2 6 4 2 8 14 5 10 8 2 8 8

5 8 9 5 12 18 15 18 10 6 15 20

8 4 4 2 2 10 10 15

15 10 5 4 5 16 15 20

10

20

8 5 5

15 12 15 16

1 2 1 6 3 5 2

1

5 6

Epi. (10)

7

Epi. (9)

8

9

10

11

Trans. (20)

Trans. (20)

Trans. (24)

Trans. (12)

10 Seconds

Min. 1

2

5 Seconds

7 2 4 3 5 5 5 5 6

10 7 8 11 8

15

20

10

25

12 2

18

8 4 3

6 9 7 9

5

12

4 5 3

8 12 10

8

14

2 6 5

6 15 10

1

a

Pt. No.

Sensing (NSR-mV*)

12

Epl. (17)

13 14

Epi. (15)

15

Epi. (14)

Epi. (15)

17

Epi. (9)

ia

Trans. (10)

19

Epi. (14)

10

20

Epi. (12)

21

Trans.(6)

10 Seconds

Min.

Max.

Min.

Max.

Min.

Max.

5 5 5 6 5 12 6 12

12 11 15 19 10 20 8 16 16 18 20 20 20 20 20 25 20 3 3 4 4 8 12 8 7 10 16 8 4 3 5 6 10 4 4

6 5 5 10 5 4 5 7 8 5 15 8 8 10 15 20 12 2 1 2 2 4 10 10 5 10 14 5 6 6 6 6 1
12 15 12 14

2 2 5 5 3 3 2 10 8 12 5 4 5 7 14 20 10 1 1 2 1 5 8 10 5

10 8 15 19 7 8 5 13 14 16 25 15 15 12 25 22 20 3 3 3 3 12 10 12 12 10 17 12 10 5 10 7 2 2 5

a a 10 6 12

16

5 Seconds

10 15 15 11 2 1 2 2 5 10 4 5

a 14 6 2 1 2 3 1 2 1

a 10 10 12

ia 20 25 28 20 14 25 22 15 4 3 4 3 9 12 11 12 12 17 10 10 10 12 8 2 2 4

a 14 6 2 2 3 4
*The amplitude of the ventricular electrogram during normal sinus rhythm expressed in millivolts. Epi = epicardial: Max. = maximal; Min.= minimal; NSR = normal sinus rhythm: Trans. = Transvenous.

VENTRICULAR ELECTROGRAM AMPLITUDE DURING VENTRICULAR FIBRILLATION

1019

ICEGM amplitude with time during VF is listed in Table III. The correlation of amplitude of ICEGM in sinus rhythm with the amplitude of ICEGM during all ventricular tachyarrhythmias was r = 0,61 (p 50% change in ICEGM amplitude between 1 and 10 set onds. Of these episodes, 30% showed a 50 to 75% change and 10%a >75% change in ICEGM amplitude (Table III).

or decreasing ICEGM amplitudes during episodes 2 and 3 (Table III). Intraeardac ektrogram

amplhh

after an unsuc-

eessfd deMdMbn shodc There were 25 episodesof VF during which the first shock did not cause conversion of VF to normal sinus rhythm. Analysis of ICEGM amplitude after the first shock did not show a decrease in ICEGM amplitude at 10, 15 or 20 seconds.There was no consistent pattern of change in ICEGM amplitude after an unsuccessfulshock.

MsCUssl0N The major findings of our study are that mean amplitude of the ventricular electrogram during VT and VF are similar whether measured with transvenousor epicardial sensingleads.However, there was a trend for transvenous leads to record larger amplitude electrograms at 1,5 and 10 secondsduring VF only. The mean amplitude of the ventricular electrogram did not change significantly from 1 to 5 or 10 secondsafter the induction of VF, however,there was considerablevariation in electrogram amplitude in individual patients at 1, 5 and 10 seconds. There was also significant variation in ICEGM amplitude during different episodesof VF in V~,WOen~inhdMilud~: All patients with VF had L3 episodesinduced. There the same patient. Finally, the correlation between VF was considerable variability between different episodes and the sinus rhythm electrogram amplitude was poor, in the same patient. In 50% of patients, a >5 mV with significant variation seenbetween and among pachange occurred in ICEGM amplitude or pattern of tients. It is unlikely that electrogram amplitude during ICEGM amplitude change over time between individu- sinus rhythm will be adequate for predicting ICEGM al episodesof VF. For example, 1 patient may have had amplitude during VF. ICDs must be capable of measuring signals that diflittle variability during 1 episodeof VF and increasing fer in amplitude by factors of lO- to 20-fold. Both pace makers and detibrillators must have bandpass filters Linear Regression for ‘all NSR versus that eliminate sensing of unwanted signals such as T all 1 second after episodes wavesand external or environmental signals. Pacemaky = 0.5a7x + 1.798 ers, however,may have long refractory periods, whereas detibrillators are limited in refractory period durations r= 0.61 becauseof the need to sense rapid tachyarrhythmias rz= 0.37 (RR intervals of 120 to 200 ms). Automatic gain conp=0.0001 trol refers to the ability of an amplifier to sensesignals of markedly differing amplitude by using an algorithm that allows amplifier gain to increaserapidly to a maximum if no signal is sensed,and to decline slowly following a sensedsignal. Another approach to avoid undersensingof ventricular tachyarrhythmias in deviceswith a fixed gain is to program the sensitivity of the ICD to a lower value. This may lead to detection of ventricular repolarization, T waves, and in occasional patients may still lead to signal dropout during polymorphic VT and VF. Saksena and Wilber both emphasized the importance of carefully assessingsensing during induced ventricular tachyarrhythmias in patients with fmed gain ICDs. They found that a significant percentageof patients had sensing problems when studied following implantation 20 30 10 of the Telectronics Guardian 420214203,with failure to NSR (mV) senseand signal dropout at someprogrammed sensitivities-3 Most sensingproblems were easily corrected by reprogramming the ICD’s sensitivity or repositioning or changing sensing leads. In occasional patients, sensing problems necessitatedremoval of the ICD and replace

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THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70

OCTOBER 15, 1992

ment with one that has automatic gain control. We recently reported 2 patients in whom fmed gain sensing devices failed to recognize polymorphic VT or VF.4 There are several important limitations to this study that must be emphasized. Most patients in this study were enrolled at the time of intraoperative placement of sensing leads and patches. The long-term reliability of epicardial leads has been studied in some detail in children with permanent pacemakers and congenital heart disease, but has not been adequately studied in adults5-* In children, the incidence of pacing exit block at 5 years varies from 18 to 45?L5 In at least 1 series, epicardial leads lasted longer when implanted on the left ventricle rather than on the right ventricle.5 The incidence of sensing problems is not specifically addressed in most of these studies.s-8 In many studies,

transvenous leads have fewer pacing threshold problems than epicardial leads. 7,9 Nevertheless, one cannot conclude that superior acute and chronic pacing thresholds will also result in superior acute and chronic sensing thresholds. The quality of chronic signals during VF may increase with time, emphasizing the importance of obtaining the “best” possible intracardiac signals at implant. Sensing of an intracardiac signal depends on more than amplitude alone. The slew rate, or dV/dT is 1 determinant of the ability of an ICD or pacemaker to sense the ICEGM.‘O In addition, the frequency spectrum of the intracardiac electrogram will determine to what extent the signal will be altered by the high and low bandpass filters in the ICD. To accurately determine the ability of an ICD to sense a signal, the exter-

VENTRICULAR ELECTROGRAM AMPLITUDE DURING VENTRICULAR FIBRILLATION

1021

nal device analyzing signals must have identical filters as the ICD being implanted. Signal characteristics,such as slew rate and frequency content, play a significant role in determining how well the signal is sensed.An earlier study designed to measure ventricular electrogram amplitude during VF included only a small number of patients and did not include patients with transvenous sensing electrodes.l1 Future studies should use accurate measuring techniques by recording signal on tape and using digital signal processingsoftware to analyze waveforms.Furthermore, the effect of antiarrhythmic agents on acute and chronic sensing thresholds should be determined. In some patients, it would be useful to compare transvenous and epicardial recordings during the same arrhythmia in a patient. Longterm studies that compare ICEGMs during ventricular tachyarrhythmias at the time of implant, at follow-up, and at the time of generator replacement must be performed. It is hoped that future studies will be able to analyze each of these variables and be better able to discern the relation between amplitude, frequency content and other signal characteristics such as slew rate. Left ventricular epicardial signals may provide better electrogramsbecausethe left ventricular massis greater. The differencesbetweenright ventricular endocardial and left ventricular electrogramsmight be less.Finally, delivering of alternating current via the sensingleads may have changed or caused deterioration of electrograms. We do not believe this is the case,becauseelectrogram amplitude was often greater at 1 or 5 seconds than at 10 seconds. Grubb et all* measured acute changes in pacing thresholds, electrogram amplitudes, slew rates and resistancebefore and after induction of 23 episodesof VF through rate sensingelectrodesand noted no changes. Kroll et all3 published preliminary results suggesting that transvenous leads may be superior to epicardial leads for detecting VF. We have seen1 patient in whom a transvenouslead failed to detect VF with a fmed gain sensingdevice. There are also severalreports of patients who had sensingproblems during VT or VF with one of the early Cardiac PacemakersInc. deviceshaving automatic gain control.14~15 In our study, ICEGM amplitude during VF tended to be better with transvenous than epicardial leads. The intracardiac signals from the transvenousleads appearedto be more easily measured than the signals recorded with the epicardial leads during VF. There was little difference in ICEGM amplitude from transvenousand epicardial leads during VT. Overall, the signals in VT were greater in amplitude than the signals recorded during VF. Long-term studies may ultimately discern whether the differencesbetween epicardial and transvenousleads becomelarger, smaller,

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THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70

or do not change significantly over time. Finally, it would be important to compare electrogram amplitude directly with transvenous and epicardial leads in the same patient. In summary, we were able to show that transvenous leads tend to record larger signals than epicardial leads during VF, but not during VT. The amplitude of the mean intracardiac electrogram does not significantly changewith time during VF or VT. However, there is a significant change in ICEGM amplitude for most individual patients over time during VF, and in most patients this variability in ICEGM amplitude over time and between different episodesof VT/VF emphasizes the importance of careful measurementof ICEGM amplitude during intraoperative testing of ICDs. AdtnowkdgmoM We thank John Snyder for help with data analysis, and Kay Lentz for excellent help with manuscript preparation.

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6. Walls JT, Maloney JD, Pluth JR. Clinical evaluation of a suturelesscardiac pacing lead chronic threshold changesand lead durability. Ann Thorac Surg 1983;36:328-331. 7. Simon AB, Dick M, Stern AM. Ventricular pacing in children. PACE 1982;5:836-844. 6. Ward DE, JonesS, Camm AJ. Long-term endowdial pacing in congenital heart disease.Clin Prog Ekctrophysiol Pacing 1985;3:133-144. 9. Gillette PC. Shannon C. Blair H. Garson A. Porter CJ. McNamara DG. Transvenouspacing in pediatric pat&&. Am H&t J 1983$05:843-847. 10. Furman S, Hurseler P, DeCaprio V. Cardiic pacing and pacemakersIII. Sensingthe cardiac electrogmm.Am Heart J 1977;93:794-801. 11. Leitch JW, Yee R, Klein GJ, JonesDL, Murdock CJ. Correlation between the ventricular electrogramamplitude in sinusrhythm and in ventricular Ubrillation. PACE 1990;13:1105-1109. 12. Grub BP, Durzinsky D, Mancini MC, Temesy-ArmesP. Serum creatinine kinaseactivity and sensingcharacteristicsafter intraoperative arrhythmia induction using implantable defibrillator rate sensingleads.PACE 1992;15:9-13. 13. Krol R, SaksenaS, Tullo N, Singh S, SaxenaA, Karanam R, Gielchinsky I, Burkhardy E, Gordon M, Hibbard D. Gptimal pacing and sensinglead systems for implantable hybrid pacemaker-cardioverterdeflbrillators (abstr). J Am Coil Cardtol 1991;15(supplA):SSA. 14. Bardy GH, Ivy TP, Stewart R, Graham EL, Greene HL. Failure of the automatic implantable defibrillator to detect ventricular fibrillation. Am J Cardial 1986$&l 1061108. IS. Glicksman FL, Zaman L, Huikuri HV, CastellanosA, Myerburg RJ. Reversible failure to senseventricular tachycardii early after surgical implantation of the automatic implantable cardiowrter defibrillator. Am J tidiol 1988;62: 833-834.

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