Transcutaneous Jonathan

Pacing in Patients Undergoing Coronary Artery Bypass Grafting: Effect of Previous Cardiac Surgery

V. Roth, MD, Bonnie L. Heyer, MD, Laurence J. Krenis, MD, and John Bell-Thomson,

Temporary transcutaneous pacing thresholds were measured in 10 patients undergoing primary coronary artery bypass grafting (CABG) operations and 10 patients having reoperative CABG operations 7 months to 14 years after their previous cardiac surgery. All surgeries were performed via median stemotomy. After anesthetic induction using either fentanyl or sufentanil in combination with enflurane, the pacing stimulation thresholds were determined. There was

T

EMPORARY TRANSCUTANEOUS pacing (TP),’ originally described by Z~ll,~ has been improved and has become an alternative modality for treating bradyarrhythmias.3-5 TP is hemodynamically similar to right ventricular endocardial pacing.6 Berliner et al reported 100% successful TP with no adverse effects in 21 patients undergoing noncardiac surgery under genera1 anesthesia, but did not describe the genera1 anesthetic techniques used.’ Kelly et al demonstrated 100% successful TP in patients anesthetized with high-dose narcotics (fentanyl or sufentanil) in combination with pancuronium and enflurane.’ Zaidan et al demonstrated that halothane, enflurane, and isoflurane did not change the pacing stimulation thresholds of temporary epicardial electrodes.Y Therefore, it might be concluded that TP is effective during a wide variety of genera1 anesthetic techniques. However, Kelly et al documented increased TP thresholds of cardiac surgical patients in the immediate postoperative period.8 NO other studies are available that investigate the effectiveness and thresholds of TP in patients who have had prior cardiac surgery. Studies involving other modalities of pacing have shown a disparity of pacing thresholds in patients who have had prior cardiac surgery. It is sometimes more difficult to establish temporary epicardial pacing in patients who are presenting for reoperative cardiac surgeries, possibly as a result of epicardial and pericardial fibrosis.” It is not known if the healing process significantly increases TP thresholds. Alternatively, a previous sternal closure with conductive wires may establish a preferential current pathway close to the heart, facilitating transcutaneous pacemaker Capture with a lower than expected current. Buchanan et al found that esophageal atria1 pacing current threshold is not influenced by previous cardiac surgery.” Because it can be postulated that TP thresholds may be higher, unchanged, or lower after cardiac surgery by median sternotomy, TP was studied in patients who had previous median sternotomies. MATERIALS AND

METHODS

After institutional approval and written informed consent had been obtained, 20 patients scheduled for coronary artery bypass grafting (CABG) were studied. Ten patients were having their first CABG performed (group 1); 10 patients had undergone CABG more than 6 months prior to reoperation (group 2). Al1 cardiac surgeries, past and present, were performed through a median sternotomy. Exclusion criteria included: heart rate (HR) at time of study greater than 75 beats/min, hemodynamic instability, significant ventricular dysrhythmias, significant atrial dysrhythmias, isJournalof Cardiothoracic and VascularAnesthesia,

MD

no significant differente (P < 0.05) between the pacing thresholds of the reoperative group and the primary procedure group (78.2 f 6.2 Y 79.2 f 4.8 mA, respectively). Transcutaneous pacing was successful in al120 patients. Therefore, transcutaneous pacing thresholds appear unaffected by previous cardiac surgery. Copyright 8 1991 bbyW.B. Saundars Company

chemia at the time of study, congestive heart failure, expected dependence on atrial contraction, emergency surgery, intraaortic balloon pump insertion, temporary or permanent pacemaker insertion, potassium leve1 less than 3.5 mEq/L, or evidente of digoxin toxicity. Al1 patients were premedicated with midazolam and morphine sulfate. Calcium Channel antagonists, p-blockers, and nitrates were continued on the morning of surgery. Peripheral intraveneus, radial artery, and pulmonary artery catheters were inserted using lidocaine local anesthesia prior to induction of genera1 anesthesia. All patients received either 3 mg of fentanyl or 0.5 to 1.0 mg of sufentanil in addition to 10 mg of vecuronium for induction. Pancuronium was administered as necessary to prevent or treat bradycardia. Enflurane and/or nitroglycerin were used as necessary to prevent or treat hypertension; phenylephrine and/or volume infusion were used as necessary to prevent or treat hypotension. After endotracheal intubation, but prior to surgical preparation and draping, the study was performed. A ZOLL NTP transcutaneous pacemaker generator (ZMI Corporation, Woburn, MA) was used with ZOLL NTP noninvasive temporary pacing electrodes. This is a demand pulse generator with a rectilinear constant current output continuously variable from 0 to 140 mA, a continuously variable rate from 30 to 180 beats/min, and a pulse duration of 40 milliseconds. The posterior electrode was placed on the back of the patient to the left of the midline and the anterior electrode on the left precordium, as recommended in the operator’s manual.12 If the patient’s HR was 65 beats/min or less, the generator rate was set at 15 beats/min higher than the patient’s HR. If the patient’s HR was 66 to 75 beats/min, the generator rate was set at 80 beats/min. The current output was gradually increased from 0 mA and recorded (Tl) when consistent Capture was obtained. The current was then gradually decreased from Tl and recorded (T2) as Capture was lost. Consistent Capture was defined as continuous Capture over two respiratory cycles. The electrodes were then removed from the

From the Department of Anesthesiology, Albert Einstein Medical Center, Philadelphia, PA. The ZMI Corporation, Woburn, MA, supplied the temporary electrodes used in this study. Presented ut the 11th Ann& Meeting of the Society of Cardiovascular Anesthesiologists, Seattle, WA, April 16-19, 1989, and the 1989 Annual Meeting of the American Society of Anesthesiologists, New Orleans, LA, October 18, 1989. Address reptint requests to Jonathan K Roth, MD, Chairman, Department of Anesthesiology, Albert Einstein Medical Center, 5501 Old YorkRd, Philadelphia, PA 19141-3098. Copyright 6 1991 by W. B. Saunders Company 1053-0770/9110501-0010$03.00/0

Vol 5, NO 1 (February), 1991:

pp 51-53

51

52

ROTH ET AL

patient and surgery proceeded. (The ZOLL NTP noninvasive temporary pacing electrodes can be left in place to function during cardiac surgery. They have a low profile and it is possible to

ventricular pacing, TP, by virtue of being noninvasive, has fewer complications and can be established more quickly. Additionally, there is negligible morbidity in having TP available, seconds away from therapeutic use, such as during the insertion of a pulmonary artery catheter in the presence of a left bundle branch block.‘s,‘h The operator’s manual for the ZOLL NTP transcutaneous pacemaker generator states that typical thresholds (equivalent to Tl, not T2-Zo11 PM: Personal communication, 1988) are 40 to 60 mA, averaging 55 mA.” The Tl thresholds in this study were higher; the T2 thresholds were within the expected range. In the experimental trials of this device on volunteers, the differente between Tl and T2 was generally 5 mA (Zo11 PM: personal communication). If the pacing rate was only slightly faster than the intrinsic rate and the TP current was increased at a rapid rate in trying to determine Tl, then the value of Tl obtained may be erroneously high. However, the current output was increased slowly and it did not contribute to this finding. The Tl to T2 disparity may be clinically significant in the situation where the patient’s intrinsic HR is varying, thereby causing intermittent pacing. The current output needs to be set high enough to assure pacemaker Capture. NO correlations were demonstrated between TP thresholds and age, height, weight, or body surface area. Similarly, a study in children (aged 0.9 to 17.9 years, weighing 6.96 to 51 kg) undergoing cardiac surgery demonstrated no correla-

surgically drape over the anterior pad.) The unpaired t test was used to compare the two groups for age, height, weight, body surface area, and pacing thresholds Tl and T2. Regression analysis was used to determine if there was any correlation between Tl and T2 for both groups and age, height, weight, or body surface area. RESULTS

patients were successfully paced. The data presented in Table 1 demonstrate no significant differences between the two groups in age, height, weight, body surface area, Tl, or T2. NO significant correlations between Tl or T2 with either age, height, weight, or body surface area were found. Transient erythema of the skin was commonly noted after electrode removal. There was no obvious internal tissue damage noted by the surgeon in the vicinity of the old sternal wires. None of the patients experienced postoperative wound infections or wound healing complications. Al1

DISCUSSION

Previous cardiac surgery does not appear to alter TP thresholds. The significante of this study is that approximately 400,000 patients per year undergo cardiac surgery in the United States.“.14 Some of these patients wil1 eventually require cardiac pacing. Compared with other modalities of

Table 1. Summary

of Patient Data Body

surface Redo

Age

(vr ago)

(vr)

Height (cmI

Weight kg)

AX?a (m’)

Tl (mA)

T2 (mA)

NO

61

170

75

i .a7

90

ai

NO

59

179

76

1.95

84

75

NO

74

168

1.92

100

65

NO

76

168

82 93

2.02

JO

40

Groupl

NO

72

ia0

66

I .a5

79

50

NO

66

175

74

1.90

58

54

NO

81

152

64

1.60

80

65

NO

57

175

89

2.05

80

58

NO

63

175

86

2.02

54

35

NO Mean 2 SEM

JO

64

152

67.3 t 2.5

169.4 k 3.2

77.5 + 3.0

1.67

97

84

11.a9 1+0.04

79.2 2 4.8

60.7 + 5.2

Group 2 10

61

175

45

40

62

175

88 80

2.04

10

1.96

55

7

63

178

85

2.00

80 88

0.6

61

175

80

1.96

95

80

12

63

157

JO

1.71

110

30

14

56

175

1.93

74

58

8

71

173

78 88

2.02

75

60

7

65

157

73

1.74

95

75

14

59

178

75

1.96

60

45

60

ia0 173.3 i 2.6

12

Mean ) SEM

62.1 + 1.3

NOTE. Group 1 are those patients having their first median sternotomy. median sternotomy.

There were no significant

differences

100 al.7

k 2.8

2.20 1.95 + 0.04

In Group 2, the redo column represents

60 78.2 t 6.2

JO

45

55.8 + 5.0

the elapsed time since the previous

between group 1 and group 2 for age, height, weight, body surface area, Tl, or T2.

TRANSCUTANEOUS

53

PACING IN REPEAT CABG

tion between TP thresholds and age, weight, body surface area, chest circumference, or anteroposterior chest diameter; the TP thresholds were similar to those of adults.” NO patients were studied who had undergone cardiac surgery within the previous 6 months. Pacing thresholds increase after endocardial or epicardial lead placement and then decrease; this has been attributed to edema and inflammation separating the electrode from functional myocardium.‘s This should not be a factor with TP. However, it should be noted that the electrical properties of the mediastinum are not completely known and possibly vary with the healing process, fluid and air resorption, and star formation. Kelly et al successfully transcutaneously paced patients immediately after chest closure and at 4 and 24

hours after cardiac surgery.” Although al1 these thresholds were higher than the preoperative thresholds, the highest thresholds were obtained immediately after chest closure, decreased at 4 hours, and decreased further at 24 hours. The primary purpose of this study was to investigate the effect of previous cardiac surgery via median sternotomy on TP thresholds. The results of this study should not be extrapolated to situations that were not studied, such as the effectiveness of TP in patients with an ischemic bradydysrhythmia, severe chronic obstructive pulmonary disease, or massive obesity. Also, this pacing modality provides only ventricular demand pacing; it may be inadequate for those patients dependent on atria1 systole.

REFERENCES

1. Transcutaneous pacemakers in technology for anesthesia. ECRI 8:1-8,1988 2. Zoll PM: Resuscitation of the heart in ventricular standstill by external electrical stimulation. N Eng1 J Med 248:768-771,1952 3. Falk RH, Zo11 PM, Zoll RH: Safety and efficacy of noninvasive cardiac pacing: A preliminary report. N Eng1 J Med 309:11661168,1983 4. Kirschenbaum LP, Eisenkraft JB, Mitchell J, Hillel Z: Transthoracic pacing for the treatment of severe bradycardia during induction of anesthesia. J Cardiothorac Anesth 3:329-332, 1989 5. Dunn DL, Gregory JJ: Noninvasive temporary pacing: Experience in a community hospital. Heart Lung 18:23-28,1989 6. Niemann JT, Rosborough JP, Garner D, et al: External noninvasive pacing: A comparative hemodynamic study of two techniques with conventional endocardial pacing. PACE 7:230236,1984 7. Berliner D, Okun M, Peters RW, et al: Transcutaneous temporary pacing in the operating room. JAMA 254:84-86, 1985 8. Kelly JS, Royster RL, Angert KC, Case D: Efficacy of noninvasive transcutaneous cardiac pacing in patients undergoing cardiac surgety. Anesthesiology 70:747-751,1989 9. Zaidan JR, Curling PE, Craver JM: Effect of enflurane, isoflurane, and halothane on pacing stimulation thresholds in man. PACE 8:32-34, 1985

10. Atlee JL: Pacemakers and cardioversion, in Kaplan JA (ed): Cardiac Anesthesia, vol 2 (ed 2). Philadelphia, PA, Grune & Stratton, 1987, pp 855-879 ll. Buchanan D, Clements F, Reves JG, et al: Atria1 esophageal pacing in patients undergoing coronary artery bypass grafting: Effect of previous cardiac operations and body surface area. Anesthesiology 69:595-598,1988 12. Zoll NTP Non-invasive Temporary Pacemaker Operators Manual. Woburn, MA, ZMI Corporation, 1987 13. National Center for Health Statistics: National hospita1 discharge survey. Hyattsville, MD, Public Health Service, 1985 14. Clark RE: Who, Hobbies, and Heroes. Ann Thorac Surg 49:515-521, 1990 15. Abernathy WS: Complete heart black caused by the SwanGanz catheter. Chest 65:349,1974 16. Thomson IR, Dalton BC, Lappas DG, Lowenstein E: Right bundle-branch black and complete heart black caused by the Swan-Ganz catheter. Anesthesiology 51:359-362,1979 17. Beland MJ, Hesslein PS, Finlay CD, et al: Noninvasive transcutaneous cardiac pacing in children. PACE 10:1262-1270, 1987 18. Moses HW, Taylor GJ, Schneider JA, et al: A Practica] Guide to Cardiac Pacing. Boston, MA, Little, Brown, 1983, pp 55-56

Transcutaneous pacing in patients undergoing coronary artery bypass grafting: effect of previous cardiac surgery.

Temporary transcutaneous pacing thresholds were measured in 10 patients undergoing primary coronary artery bypass grafting (CABG) operations and 10 pa...
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