| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Ann Thorac Surg 2002;74:2072-2075
© 2002 The Society of Thoracic Surgeons
a Department of Surgery, Kuopio University Hospital, Kuopio, Finland
b Department of Internal Medicine, Kuopio University Hospital, Kuopio, Finland
Accepted for publication July 22, 2002.
* Address reprint requests to Dr Hakala, Department of Surgery, Kuopio University Hospital, PL 1777, 70211 Kuopio, Finland.
e-mail: tapio.hakala{at}kuh
 |
Abstract |
|---|
 Top Abstract IntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
METHODS: Eighty patients having on-pump CABG without additional procedures were included in the study. After cannulation but before initiation of cardiopulmonary bypass two pacing wires were placed on the lateral surface of the right atrium. The right atrium was paced with the rate of 200 beats per minute for 10 seconds. If the patient was in sinus rhythm after the high-rate pacing, the pacing test was repeated with the rate of 250 and finally 300 beats per minute.
RESULTS: Postoperatively AF developed in 28 patients (35%). The high-rate atrial pacing test induced AF in 27 patients (33.7%). Of the 28 patients who experienced AF during the postoperative period, 17 patients were inducible in the atrial-pacing test (sensitivity 0.61). Of the 52 patients who did not develop AF postoperatively, 42 patients were not inducible in the atrial-pacing test (specificity of the test was 0.81). Positive and negative predictive values of the test were 0.63 and 0.79, respectively.
CONCLUSIONS: The intraoperative high-rate atrial pacing test turned out to be a simple, safe, and fast way to identify the patients at risk for AF after CABG. The diagnostic accuracy of this test is sufficient to identify a group of patients to whom prophylactic treatment could be directed.
|
Introduction |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
Numerous trials have investigated the efficacy of antiarrhythmic drug prophylaxis to prevent AF after CABG. Prophylactic amiodarone has been shown to decrease the incidence of AF after CABG [6, 7]. Oral amiodarone at a dosage of 600 mg per day for 7 days before surgery and 200 mg per day postoperatively until hospital discharge decreased the incidence of AF by 45% [6]. However the clinical issue is that by using routine prophylactic treatment on all CABG patients approximately 70% of the patients would be treated in vain and exposed to the possible side effect of medication.
Thus there is a need for a reliable and easy method to identify the patients at high risk for AF after CABG that could be used to guide the medical prophylactic treatment of these patients. The purpose of this study was to test whether intraoperative atrial high-rate pacing induced AF can be used to identify the patients at risk for postoperative AF.
|
Material and methods |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
The ascending aorta was cannulated for an arterial line and a single-stage venous cannula was introduced through the right atrial appendix. Two epicardial pacing electrodes (Flexon-0; Tyco Healthcare Finland, Helsinki, Finland) were sutured to the right atrial wall. One electrode was sutured to the sinoatrial node region and the other was sutured 2 cm from it to the lateral wall of the right atrium. The interelectrode distance was the same for all patients. Before initiation of cardiopulmonary bypass the right atrium was paced with an output programed at two times the capture threshold using a rate of 200 beats per minute for 10 seconds. The rhythm was determined after the high-rate pacing was stopped. The patient was monitored by electrocardiograpy (ECG) during the test and the test was determined positive if the pulse rate was irregular and there were no P waves before the QRS complexes. If the patient was in sinus rhythm the test was repeated after 1 minute with a rate of 250 beats per minute. If sinus rhythm was still present after the pacing, the test was repeated after 1 minute with a pacing rate of 300 beats per minute. Thereafter the cardiopulmonary bypass was initiated.
Aortic root venting was used routinely. Cardiopulmonary bypass with moderate systemic hypothermia (temperature of venous blood 32°C) and moderate hemodilution (hematocrit > 0.22) was used with flow rates of 2.2 to 2.4 L/m2 and mean perfusion pressure of 50 to 85 mm Hg. Intermittent cold crystalloid cardioplegia was administered through the antegrade route. Distal and proximal anastomoses were constructed during a single aortic occlusion. Cardioplegia solution consisting of magnesium 16 mmol/L and no extra magnesium substitution was given.
After the operation patients were transferred to the intensive care unit and were weaned off the ventilator when they fulfilled the following criteria: hemodynamic stability, peripheral temperature more than 32°C, cooperativity, and no major bleeding. Creatine kinase-MB enzymes were collected for every patient 1 hour after the operation. Drains were removed on the first postoperative day and the patients were moved to the surgical ward when they had hemodynamic and respiratory stability. ß-Blocking medication (Metoprolol) was administered to all patients starting on the first postoperative day and the dosage was titrated according to pulse rate (target pulse rate 60 to 80 beats per minute).
Postoperative ECG monitoring was continued during the entire hospital stay to detect all episodes of AF and 12-lead ECG recording was performed as necessary to confirm the rhythm abnormality. The rhythm was determined to be AF when the pulse rate was irregular and there were no P waves before the QRS complexes.
Statistical analysis
An unpaired t test was used to study for the differences in continuous variables and the 
2 test for categorized variables. The limit for statistical significance was p less than 0.05. All the statistical procedures were performed by SPSS 9.0 statistical package (SPSS, Chicago, IL).
|
Results |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
During the postoperative period AF developed in 28 patients (35%). The first AF episode appeared on average 52 hours (range 5 to 100) postoperatively. AF was treated medically and all the patients were in sinus rhythm at the time of discharge. Patients who developed AF tended to be older (p = 0.09), have higher CK-MB postoperatively (p = 0.05), and were more often female (p = 0.08) compared with patients who remained in sinus rhythm (Table 1).
|
|
|
Comment |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
AF may begin as a rapid atrial tachycardia from the pulmonary veins, with tachycardia remodeling promoting the transition to multiple-circuit reentry AF [8, 9]. Reentry and atrial fibrillation are facilitated when adjacent atrial regions have widely disparate refractory periods [10–12]. This abnormal dispersion of refractoriness makes the atrium more vulnerable to the development of AF after CABG. Our study suggests that high-rate atrial pacing mimics the rapid atrial tachycardia in patients vulnerable to AF by identifying many of those with an increased dispersion of refractoriness. Atrial pacing with a high rate induces AF in the presence of increased dispersion of refractoriness, ie, where some parts of atrial tissue are repolarized while the adjacent tissue is still depolarized. Slowed atrial conduction also facilitates reentry and there is a relation between prolonged P-wave duration and the increased risk of AF after cardiac surgery [13].
The electrophysiologic properties of atrias may be influenzed by intraoperative events related to cardioplegia, possible ischemia during cross clamp time, and possible mechanical injury to the atrium during the operative procedure. These events occur after our pacing protocol and therefore they may have influenced the accuracy of the test.
We performed the atria pacing protocol before the initiation of cardiopulmonary bypass because if performed after the termination af cardiopulmonary bypass it induces AF in one third of patients and at that stage AF may cause hypotension and low cardiac output.
Lowe and coworkers [14] developed an intraoperative screening test to identify patients at risk for development of postoperative AF. In contrast to our study they did not use high-rate pacing but stimulated the mid-right atrium with a bipolar probe and alternating current to induce AF. The test induced AF in 36 of 50 patients. The sensitivity and negative predictive value of their test were reported to be better than in our test (0.94 versus 0.61 and 0.93 versus 0.79, respectively). Conversely in our study the specificity, positive predictive value, and accuracy were better (0.81 versus 0.41, 0.63 versus 0.47, 0.74 versus 0.60, respectively). This suggests that the alterating current protocol employed in the other study may be more aggressive and results in too many false-positive cases and therefore it is not as suitable as the present protocol for determining patients needing antiarrhythmic therapy.
Several studies have demonstrated that signal-averaged P-wave analysis performed preoperatively is also useful in identifying patients at high risk for developing AF after cardiac surgery [13, 15–17]. The criterion for abnormal signal averaged P-wave duration varied from 140 ms to 155 ms and the sensitivity of signal-averaged P-wave duration for identifying the patients who developed AF ranged from 0.63 to 0.77, with a specificity from 0.48 to 0.79. The positive predictive values were reported to be 0.34 to 0.65 while the negative predictive values have been from 0.82 to 0.87. Thus the results of our high-rate atrial pacing test are comparable with these results in identifying patients at risk for AF after CABG.
We conclude that intraoperative high-rate atrial pacing is a simple, safe, and quick test to identify many of the patients at greater risk for AF after CABG; it is easily performed by the surgeon. The epicardial pacing electrodes used in the test can also be used postoperatively for atrial pacing. The sensitivity of the test was moderate and the specificity was very high. The diagnostic accuracy of this test is sufficient to identify a group of patients to whom prophylactic treatment could be directed.
We excluded patients with unstable angina from our study and our patients had relatively good ejection fractions and a low incidence of comorbidities. Thus our patient population is not very representative of patients generally seen in practice. All our patients had ß-blocking medication postoperatively. It is a preventive strategy to avoid postoperative AF and is common policy in our institution. That may have influenced the results of the study.
|
Acknowledgments |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
|
References |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
This article has been cited by other articles:
|
|
 |
|
  K. Iino, N. Yui, T. Ooya, R. Kawabata, S. Tomita, and G. Watanabe Successful low-energy cardioversion using a novel biodegradable gel pad: Feasibility of treating postoperative atrial fibrillation in animals. J. Thorac. Cardiovasc. Surg., December 1, 2007; 134(6): 1519 - 1525. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. N. Patel, B. L. Hamman, A. N. Patel, R. F. Hebeler, R. E. Wood, C. A. Cockerham, B. A. Willey, and H. C. Urschel Jr Epicardial atrial defibrillation: successful treatment of postoperative atrial fibrillation Ann. Thorac. Surg., March 1, 2004; 77(3): 831 - 837. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |
