Transmyocardial Laser Revascularization: Epicardial ECG Detection Provides Efficient R-Wave Triggering during Mobilization of the Heart

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1 Journal of Clinical Laser Medicine & Surgery Volume 21, Number 3, 2003 Mary Ann Liebert, Inc. Pp Transmyocardial Laser Revascularization: Epicardial ECG Detection Provides Efficient R-Wave Triggering during Mobilization of the Heart THOMAS WILD, M.D., 1 NERMIN SERBECIC, M.D., 2 SVEN CHRISTOPH BEUTELSPACHER, M.D., 4 MEINHARD PLONER, Ph.D., 1 ZENO DECKERT, 1 and RAINALD SEITELBERGER, M.D. 3 ABSTRACT Objective: In order to achieve an accurate intraoperative ECG detection, a new technique in detecting the trigger-signal was developed. In contrast to the traditional three-lead ECG-configuration, the left leg electrode was connected to a transient epicardial pacemaker electrode on the left-ventricular surface. Background Data: The Holmium:YAG-Laser for Transmyocardial Laser Revascularization (TMLR) is R-wave-triggered, providing the release of energy only during the refractory period of the heart cycle. However, an exact ECG-triggering during mobilization of the apex and/or posterior wall is difficult to achieve by using conventional ECGconfiguration, therefore increasing the risk for mistriggering and induction of arrhythmias during TMLR. Materials and Methods: Two groups of patients, all undergoing stand alone TMLR-procedures via left minithoracotomy, were compared. Ten patients were operated with the conventional ECG configuration (group 1) and ten patients with the modified epicardial ECG configuration (group 2). Results: In patients of group 1, as a result of a loss of the trigger signal or due to the triggering of artifacts, the incidence of correctly triggered QRScomplexes was 56% of all documented QRS-complexes. In contrast, an excellent triggering was observed in 98% (p < 0.001) in group 2, resulting in a reduction of laser operative time by 35% (p < 0.001) and a decrease in the incidence of intraoperative ventricular fibrillation (0 vs. 3). Conclusion: In conclusion, this new ECG configuration is a simple but effective method in achieving an excellent ECG signal during all stages of TMLR. As a consequence, a reduction in operative time and incidence of ventricular fibrillation can be achieved. T HREE INTRODUCTION DIFFERENT TYPES OF LASERS, namely the CO 2, the holmium:yag, and the excimer laser are currently used for transmyocardial laser revascularization (TMLR). 1 6 The CO 2 and the holmium:yag laser are R-wave triggered, avoiding the repolarization period of the heart cycle. This approach reduces the incidence of ventricular arrhythmia and fibrillation. 7 Up to now, the detection of the ECG-trigger has always been achieved by using the Einthoven s triangle configuration (electrodes positioned at right and left arm and left leg). However, in order to create laser channels in the apex and posterior wall via a left thoracotomy, it is necessary to mobilize the heart from its anatomical position, which frequently leads to an inaccurate detection of the ECG-potentials due to a change of the Einthoven s ECG configuration. As an additional consequence during this procedure, the laser may use artifacts (potentials other than R-wave) as a trigger signal or prevent the release of the laser energy. The goal of our study was to develop an advanced technique for ECG detection during TMLR in order to make the procedure safer and faster. MATERIALS AND METHODS All TMLR procedures (holmium:yag laser; CardioGenesis Corp.) were performed on the beating heart via a left anterolateral minithoracotomy. To achieve an effective ECG signal The Department of 1 General Surgery, 2 Cardiology, and 3 Cardio-Thoracic Surgery, General Hospital, University Vienna, Austria. 4 Department of Ophthalmology, University of Heidelberg, Germany. 145

2 146 Wild et al. during maximal mobilization of the heart, a stable Einthoven s triangle was configured by positioning a transient ventricular pacemaker electrode (Dr. Osypka Corp, Germany) close to the apex of the left ventricle. The left leg ECG-electrode was disconnected and then linked to the ventricular pacemaker electrode, providing an Einthoven s triangle in any position of the mobilized heart. To verify this new way of ECG-detection, two groups of patients (n = 20) were investigated. All patients had diffuse coronary artery disease with stable angina pectoris and no option for further interventional or surgical treatment. Ten patients were operated by using the conventional ECG configuration (group 1), and 10 patients received the modified epicardial ECG electrode (group 2). Both groups were compared with concern to time of laser procedure, induction of ventricular arrhythmias, loss of the trigger signal, and incidence of exact detection of the ECG signal. The ECG was documented at baseline preoperatively and continuously from the onset of the laser procedure (start of first channel). All QRS complexes and arrhythmias were numbered. Creatine kinase (CK, U/L, normal values: 0 70) and the MB isoenzyme of CK (CK-MB, U/L, normal values 0 10) were measured immediately before the procedure and at 4, 12, 24, and 36 h after TMLR using enzymatic fluorometric methods. Statistical analysis All data are presented as mean 6 standard deviation (SD). Group 1 was compared with group 2. Patients were randomized into one of two arms without stratification. At first, a Kolmogorov-Smirnov adaptation test was performed to test if the sample was normal, otherwise a transformation was adapted. Statistical significance was performed due to a t-test. The significance level was set at A Levene test was then performed to check if variances were equal. The samples were additionally analysed using empirical quantiles and showed in Box- and Whiskers plots. For statistical data analysis, the SPSS 9.0 Inc. statistical package was used. RESULTS Clinical and anamnestic data of all patients included in the study are shown in Table 1 and revealed no differences between both groups. Except one, all patients had already undergone at least one prior CABG procedure. None of the patients had a history of preoperative ventricular arrhythmias. Intraoperative characteristics are presented in Table 2 and Figures 1 and 2. No differences were observed with regard to overall numbers of laser channels and their respective locations. The incidence of correctly triggered QRS complexes was markedly lower in group 1 (56%) as compared to group 2 (98%, p < 0.001; Fig. 1). In accordance, inadequate triggering lead to ventricular fibrillation in 3 patients of group 1 but was not observed in group 2. All three patients were successfully cardioverted using electroversion within 60 sec after the onset of fibrillation. Whereas two of those patients had uneventful postoperative courses without ventricular arrhythmias, one patient died 24 h after the TMLR procedure due to acute left ventricular failure although an intraaortic balloon pump was inserted. In this patient, additional intermittent ventricular arrhythmias were also documented. During autopsy, no evidence of a new myocardial infarction was observed, although postoperative CPK had reached the maximum of 1490 U/L. As a consequence of the significantly higher incidence of correctly triggered QRS complexes in group 2, the laser-related operating time was markedly lower in group 2 as compared to group 1 ( vs min, p < 0.001). A Kolmogorov- Smirnov test for each group confirmed no significant deviation from the standard distribution of operative time and number of QRS-complexes. After examining the equality of variance by Levene test (p = 0.267), a t-test for independent samples was done refusing the null hypothesis of equal mean values. In group 1, postoperative CK peak values were significantly higher as compared to group 2 ( vs U/L, p < 0.05). However, no differences between both groups were observed with regard to postoperative CK MB peak values ( vs U/L, Fig. 3). DISCUSSION Various experimental studies and empirical observations during clinical cases have clearly shown that an accurate triggering of the laser device to the ECG is crucial for the safety and effectiveness of TMLR. 4,8 11 Since chronically ischemic hearts appear specifically vulnerable to mechanical interference, the actual operative procedure of lasering should be kept to a minimum with regard to the duration of the procedure and the number of laser attempts. A shorter duration of the laser procedure in combination with a decrease in actual laser attempts may decrease both the incidence of ventricular arrhythmias and the duration of periods of unstable hemodynamic conditions, that is, a decrease in blood pressure during mobilization of the heart. 7,11 A direct relationship between incidence of ventricular arrhythmias and amount of tissue damage during TMLR has already been documented under experimental conditions. 11 The incidence of ventricular arrhythmias usually increases during the period of mobilization of certain myocardial areas such as apex or posterior wall. Mobilization of the heart from TABLE 1. ANAMNESTIC DATA Without With electrode electrode Variable (group 1) (group 2) No. of patients Age Ejection fraction in % % % CCS score Previous PTCA 5 4 Previous CABG 10 9 Pre-operative ventricular No No arrhythmias Pre-operative pacemaker 0 1

3 Transmyocardial Laser Revascularization 147 TABLE 2. SURGICAL DATA Without electrode With electrode Variable (group 1) (group 2) No. of patients Number of channels Anterior wall Posterior wall Number of all QRS complexes Number of correct detection of R waves (%) (56%) (96%) Intraoperative ventricular fibrillation 3 0 Time of laser procedure in min CK peak value (U/I) CK-MB peak value (U/I) Perioperative death 1 0 its anatomical position often leads to inadequate detection of QRS complexes due to a change in the Einthoven s triangle ECG configuration. As a consequence, nontriggered QRS complexes may prevent the release of the laser energy, whereas mistriggered QRS complexes increase the probability for induction of arrhythmias. One way to minimize arrhythmic disturbances during TMLR is to synchronize the trigger device of the laser by means of transesophageal echocardiography. 9 However, it appears more reliable to establish an exact and continuous detection of R-wave during all stages of the laser procedure. The results of our study clearly demonstrate that a simple modification of the Einthoven s triangle ECG configuration with repositioning of the left leg electrode to an epicardial pacemaker electrode provides a reliable and easy-to-trigger ECG signal throughout an entire laser procedure (Figs. 1 and 4). Consequently, we were able to demonstrate that the incidence of correctly triggered QRS complexes was markedly increased and lead to both, a decrease in the duration of the laser procedure and a substantial increase in the number of correctly detected QRS complexes. Although the relatively small numbers of patients in both groups make it difficult to FIG. 1. Box- and Whisker-Plot of save R-wave triggering for both groups. First group without and second group with epicardial ECG-triggering. Data are given as percentiles. The central box shows the data between the quartiles (25- and 75-percentiles), with the median represented by a bold line. Considering time of operation and reliable ECG-triggering, both groups were highly significant (p < 0.001).

4 148 Wild et al. FIG. 2. Box- and Whisker-Plot of TMLR operation time for both groups. First group without and second group with epicardial ECG-triggering. Data are given as percentiles. The central box shows the data between the quartiles (25- and 75-percentiles), with the median represented by a bold line. Considering time of operation and reliable ECG-triggering, both groups were highly significant (p < 0.001). FIG. 3. Box- and Whisker-Plot of postoperative CK-MB values for both groups. First group without and second group with epicardial ECG-triggering. Data are given as percentiles. The central box shows the data between the quartiles (25- and 75-percentiles), with the median represented by a bold line.

arrhythmic disturbances during TMLR. FIG. 5.

5 Transmyocardial Laser Revascularization 149 FIG. 4. Synchronizing the trigger device of the laser by means of an epicardial electrode provides an exact and continuous detection of R-waves during all stages of the laser procedure thereby minimizing arrhythmic disturbances during TMLR. FIG. 5. A reliable and easy-to-trigger ECG-signal throughout an entire laser procedure is achieved through a simple modification of the Einthoven s triangle ECG-configuration by repositioning of the left leg electrode to an epicardial pacemaker electrode. prove any beneficial effect on perioperative outcome, two observations strongly indicate the clinical relevance of this new approach. Ventricular fibrillation occurred in three patients using the conventional ECG configuration. Whereas no adverse impact of ventricular fibrillation on peri- and postoperative outcome was observed in two of those patients, one patient eventually died due to sustained cardiogenic shock at 24 h postoperatively. In addition, analyses of perioperative CK and CK-MB levels indicate that shortening of the operative procedure 12,13 and avoidance of mistriggering may decrease the extent of tissue damage following TMLR. 11,14 Whereas the higher CK-MB levels in group 1 did not reach statistical significance, postoperative CK levels were markedly lower in patients with the new ECG detection method (group 2). The higher CK may have been due to the longer operative time and a lower cardiac output during the longer period of mobilization of the heart in group 1. In conclusion, the results of this study demonstrate that the newly developed ECG configuration, using an epicardial pacemaker electrode placed to the left ventricle (Fig. 5), is a simple but effective method and provides excellent ECG triggering throughout a laser procedure. As a result, a significant reduction of operating time and a decrease in the incidence of ventricular arrhythmias could be achieved. Clinical data strongly imply that this approach may also have a beneficial effect on clinical outcome after TMLR. REFERENCES 1. Hughes, G.C., Landolfo, K.P., Lowe, J.E., et al. (1999). Diagnosis, incidence, and clinical significance of early postoperative ischemia after transmyocardial laser revascularization. Am. Heart J. 137, Hughes, G.C., Landolfo, K.P., Lowe, J.E., et al. (1999). Perioperative morbidity and mortality after transmyocardial laser revascularization: incidence and risk factors for adverse events. J. Coll. Cardiol. 33, Hughes, G.C., Shah, A.S., Yin, B., et al. (2000). Early postoperative changes in regional systolic and diastolic left ventricular function after transmyocardial laser revascularization: a comparison of holmium:yag and CO 2 lasers. J. Am. Coll. Cardiol. 15, Jones, J.W., Schmidt, S.E., Richman, B.W., et al. (1999). Holmium:YAG laser transmyocardial revascularization relieves angina and improves functional status. Ann. Thorac. Surg. 67, Wild, T., Wolfram, J., Beutelspacher, S.C., et al. (1999). Transmyocardial laser revascularization with a holmium:yaglaser, clinical experiences. Acta Chir. Austriaca 31, Mack, C.A., Magovern, C.J., Hahn, R.T., et al. (1997). Channel patency and neovascularization after transmyocardial laser revascularization using an excimer laser. Circulation 96, Suppl II, Mirhoseini, M., Muckerheide, M., and Cayton, M.M. (1982). Transventricular revascularization by laser. Lasers Surg. Med. 2, Horvath, K.A., Mannting, F., Cummings, N., et al. (1996). Transmyocardial laser revascularization: operative techniques and clinical results at two years. J. Thorac. Cardiovasc. Surg. 111, Seitelberger, R., Wild, T., Wolfram, J., et al. (1998). Transmyocardial laser revascularization with a holmium:yag-laser: initial clinical experience, in: TMLR: management of coronary artery disease. New York: Springer Verlag, pp

6 150 Wild et al. 10. Spanier, T.B., Burkhoff, D., and Smith, C.R. (1997). Role for holmium:yag-lasers in transmyocardial laser revascularization. J. Clin. Laser Med. Surg. 15, Kadipasaouglu, K.A., Sartori, M., Masai, T., et al. (1999). Intraoperative arrhythmia s and tissue damage during transmyocardial laser revascularization. Ann. Thorac. Surg. 67, Van Lente, F., Martin, A., Ratliff, N.B., et al. (1989). The predictive value of serum enzymes for perioperative myocardial infarction after cardiac operations. J. Thorac. Cardiovasc. Surg. 98, Devine, J.E., Wiens, R.D., Halstead, J.M., et al. (1986). Quantitation of CK-MB release: Diagnostic utility in coronary bypass grafting. Clin. Chim. Acta 156, Burkhoff, D., Wesley, M.N., Resar, J.R., et al. (1999). Factors correlating with risk of mortality after transmyocardial revascularization. J. Am. Coll. Cardiol. 34, Address reprint requests to: Thomas Wild, M.D. Department of General Surgery University of Vienna Waehringer Guertel Postfach Vienna, Austria nerminovich@hotmail.com

Journal of the American College of Cardiology Vol. 34, No. 1, by the American College of Cardiology ISSN /99/$20.

Journal of the American College of Cardiology Vol. 34, No. 1, 1999 1999 by the American College of Cardiology ISSN 0735-1097/99/$20.00 Published by Elsevier Science Inc. PII S0735-1097(99)00162-X Factors