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Ann Thorac Surg 1997;63:1511-1512
© 1997 The Society of Thoracic Surgeons
Cardiothoracic Department, St. Mary's Hospital, Praed Street, London W2 1NY United Kingdom
To the Editor:
We read with interest the editorial by Dr Ullyot [1], who considers minimally invasive coronary revascularization (MICR) without cardiopulmonary bypass to carry no significant advantages. However, Akins and associates [2] have provided some evidence that such procedures are not associated with significant myocardial dysfunction postoperatively. Because there has not to date been accurate information about the degree of myocardial damage imposed by normothermic regional ischemia, we investigated the release of troponin-T (cTnT), a highly sensitive and specific marker of myocardial damage, in patients undergoing MICR.
After obtaining informed consent, we studied 11 consecutive patients who underwent MICR for stable angina. Eleven additional patients who had uncomplicated elective coronary artery operations with cardiopulmonary bypass were used as a comparison group. Anesthesia in both groups consisted of fentanyl, pancuronium, and isoflurane. In the MICR group, after making a 5- to 7-cm left vertical parasternal incision and removing two costal cartilages, we mobilized the left internal mammary artery. After systemic heparinization with 300 IU/kg of body weight, the left anterior descending artery was occluded proximally and distally, then incised for 4 to 5 mm, and the anastomosis was performed in a standard fashion. Neither methods of preconditioning nor pharmaceutical means to stabilize the artery were used. In the standard coronary artery bypass grafting group, the internal mammary artery was mobilized after a median sternotomy was made. After systemic heparinization with 300 IU/kg of body weight, cardiopulmonary bypass was established between a two-stage venous cannula in the right atrium and arterial return to the ascending aorta. A membrane oxygenator (CML membrane hollow fiber oxygenator; Cobe Inc, Arvada, CO) was used for extracorporeal circulation, and the system was primed with 1 L of Ringers' lactate. The pH management was pH-stat. Myocardial protection was achieved with the use of antegrade cold crystalloid cardioplegia (St. Thomas' cardioplegic solution) and topical hypothermia with ice slush. The nasopharyngeal temperature was maintained at approximately 28°C during the cardiopulmonary bypass period. After the completion of all distal anastomoses, the aortic cross-clamp was released and the proximal anastomoses were performed with the heart beating. After the completion of the operation, the remaining heparin was reversed with protamine sulfate given in a dose of 1.5 mg/100 IU heparin in both groups.
Peripheral venous blood samples for cTnT were obtained before and 1, 6, 24, and 72 hours after the operation. The venous blood samples were drawn into vacuum tubes containing dry lithium-heparin and placed immediately on ice, and the plasma was separated on a centrifuge (4°C, 3,000 rpm, 10 minutes) within 30 minutes. The separated plasma was then immediately frozen to -75°C until assayed. The level of cTnT was measured by using an enzyme immunoassay using the Enzym-Test Troponin-T on an E.S. 300 immunoassay analyzer (Boehringer Mannheim, Lewes, UK). Two-way analysis of variance and multiple range test was used to describe cTnT level changes over time. Variables between groups were compared with Student's t test and Fisher's exact test. Results were expressed as mean ± standard error, and differences were considered significant at a probability level of p less than 0.05.
Patients' characteristics are presented in Table 1
. No patient received inotropic support during or after the operation, and none of them had any significant complication over the 72 hours of observation. In the MICR group the ST segment elevation during ischemic periods was 1.07 ± 0.31 mm (range 0 to 4 mm) and the ischaemic time per anastomosis was 16.1 ± 1.39 minutes (range, 12 to 28 minutes). Time changes of cTnT level are presented in Figure 1.
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References
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  S. L. Braun, A. Barankay, and D. Mazzitelli Plasma Troponin T and Troponin I after Minimally Invasive Coronary Bypass Surgery Clin. Chem., February 1, 2000; 46(2): 279 - 281. [Full Text] [PDF]
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 R. D. L. Stanbridge and L. K. Hadjinikolaou Technical adjuncts in beating heart surgery Comparison of MIDCAB to off-pump sternotomy: a meta-analysis Eur J Cardiothorac Surg, November 1, 1999; 16(Supplement_2): S24 - S33. [Abstract] [Full Text] [PDF]
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 J. Bonatti, H. Hangler, C. Hormann, J. Mair, J. Falkensammer, and P. Mair Myocardial damage after minimally invasive coronary artery bypass grafting on the beating heart Ann. Thorac. Surg., September 1, 1998; 66(3): 1093 - 1096. [Abstract] [Full Text] [PDF]
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R. H. Heijmen, C. Borst, R. van Dalen, C. W.J. Verlaan, C. M. Moues, Y. J.M. van der Helm, and P. F. Grundeman Temporary luminal arteriotomy seal: II. coronary artery bypass grafting on the beating heart Ann. Thorac. Surg., August 1, 1998; 66(2): 471 - 476. [Abstract] [Full Text] [PDF]
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