Gummert, Jan F. MD*; Raumanns, Joerg MD†; Opfermann, Ulrich T. MD‡; Bossert, Torsten MD*; Ender, Joerg MD†; Rastan, Ardawan MD‡; Falk, Volkmar MD, PhD‡; Walther, Thomas MD, PhD‡; Mohr, Friedrich W. MD, PhD‡
Off-pump coronary artery bypass (OPCAB) grafting has gained widespread popularity during the past decade. To date, approximately 30% of coronary revascularization procedures worldwide are done on a beating heart, exceeding 80% in some countries.
Elimination of cardiopulmonary bypass and aortic cannulation has been proven to lead to a significant reduction in patient morbidity such as renal failure,1,2 requirement for blood transfusions, perioperative myocardial infarction, and stroke.3–5 Furthermore, it was demonstrated that complete revascularization is possible on the beating heart.6 The invention of cardiac stabilizers and intraoperative techniques such as Trendelenburg positioning, opening of the pericardium, and deep pericardial sutures have made grafting of the circumflex and right coronary territory easier. Nevertheless, there still is a conversion rate from OPCAB to conventional bypass grafting with use of cardiopulmonary bypass because of hemodynamic instability, especially during exposure of posterior and inferior grafting territories between 0.5 and 2.8% in large series.7,8
To facilitate grafting of the circumflex territory, placement of either four pericardial retraction sutures (PS), as originally described by Ricardo Lima, or a modified single suture in the oblique sinus9 has been proposed. Apical suction devices such as the Xpose system (Guidant, Cupertino, CA) were developed aiming at a reduction of the risk for hemodynamic deterioration during grafting of the right coronary and especially circumflex territory. It consists of an articulating arm with a bell-shaped cup attached at the end by a swivel-joint. With the use of suction, the cup is positioned on the cardiac apex, and the target grafting area can be exposed without the use of pericardial sutures.
The aim of the study was to compare hemodynamic performance during exposition of the inferior and posterior wall while using either pericardial stitches or the Xpose apical suction device.
Thirty consecutive patients with two- or three-vessel coronary artery disease electively scheduled for multivessel-coronary artery bypass graft (CABG) were enrolled in the study to undergo OPCAB surgery with a minimum of two distal anastomosis. The only inclusion criterion isolated was coronary surgery. The study was approved by the local Institutional Review Boards (IRB) and informed consent was obtained from all patients. Preoperative patient characteristics are listed in Table 1.
Patients were premedicated with lorazepam (2–4 mg). Induction was achieved with midazolam (15–20 μg/kg) and fentanyl (10–100 μg/kg). Muscle relaxation was achieved with vecuronium bromide (0.10–0.15 mg/kg) and fentanyl (10–100 μg/kg). Anesthesia was maintained with oxygen, air, and incremental doses of midazolam and fentanyl.
A central venous catheter was placed into the jugular vein for continuous monitoring of central venous pressure. In addition, a Swan Ganz catheter was placed for measurements of cardiac index. An arterial line was inserted into the left radial artery for continuous monitoring of mean arterial pressure. A pulscontour continuous cardiac output catheter (Pulsion, Munich, Germany) was placed in the femoral artery to allow online cardiac output and intrathoracic blood volume index measurements. A transesophageal echo probe was inserted for assessment of left and right atrial diameter, left ventricular length, superior and inferior vena cava diameter. After induction of anesthesia, all patients received volume to achieve an intrathoracic blood volume index of >900 mL/m2.
All operations were performed by the same team (surgeon and anesthesiologist). After standard harvesting of the internal thoracic artery and saphenus vein, the patient was heparinized with a dose of 150 I.U./kg body weight. Activated clotting time was kept at >300 seconds. Initially, two 2–0 Vicryl sutures were placed on the posterior aspect of the left pericardium above the left upper pulmonary vein and well below the left inferior pulmonary vein staying away from the phrenic nerve. Coronary artery stabilization was achieved using a Cardiothoracic Systems Inc. tissue stabilizer (Guidant, Cupertino, CA). Exposure of the target area with the XS was achieved by positioning of the cup on the apex of the heart and application of 200 to 300 mm Hg vacuum. By disengagement of the arm from the stabilizer with the cardiac apex in the suction bell, the heart was moved in the desired position and the arm repositioned on the stabilizer.
Initially, all patients received LIMA to left anterior descending (LAD) grafting. Then the heart was replaced in the pericardium to get a hemodynamic baseline measurement.
Three patients were excluded from the study per protocol because of the necessity of vasoactive drugs during the initial hemodynamic measurements. In all other patients, vasoactive drugs were not necessary during the hemodynamic measurements. The operating table was kept in a neutral position at all times to achieve comparable conditions for all patients.
Thereafter, hemodynamic measurements after exposure of the right coronary and circumflex artery territories were performed. The vessels were exposed in a way that an actual dissection and anastomosis of the vessel was possible with the tissue stabilizer in place. Either PS or the XPose-Device (XS) was used first after a randomization protocol. Then after hemodynamic normalization (compared with baseline) the other exposure technique was applied and measurements performed. Thus each hemodynamic measurement for each individual target was done with both techniques in the same patient under comparable conditions including the intrathoracic blood volume index.
For the actual anastomosis, the second technique was used, and the patient was placed in a head down position to increase the stroke volume.
Intraoperative Hemodynamic Measurements
Baseline values of central venous pressure, mean arterial pressure, cardiac index, and echocardiographic data were recorded after skin incision. After exposure and stabilization of the LAD, measurements were repeated every 5 minutes. After revascularization of the LAD, baseline values were again recorded, followed by exposure of the circumflex or right coronary artery territory by PS and XS and repeated hemodynamic measurements during exposure using the randomized protocol described above.
Continuous variables are shown as mean ± standard deviation, if normal distribution could be demonstrated. Categorial variables are shown as a percentage. Comparisons were made with Wilcoxon rank sum tests. In all cases, a P < 0.05 was considered to be statistically significant. All statistical analyses were performed using SPSS for Windows Version 12.0 (SPSS, Chicago, IL).
All 27 patients measured received myocardial revascularization off-pump without conversion to cardiopulmonary bypass. Mean operative time was 166 ± 34 minutes, patients received an average of 2.9 ± 0.7 distal anastomoses. Distribution area of the grafts is demonstrated in Table 2. There was neither perioperative nor postoperative mortality. Mechanical ventilation was quired for 17 ± 6.5 hours with a mean intensive care unit stay of 20.5 ± 5.6 hours.
Minor complications consisted of transient atrial fibrillation in 8 patients (29%), which could be successfully converted to sinus rhythm by either medical therapy or electrical cardioversion. One patient developed mediastinitis requiring reoperation and prolonged systemic antibiotic therapy.
During stabilization of the LAD territory, a slight decrease of mean arterial pressure was noted, accompanied by a markedly increased central venous pressure (+35.9%). Cardiac index dropped by 13% (Table 3) (Figs. 1, 2).
Posterior Wall Exposure
Eighteen patients required a bypass graft to the right coronary artery (RCA) territory. Out of those, the RCA was grafted in eight patients. A significant decrease in cardiac index and mean arterial pressure could be noted (Table 4) without a significant difference between exposure with PS or XS. Grafting of the posterior descending artery (PDA) (n = 10) resulted in a moderate drop in cardiac index, ranging between values of the LAD and RCA territory. Statistically, exposure using XS did not result in better preserved cardiac index (Table 5). However, in individual patients a better hemodynamic performance (confidence interval and blood pressure) was noted (Fig. 3).
Lateral Wall Exposure
Eighteen patients received bypass grafting to the lateral wall to any of the marginal branches. In comparison to the other coronary territories, exposure of the obtuse marginal artery (OM) and circumflex artery territory resulted in the highest decrease in mean arterial pressure, accompanied by a drop in cardiac index by 29% (Table 6). No significant difference between the two exposure techniques was found.
Transesophageal echocardiography showed no difference between PS or XS regarding contractility or volume state of the right atrium or ventricle. Especially, there was no incidence of acute mitral valve insufficiency with any of the two techniques.
Even though multifactorial, the main reason for hemodynamic deterioration during exposure of posterior and lateral vessels seems to be a compression of the right-sided cardiac chambers. In particular, compression of the right ventricle between the interventricular septum and the pericardial cradle, results in disturbed diastolic filling and decreased left ventricular preload. In an animal study, Grundeman et al10 could demonstrate that significant reduction of arterial pressure and CO during vertical displacement of the beating heart could be reversed by concomitant use of a right heart bypass. In contradiction, utilization of left heart bypass did not result in a hemodynamic improvement.11
To decompress the right ventricle during exposure of the lateral and posterior aspect of the heart, various surgical techniques are used: opening of the right pleura or a cut into the right lower corner of the pericardium to allow the left atrium to herniate into the chest, Trendelenburg positioning, and rotation of the patient towards the surgeon, or the use of deep pericardial sutures. Even though widely applied, the placement of pericardial sutures can cause subsequent massive hypotension, especially in patients with severely impaired left ventricular function.
Theoretically, there are advantages of an apically positioned suction device to expose lateral and inferior coronary arteries. Exposure of the OM and right coronary territory with the XPose-Device may lead to an elongation of the long axis of the left ventricle with concomitant improved diastolic filling of the compressed right ventricle and atrium.
In 2000, a feasibility study for clinical use of the device was published by Dullum and Resano.12 Five patients underwent off-pump bypass grafting including the lateral and posterior wall using XS techniques. Hemodynamic monitoring of cardiac index and mean arterial pressure during exposure of the circumflex and right coronary territory demonstrated contradictory values for changes of hemodynamics in that study. Two patients showed markedly reduced values, mainly during exposure of the lateral wall, whereas in two patients, cardiac index and mean arterial pressure were higher during exposure compared with preoperative values. In one patient, preoperative cardiac index was not measured. In an animal study, Sepic et al compared lateral and posterior wall exposure in five healthy pigs using PS and XS.13 While using PS for exposure of the OM and PDA territory, they found a decrease in cardiac index comparable to our results. However, utilization of XS did result in only 15% reduction in cardiac index.
In a study comparing two patient groups with either suction device or PS published by Chang et al,14 a significant improvement in hemodynamics in the suction device group was noted.
However, our observations could not support the results of Chang et al.
In our study, exposure of the right coronary and circumflex territory using deep pericardial sutures resulted in a significant depression of CO and mean arterial pressure and an elevated central venous pressure. However, the use of the XPose-Device for exposure of these coronary targets did not result in significantly better preserved cardiac performance. Only in individual patients, either XS or PS exposure yielded a better preservation of Cardiac index and blood pressure compared with baseline (Fig. 3). A limitation of the study is certainly the small sample size; in a larger study population a different result may be possible.
In contrast to the study published by Chang et al, our study is the first prospectively randomized evaluation comparing different exposure techniques for off-pump beating heart myocardial revascularization in the same patient. The study design with reliable intraindividual controls allowed for meaningful comparison of the two techniques.
This could be the explanation for the discrepancy between our the results and the results published by Chang et al.14
In summary the use of apical suction devices may be only necessary in individual patients with an unfavorable anatomic situation for pericardial stitches, for example, dilated left ventricle with significantly reduced ejection fraction. In patients with severely compromised hemodynamics using just pericardial stitches, it might be worth to try an apical suction device as an alternative. Other indications may evolve for endoscopic beating heart surgery. Routine application of apical suction devices in full sternotomy OPCAB surgery, however, does not seem to provide any hemodynamic benefit over conventional pericardial stay sutures.
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