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Ann Thorac Surg 2002;73:1874-1879
© 2002 The Society of Thoracic Surgeons
a Pensacola Heart Institute, Pensacola, Florida, USA
* Address reprint requests to Dr Vassiliades, Jr, 5151 North Ninth Avenue, Suite 200, Pensacola, FL 32504, USA
Presented at the Forty-eighth Annual Meeting of the Southern Thoracic Surgical Association, San Antonio, TX, Nov 8–10, 2001.
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Abstract |
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Methods. During a 54-month period, we performed 1420 elective OPCAB procedures through a sternotomy, constituting 71.2% of the total CABG procedures performed. Twenty-three patients (1.6%) experienced hemodynamic collapse intra-operatively requiring immediate cardiopulmonary bypass. Preoperative characteristics, intraoperative data, and postoperative outcome were retrospectively reviewed in each patient.
Results. In all cases, improvements in intra-operative technique and/or judgment could be made retrospectively. Twenty (20/23) of these patients had an uneventful postoperative course and three (3/23) patients had an unstable course with two deaths.
Conclusions. The causes of hemodynamic collapse during elective OPCAB were ischemic, mechanical, or a combination of both. A detailed review of our five and a half year experience has revealed a number of suggestions for improving the conduct of the operation.
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Introduction |
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TopAbstractIntroductionPatients and methodsResultsCommentDiscussionReferences |
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Patients and methods |
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TopAbstractIntroductionPatients and methodsResultsCommentDiscussionReferences |
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Indications
All three surgeons began performing off-pump procedures in highly selected patients. In the first year, patients requiring a graft to the posterolateral wall were not felt to be bypassable using the existing technology. The existing OPCAB technique at the time (1996) consisted of a placing lap pads behind the heart to present the LAD, RCA or diagonal coronary artery. A hand-held stabilizer (fork-type configuration) was used during the performance of the distal anastomosis. Ischemic pre-conditioning was used before every anastomosis, as intra-coronary shunts were not available. The heart rate was usually slowed with beta blockade and adenosine was occasionally given to transiently arrest the heart and facilitate placing difficult stitches. Approximately 20 to 30% of elective CABG procedures were performed in this manner.
In the second and third years (1997, 1998), we adopted the use of the deeply placed pericardial sutures to facilitate grafting of the posterolateral wall. Additionally, the use of a right vertical pericardiotomy, taken down to the phrenic nerve, improved space for the right ventricle to fill and greatly improved the hemodynamics of grafting the posterolateral wall vessels. Ischemic pre-conditioning was abandoned in favor of intra-coronary shunts, passive aorto-coronary shunts or active aorto-coronary shunting (Perfusion Assisted Direct CAB technique) (MPS SystemTM Quest, TX). The evolution of stabilizers and cardiac positioning devices in recent years (1999 to present) has obviated the need for pharmacological slowing of the heart. We continue to use atrial pacing in cases of significant bradycardia. We have used the right heart assist device (AMED, West Sacramento, CA) as well as the available cardiac positioning devices (StarfishTM Medtronic, Minneapolis, MN; Expose TM Guidant, Indianapolis, IN), but these have not been part of our routine practice.
Definition of terms
Elective operation
A hemodynamically stable patient when brought to the operating room, regardless of angina class or admission status.
Emergency operation
An acutely ischemic or hemodynamically unstable patient requiring immediate operation.
Hemodynamic collapse
Severe and sustained derangements in the patient’s vital signs, refractory to pharmacological therapy and likely to result in death without the institution of cardiopulmonary bypass; excludes transient hemodynamic derangements. The cause of hemodynamic collapse can be ischemic, mechanical or both.
Ischemic collapse
The primary or inciting cause of hemodynamic collapse is myocardial ischemia.
Mechanical collapse
The primary or inciting cause of hemodynamic collapse is the alteration of the normal geometry or architecture of the heart from mechanical manipulation (for example, compression, retraction, elevation).
Cardiomegaly
Cardiac diameter to thoracic cavity diameter ratio on PA CXR greater than 0.5
Surgical technique
Our technique of off pump grafting has been described previously [9]. All patients are on aspirin prior to operation. A pulmonary artery catheter and a radial arterial catheter are placed for monitoring during the off-pump bypass procedure. The patient is kept between 36.0 and 36.5 degrees C during the procedure. The CPB machine is "dry ready" and in the room. The circuit is not primed and the cannulation equipment and lines are not opened. A perfusion is assigned to each case and manages the cell-saver circuit and the patient’s anticoagulation. The heart is exposed through a median sternotomy. After harvesting of the internal mammary arteries, the patient is given 3mg/kg of heparin and the activated clotting time is kept above 400 seconds throughout the procedure. The Genzyme OPCAB stabilization is utilized (Genzyme Biosurgery, Cambridge, MA). A right vertical pericardiotomy is performed two to three centimeters off the diaphragm and the incision is carried down to the right phrenic nerve. The pleura and accompanying fat pad are divided to allow room for the heart to herniate into the right pleural space. A 10 mm flat drain is placed in the transverse sinus and sutured in place to the pericardium to the right of the ascending aorta. It is connected to the cell saver suction and continuously scavenges shed mediastinal blood during the procedure. A standard cardioplegia cannula is placed in the aorta at this time and connected to the multi-armed delivery tubing. After each free graft, the proximal end is connected to the tubing so as to provide immediate blood flow to the heart. This has the physiologic effect of performing the proximal anastomoses first without the anatomic inconvenience. Additionally the small aortic cannula can provide blood for distal coronary perfusion during the anastomoses if this becomes necessary. A soft 2 or 3mm olive tipped catheter (Medtronic DLP, Grand Rapids, MI) is passed distally through the coronary arterotomy to provide sufficient coronary perfusion.
Three stitches are placed in the posterior pericardium which will eventually serve to cradle the heart and lift it up and over toward the right pleural space. These stitches (0 silk on a large needle) are superficial one centimeter bites of the pericardium just inferior to the left inferior pulmonary vein, just left of the inferior vena cava, and the last one equidistant between the first two. The third stitch provides the most exposure of the posterior wall of the heart and is placed as far behind the left atrium as possible. Mild trendelenburg also facilitates rotation of the heart as well as making dependent the pericardial drain lying in the transverse sinus. Pulling the deep pericardial stitches up and securing them to the secured drape on the patient’s left chest exposes the posterior wall. The heart is rotated toward the patient’s right and the apex of the heart is placed into the right pleural space. Soft silicone elastomer tapes (Quest Medical, TX) and a plastic platform (Genzyme Biosurgery, Cambridge, MA) are used to stabilize and occlude the coronary artery proximally. The distal anastomoses are constructed with a continuous 7-0 monofilament suture. The proximal anastomoses are then carried out with 5-0 or 6-0 monofilament sutures under a partial occlusion clamp.
Data analysis
The hospital and clinic records as well as the coronary angiogram of each patient were reviewed in detail. In nine patients, a digital record of the intra-operative hemodynamic data had been recorded. Descriptive data was analyzed using chi squared or Fischer’s exact test as appropriate.
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Results |
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The clinical characteristics of the 23 patients in this study are shown in Table 1. There were 16 male and 7 female patients with a mean age of 65.9 years (range 43 to 81). Twenty-one of 23 patients presented with angina class III (11/23 = 47.8%) or IV (10/23 = 43.5%). The mean preoperative ejection fraction was 44.3% (range 25–55). Cardiomegaly was present in 15 patients (65.2%), left main disease in five patients (21.7%), and triple-vessel disease in 21 patients (91.3%). The mean number of grafts per patient was 3.1 with 22 (95.7%) patients receiving a graft to the LAD, 18 (78.3%) to the circumflex, and 17 (73.9%) to the RCA distribution. Eight patients (34.8%) received a graft to the main RCA. The use of arterial and venous conduits was uniformly distributed. There was not a preponderance of patients operated on by any one of the three surgeons or seven anesthesiologists over the five-year period. There was no concentration of cases in any single year, although the percentage and total number of OPCAB cases steadily increased from one year to the next.
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All 23 patients were ultimately placed on CPB. Fifteen patients were grafted with the heart still beating and seven using a standard cardioplegic arrest technique. Inotropic support was used in 18 (78.3%) patients after weaning from CPB and in the first 12 to 24 hours postoperatively. Twenty patients had an uneventful postoperative course. The remaining three patients had a complicated hospital course including two in-hospital deaths. Mean follow-up (100%) for the surviving 21 patients was 19.6 months (range 4.5–38.2). No patients have required re-intervention.
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Comment |
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Review of the preoperative patient variables demonstrates a more severe angina class in the 23 patients experiencing hemodynamic collapse (NYHA 3.25 ± 0.75) compared with the larger group of successful OPCAB patients (NYHA 2.70 ± 0.81) (p = 0.001). Similarly, the prevalence of preoperative myocardial infarction was higher in the patients experiencing collapse in the operating room (73.9% verses 24.5%, p < 0.001). However, overall left ventricular ejection fraction was similar in both groups (p = 2.2). In our OPCAB experience, significant cardiomegaly can make it more technically challenging to perform grafting of the posterolateral wall. Enlarged, stiff ventricles can be difficult to position at times especially if the heart is displaced into the left pleural space, as is often the case. Additionally, the hypertrophied left ventricle with baseline diastolic filling dysfunction is more sensitive to a reduction in preload as is seen with right ventricular compression that sometimes occurs in exposing the posterolateral wall. In this review, 73.4% of the patients experiencing collapse had cardiomegaly compared with a prevalence of 49.9% in our OPCAB patients as a whole (p = 0.043). Patients experiencing collapse also had a statistical smaller body surface area (p < 0.001), perhaps indicating overall smaller coronaries (table). Unfortunately, we did not have sufficient documentation to compare target vessel size between the two groups. However, the incidence of incomplete revascularization (< 5%) and the prevalence of female patients (28%) were similar in both groups.
Review of the graft and conduit data shows grafting the main coronary artery was performed significantly more in the patients who experienced hemodynamic collapse (p < 0.001). In cases where the posterior descending and posterolateral coronary arteries are less favorable targets for grafting, the main right coronary artery (RCA) was grafted. It is known that occlusion of the moderately stenotic (less than 90%) RCA often results in significant ECG changes starting with ST elevation and progressing to a widened QRS complex and eventual heart block [10]. Unless the RCA is perfused during the anastomosis with a shunt from the aorta or with an intra-coronary shunt, severe hemodynamic alterations occur [10, 11]. In the vast majority of cases where the RCA was grafted off-pump, the shunt prevented any significant ischemia and subsequent hemodynamic compromise. In some cases, the use of an intra-coronary shunt provided inadequate perfusion by virtue of the small size of the shunt or because elevation of the acute margin of the heart causing kinking of the RCA proximal to the shunt. This situation was rectified by using a 2mm shunt from the aorta and passed down the distal limb of the arteriotomy. If adequate blood flow still could not be delivered downstream, the patient was paced through the ischemic period. Despite the use of these techniques, five patients in our study received insufficient perfusion of the RCA resulting in ultimate hemodynamic collapse. In a series from Baumgartner, et al. [3], five of 141 OPCAB patients experienced intraoperative cardiac arrest (3.5%). They concluded, as do we, that increased risk arose from vascular isolation of the right coronary artery and recommended grafting the posterior descending or posterolateral branches whenever possible. However, in this study, patients with left main disease were at no greater risk for hemodynamic problems intra-operatively. A similar experience has been previously reported [12]. This is probably because occlusion of the LAD is well tolerated and the LIMA is grafted early to the LAD before any substantial manipulation of the heart.
Hemodynamic compromise and ultimately collapse during OPCAB is likely the result of substantial changes in the existing blood flow and/or the normal geometry of the heart [5, 13–15]. Minor alterations in the supply/demand balance in coronary blood flow can be caused by any number of factors without any manipulation of the heart [9]. However, significant hemodynamic compromise occurs when ischemia is compounded by mechanic alterations such as right ventricular compression, reduction in right ventricular outflow size and reduction in left ventricular pre-load, as can be caused in exposing the posterolateral wall [13–15]. When allowed to continue, this may result in a down-turning spiral (ischemia causing worsening cardiac function and worsening cardiac function resulting in further ischemia) that may not be salvageable without immediate cardiopulmonary bypass. Unlike on-pump bypass surgery, the order of grafting may be critical in many patients. While most patients with normal ventricular function, a normal left main coronary, and no total or sub-total occlusions will tolerate grafting in almost any order, there is a preferred "safer" sequence in many patients [11, 12, 16–18]. In general it has been our experience that hemodynamics tend to be more stable when the anterior vessels are grafted and perfused before approaching the posterolateral wall targets (i.e. the ramus intermedius and obtuse marginal vessels). This becomes even more important when one is dealing with poor baseline ventricular function [19], acute ischemia [20] or perhaps significant cardiomegaly, as suggested in this study.
Postoperative outcomes were adversely affected as a result of hemodynamic collapse and the need for emergent cardiopulmonary bypass. The incidence of peri-operative myocardial infarction, renal failure and the rate of major complications were higher in these patients (p < 0.001). Additionally, this subset of patients had a higher rate of transfusion, need for inotropic support, IABP use, and total mechanical ventilation time (p < 0.001). Overall, the length of stay in the intensive care unit and the hospital was prolonged (Table 1).
In summary, the incidence of sudden hemodynamic collapse in off-pump coronary artery bypass grafting appears to be extremely low, 0.97% in this series. Prevention of such a catastrophe requires (1) careful attention to patient selection, (2) recognizing potential preoperative risk factors, (3) preoperative determination of the optimal grafting sequence, (4) meticulous and gentle cardiac manipulation, positioning and stabilization, (5) early recognition of significant ischemia and mechanically-induced cardiac dysfunction before beginning the anastomosis, and (6) consideration of alternative assist technologies in highly selected cases: the simplest of which is the on-pump beating heart technique. Such an approach avoids global cardiac ischemia that may in fact be the primary determinant of post-operative cardiac dysfunction in grafting poorly contractile ventricles [21]. Other OPCAB aids include the placement of an intra-aortic balloon pump [19], right-heart assist (right atrium to main pulmonary artery shunt) [15, 22, 23] and perfusion assisted direct coronary artery bypass (PADCAB). All of which have been shown to be useful adjuncts, particularly in grafting the posterolateral wall in large hypo-contractile hearts [10]. These methods, however, are designed to be enabling rather than salvaging. In this review, patients who experienced hemodynamic collapse in the OR had a higher preoperative angina class, a lower body surface area, a higher prevalence of cardiomegaly, and a higher prevalence of preoperative myocardial infarction when compared with the remaining OPCAB patients. These same patients (who developed hemodynamic collapse) underwent grafts to the main right coronary more often than the overall OPCAB population. As a group, these 23 patients, experienced adverse postoperative events at a higher rate than the successfully completed OPCAB procedures. Further, the complication rate of the hemodynamic collapse patients was higher than the mean complication rate for our elective on-pump cases.
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Discussion |
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TopAbstractIntroductionPatients and methodsResultsCommentDiscussionReferences |
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Dr Carrel was severely limited by the constraints of ischemia, occlusion time, and lack of heparin. About 40 years ago, I was given the task of doing bypass surgery in dogs, and I had the luxury of heparin, a heart-lung machine, and cardioplegia. We did a series of dogs with great anastomoses, but they all failed to survive. Since we had some clinical and experimental experience with hypothermia, we used veno-veno cooling as an adjunct and were able to slow the heart enough to make these bypasses, and obtain survivors.
I am suggesting, after listening to the different methods of bypass surgery and their associated complications, that a method that would allow for complete revascularization without the hazards of total cardiopulmonary bypass would be to use a venopulmonary arterial bypass, or right heart bypass with a heat exchanger in the line—which would avoid some of the problems with complete cardiopulmonary bypass, produce decompression of the right side, allow repositioning of the beating heart, slow the heart with hypothermia, and not least of which give an unanticipated bonus. Amazingly, at the conclusion of the procedure in dogs, the blood was rewarmed and circulated, resulting in immediate resuscitation of the myocardium with excellent cardiac function. Right heart bypass with hypothermia might be a useful method for those beginning a program of off-pump bypass, or to train fellows, or in anticipation of a difficult case.
Again, congratulations and thanks for an excellent presentation. Very nice job.
A brief comment with regard to right heart assist and patient temperature. As you may be aware, Amed Corporation has a system to assist the right ventricle during OPCAB. We have used it on several patients and it has been quite an enabling tool, particularly in patients with dilated, poorly contractile ventricles. With respect to patient temperature, it is not difficult to maintain normothermia with some of the new patient warming devices; for example, the Arctic Sun system by Medivance Corporation. In short, the combination of these two devices does achieve your stated objectives.
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