Intracoronary shunt prevents left ventricular function impairment during beating heart coronary revascularization

A novel coronary active perfusion system using a conventional intra-aortic balloon pump for off-pump coronary artery bypass grafting

OBJECTIVE

It is important for coronary active perfusion systems to avoid myocardial ischemia during off-pump coronary artery bypass grafting. We have developed a new concept for a perfusion system to pump blood based on changes in helium gas volume. This system uses a conventional intra-aortic balloon pump to activate the perfusion pump. Our study used basic and animal experiments to investigate the most suitable system for coronary perfusion using this new concept.

METHODS

A conventional intra-aortic balloon pump was used to supply power. A device for perfusion was developed with a balloon placed inside a stiff syringe barrel. The device was connected to the helium gas line of the intra-aortic balloon pump. Changes in flow with changes in augmentation level were noted when volumes outside and within the balloon were changed. Six pigs with occlusion of the left anterior descending artery were used for system validation, with monitoring to identify changes in hemodynamics and cardiac enzyme levels.

RESULTS

In the basic experiment, an 80-mL outside volume and 3.0-mL inner volume resulted in the greatest percentage change in flow rate with respect to changes in augmentation. In the animal experiment, the new coronary active perfusion system prevented myocardial ischemia during coronary occlusion.

CONCLUSIONS

We clarified the most suitable method for our new coronary active perfusion system. Using this system, safe anastomosis was consistently performed in animal experiments. Clinically, off-pump coronary artery bypass may potentially be performed more safely and easily using this new system.

Preservation of myocardium during coronary artery bypass surgery

Myocardial protection aims to prevent reversible post-ischemic cardiac dysfunction (myocardial stunning) and irreversible myocardial cell death (myocardial infarction) that occur as a consequence of myocardial ischemia and/or ischemic-reperfusion injury. Although the mortality rate for isolated coronary artery bypass grafting has been markedly reduced during the past decade, myocardial death, as evidenced by elevation in creatine kinase-myocardial band and/or cardiac troponin, is common. This is ascribed to suboptimal myocardial protection during cardiopulmonary bypass or with off-pump technique, early graft failure, distal embolization, and regional or global myocardial ischemia during surgery. An unmet need in contemporary coronary bypass surgery is to find more effective cardioprotective strategies that have the potential for decreasing the morbidity and mortality associated with suboptimal cardioprotection. In the present review article on myocardial protection in contemporary coronary artery bypass surgery, we attempt to elucidate the clinical problems, summarize the outcomes of selected phase III trials, and introduce new perspectives.

Elective minimally invasive coronary artery bypass: shunt or tournique occlusion? Assessment of a protective role of perioperative left anterior descending shunting on myocardial damage. A prospective randomized study

Background

To determine impact of intraluminal-left anterior descending shunt to prevent myocardial damage in minimally invasive coronary artery bypass.

Methods

38 patients were randomly assigned to external tournique occlusion (n = 19) or intraluminal-left anterior descending shunt group (n = 19). Blood samples for cardiac troponin T were collected at 30 minutes prior to, 6 and 24 hours after surgery.

Results

One patient in external tournique occlusion and two patients in intraluminal-left anterior descending shunt group were excluded from futher analysis due to preoperative cardiac troponin T level above the 99th-percentile. Postoperatively, each six patients in external tournique occlusion (33.3%) and intraluminal-left anterior descending shunt (35.3%) group were above the 99th-percentile. Two patients from each group (external tournique occlusion group 11.1% vs. intraluminal-left anterior descending shunt group 11.8%) had peak values above 10-% coeficient of variation cutoff (p = 1). There were no significant differences in between both groups at all studied timepoints.

Conclusion

There was no protective effect of intraluminal shunting on myocardial damage compared to short-term tournique occlusion. It is upon the surgeon's discretion which method may preferrably be used to achieve a bloodless field in grafting of the non-occluded left anterior descending in minimally invasive coronary artery bypass.

A randomized trial of on-pump beating heart and conventional cardioplegic arrest in coronary artery bypass surgery patients with impaired left ventricular function using cardiac magnetic resonance imaging and biochemical markers

BACKGROUND

Beating heart coronary artery bypass grafting (CABG) improves early postoperative cardiac function in patients with normal ventricular function, but its effect in patients with impaired function is uncertain. We compared a novel hybrid technique of on-pump beating heart CABG (ONBEAT) with conventional on-pump CABG (ONSTOP) in patients with impaired ventricular function.

METHODS AND RESULTS

In a single-center randomized trial, 50 patients with impaired ventricular function were randomly assigned to ONBEAT or ONSTOP. Patients underwent cardiac magnetic resonance imaging for function and delayed hyperenhancement early and later after surgery. Serial assessment of biochemical markers was also undertaken. Preoperative characteristics were well matched; cardiac index was 2.85+/-0.53 (ONBEAT) and 2.62+/-0.59 L x min(-1) x m(-2) (ONSTOP). Early after surgery, there was a trend toward a greater reduction in end-systolic volume index in ONSTOP patients versus ONBEAT (-9+/-8 versus -4+/-11 mL x m(-2); P=0.06). The changes were sustained and significant at 6 months (-14+/-18 versus -2+/-19 mL x m(-2); P=0.04). Furthermore, the incidence of new hyperenhancement at 6 days was higher in ONBEAT patients (P=0.05), with 6 of 17 (35%) sustaining 8.2+/-5.2 g of new hyperenhancement each versus 2 of 23 (9%) in the ONSTOP group, each with 9.8+/-9.0 g (P=0.86). Finally, median area under the curve for troponin was higher in ONBEAT at 461 (interquartile range, 226 to 1141) microg/L versus 160 (interquartile range, 98 to 357) microg/L for ONSTOP (P=0.002).

CONCLUSIONS

The incidence of new irreversible myocardial injury was significantly higher in ONBEAT than in ONSTOP patients. Furthermore, at 6 months, only ONSTOP patients demonstrated an improvement in ventricular geometry. The most likely mechanism is inadequate coronary perfusion to distal myocardial territories in patients with severe proximal coronary disease.

Comparison of active and passive coronary perfusion in off-pump coronary artery bypass grafting

The myocardial protective effects of active and passive coronary perfusion were compared during off-pump coronary artery bypass grafting (OPCAB) in coronary stenosis model. An internal shunt tube was placed in the proximal left anterior descending arteries of adult dogs to produce a 75% coronary stenosis model. In 10 animals passive coronary perfusion was performed using an internal shunt tube placed in a pseudo-anastomotic site, and active coronary perfusion was performed through an external shunt tube. Ischemia was examined at normal and low blood pressure, based on hemodynamics, regional myocardial blood flow, and oxygen and lactate extraction in the perfused area. With passive perfusion, regional myocardial blood flow decreased and oxygen extraction and regional lactate production increased at normal blood pressure, indicating myocardial ischemia. Regional myocardial blood flow further decreased at low blood pressure. In contrast, regional myocardial blood flow with active perfusion did not change at normal or low blood pressure, and oxygen and lactate extraction were unchanged, indicating prevention of myocardial ischemia. Myocardial ischemia can occur with passive perfusion even at normal blood pressure. Active coronary perfusion that provides sufficient regional perfusion prevents myocardial ischemia during coronary artery anastomosis in OPCAB.

Effect of intracoronary shunt on right ventricular function during off-pump grafting of dominant right coronary artery with poor collateral

Although numerous studies have validated the efficacy of intracoronary shunt on reducing left ventricular dysfunction during off-pump coronary artery bypass surgery (OPCAB), there is lack of evidence supporting its role on right ventricular (RV) function during right coronary artery (RCA) revascularization. Therefore, we studied the effect of intracoronary shunt during grafting of dominant RCA without visible collateral supply on global RV function using thermodilution method. Forty patients scheduled for multivessel OPCAB with right dominant coronary circulation without collateral supply confirmed by angiography were randomized to RCA revascularization either with a shunt (n=20) or soft snare occlusion (n=20). RV ejection fraction (RVEF) was recorded at baseline, during RCA grafting, and 15 min after reperfusion. Corresponding RV stroke work index (RVSWI) was calculated. RVEF and RVSWI decreased significantly during RCA grafting and returned to baseline values after reperfusion in both groups without any significant differences between the groups. Intracoronary shunt did not exert any beneficial effect on global RV function during RCA grafting, even in the absence of visible collateral supply. Regarding the possibility of graft failure by intracoronary shunt-induced endothelial damage, routine use of intracoronary shunt during RCA grafting is not recommended in patients with preserved biventricular function.

Intracoronary shunt versus bulldog clamp in off-pump bypass surgery. Endothelial trauma: shunt versus clamp

BACKGROUND

During off-pump coronary bypass grafting, local vascular control of the target vessel and a bloodless field are crucial. The aim of this study is to asses the histopathological outcomes of intracoronary shunts and bulldog clamping on the beating heart in a canine model.

METHODS

Twelve healthy adult mongrel dogs weighing between 15 to 25 kg were included in the study. Following left thoracotomy, proximal left anterior descending artery segment 1 cm to distal of diagonal branch was marked. Arteriotomy at this site was performed and a shunt was inserted for 10 min in the shunt group. The bulldog clamp was applied 3 cm distal to the mark for 10 min after heparinization in the bulldog group. Thirty days after the procedure, the specimens of left anterior descending artery from both regions were collected and were examined. Vascular damage, presence of intimal hyperplasia, and denudation were noted.

RESULTS

Only intimal denudation was found significantly higher in the shunt group (P < 0.05). In this group, only one case had grade 0 endothelial damage. In the bulldog group, all cases had endothelial damage of various grades.

CONCLUSION

The proven advantages of temporary intracoronary shunts are well-known, e.g., preserving the ventricular functions. Despite these advantages, our study revealed an ultimate bad result for an off-pump coronary by pass patient: intimal denudation. We conclude that further studies with a larger number of subjects are needed to decide whether routine shunt insertion into coronary arteries during off-pump coronary bypass surgery is appropriate or not.

Controversies in the Use of Intraluminal Shunts During Off-Pump Coronary Artery Bypass Grafting Surgery

Technical advances have made the performance of multivessel off-pump coronary artery bypass feasible. Snaring and intraluminal shunts are the techniques used for vascular control. Snaring provides a bloodless surgical field, is usually well tolerated by the patient, and is supported by years of clinical experience. Intraluminal shunts aim to achieve hemostasis at the arteriotomy site and to allow antegrade flow to provide myocardial protection. There are unresolved issues regarding whether shunts have a clinical benefit, do provide adequate flow to provide myocardial protection, and whether they cause significant endothelial damage. In this article, we have reviewed the literature to lend perspective to these issues.

Intravenous glucose-insulin-potassium during off-pump coronary artery bypass surgery does not reduce myocardial injury

BACKGROUND

This randomized, double-blind, placebo-controlled study was designed to determine whether an intra-operative, intravenous infusion of glucose-insulin-potassium (GIK) could be helpful in the prevention of myocardial ischemia and in the maintenance of intra-operative cardiac performance in patients undergoing off-pump coronary artery bypass (OP-CAB) surgery.

METHODS

Eighty two adults undergoing elective OP-CAB surgery were randomly divided into two groups that received intravenously either 5% dextrose in water or GIK (50% dextrose in 500 ml of water; regular insulin, 125 IU; potassium, 80 mmol) at 0.75 ml/kg/h immediately before the induction of anesthesia to the end of surgery. To evaluate myocardial damage, creatine kinase MB and troponin T were measured before surgery, immediately after arrival in the intensive care unit and on the first post-operative day. To assess cardiac performance, hemodynamic data were obtained before and after the induction of anesthesia, before and after the bypass graft and after sternal closure. Blood glucose was measured at the same time.

RESULTS

There was no significant difference in cardiac enzymes, hemodynamic parameters and blood glucose between the two groups. The use of vasoactive, inotropic and/or anti-arrhythmic agents, insulin and supplemental glucose was not significantly different between the groups.

CONCLUSION

The results suggest that the intravenous administration of GIK during OP-CAB surgery neither reduces myocardial damage nor improves intra-operative cardiac performance in patients without contractile dysfunction.

Portable coronary active perfusion system for off-pump coronary artery bypass grafting

PURPOSE

The present study was performed to develop a new perfusion system for off-pump coronary artery bypass grafting and to examine whether even a simple coronary perfusion system can maintain adequate blood flow delivery during anastomosis.

DESCRIPTION

The experiment was performed in two stages. In procedure 1, 3 pigs with left anterior descending artery occlusion were used to evaluate optimal perfusion flow rate and coronary artery internal pressure, and to evaluate the safety area of perfusion. In procedure 2, 6 pigs were used to validate the new portable coronary perfusion system.

EVALUATION

The optimal blood flow in the portable coronary active perfusion system was less than approximately 40 mL/min. The small, easy to use pump system (ie, the portable coronary active perfusion system) may prevent hemodynamic deterioration and ventricular arrhythmia during coronary occlusion, resulting in better maintenance of left ventricular function.

CONCLUSIONS

Even a simple pump system can achieve effective perfusion for safe anastomosis. Further studies are required to allow the clinical use of this system.

A Technique for Salvaging a Critical Internal Mammary Artery Bypass Graft Damaged During Resternotomy

Resternotomy in the presence of a patent internal mammary artery graft poses an addition hazard to the reoperation. We describe a situation in which the patent mammary artery graft to the left anterior descending artery was severed and retracted during sternal reentry for an aortic valve replacement. We illustrate a simple technique for restoring the blood supply using a coronary artery shunt.

Perfusion Flow Assessment of Coronary Shunt during Off-Pump Coronary Artery Bypass Grafting

BACKGROUND

Coronary shunts are widely used to prevent myocardial ischemia during off-pump coronary artery bypass graft (OPCAB) procedures. Although clinical effectiveness has been reported, actual perfusion flow has not been well assessed. The purpose of this study was to evaluate actual shunt flow and its pattern during passive coronary perfusion in clinical OPCAB.

METHODS

In 15 OPCAB cases, the coronary perfusion flow of the external shunt (1.7 or 2.0 mm) during anastomosis and the free flow of the shunt were measured with an in-line electromagnetic or ultrasonic flow probe. The perfused coronary blood vessel was either the left anterior descending coronary artery or the right coronary artery. The inflow vessel of the external shunt was either the femoral artery (FA) or the ascending aorta (AA).

RESULTS

Free flow values of a 1.7-mm FA shunt, 1.7-mm AA shunt, and 2.0-mm FA shunt were 34+/- 7, 39 +/- 3, and 44 +/- 7 mL/min. Perfusion flows were 13 +/- 4, 14 +/- 3, and 22 +/- 4 mL/min, respectively. Perfusion flow was significantly lower than free flow and correlated well with coronary resistance. Although inflow site did not influence net perfusion flow, diastolic/systolic flow fraction ratio was significantly greater when the shunt was perfused from the FA.

CONCLUSIONS

External shunt from FA would provide limited but effective perfusion flow with a physiological pattern, which is passively regulated by coronary resistance.

The History and Development of Direct Coronary Surgery without Cardiopulmonary Bypass*

The history of direct myocardial revascularization without cardiopulmonary bypass dates to 1961 in the dawn of coronary artery surgery. With the introduction and development of techniques of extracorporeal circulation around the same time, beating heart surgery was largely abandoned. Over the subsequent decades, cardiopulmonary bypass and electromechanical cardioplegic arrest became popular as means of revascularization in a bloodless and motionless field. While coronary artery surgery on the arrested heart remained undisputed for decades, myocardial revascularization on the beating heart was pursued by a few pioneering surgeons around the world, based on the belief that coronary revascularization could be performed equally well without the detrimental effects of cardiopulmonary bypass and electromechanical arrest. Various concepts and techniques developed during the 1980s by these pioneers enabled minimally invasive coronary surgery to be performed in the early 1990s. This break from the mainstream allowed selective myocardial revascularization using a minimal incision and no cardiopulmonary bypass to develop and constructed a base for future extensive revascularizations off-pump. With the subsequent explosion of new techniques for coronary exposure and myocardial stabilization, complete revascularization without cardiopulmonary bypass became possible with consistent results. Emerging from the preview of only a few surgeons just a decade ago, off-pump surgery is currently one of the accepted modalities for complete myocardial revascularization worldwide. This paradigm shift in the approach to myocardial revascularization has led to exiting new future possibilities, such as beating heart totally endoscopic coronary artery surgery.

New Intraluminal Coronary Shunt Tube for Off-Pump Coronary Artery Bypass Grafting

PURPOSE

In cooperation with JMS Co., Ltd. (Hiroshima, Japan), we have developed a new intraluminal coronary shunt tube to allow easier, safer, and more accurate off-pump coronary artery bypass grafting (OPCABG).

DESCRIPTION

Between September 2000 and July 2002, the new shunt tube was used in 100 consecutive patients undergoing OPCABG. Patient characteristics, experimental data, and clinical results for our new shunt tube are provided.

EVALUATION

Our new coronary shunt tube was easily implanted in nearly all (97.2%) target vessels during reconstructions. All 100 cases were performed completely during off-pump operation. Early postoperative coronary angiography was performed in all 100 cases, demonstrating excellent patency in arterial grafts (99.5%) and venous grafts (96.2%). The shunt tube displayed good flow rates under experimental conditions according to diameter, and effectively prevented ischemia during coronary arterial reconstructions in all cases. No target vessels were injured on insertion or removal of shunt tubes. Neither perioperative complications nor hospital deaths were encountered.

CONCLUSIONS

This new shunt tube improves the safety, accuracy, and ease of OPCABG surgery.

Transesophageal Echocardiography for Monitoring Segmental Wall Motion During Off-Pump Coronary Artery Bypass Surgery

In this prospective, observational study, we evaluated whether transesophageal echocardiography allows for monitoring left ventricular segmental wall motion during cardiac displacement for off-pump coronary artery bypass (OPCAB) surgery. On the basis of a pilot study that showed frequent loss of transgastric views during OPCAB surgery, we analyzed only midesophageal views. The midesophageal 4-chamber view, 2-chamber view, and long-axis view were recorded in 60 patients after opening the chest and placing an epicardial stabilizer on the displaced heart. Using the 16-segment model, 2 echocardiographers independently performed offline analysis of segmental wall motion. The percentage of patients in whom >or=14 left ventricular segments were readable was calculated at baseline and after cardiac displacement and placement of an epicardial stabilizer. At baseline, >or=14 segments were readable in 59 (98%) of 60 patients. After cardiac displacement, >or=14 segments were readable during 58 (76%) of 76 revascularizations of the left anterior descending coronary artery (P < 0.01 versus baseline), during 33 (83%) of 40 revascularizations of the left circumflex coronary artery (P < 0.01 versus baseline), and during 29 (94%) of 31 revascularizations of the right coronary artery (not significant). We conclude that the number of readable segments decreased after cardiac displacement but that availability of >or=14 readable segments allowed for reliable monitoring of segmental wall motion in 4 of 5 patients during OPCAB surgery.

Chronic ultrastructural effects of temporary intraluminal shunts in a porcine off-pump model

BACKGROUND

Temporary intraluminal shunts (TILS) are routinely used in off-pump revascularization to facilitate the anastomosis while maintaining myocardial blood supply. Whereas tourniquet-occlusion can cause vessel wall trauma, potentially adverse chronic effects of TILS on the coronary intima have not been evaluated yet. This chronic large animal study investigated ultrastructural effects of TILS on the vessel wall.

METHODS

Four groups of acute and chronic pigs with either tourniquet-occlusion (TOUR) or TILS (40 kg; acute, n = 12; chronic, n = 20) were analyzed. Animals underwent median sternotomy, heparin (150 U/kg) administration, and left anterior descending coronary artery exposure. In groups with TOUR the left anterior descending coronary artery was temporarily occluded (10 minutes) with a tourniquet. In groups with TILS a silicone shunt (1.5 mm diameter, 12 mm length) was placed in the left anterior descending coronary artery more than 10 minutes and then removed, and the insertion was repaired. Thirty minutes after reperfusion all acute animals were sacrificed whereas chronic animals were extubated, maintained for 3 months, and then sacrificed. The left anterior descending coronary artery regions of occlusion or placement of the TILS silicone bulbs were examined histopathologically by scanning and transmission electron microscopy by a blinded pathologist.

RESULTS

In both acute and chronic investigations animals in the TILS group exhibited significantly less morphologic damage than animals in the TOUR group. In the acute phase significantly more loss of cell junction (p = 0.037), loss of endothelium (p = 0.032), and intimal edema (p = 0.037) in the TOUR group than in the TILS group was observed. Three months later, characteristic features with a changed pattern were detected: vacuolization of the cell (p = 0.03), loss of cell junction (p = 0.042), and removal of basal membrane (p = 0.046) as well as extensive loss of endothelium (p = 0.003) in the TOUR group compared with the TILS group.

CONCLUSIONS

Intimal lesions occur with both maneuvers early and late. However, animals in the TOUR group exhibited injuries significantly more often and more severely. Therefore, acute and chronic intimal integrity of the coronary vessel may be better preserved using TILS and may thus have a positive impact on the extent of de novo stenosis and long-term prognosis of the revascularized region.

Instant myocardial blood flow monitor: its calibration and assessment of flow capacity of the intracoronary shunt tube

BACKGROUND

We developed a new instant regional myocardial blood flow (RMBF) monitor utilizing the thermal diffusion method in which the RMBF value is presented as the value inversely proportional to the thermocouple voltage output (1/V). The purposes of this study were (1) to validate the accuracy of RMBF measurement by the instant RMBF monitor in comparison with the colored microsphere method for calibration; (2) to investigate influences of it on the RMBF; and (3) to assess changes in RMBF caused by the shunt tube insertion.

METHODS

Twenty pigs were used for this study: 4 for comparison between the instant RMBF meter and the colored microsphere method, 4 for validation of reproducibility, and 6 for measurement of RMBF during shunt tube.

RESULTS

The relation between RMBF values obtained by the colored microsphere method and 1/V values by instant RMBF monitor was colored microsphere = 140,992 (1/V)--231 in epicardial layer (R2 = 0.819) and colored microsphere = 111,381 (1/V)--165 in endocardial layer (R2 = 0.693). The correlation coefficient and R2 values between RMBF values measured by both methods were 0.985 and 0.839 in epicardial layer, and 0.963 and 0.679 in endocardial layer, respectively. The RMBF at each layer did not change after the attachment of the monitor. Fifteen minutes after shunt tube insertion, RMBF measured by the colored microsphere method decreased to 31.1% (p = 0.0001) and 33.7% (p = 0.0001) in epicardium and endocardium, respectively, and no difference was observed from the value measured by the instant RMBF monitor.

CONCLUSIONS

This instant RMBF monitor can provide instantaneous and continuous information of RMBF without requiring tissue examination.

Off-pump coronary artery bypass surgery: physiology and anaesthetic management †

Increasing interest is being shown in beating heart (off-pump) coronary artery surgery (OPCAB) because, compared with operations performed with cardiopulmonary bypass, OPCAB surgery may be associated with decreased postoperative morbidity and reduced total costs. Its appears to produce better results than conventional surgery in high-risk patient populations, elderly patients, and those with compromised cardiac function or coagulation disorders. Recent improvements in the technique have resulted in the possibility of multiple-vessel grafting in all coronary territories, with a graft patency comparable with conventional surgery. During beating-heart surgery, anaesthetists face two problems: first, the maintenance of haemodynamic stability during heart enucleation necessary for accessing each coronary artery; and second, the management of intraoperative myocardial ischaemia when coronary flow must be interrupted during grafting. The anaesthetic technique is less important than adequate management of these two major constraints. However, experimental and recent clinical data suggest that volatile anaesthetics have a marked cardioprotective effect against ischaemia, and might be specifically indicated. OPCAB surgery requires team work between anaesthetists and surgeons, who must be aware of each other's constraints. Some surgical aspects of the operation are reviewed along with physiological and anaesthetic data.

Off-pump coronary surgery: how do the anesthetic considerations differ?

In recent years, there has been much interest in performing coronary artery bypass graft (CABG) surgery without the aid of cardiopulmonary bypass (CPB). Initial efforts focused on "minimally invasive" direct coronary artery bypass, wherein the left anterior descending artery is bypassed with an in situ left internal mammary artery graft through a small left anterior thoracotomy. A more widely adopted approach however, is off-pump CABG (OPCAB), in which CABG surgery is performed on one or more vessels through the usual median sternotomy approach without the aid of CPB. This article reviews the differences in the anesthetic considerations of OPCAB compared to conventional CABG using CPB.

Perfusion-assisted direct coronary artery bypass provides early reperfusion of ischemic myocardium and facilitates complete revascularization

BACKGROUND

Perfusion-assisted direct coronary artery bypass (PADCAB) was developed to initiate early reperfusion of grafted coronary artery segments during off-pump operations to resolve episodes of myocardial ischemia and avoid its sequelae. This case series outlines intraoperative findings and clinical outcomes of our first year clinical experience with PADCAB.

METHODS

From November 1999 to November 2000, 169 PADCAB and 358 off-pump coronary artery bypass procedures were performed at the Emory University Hospitals. The decision to use PADCAB was predicated on surgeon preference. Perfusion pressure and flow, amount of intracoronary nitroglycerin, and total perfusion time and volume were recorded at the time of operation.

RESULTS

One off-pump coronary artery bypass patient required emergent conversion to cardiopulmonary bypass. Two PADCAB patients had ischemic ventricular arrhythmias during target vessel occlusion that resolved once active perfusion had begun. Perfusion pressure in PADCAB grafts was on average 44% higher than mean arterial pressure (p < 0.001). Nitroglycerin, infused locally by PADCAB, was used in 67 patients to resolve ischemic episodes and increase initial coronary flows. The mean number of diseased coronary territories and grafts placed was 2.8 +/- 0.5 and 3.4 +/- 0.7, respectively, in the PADCAB group, and 2.3 +/- 0.8 and 2.7 +/- 1.0, respectively, in the off-pump coronary artery bypass group (p < 0.001 for both comparisons). More PADCAB patients received lateral wall grafts than off-pump coronary artery bypass patients (83.4% vs 59.4%; p < 0.001). Hospital death and postoperative myocardial infarction were not different between groups.

CONCLUSIONS

PADCAB can provide suprasystemic perfusion pressures and a means to add vasoactive drugs to target coronary vessels. PADCAB provides early reperfusion of ischemic myocardium and facilitates complete revascularization of severe multivessel coronary artery disease.

Future technology for off-pump coronary artery bypass (OPCAB)

Over the past 5 years, many coronary artery surgeons have embraced technology and advanced the field of beating heart surgery to the point where off-pump coronary artery bypass (OPCAB) is becoming a mature procedure. Enabling technologies are now available for all stages of the procedure, including cardiac positioning, coronary artery stabilization, coronary artery visualization, and performance of the proximal and distal anastomoses. Despite these successes, only a minority of cardiac surgeons performs this procedure routinely. Proponents of OPCAB and the medical device industry will need to continue to develop new technologies to make OPCAB less technically challenging and more widely accepted. Progress towards routine single-vessel off-pump totally endoscopic coronary artery bypass has been slow. Translating the benefits of multivessel OPCAB to an endoscopic setting remains a formidable challenge that will require further technologic breakthroughs.

Evolution of OPCAB surgery in a single institution

Off-pump coronary artery bypass (OPCAB) grafting is becoming popular worldwide. The development of exposure and stabilization techniques have made this surgery a simple, safe, and routine procedure. The evolution of OPCAB surgery at our institution is presented and discussed.

Intracoronary shunts reduce transient intraoperative myocardial dysfunction during off-pump coronary operations

BACKGROUND

This study investigated the hemodynamic changes in patients undergoing multiple vessel beating heart coronary revascularization in the presence or absence of an intracoronary shunt.

METHODS

Forty patients were randomized to off-pump with a shunt (n = 20) or with the proximal coronary artery occluded by a soft snare (n = 20). Hemodynamic measurements were recorded at base line, during construction, and after completion of each distal anastomosis.

RESULTS

Grafting of the left anterior descending coronary artery anastomosis was associated with a significant decrease in stroke volume, cardiac index, and mean arterial pressure, and an increase in pulmonary capillary wedge pressure and systemic vascular resistance in the snare but not in the shunt group. During grafting of the posterior descending coronary artery there was a marked decrease in stroke volume and cardiac index, and an increase in central venous pressure in both groups, and an increase in heart rate, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, and systemic vascular resistance only in the snare group. The most extensive changes were observed during the circumflex coronary artery anastomosis with a reduction in stroke volume, cardiac index, and mean arterial pressure, and an increase in central venous pressure, pulmonary capillary wedge pressure, pulmonary arterial pressure, and systemic vascular resistance in both groups. In all settings, these changes were transient and recovered after the heart was returned to its anatomical position in the shunt group, whereas stroke volume and cardiac index remained reduced, and systemic vascular resistance was elevated in all settings in the snare group.

CONCLUSIONS

Stabilization of the left anterior descending coronary artery to perform the anastomosis resulted in temporary hemodynamic changes, which are prevented by the use of an intracoronary shunt. The hemodynamic deterioration during the construction of the posterior descending coronary artery and circumflex coronary artery anastomoses is transient in the shunt group, whereas the snaring technique is associated with an impairment of early functional recovery.

Occlusion versus shunting during MIDCAB: effects on left ventricular function and quality of anastomosis

BACKGROUND

Minimally invasive direct coronary artery bypass is an established clinical procedure for revascularization of the left anterior descending coronary artery. Mechanical stabilization and temporary occlusion is currently used to perform the anastomosis of the internal thoracic artery to the left anterior descending coronary artery. However, critical reduction of cardiac function can occur as a result of temporary ischemia. The purpose of this study was to evaluate whether ischemic sequelae can be avoided by using temporary intraluminal shunts and whether this alters early outcome.

METHODS

Thirty-five patients underwent minimally invasive direct coronary artery bypass revascularization using a mechanical stabilizer. In group A (n = 20), the anastomotic site was temporarily occluded by tourniquets. In group B (n = 15), temporary intraluminal shunts were inserted into the anastomotic site without any occlusion of the left anterior descending coronary artery. Anastomosis of the internal thoracic artery to the left anterior descending coronary artery was performed in an identical fashion. A Swan-Ganz catheter was inserted, and transesophageal echocardiographic measurements were obtained for analysis of left ventricular (LV) function. Regional wall motion, cardiac index, stroke volume index, systolic and diastolic LV diameters, and fractional area change were measured during four periods: at the start of the operation (baseline), placement of the stabilizer (stabilization), left anterior descending coronary artery occlusion (occlusion) or insertion of temporary intraluminal shunts (shunt), and 30 minutes after reperfusion (reperfusion). Angiograms were obtained 4 to 6 days postoperatively.

RESULTS

In group A, LV performance, cardiac index, stroke volume index, and fractional area change decreased during occlusion whereas systolic diameters increased. Almost two myocardial segments per patient developed severe hypokinesia in the perfusion area. These changes disappeared after 30 minutes of reperfusion, with increased LV function. In group B, LV function remained stable whereas hypokinetic wall motion was only detected in 2 patients. Early angiograms revealed 90% of the grafts were patent in group A versus 100% in group B. The need for percutaneous intervention during the first 6 months was 20% in group A versus 6.7% in group B.

CONCLUSIONS

The use of temporary intraluminal shunts resulted in reduced acute ischemia and revealed wall motion abnormalities and maintained LV function. Furthermore, this technique suggests an improvement of early graft patency and a lower reintervention rate within the first 6 postoperative months. Thus, use of temporary intraluminal shunts appears to be superior to the occlusion technique early after minimally invasive direct coronary artery bypass procedures.

Early and midterm outcome after off-pump and on-pump surgery in Beating Heart Against Cardioplegic Arrest Studies (BHACAS 1 and 2): a pooled analysis of two randomised controlled trials

BACKGROUND

Although no randomised controlled trial has assessed the midterm effects of coronary-artery bypass surgery on the beating heart, this technique is being used in more and more patients. We did two randomised trials to compare the short-term morbidity associated with off-pump and on-pump myocardial revascularisation. Our aim was to pool the results to assess midterm outcomes.

METHODS

From March, 1997, to November, 1999, we randomly allocated 200 patients to off-pump and 201 to on-pump coronary surgery. In Beating Heart Against Cardioplegic Arrest Study (BHACAS) 1, we excluded patients who had had myocardial infarction in the past month or who required grafting of the circumflex artery distal to the first obtuse marginal branch. In BHACAS 2, we included such patients. Primary outcomes were all-cause mortality and cardiac-related events at midterm follow-up (1-3 years). Analysis was by intention to treat.

FINDINGS

Analyses of combined data from both trials showed the following risk differences with off-pump compared with on-pump surgery: atrial fibrillation -25% (95% CI -33% to -16%); chest infection -12% (-19% to -5%); inotropic requirement -18% (-25% to -10%); transfusion of red blood cells -31% (-41 to -21); and hospital stay longer than 7 days -13% (-21 to -5). Mean follow-up was 25 0 months (SD 9.1) for BHACAS 1 and 13.7 months (5 5) for BHACAS 2. Four (2%) of 200 patients in the off-pump groups died from any cause, compared with seven (3%) of 201 in the on-pump group (hazard ratio 0.57, 95% CI 0.17-1.96). 33 (17%) of 200 patients in the off-pump group died or had a cardiac-related event, compared with 42 (21%) of 201 in the on-pump group (0.78, 0 49-1.22).

INTERPRETATION

Off-pump coronary surgery significantly lowers in-hospital morbidity without compromising outcome in the first 1-3 years after surgery compared with conventional on-pump coronary surgery.

The use of off pump surgery for management of penetrating coronary artery injury

Penetrating trauma to the chest leading to coronary artery injury is associated with a high mortality rate, especially in the case of injury to the left anterior descending (LAD) coronary artery. The mortality rate remains high whether they are managed with primary ligation or with coronary artery bypass grafting using conventional cardiopulmonary bypass techniques. We report a case of proximal LAD coronary artery injury successfully treated with off pump coronary revascularisation.

Off-pump coronary artery bypass grafting: new developments but a better outcome?

Off-pump coronary artery surgery is now performed safely and effectively without cardiopulmonary bypass. This review includes indications, approaches, anaesthetic and haemodynamic management, and compares the occurrence of postoperative complications and multiorgan dysfunction with conventional cardiac surgery.

Preserved myocardial blood flow and oxygen supply-demand balance with active coronary perfusion during simulated off-pump coronary artery bypass grafting

BACKGROUND

During off-pump coronary artery bypass surgery, concern remains about the possible myocardial injury associated with the transient occlusion and stabilization of the target vessels. Although intraluminal shunts are used to avoid ischemia during graft anastomosis, blood flow through the shunts can be affected by upstream pressure and inherent resistance, resulting in reduced blood flow during hypotension or severe proximal stenosis.

METHODS

In anesthetized dogs regional myocardial blood flow (microspheres), oxygen consumption, lactate extraction, and systolic shortening (sonomicrometry) were measured in the myocardium served by the left anterior descending coronary artery with native perfusion after interposition of a 2.25-mm shunt (> or = 90% of left anterior descending diameter) and during active coronary perfusion with a constant flow pump. Measurements were made under normotension and hypotension produced by partial caval occlusion to reduce arterial pressure by 50%.

RESULTS

Interposition of the shunt reduced blood flow by 67.8%, regional oxygen delivery by 59.8%, and systolic shortening by 45.6% relative to baseline, but lactate extraction (31.0% vs 31.2%) and oxygen supply-consumption (O(2)S/myocardial oxygen consumption ratio, 2.7 +/- 0.5 vs 2.6 +/- 0.5) were comparable with baseline values. Hypotension further decreased these physiologic values and was associated with local lactate production (-67.4% extraction) and decreased O(2)S/myocardial oxygen consumption ratio (1.3 +/- 0.1). Active coronary perfusion was associated with regional blood flow, oxygen delivery, systolic shortening, and lactate extraction comparable with baseline values. In contrast to the shunt, active perfusion maintained myocardial flow, oxygen delivery, and lactate extraction during hypotension and normalized the O(2)S/myocardial oxygen consumption ratio, although systolic shortening decreased as a result of ventricular unloading.

CONCLUSION

Intraluminal shunts may impede oxygen delivery to the target myocardium, which precipitates regional ischemia during transient hypotension. Active coronary perfusion provides adequate oxygen supply independent of systemic blood pressure.

Off-pump coronary operations can be safely taught to cardiothoracic trainees

BACKGROUND

Off-pump coronary artery bypass (OPCAB) operations are evolving rapidly and becoming established in many cardiothoracic centers. For the technique to be widely applicable, teaching methods must be developed for surgical trainees. Early and midterm clinical outcomes of OPCAB performed at our institution by trainees as first operators under supervision were compared to those obtained in patients operated on by consultants.

METHODS

Analysis was undertaken on data prospectively inserted in the Patient Analysis & Tracking System. Of the 559 OPCAB operations performed between January 1997 and May 2000, 124 (22%) were carried out by a supervised trainee and 435 (78%) by a consultant.

RESULTS

There was no difference in age, sex, angina class, New York Heart Association functional class, or operative priority and extent of coronary artery disease in the two groups. More patients operated on by consultants had a history of congestive heart failure requiring medical therapy, significantly lower ejection fraction, and higher Parsonnet score compared with patients operated on by trainees. Early and midterm clinical results, in terms of morbidity and mortality, were similar in patients operated on by trainees or by consultants.

CONCLUSIONS

Our data show no differences in early and midterm clinical outcome for patients undergoing OPCAB operations performed either by consultants or by trainees under supervision. The improvements in exposure and stabilization techniques, as well as the use of intracoronary shunts, have made it possible and safe to teach trainees off-pump multivessel coronary artery revascularization.

Haemodynamic changes during beating heart coronary surgery with the 'Bristol Technique'

OBJECTIVES

Optimal exposure and stabilization of the target coronary vessel is essential to allow the construction of a precise coronary anastomosis during off pump coronary surgery. However, this might be achieved at the expense of significant haemodynamic deterioration, particularly while grafting the circumflex and the posterior descending coronary arteries. The present study was designed to assess the haemodynamic changes with the beating heart positioned for grafting the three main coronaries.

METHODS

Twenty-nine consecutive patients (21 male, mean age 62.6+/-7.1 years) undergoing off pump coronary surgery were enrolled in the study. Three different surgical settings of exposure and stabilization were used according to the site of anastomosis: left anterior descending (LAD - set-up 1; n=29), posterior descending (PDA - set-up 2; n=15), and circumflex (Cx - set-up 3; n=21) coronary arteries. Haemodynamic measurements were recorded before any cardiac manipulation (baseline) in set-ups 1, 2 and 3, and immediately after the completion of each distal anastomosis with the heart returned to its anatomical position.

RESULTS

There were no marked changes in heart rate (HR) and systemic mean arterial pressure during the construction of the anastomoses for any of the three surgical settings. Set-up 1 (LAD) showed a decrease of 15.5% in stroke volume (SV) and an increase of 9% in pulmonary capillary wedge pressure (PCWP) compared to baseline (both P<0.05), with all the other haemodynamic parameters remaining unchanged. Set-up 2 (PDA) showed a marked decrease in SV and cardiac index (CI), and an increase in central venous pressure (CVP) when compared to baseline (all P<0.05). The most extensive changes were observed in set-up 3 (Cx) with a considerable reduction in SV and CI, and an increase in CVP, PCWP, pulmonary arterial pressure, and systemic vascular resistance index (all P<0.05). These haemodynamic changes were transient and totally recovered after the heart was returned to its anatomical position.

CONCLUSIONS

Exposure and stabilization of the three main coronary arteries during beating heart surgery does not produce any appreciable change in systemic blood pressure and HR. The haemodynamic deterioration observed during the construction of the circumflex and posterior descending coronary arteries distal anastomoses is transient and well tolerated with no adverse clinical events.

External shunt for off-pump coronary artery bypass grafting: distal coronary perfusion catheter

We invented a simple external shunt catheter for off-pump coronary artery bypass grafting. This catheter maintains coronary perfusion from femoral artery, prevents ischemia, reduces back-bleeding, and acts as a suture guide by preventing accidental missuturing of the posterior coronary wall. The insertion and withdraw technique is easier than intraluminal shunt. This catheter would be a useful tool for myocardial protection during off-pump revascularization.

Transesophageal echocardiography

Anesthesiologists are increasingly using transesophageal echocardiography in both cardiac and noncardiac cases. In cardiac anesthesia, considerable progress has been made in the evaluation of mitral valvular disease. Transesophageal echocardiography has also become more useful in the hemodynamic evaluation of patients undergoing coronary artery bypass grafting. It is particularly valuable in minimally invasive surgery and in heart surgery to correct congenital defects.