Asian Cardiovasc Thorac Ann 1998;6:118-124
© 1998 Asia Publishing EXchange Pte Ltd
Profile of Coronary Artery Bypass Surgery in United Arab Emirates: Dubai Hospital Experience
Rajan Sadanandam, MS,
Najib Al Khaja, PhD,
Mohd A Aziz, MD,
Murdo A Turner, FRCS
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Department of Cardiothoracic Surgery Dubai Hospital Dubai, United Arab Emirates
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For reprint information contact: Najib Al Khaja, PhD Department of Cardiothoracic Surgery Dubai Hospital P.O. Box 7272 Dubai, United Arab Emirates Tel: 971 4 71 4444 Fax: 971 4 71 9340
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ABSTRACT
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Although coronary artery bypass surgery has become a common procedure, there were no data available regarding this type of surgery in the United Arab Emirates. Therefore, we undertook this retrospective study of the first 522 consecutive patients undergoing coronary artery bypass graft surgery between October 1992 and July 1997. The mean age was 49.1 years at operation with a 97.1% male predominance. Patients of Asian origin accounted for 75.8%, Arabs 22.4%, and Europeans 1.7%. Chronic stable angina was the most frequent presenting symptom (70.4%) and 62.1% patients had at least one prior myocardial infarction. There was a 44.6% incidence of hypertension and 32.9% of patients were diabetic. Other prominent risk factors were smoking (55.7%), hyperlipidemia (53.9%), and family history of ischemic heart disease (10.7%). Left main coronary artery obstruction was evident in 6.5% of patients. An average of 3.4 grafts per patient were performed using reverse saphenous vein and endarterectomies were needed in 2.2%. The early mortality rate in elective cases was 2.4%. This study suggests that in spite of a high incidence of multiple risk factors, our patients tolerated coronary artery bypass surgery well. Our findings highlight the trend towards more urgent operations and the decreasing age of patients with severe coronary artery disease.
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INTRODUCTION
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Although coronary artery bypass surgery (CABG) has become the most common operative procedure performed for cardiac disease and a vast amount of data is available regarding coronary surgery from centers all over the world, there have been no previously published data regarding this type of surgery in the population of the United Arab Emirates.1 In October 1992, we started a cardiac surgical program at Dubai Hospital and since then, coronary artery bypass surgery has indeed become the most common surgical procedure performed in our unit. As a newly established unit, we have constantly endeavored to improve our clinical outcome. We have a large, predominantly male, young population in this country and the pattern of coronary disease we see here is distinctly different from that seen in Western countries. Being the only center providing cardiac surgical services in Dubai, we wished to achieve a better understanding of coronary disease in our population. Therefore, we undertook this retrospective study of all patients who underwent coronary surgery in Dubai Hospital up to July 1997.
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PATIENTS AND METHODS
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This study included all patients who underwent CABG at the department of cardiothoracic surgery at Dubai Hospital from the establishment of this department in October 1992 until July 1997. The total number of open-heart operations performed was 691. Of these, 522 (75.5%) were coronary artery bypass graft operations. These included 14 operations for CABG with concomitant procedures comprising aortic valve replacement (3), mitral valve replacement (1), open mitral commissurotomy (2), mitral ring annuloplasty (1), left ventricular aneurysmectomy (3), and repair of postinfarction ventricular rupture (4).
PREOPERATIVE WORK-UP
All patients who underwent coronary angiography were discussed at the weekly cardiology-cardiac surgical meeting. Surgery was offered to patients if they fulfilled any of the following selection criteria for surgical revascularization: severe disabling angina pectoris unresponsive to medical therapy; double-vessel or triple-vessel coronary disease with left ventricular dysfunction at rest and a positive treadmill test showing inducible ischemia; coronary artery disease and left ventricular dysfunction at rest with evidence of reversible ischemia shown by radioisotope studies; or left main coronary artery disease. Patients with unstable angina were not subjected to a stress test.
Surgical candidates were referred by their cardiologist to the cardiac surgery clinic where a thorough review of the patient's previous history, risk factor profile, current symptomatology, and coronary angiography findings was carried out and the need for surgery was discussed with the patient by a member of the cardiac surgical team. Those who agreed to undergo surgery were scheduled for a preoperative work-up and were advised to stop taking aspirin two weeks prior to surgery.
The following details were collected from the patients' interviews and the hospital medical records and entered into a coronary surgery case protocol: history of angina pectoris; duration of symptoms; New York Heart Association functional class; myocardial infarction; hypertension; diabetes mellitus; congestive heart failure; obstructive lung disease requiring medication; cerebrovascular disease; smoking habits; previous percutaneous transluminal coronary angioplasty; intermittent claudication; hypercholesterolemia; raised serum creatinine; family history; and obesity. Coronary angiography findings regarding the number of vessels involved, the presence of left main disease, and left ventricular function were recorded. All elective cases were admitted to the ward one day before surgery.
DEFINITION OF TERMS
Diabetes was considered to be present if the patient was being treated with oral medication or insulin. Obesity was defined as weight of 15% or more than expected according to height. Hypertensive patients were included if the patient had a history of high blood pressure, if the blood pressure frequently exceeded 140/90 mm Hg, or if the patient was taking antihypertensive medication. Renal dysfunction was defined as a preoperative serum creatinine concentration of 20 mg•L–1 or more. Hypercholesterolemia was defined as a fasting serum cholesterol level above 200 mg•mL–1. Smoking history was considered positive if the patient confirmed any form of tobacco used in the past. Family history of coronary artery disease related to a history of this disease in the parents or siblings of the patient. Unstable angina was defined as prolonged angina (more than 15 minutes) at rest (usually with reversible ischemic electrocardiographic changes) requiring surgical intervention during the same hospital stay because of a lack of response or an incomplete response to maximal medical therapy. Cerebrovascular disease comprised any transient ischemic attack, reversible ischemic neurologic deficit, stroke, or history of cerebrovascular surgery. The priority of the operation was designated as elective: waiting list patients without priority and those staying in hospital waiting for an operation but without unstable angina; urgent: patients in hospital with unstable angina with ongoing nitroglycerine infusion; emergency: patients with acute myocardial infarction complicated by ventricular septal rupture or cardiogenic shock.
ANESTHESIA AND SURGICAL PROCEDURE
All operations were performed using cardiopulmonary bypass and moderate systemic hypothermia (27°C to 28°C rectal temperature). Anesthesia was induced with thiopentone and fentanyl followed by pancuronium and maintained with a combination of nitrous oxide and the intermittent administration of a volatile anesthetic.
Ascending aortic and two-stage single venous cannulation was used by all surgeons. Ascending aorta venting was performed through a catheter with a Y-connector to the cardioplegic line. The cardiopulmonary system was primed mainly with crystalloid solution and occasionally with banked blood to maintain a hematorcrit value of about 20%. The extracorporeal circulation was established with a heart-lung machine using a membrane oxygenator. All distal anastomoses were performed during a single interval of aortic cross-clamping; the aortic anastomoses were carried out during tangential aortic cross-clamping while the heart was kept in the empty beating state. Moderate hemodilution (hematocrit 20% to 25%) and systemic hypothermia were maintained during cardiopulmonary bypass. Topical core cooling was established with cold saline solution. Multidose cold nonoxygenated crystalloid cardioplegia (modified St. Thomas' Hospital cardioplegic solution) was administered antegradely in 48.1% of patients and via a combined antegrade-retrograde route in 51.9% of patients. Cold blood cardioplegia was introduced into use at our institution in September 1996 and has been used routinely since then. All surgeons used the internal mammary artery whenever possible. The patients were heparinized and the internal mammary artery was kept in continuity until the time of anastomosis. Variables related to the surgical procedure such as cardiopulmonary bypass time, aortic cross-clamp time, number of grafts, the use of internal mammary artery grafts, and the need to perform an endarterectomy were noted. Since its introduction in April 1995, patients routinely underwent transesophageal echocardiography intraoperatively before and after bypass to assess left ventricular function and document any improvement in regional wall motion abnormalities. An intra-aortic balloon pump (IABP) was used to wean patients off bypass if they had low cardiac output unresponsive to inotropic medication and adequate volume loading. Other major indications for IABP use were preoperative stabilization of refractory angina pectoris and severe left ventricular dysfunction complicating acute myocardial infarction that was refractory to pharmacologic therapy. We routinely placed temporary pacing wires in all cases. All patients received prophylactic antibiotic in the form of intravenous cefuroxime 1.5 g, 12 hourly for 48 hours.
POSTOPERATIVE TREATMENT
In the intensive care unit, all patients received intravenous glyceryl trinitrate and dopamine in the early postoperative period. If there were no contraindications, patients were extubated within 24 hours of surgery and transferred out of the intensive care unit within 48 hours. Low-dose soluble aspirin (150 mg) was started from postoperative day 1 to improve graft patency. All patients who made an uneventful recovery were discharged from the hospital within 7 to 10 days after the surgery. They were seen at the follow-up clinic 2 weeks and 6 weeks from the discharge date. At the end of 6 weeks, patients were referred back to the cardiology clinic for further follow-up.
Postoperative morbidity and mortality rates were recorded retrospectively. Each case was reviewed by one of the authors who recorded any adverse events. Postoperative complications were defined as those with an onset that occurred during the hospital stay. Early mortality was defined as death occurring within 30 days of the operation or during the hospital stay. Early mortality is reported in relation to the risk of the operation assessed by a severity score in which urgent and emergency surgical cases were considered high risk (Table 1
). Perioperative myocardial infarction was defined as the appearance of new Q waves on the electrocardiogram, an elevation of serum creatine kinase MB-isoenzyme levels greater than 50 units•L–1 or more than 8% of the total creatine kinase activity. Preoperative insertion of an IABP was necessary in the coronary care unit among patients with unstable angina that was unresponsive to maximal medical therapy or in the operating room among patients with unstable angina who had ventricular dysfunction or electrocardiographic changes. After surgery, low-output syndrome was diagnosed when inotropic medication was required for longer than 30 minutes in the intensive care unit to maintain systolic blood pressure above 90 mm Hg and a cardiac index greater than 2 L•min–1 or when an IABP was required to sustain the circulation. Patients who had a balloon pump inserted before the operation were considered to have low-output syndrome postoperatively if they also required inotropic medication. Supraventricular arrhythmias were defined as atrial fibrillation or flutter that led to the administration of antiarrhythmic agents or cardioversion. Postoperative stroke was diagnosed if a persistent neurologic deficit was present at the patient's discharge. Pneumothorax verified by radiography was treated with chest drainage. Reoperation was undertaken for bleeding, suspected tamponade, or graft occlusion.
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Table 1. Severity Scoring for Assessment of Postoperative Risk* in Patients Undergoing Coronary Artery Bypass Surgery
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An infection was noted to be present if incision and drainage was performed, if there was a positive culture, or if the patient was treated with antibiotics. The nature of the infection was classified as sternum-superficial (skin, subcutaneous tissue), sternum-deep (muscle, mediastinum, bone), leg (incision site), IABP site, or septicemia (positive blood cultures). Sternal wound infections were diagnosed if prolonged hospitalization was required because of antibiotic therapy or if a surgical procedure to remove infected tissue was needed. Morbidity was defined as the occurrence of low-output syndrome, myocardial infarction, perioperative stroke, or infection.
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RESULTS
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In general, the coronary arteries were smaller and thinner-walled in our Asian patients than those seen in Caucasian patients, making grafting more difficult. Diffusely diseased coronary arteries were often seen. The diffuse nature of the disease resulted in extensive use of sequential grafts and a high number of triple and quadruple grafts. The preoperative clinical characteristics of all 522 patients undergoing CABG are listed in Table 2 and the risk factors recorded in these patients are shown in Table 3. Of the 355 patients with stable angina, 275 (76.1%) had triple-vessel disease, 71 (20%) had double-vessel disease, and only 9 (3.9%) had single-vessel disease. Table 4 details the angiographic findings in the patients. Intraoperative data are shown in Table 5. Of the 522 patients, 433 (82.4%) were transferred out of the intensive care unit within 48 hours and 471 patients (90.2%) were extubated within 24 hours. The major postoperative complications are shown in Table 6. Reoperation within 24 hours was necessary in 23 patients (4.4%); in all cases this was due to excessive bleeding. Inotropic drugs were used to treat low cardiac output in the perioperative period in 113 patients (22.4%). In 38 of the 39 patients who required IABP support, the IABP was used to wean them from cardiopulmonary bypass intraoperatively. In one patient, the balloon was inserted postoperatively because of acute low cardiac output secondary to postoperative myocardial infarction. The rate of survival in patients who required IABP support was 84.6% (33/39 patients).
Pulmonary complications were noted in 165 patients (31.6%). Atelectasis was the most common, seen in 114 patients (21.8%). In order of frequency, atelectasis involved segments of left lower lobe (68.4%), bilateral lower lobe (25.4%), and right lower lobe (2.4%). Total lung collapse occurred in 4 patients (3.5%). Urgent bedside bronchoscopy was performed in these cases. Three patients recovered after ventilatory support and intensive chest physiotherapy. One patient had a prolonged air leak with total lung collapse from a bronchial tear and had to undergo thoracotomy for repair of the bronchial laceration. She recovered uneventfully. Pneumothorax requiring intercostal drainage was seen in 12 patients (2.3%). Pleural effusion requiring drainage occurred in 39 patients (7.4%). Ten patients (1.9%) developed acute renal failure requiring dialysis. All of these required dialysis around the 5th postoperative day; only 2 had elevated serum creatinine levels preoperatively. Postoperative renal failure was seen only in patients who had severe perioperative low cardiac output secondary to perioperative myocardial infarction requiring the use of intra-aortic balloon pumping and inotropic agents. There was a high mortality (7 patients) when low cardiac output was associated with renal failure. Hemodialysis was carried out in 4 patients, peritoneal dialysis in 4 patients, and hemofiltration in 2 patients. Of the 8 patients (0.2%) who developed a neurologic complication, 6 had delirium, one patient developed acute left hemiparesis and one patient displayed signs of acute cerebral insufficiency. Only one patient developed acute peritonitis on the 4th day after surgery. Exploratory laparotomy revealed perforation of a previous duodenal ulcer. He recovered uneventfully.
Incidents of mortality are classified in Tables 7 and 8. In 403 patients undergoing elective CABG, the hospital mortality was 2.4%. Operative mortality in 115 consecutive patients with unstable angina was 9.5%. With increased urgency of operation, the mortality rate increased. Significantly, of 115 patients operated on urgently, 11 (9.5%) did not survive, and 3 out of 4 patients (75%) undergoing emergency operative procedures died. It was observed that mortality increased when CABG was combined with a second procedure. Of the 14 patients with complicated CABG procedures, only one survived.
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DISCUSSION
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This study describes the profile of patients undergoing CABG surgery at Dubai Hospital and identifies the various risk indicators in these patients. In spite of the amount of data available regarding all aspects of coronary surgery from different centers all over the world, there is no previously published data available regarding coronary surgery in the population of the United Arab Emirates. There is increasing evidence from Western countries that rates of coronary artery bypass grafting are related to certain sociodemographic factors peculiar to each society.2 Therefore, being the only cardiac surgical center in Dubai, we needed to assess the pattern of coronary disease in our population.
Although the profile of patients undergoing CABG in Western countries is changing with a trend towards older patients with more associated diseases, our clinical data reveal a high prevalence of advanced coronary disease in younger patients.2,3 It is notable that 97% of our patients were male and 50% were below 50 years of age. The rate in men in this series was approximately 30 times that in women and the highest rates occurred in those aged between 40 to 50 years. This unusual predominance of males is not surprising considering the demography of Dubai, which has a mainly young male Asian and Arab expatriate population.
The high prevalence of multiple risk factors such as diabetes, hypertension, smoking, and hyperlipidemia, coupled with diffuse coronary disease and smaller coronary vessels in our CABG patients puts them in the high-risk category. Nearly two-thirds of our patients had a history of previous myocardial infarction. The number of grafts per patient in our study (3.4) is reflective of the severity of coronary artery disease in comparison to other studies where the average number of grafts per patient was in the range 2.3 to 2.5 grafts per patient.4,5 The smaller and thinner coronary vessels caused increased technical difficulty in grafting. Diffusely diseased coronary arteries required a greater use of sequential grafts and a greater number of triple and quadruple grafts. These findings confirm the reports of other authors on studies involving patients of Indian and Arab origin.6–9 Our preferential use of left internal mammary artery rather than saphenous vein in these relatively young patients was based on the superior patency of arterial grafts and was considered important for improving long-term results.10
Another notable finding in this series is the high number of patients undergoing urgent surgical revascularization, constituting 22% of all CABG procedures. The most likely explanation is that CABG is increasingly performed for the treatment of unstable angina on an urgent basis.11 Our center is the only one serving the population of Dubai and therefore obliged to give priority over elective cases to severely ill patients.
Following surgery, only 17.6% of our patients required a stay of more than 48 hours in the intensive care unit which is comparable to that reported by Michalopoulos and colleagues.12 The main cause of prolonged stay in the intensive care unit was low cardiac output syndrome. In spite of the younger profile of our study population, early or 30-day mortality in elective operations not given priority was 2.4%, which is well within the range of 1.4% to 5.6% reported in the European Coronary Surgery Study Group, Veterans Administration Cooperative Study, and the Coronary Artery Surgery Study randomized trial.13–15 In our series, patients who were operated on urgently had very similar baseline characteristics to patients who were operated on electively.
Although the surgical values appeared to be similar in patients operated on urgently and electively, various postoperative complications including death were more common if patients were operated on urgently. These findings correlate well with earlier reports in which bleeding, tamponade, and acute myocardial infarction were more common among patients who were operated on urgently.16
The emergence of surgical priority as an important predictor of in-hospital mortality has been well documented.3,12,17–26 In this study, we noted a high percentage of patients (22.8%) who underwent urgent CABG surgery compared to elective cases. Although our patients were younger, they had more comorbid factors (hypertension, smoking, and diabetes) and they also had more previous myocardial infarctions than those in other reports. The predicted risk of in-hospital mortality associated with CABG was 4%. This is lower than the 5.2% mortality reported by Disch and colleagues.11 Increases in the percentage of patients requiring urgent operations made the most substantial contribution to the increase in mortality.
Operative risk increased significantly from 2.4% in patients undergoing elective operations to 9.5% and 75% in patients undergoing urgent or emergency operative procedures, respectively. From the data in Table 7
, it can be seen that in the first 3 months of our program, there were 4 operative deaths among 26 patients undergoing CABG, with a crude mortality rate of 15.4%. Three patients died within 24 hours due to perioperative myocardial infarction, while the 4th patient suffered from acute pulmonary embolism. These deaths were attributed to the initial learning curve of team members in a newly established unit. Excluding this unfavorable result in the early period, from 1993 to 1997 our operative mortality dropped to 4% (20 deaths in 496 patients). Excluding emergency surgery, the operative mortality was 3.4%. There is a wide variability of operative mortality reported during the early years of coronary surgery from different centers ranging from 0.3% to 6.4%.27
During the period 1993 to 1997, 112 patients (22.6%) were operated for unstable angina with an operative mortality of 8%. In a review of 14 reports published from 1978 to 1988, Kennedy and colleagues28 cited an overall operative mortality ranging from 1.2% to 8.5%. At our institution, the operative mortality for patients undergoing elective coronary surgical procedures since 1993 was 2.1%. This compares favorably with reports from other centers. The trend towards improvement of operative mortality with increasing experience observed by us is in agreement with the experience of others.
This study suggests that in spite of a high incidence of multiple risk factors such as hypertension, diabetes, hyperlipidemia, smoking, and diffuse coronary artery disease in young patients, coronary artery bypass surgery was well tolerated. It also highlights the trend towards more urgent operations and severe coronary artery disease at an earlier age. Our findings support the previously documented safety of CABG surgery in all age groups in spite of the high prevalence of multiple risk factors and diffuse coronary artery disease. However, long-term follow-up is essential to evaluate the longevity of graft survival in these patients.
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Acknowledgments
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We thank Ms. Helen Pinto for her excellent secretarial services and the staff of the medical records departments of Dubai, Rashid, and Al Maktoum Hospitals for their assistance.
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ABSTRACT
INTRODUCTION
