Walid C. Dihmis

Preoperative calculation of risk for prolonged intensive care unit stay following coronary artery bypass grafting

ObjectivePatients who have prolonged stay in intensive care unit (ICU) are associated with adverse outcomes. Such patients have cost implications and can lead to shortage of ICU beds. We aimed to develop a preoperative risk prediction tool for prolonged ICU stay following coronary artery surgery (CABG).Methods5,186 patients who underwent CABG between 1st April 1997 and 31st March 2002 were analysed in a development dataset. Logistic regression was used with forward stepwise technique to identify preoperative risk factors for prolonged ICU stay; defined as patients staying longer than 3 days on ICU. Variables examined included presentation history, co-morbidities, catheter and demographic details. The use of cardiopulmonary bypass (CPB) was also recorded. The prediction tool was tested on validation dataset (1197 CABG patients between 1st April 2003 and 31st March 2004). The area under the receiver operating characteristic (ROC) curve was calculated to assess the performance of the prediction tool.Results475(9.2%) patients had a prolonged ICU stay in the development dataset. Variables identified as risk factors for a prolonged ICU stay included renal dysfunction, unstable angina, poor ejection fraction, peripheral vascular disease, obesity, increasing age, smoking, diabetes, priority, hypercholesterolaemia, hypertension, and use of CPB. In the validation dataset, 8.1% patients had a prolonged ICU stay compared to 8.7% expected. The ROC curve for the development and validation datasets was 0.72 and 0.74 respectively.ConclusionA prediction tool has been developed which is reliable and valid. The tool is being piloted at our institution to aid resource management.

Effect of preoperative aspirin use in off-pump coronary artery bypass operations

BACKGROUND The effect of preoperative aspirin use until the day of operation on mortality rate and bleeding risks in patients who had on-pump coronary artery bypass operation has been well documented. However, the effect of aspirin use in patients undergoing off-pump coronary artery bypass operation (OPCAB) with regard to postoperative blood loss and morbidity has not been studied. We aimed to determine the effects of continuing aspirin therapy preoperatively. METHODS We performed a retrospective study of 340 patients who had first-time OPCAB between January 1998 and September 2001. A propensity score for receiving aspirin until the day of operation was constructed from core patient characteristics. All aspirin users (n = 170) were matched with unique 170 nonaspirin users by identical propensity score. The primary outcome measures were in-hospital mortality rate and hemorrhage-related outcomes (postoperative blood loss in the intensive care unit, reexploration for bleeding, and blood product requirements). Secondary outcome measures were stroke, myocardial infarction, gastrointestinal bleeding, and sternal wound infections. RESULTS There were no differences in patient characteristics between aspirin users and nonaspirin users. The average postoperative blood loss (845 mL versus 775 mL; p = 0.157) and the rate of reexploration for bleeding (3.5% versus 3.5%; p > 0.99) were similar in aspirin users and nonaspirin users. We found no significant difference between blood product requirements for the two groups. Similarly, we found no significant difference in the incidence of the secondary outcomes. CONCLUSIONS Preoperative aspirin did not increase bleeding-related complications, mortality rate, or other morbidities in patients who had off-pump coronary artery operation.

Phenoxybenzamine treatment is insufficient to prevent spasm in the radial artery: the effect of other vasodilators

OBJECTIVES After its reintroduction as an arterial graft in coronary artery surgery, the radial artery is now established as an alternative arterial conduit, with good early and midterm patency. However, because of the concern about its vasospasticity, numerous vasodilator strategies have been used. Recently the use of the irreversible alpha-adrenergic antagonist phenoxybenzamine has been proposed. Although this treatment is effective in eliminating the vasoconstriction mediated by noradrenaline, the contribution of other circulating vasoconstrictors to vasospasm could be as important. This study investigates the response of radial arteries treated with phenoxybenzamine to vasoconstrictor stimuli and possible preventative strategies. METHODS In vitro, sections of radial artery, pretreated with phenoxybenzamine after harvesting, were stimulated with maximal concentrations of the vasoconstrictors noradrenaline, vasopressin, angiotensin II, KCl, and endothelin-1. In matched segments of artery, vasoconstrictor responses were recorded in the presence of diltiazem, glyceryl trinitrate, and papaverine and compared with phenoxybenzamine-treated samples. RESULTS Phenoxybenzamine-treated radial artery failed to respond to noradrenaline but did respond to vasopressin, angiotensin II, endothelin-1, and KCl. Diltiazem was largely ineffective against contractile stimuli apart from KCl. Glyceryl trinitrate and papaverine significantly reduced responses to all of the vasoconstrictors tested. CONCLUSION In phenoxybenzamine-treated sections of radial artery, circulating vasoconstrictor agonists may still contribute to the induction of spasm. Additional vasodilator strategies may be required to completely prevent vasospasm.

Improving mortality of coronary surgery over first four years of independent practice: retrospective examination of prospectively collected data from 15 surgeons

Abstract Objective To study the “learning curve” associated with independent practice in coronary artery surgery. Design Retrospective analysis of prospectively collected data. Setting All NHS centres in north west England that carry out cardiac surgery in adults. Participants 18 913 patients undergoing coronary artery surgery for the first time between April 1997 and March 2003, 5678 of whom were operated on by 15 surgeons in the first four years after their consultant appointment. Main outcome measures Observed and predicted mortality (EuroSCORE) for surgeons in their first, second, third, and fourth years after appointment as a consultant compared with figures for established surgeons. Results Overall mortality decreased over the six years of study (P = 0.01). Of the patients operated on by established surgeons or newly appointed consultants, 265/13 235 (2.0%) and 109/5678 (1.9%), respectively, died (P = 0.71). There was a progressive decrease in observed mortality with time after appointment as a consultant from 2.2% in the first year to 1.2% in the fourth year (P = 0.049). This result remained significant after adjustment for time and case mix (P = 0.019). Conclusions Mortality in patients operated on by newly appointed consultant surgeons is similar to mortality in patients operated on by established surgeons. There are significant decreases in crude and risk adjusted mortality in the four years after appointment. These findings should influence the nature of practice in newly appointed surgeons.

Effect of avoiding cardiopulmonary bypass in non-elective coronary artery bypass surgery: a propensity score analysis

OBJECTIVE Non-elective coronary artery surgery (emergent/salvage or urgent) carries an increased risk in most risk-stratification models. Off-pump coronary surgery is increasingly used in non-elective cases. We aimed to investigate the effect of avoiding cardiopulmonary bypass on outcomes following non-elective coronary surgery. METHODS Of the 3771 consecutive coronary artery bypass procedures performed by five surgeons between April 1997 and March 2002, 828 (22%) were non-elective and 417 (50.4%) of these patients had off-pump surgery. Multivariate logistic regression was used to assess the effect of off-pump on in-hospital outcomes, while adjusting for treatment selection bias. Treatment selection bias was controlled for by constructing a propensity score from core patient characteristics, which was the probability of avoiding cardiopulmonary bypass. The C statistic for this model was 0.8. RESULTS Off-pump patients were more likely to be hypertensive, stable, had less extensive disease and better left ventricular function. The left internal mammary artery was used in 91.8% (n=383) of off-pump patients compared to 79.3% (n=326) of on-pump cases (P<0.001). After adjusting for the propensity score, no difference in in-hospital mortality was observed between off-pump and on-pump (adjusted odds ratio (OR) 0.83 (95% confidence intervals (CI) 0.36-1.93); P=0.667). Off-pump patients were less likely to require intra-aortic balloon pump support (adjusted OR 0.44 (95% CI 0.21-0.96); P=0.039), less likely to have renal failure (adjusted OR 0.44 (95% CI 0.22-0.90); P=0.025), and have shorter lengths of stay (adjusted OR 0.51 (95% CI 0.37-0.70); P<0.001). Other morbidity outcomes were similar in both groups. CONCLUSIONS In this experience, off-pump coronary surgery in non-elective patients is safe with acceptable results. Non-elective off-pump patients have a significantly reduced incidence of renal failure, and shorter post-operative stays compared to on-pump coronary artery bypass surgery.

Endothelin receptors in cultured and native human radial artery smooth muscle

In human vascular smooth muscle cells endothelin-1, acting at both endothelin A and endothelin B receptors, has been demonstrated to be both a potent vasoconstrictor and mitogen. Our aim was to study the functional expression of endothelin receptors in human radial artery smooth muscle using both native tissue and cultured cells (RASMCs). Radial artery smooth muscle cells were cultured from arterial explants and loaded with the calcium fluorescent dye fura-2. Cells responded to endothelin-1 and a variety of other vasoconstrictors with rises in cytoplasmic calcium ([Ca 2+ ] c ). Arterial rings responded to endothelin-1 with an increase in tension. The response of both cells and arterial rings to endothelin-1 was characterized using the selective endothelin A receptor antagonist BQ123 and the endothelin B receptor antagonist BQ788. The RASMCs were found to express [Ca 2+ ] c responses consistent with the expression of only the endothelin A receptor. Endothelin-1-mediated vasoconstriction in radial artery rings was unaffected by BQ788 but was completely blocked by BQ123. Using the selective radioligands [ 125 I]-PD151242 and [ 125 I]-BQ3020 and a combination of in vitro receptor autoradiography and isolated cell preparations, endothelin A receptors were confirmed to be present on RASMCs and on arterial sections, whereas endothelin B binding was barely detectable on native smooth muscle and on RASMCs.

Is off-pump coronary surgery justified in EuroSCORE high-risk cases? A propensity score analysis.

We aimed to quantify the effect of avoiding cardiopulmonary bypass on outcomes in high-risk patients. Of the 2079 consecutive CABGs performed by three surgeons between April 1997 and September 2002, 389 were classified as high-risk according to the European System for Cardiac Operative Risk Evaluation (EuroSCORE) risk stratification, with a score of >5. The off-pump group had 196 patients and the on-pump group had 193 patients. Multivariate logistic regression was used to assess the effect of off-pump on in-hospital outcomes, while adjusting for treatment selection bias with a propensity score. The incidence of hypertension, hypercholesterolaemia, and renal dysfunction were higher in the off-pump group. The median EuroSCORE for off-pump patients was 7 (6-8), while for the on-pump patients was 7 (6-8; P=0.31). After adjusting for the propensity score, off-pump patients were less likely to have stroke (OR 0.17; P=0.041), renal failure (OR 0.35; P=0.029), blood transfusion (OR 0.12; P<0.001), prolonged mechanical ventilation (OR 0.36; P=0.021), and inotrope support (OR 0.35; P<0.001). Off-pump patients also had significantly shorter post-operative hospital stays. There was no significant difference between off-pump and on-pump patients in terms of in-hospital and mid-term mortality. Off-pump CABG is justified in EuroSCORE high-risk cases.

Contained rupture of a myocardial abscess in the free wall of the left ventricle

Contained rupture of the left ventricle is uncommon; rupture secondary to a myocardial abscess is exceedingly rare. A case is presented of a contained rupture of a myocardial abscess in a patient with Staphylococcus aureus septicemia. The rupture was repaired surgically, and the patient survived.

Attenuation of receptor-dependent and -independent vasoconstriction in the human radial artery

BACKGROUND Vasodilator strategies used to treat bypass grafts in the operating theatre, such as nitrates, phosphodiesterase inhibitors and calcium channel antagonists have a broad but short-lived effect against a variety of vasoconstrictor stimuli. Treatments that react irreversibly with proteins modulating vasoconstriction have the advantage that their effects can last well into the postoperative period. In addition systemic effects are avoided as the treatment is localised to the treated graft. This study investigated the use of two clinically applied drugs; fluphenazine (SKF7171A, HCl), an irreversible calmodulin antagonist and minoxidil sulphate, an irreversible potassium channel opener. Treatments were tested against receptor and non-receptor-mediated contraction in the human radial artery. METHOD Isometric tension was measured in response to angiotensin II, KCl and vasopressin in 108 radial artery rings (taken from 31 patients undergoing coronary artery bypass grafting). Control responses were compared with rings pretreated with fluphenazine or minoxidil sulphate. Vasopressin responses were also compared in the presence of glyceryl trinitrate or the reversible Rho kinase inhibitor Y27632. RESULTS Fluphenazine pretreatment significantly suppressed vasoconstriction to all agonists tested. Maximal responses to angiotensin II, vasopressin and KCl were reduced by 42+/-19%, 35+/-8% and 48+/-15% respectively, without any measurable effect on the EC(50). Minoxidil sulphate showed no discernable effect. Vasopressin-induced contraction was also reduced by high levels of glyceryl trinitrate (220 microM; 50 microg/ml) or 10 microM Y27632. CONCLUSIONS The irreversible calmodulin antagonist fluphenazine has potential to be developed as an inhibitor of contraction in arterial graft vessels. The involvement of Rho kinase indicates that other vasoconstrictors and surgical stress can sensitize radial artery to vasopressin-induced contraction. Strategies targeting this pathway also have future potential.

Effect of Prolonged Intensive Care Stay on Survival Following Coronary Surgery

The aim of the study was to examine midterm survival in patients who required prolonged recovery in the intensive care unit. The 5,186 consecutive patients who underwent isolated coronary surgery between April 1997 and March 2002 were retrospectively analyzed. Patients were classified as having prolonged (> 3 days) or normal (≤ 3 days) stay in the intensive care unit. Patient records were matched to the National Health Service Strategic Tracing Service which records all-cause mortality in the UK. Case-mix was controlled for by constructing a propensity score from core patient characteristics, which was included along with the comparison variable in a multivariable analysis of outcome. Prolonged intensive care unit stay was recorded in 475 (9.16%) patients. Mortality was 9.14% during the study period with a total follow-up of 19,618 patient-years (mean, 3.8 years). Adjusted 5-year survival was 78.0% for prolonged intensive care unit stay vs. 90.7% for normal stay, with an adjusted hazard ratio for midterm mortality of 2.6 (p < 0.001). Midterm mortality was significantly higher in patients with a prolonged intensive care unit stay following coronary bypass.