Keith G. Buchan

Relationship between postoperative cardiac troponin I levels and outcome of cardiac surgery.

Background— Cardiac surgery may be associated with significant perioperative and postoperative morbidity and mortality. Underlying pathology, surgical technique, and postoperative complications may all influence outcome. These factors may be reflected as a rise in postoperative troponin levels. Interpretation of troponin levels in this setting may therefore be complex. This study assessed the prognostic significance of such measurements, taking into account potential confounding variables. Methods and Results— One-thousand three hundred sixty-five patients undergoing cardiac surgery underwent measurement of cardiac troponin I (cTnI) at 2 and 24 hours after surgery. The relationship of these measurements to subsequent mortality was established. After taking into account all other variables, cTnI levels measured at 24 hours were independently predictive of mortality at 30 days (odds ratio [OR] 1.14 per 10 &mgr;g/L, 95% confidence interval [CI] 1.05 to 1.24, P=0.002), 1 year (OR 1.10 per 10 &mgr;g/L, 95% CI 1.03 to 1.18, P=0.006), and 3 years (OR 1.07 per 10 &mgr;g/L, 95% CI 1.00 to 1.15, P=0.04). Cardiac TnI levels in the highest quartile at 24 hours were associated with a particularly poor outcome. Conclusions— cTnI levels measured 24 hours after cardiac surgery predict short-, medium-, and long-term mortality and remain independently predictive when adjusted for all other potentially confounding variables, including operation complexity.

Renal Function and Outcome From Coronary Artery Bypass Grafting: Impact on Mortality After a 2.3-Year Follow-Up

Background— Severe renal dysfunction is associated with a worse outcome after coronary artery bypass graft surgery (CABG). Less is known about the effects of milder degrees of renal impairment, and previous studies have relied on levels of serum creatinine, an insensitive indicator of renal function. Recent studies have suggested that estimated glomerular filtration rate (eGFR) is a more discriminatory measure. However, data on the utility of eGFR in predicting outcome from CABG are limited. Methods and Results— We studied 2067 consecutive patients undergoing CABG. Demographic and clinical data were collected preoperatively, and patients were followed up a median of 2.3 years after surgery. Estimated GFR was calculated from the Modification of Diet in Renal Disease equation. The primary outcome was all-cause mortality. Mean±SD eGFR was 57.9±17.6 mL/min per 1.73 m2 in the 158 patients who died during follow-up compared with 64.7±13.8 mL/min per 1.73 m2 in survivors (hazard ratio [HR], 0.71 per 10 mL/min per 1.73 m2; 95% CI, 0.64 to 0.80; P<0.001). Estimated GFR was an independent predictor of mortality in both models with other individual univariable predictors (HR, 0.80 per 10 mL/min per 1.73 m2; 95% CI, 0.72 to 0.89; P<0.001) and the European system for cardiac operative risk evaluation (HR, 0.88 per 10 mL/min per 1.73 m2; 95% CI, 0.78 to 0.98; P=0.02). Conclusions— Estimated GFR is a powerful and independent predictor of mortality after CABG.

Usefulness of Neutrophil/Lymphocyte Ratio As Predictor of New-Onset Atrial Fibrillation After Coronary Artery Bypass Grafting

The neutrophil/lymphocyte (N/L) ratio integrates information on the inflammatory milieu and physiologic stress. It is an emerging marker of prognosis in patients with cardiovascular disease. We investigated the relation between the N/L ratio and postoperative atrial fibrillation (AF) in patients undergoing coronary artery bypass grafting. In a prospective cohort study, 275 patients undergoing nonemergency coronary artery bypass grafting were recruited. Patients with previous atrial arrhythmia or requiring concomitant valve surgery were excluded. The N/L ratio was determined preoperatively and on postoperative day 2. The study end point was AF lasting >30 seconds. Patients who developed AF (n = 107, 39%) had had a greater preoperative N/L ratio (median 3.0 vs 2.4, p = 0.001), but no differences were found in the other white blood cell parameters or C-reactive protein. The postoperative N/L ratio was greater in patients with AF (day 2, median 9.2 vs 7.2, p <0.001), and in multivariate models, a greater postoperative N/L ratio was independently associated with a greater incidence of AF (odds ratio 1.10 per unit increase, p = 0.003: odds ratio for N/L ratio >10.14 [optimal postoperative cutoff in our cohort], 2.83 per unit, p <0.001). Elevated pre- and postoperative N/L ratios were associated with an increased occurrence of AF after coronary artery bypass grafting. In conclusion, these results support an inflammatory etiology in postoperative AF but suggest that other factors are also important.

Use of preoperative natriuretic peptides and echocardiographic parameters in predicting new-onset atrial fibrillation after coronary artery bypass grafting: A prospective comparative study

BACKGROUND Atrial fibrillation (AF) is a common complication after coronary artery bypass grafting (CABG). We prospectively compared the ability of echocardiographic parameters and the cardiac neurohormones, brain natriuretic peptide (BNP), and N-terminal pro-brain natriuretic peptide (NT-proBNP) to predict AF in this setting. METHODS We recruited 275 patients undergoing nonemergency CABG. Patients undergoing valve surgery or with prior atrial dysrhythmia (based on clinical history and review of medical records) were excluded. Echocardiography was performed, and natriuretic peptide levels were measured, 24 hours before surgery. The primary end point was postoperative AF lasting >30 seconds. RESULTS The only significant echocardiographic predictors of postoperative AF (n = 107, 39%) were the transmitral E to A-wave ratio and the early mitral annulus velocity. Levels of BNP and NT-proBNP were higher in patients who developed AF. Both natriuretic peptides, but none of the echocardiographic parameters, remained independently predictive in multivariable analysis. The optimum cut points for predicting AF were 31 pg/mL for BNP (odds ratio [OR] 2.74, P = .001) and 74 pg/mL for NT-proBNP (OR 2.74, P = .003). CONCLUSION Levels of BNP and NT-proBNP are independent, though modestly effective, predictors of AF after isolated CABG. In contrast, none of the echocardiographic parameters assessed, including measures of LV systolic function and filling pressure, were independently predictive.

MECHANICAL PROPERTIES OF CHORDAE TENDINEAE OF THE MITRAL HEART VALVE: YOUNG'S MODULUS, STRUCTURAL STIFFNESS, AND EFFECTS OF AGING

Youngs modulus and structural stiffness were determined for chordae tendineae of the mitral valve from young (18–26 weeks) and old (over 2 years) porcine hearts. For chordae from the posterior leaflet of the valve, the Youngs modulus values were significantly higher (p < 0.05) for the thinner marginal chordae (59 ± 31 MPa young; 88 ± 21 MPa old) than for the thicker basal chordae (31 ± 4 MPa young; 28 ± 9 MPa old). Marginal chordae (both anterior and posterior) had significantly higher (p < 0.05) value for their Youngs modulus in old (88 ± 21 MPa anterior and posterior) than in young (62 ± 17 MPa anterior, 59 ± 18 MPa posterior) pig hearts. There was no significant difference in structural stiffness between marginal and basal (anterior and posterior leaflets) or between strut chordae (that are associated with anterior the leaflet only) and marginal and basal chordae. However, the value of structural stiffness of chordae was significantly higher (p < 0.05) for old (2.2 ± 0.2 kN/m) than for young (2.0 ± 0.4 kN/m) chordae. These results show that aging affects the properties of chordae and that all chordae need to be included in finite element models of valve function.

Uric acid levels and outcome from coronary artery bypass grafting.

OBJECTIVE Elevated uric acid levels have been associated with an adverse cardiovascular outcome in several settings. Their utility in patients undergoing surgical revascularization has not, however, been assessed. We hypothesized that serum uric acid levels would predict the outcome of patients undergoing coronary artery bypass grafting. METHODS The study cohort consisted of 1140 consecutive patients undergoing nonemergency coronary artery bypass grafting. Clinical details were obtained prospectively, and serum uric acid was measured a median of 1 day before surgery. The primary end point was all-cause mortality. RESULTS During a median of 4.5 years, 126 patients (11%) died. Mean (+/- standard deviation) uric acid levels were 390 +/- 131 micromol/L in patients who died versus 353 +/- 86 micromol/L among survivors (hazard ratio 1.48 per 100 micromol/L; 95% confidence interval, 1.25-1.74; P < .001). The excess risk associated with an elevated uric acid was particularly evident among patients in the upper quartile (>or=410 micromol/L; hazard ratio vs all other quartiles combined 2.18; 95% confidence interval, 1.53-3.11; P < .001). After adjusting for other potential prognostic variables, including the European System for Cardiac Operative Risk Evaluation, uric acid remained predictive of outcome. CONCLUSION Increasing levels of uric acid are associated with poorer survival after coronary artery bypass grafting. Their prognostic utility is independent of other recognized risk factors, including the European System for Cardiac Operative Risk Evaluation.

Socio-economic status and early outcome from coronary artery bypass grafting

Objective: To determine the effects of socio-economic status (SES) on the outcome of coronary artery bypass grafting (CABG). Design: Prospective cohort study. Setting: Regional cardiac surgical unit. Patients: 1994 consecutive patients undergoing non-emergency CABG. Measures: SES was determined from the patient’s postcode using Carstairs tables. The primary end-point was all-cause mortality at 30 days. Results: There were 50 deaths (2.5%) within 30 days of surgery. A higher Carstairs score demonstrated a trend towards increased 30-day mortality (odds ratio (OR) 1.09 per unit, 95% CI 1.00 to 1.20, p = 0.06). In a backward conditional model, including other predictors of early mortality, Carstairs scores were independently predictive (OR 1.12 per unit, 95% CI 1.01 to 1.24, p = 0.02). In a model including only Carstairs scores and the EuroSCORE, both were independent predictors of this outcome (OR for Carstairs score 1.11 per unit, 95% CI 1.00 to 1.22, p = 0.04). The 30-day mortality increases in each quartile of Carstairs scores, with patients in quartile 4 (most deprived) at significantly higher risk compared with quartile 1 (uncorrected OR 2.53 per unit, 95% CI 1.04 to 6.15; OR corrected for EuroSCORE, 2.56 per unit, 95% CI 1.03 to 6.34, p = 0.04 for both). Similarly, patients in the least affluent quartile were twice as likely to suffer a serious complication as those in the most affluent quartile (OR 2.14 per unit, 95% CI 1.32 to 3.46, p = 0.002). This increased risk was also independent of the EuroSCORE. Conclusions: Lower SES is associated with a poorer early outcome following CABG and is independent of other recognised risk factors.

Effect of mitral valve geometry on valve competence.

The aim of the investigation was to vary certain geometrical features of the mitral valve in vitro, in order to understand their role in valve function. Geometrical changes to mitral valve components are known to affect valve function, but complete understanding of how geometrical changes influence valve function is far from complete. Test apparatus has been used to apply pressure to porcine mitral valves. Porcine mitral valve specimens were tested both in their intact state and with a specific aspect of their geometry altered. The geometric parameters of the mitral valve varied were (1) the length between the papillary muscles and the mitral annulus (termed the annulo-papillary length), (2) the diameter of the left ventricle at the level of the papillary muscles, and (3) the mitral annular area. Six specimens were tested for each parameter investigated. A minimum annulo-papillary length was necessary to allow chordae tendineae to pull on the valve leaflets in order to prevent mitral valve failure; increasing this length further improved valve closure. Over the experimental range tested, left ventricular dilation at the level of the papillary muscles did not induce failure (P not significant). Increasing the mitral annular area was found to induce failure (P = 0.030 and P = 0.018 for medium and large annular diameters, respectively). The results demonstrate the importance of the geometry of mitral valve components on its function, and give insights into further experiments required to provide further understanding of the role of mitral valve geometry in its function. The results demonstrate that this in vitro method can be used to vary selected features of the geometry of the mitral valve.

The relationship between renal function and outcome from heart valve surgery

BACKGROUND The prognostic importance of renal function in patients undergoing surgery for valvular heart disease is poorly defined. The current study addresses this issue. METHODS Baseline demographic and clinical variables, including the European system for cardiac operative risk evaluation (EuroSCORE), were recorded prospectively from 514 consecutive patients undergoing heart valve surgery between April 2000 and March 2004. Patients with active infective endocarditis and/or requiring emergency surgery were excluded. The glomerular filtration rate was estimated (eGFR) using the Modification of Diet in Renal Disease equation. The primary outcome was all-cause mortality. RESULTS During a median follow-up of 2 years, 87 patients died. In univariable analysis, both eGFR (hazard ratio [HR] 0.69 per 10 mL/min per 1.73 m2, P<.001) and creatinine (HR 1.04 per 10 micromol/L, P<.001) predicted mortality. Estimated GFR was a stronger predictor and was used in subsequent multivariable models. It remained a powerful independent predictor of death in a multivariable model including all study variables (HR 0.70 per 10 mL/min per 1.73 m2 increase, P<.001) and in a model including EuroSCORE (HR 0.64 per 10 mL/min per 1.73 m2 increase, P<.001). After correction for preoperative EuroSCORE, an eGFR of <60 mL/min per 1.73 m2 was associated with an excess hazard of death of 2.31 (P=.001). CONCLUSION Renal function, particularly the eGFR, is a powerful predictor of outcome in patients undergoing heart valve surgery. This prognostic utility is independent of other recognized risk factors and the EuroSCORE.

Frequency and diameter dependent viscoelastic properties of mitral valve chordae tendineae

This study aimed to characterise viscoelastic properties of different categories of chordae tendineae over a range of frequencies. Dynamic Mechanical Analysis (DMA) was performed using a materials testing machine. Chordae (n=51) were dissected from seven porcine hearts and categorised as basal, marginal, strut or commissural. Chordae were loaded under a sinusoidally varying tensile load at a range of frequencies between 0.5 and 5Hz, both at a standardised load (i.e. same mean load of 4N for all chordae) and under chordal specific loading (i.e. based on in vivo loads for different chordae). Storage modulus and stiffness were frequency-dependent. Loss modulus and stiffness were frequency-independent. Storage and loss moduli, but not stiffness, decreased with chordal diameter. Therefore, strut chordae have the lowest moduli and marginal chordae the highest moduli. The hierarchy of dynamic storage and loss moduli is: marginal, commissural, basal and strut. In conclusion, viscoelastic properties of chordae are dependent on both frequency and chordal type. Future/novel replacement chordal materials should account for frequency and diameter dependent viscoelastic properties of chordae tendineae.