Incremental Value of the Preoperative Echocardiogram to Predict Mortality and Major Morbidity in Coronary Artery Bypass Surgery

Study Questions:

What is the prognostic value of a preoperative transthoracic echocardiogram (TTE) in patients undergoing coronary artery bypass surgery (CABG)?

Methods:

Patients undergoing isolated CABG at two hospitals, and for whom a preoperative TTE were available, were analyzed. A derivation cohort of 667 patients, operated on between January 2007 and December 2009 at hospital #1, was analyzed for multiple echocardiographic parameters from which prognostic echocardiographic findings were identified. The prognostically relevant findings were then tested in a validation cohort of 187 patients operated on between September 2010 and July 2011 at a different hospital. Thirteen different echocardiographic parameters were evaluated including left atrial and ventricular volume, left ventricular ejection fraction (LVEF), characterization of diastolic filling, mitral and tricuspid regurgitation, as well as indexes of right ventricular (RV) performance and pulmonary artery systolic pressure (PASP). The primary outcome was in-hospital mortality or major morbidity, and a secondary outcome was all-cause mortality. Anticipated risk was determined from the Society of Thoracic Surgeons (STS) risk score.

Results:

For the derivation cohort, average age was 67.2 ± 11.1 years, and 22.8% were female. In the derivation cohort, there were 10 deaths and 93 patients with major morbidity, as characterized by the STS outcomes. The STS score predicted 194 patients who were low risk (0%-10%), 308 intermediate risk (10%-25%), and 164 high risk (>25%). Multivariable predictors of in-hospital mortality or major morbidity were a restrictive mitral filling pattern (odds ratio [OR], 2.96; p = 0.001), RV fractional area change (FAC) <35% (OR, 3.03; p = 0.01), RV myocardial performance index (MPI) >0.4 (OR, 1.89; p = 0.02), and mitral regurgitation ≥ moderate (OR, 1.96; p = 0.07). For all-cause mortality at 3.2 years, only RV FAC (OR, 2.02; p = 0.07) and PASP ≥50 mm Hg (OR, 3.54; p < 0.001) were predictive. The area under the curve for the STS score was 0.68, which increased to 0.73 with the addition of the echocardiographic parameters. LVEF was a univariate predictor of events (OR, 5.2; p < 0.001), but was no longer significant when diastolic dysfunction and RV function were entered into the variable model. RV FAC and MPI provided complementary information in that 5% of patients with RV hypokinesis and abnormal RV FAC had 50% mortality or major morbidity, and RV MPI identified 24% with subclinical RV impairment with a 26% event rate. In the validation cohort, there were 33 (17.6%) with postoperative mortality or major morbidity. Restricted LV filling (OR, 4.73), abnormal RV MPI (OR, 2.54), and mitral regurgitation (OR, 1.65) were the optimal predictors of events.

Conclusions:

Preoperative TTE provides prognostic information in patients undergoing isolated CABG, with evidence of RV dysfunction and significant LV diastolic dysfunction having independent prognostic value for identifying patients at higher risk for mortality or major morbidity.

Perspective:

This study provides valuable information regarding echocardiographic prediction of events in patients undergoing CABG, and also provides insight to the mechanism of adverse events. Traditionally, LV systolic function has been considered the major contributor to perioperative events, and has been demonstrated to be of prognostic relevance in noncardiac surgery. This study suggests that systolic dysfunction, after accounting for RV function, is no longer prognostically relevent. The authors propose several reasons for this, including the better ability of the left ventricle to withstand the ‘insults’ of CABG and the fact that LV revascularization at the time of CABG may improve LV systolic function, and thus, mitigating at least its adverse impact in the postoperative period. Conversely, the right ventricle is more subject to intraoperative depression of performance, and as such, in patients with pre-existing RV dysfunction, the added effects of CABG-related decreases in function may tip the balance, leading to substantially worse outcomes. Whether pharmacological or surgical technique can mitigate against adverse sequelae in these high-risk patients identified by TTE would need to be the subject of further investigation.

Clinical Topics: Cardiac Surgery, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Valvular Heart Disease, Cardiac Surgery and Heart Failure, Cardiac Surgery and VHD, Interventions and Structural Heart Disease, Mitral Regurgitation

Keywords: Ventricular Function, Right, Hospital Mortality, Tricuspid Valve Insufficiency, Mitral Valve Insufficiency, Stroke Volume, Blood Pressure, Diastole, Coronary Artery Bypass, Pulmonary Artery, Heart Ventricles, Ventricular Dysfunction, Right


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