Cardiac Eval: AV disease
Generic Clinical Sciences
Preoperative cardiac evaluation of valvular disease helps identify the severity of the valvular defect, the hemodynamic changes from the valvular lesion, and changes in the pulmonary, renal, and hepatic systems as a result from the aberrant valve. Symptoms of decreased ventricular function should be obtained pre-operatively, and then stratified by the New York Heart Association classification. Symptoms include: exercise intolerance, lower extremity edema, dyspnea, orthopnea (SOB when lying flat), and paroxysmal nocturnal dyspnea (awakening at night SOB). Symptoms at rest= Class IV, symptoms with minimal activity= Class III, symptoms with moderate activity= Class II, no symptoms except with maximal exertion= Class I.
After thorough history taking, a physical exam is performed to look for signs of congestive heart failure (i.e. pedal edema, jugular venous distension, rales) or the presence of a heart murmur. Electrocardiography is generally not helpful in detecting a valvular lesion. Chest X-ray may reveal evidence for pulmonary vascular congestion or show an enlarged heart. Echocardiography remains the gold standard for detection and evaluation of valvular disease.
Aortic valve disease causes a pressure overload situation (aortic stenosis) or a volume overload situation (aortic regurgitation). Aortic stenosis is the most common cause of obstruction to left ventricular outflow, and necessitates increased left ventricular pressures to maintain forward flow. Critical aortic stenosis occurs when the valve opening is 0.5-0.7cm2, an area that correlates with an inability for the heart to increase the cardiac output in response to exertion. Aortic regurgitation causes a left ventricular volume overload because a portion of the forward flow regurgitates through the valve back into the left ventricle, effectively reducing the stroke volume of each contraction. Chronically, the left ventricle dilates but sudden development causes pulmonary venous congestion and pulmonary edema. The intra-operative management of aortic valve disease depends on the type of lesion present, punctuating the importance of pre-operative evaluation with history taking, physical exam, and echocardiography to differentiate the types of lesions.