Abstract:On LV (left ventricle) to aorta pull back, aortic pressure rises due to relief of the enhanced obstruction of the aortic orifice which had occurred while entering the LV in severe aortic stenosis. This is known as Carabello sign / effect.
Blase A. Carabello and colleagues described the Carabello effect as the change in arterial pressure when the catheter is pulled back from the left ventricle to aorta in severe aortic stenosis . When the catheter tip is in the left ventricle in severe aortic stenosis, usually with valve area less than half a square centimeter, the catheter itself enhances the obstruction across the aortic valve. This leads to a fall in the aortic pressure measured by another catheter. A simplified method is to connect the sidearm of the femoral arterial sheath to a pressure transducer. But if the catheter and sheath are of same size, the pressure tracing would be damped. For a good femoral pressure tracing the sheath should be at least one French size larger than the catheter. When the catheter is pulled out from the left ventricle, the aortic pressure (or femoral arterial pressure if the side arm pressure is being monitored) rises due to relief of the further worsening in critical aortic stenosis which was caused by the catheter across the aortic valve. This phenomenon which occurs in critical aortic stenosis has been called the Carabello sign or effect.
Carabello himself has opined in a recent editorial in Circulation  that this effect is seldom observed these days. He attributes it to the change in pattern of aortic stenosis. Forty years ago, when the sign was described, aortic stenosis was more often rheumatic or congenital in etiology. Doppler echocardiography was not available then and severe aortic stenosis used to be documented only at cardiac catheterization. Now the most common etiology is atherosclerotic aortic stenosis, occurring at a later age group and the documentation is much earlier at lesser grades of severity due to widespread use of Doppler echocardiography. Hence even if most cases of severe aortic stenosis are catheterized with entry of catheter into the left ventricle (seldom done) in the current era, Carabello sign is less likely to be observed because most severe aortic stenosis would undergo definitive treatment before they become so critical as to produce the Carabello sign. In the original report by Carabello, this effect was noted in seventy five percent of those with aortic valve area of 0.6 square centimeters. A rise in pressure of 5 mm Hg was considered as a positive Carabello sign. The sign was absent in those with aortic valve area of 0.7 square centimeters.