Stenotic Valve Formulas — How Accurate Are Computerized-Assisted Calculations? Introduction of the Embil Stenotic Valve Formula©

Objective. To introduce to the invasive and interventional cardiology community a novel formula for simplistic calculations of the orifice areas of stenotic semilunar and cuspid valves. 

In 1986, William Embil was completing calculations on a stenotic valve case. He noticed a correlation between the anacrotic notch and the diacrotic notch of the aortic pressure that was simultaneously recorded with the left ventricular pressure. Embil measured the distance between the two notches (which hemodynamically indicate the opening and closing of the aortic valve). Then he measured the width of the QRS segment of the electrocardiogram that was recorded simultaneously. He derived the quotient between the QRS measurement and the “notch” measurements. He had determined that the aortic and pulmonic waveforms produced the same “notch” phenomenon. 

With mitral valve disease, Embil measured the distance from the peaks of the “a” wave to the “v” wave on the pulmonary wedge pressure tracing. Then he measured the width of the “p” wave on the ECG cycle that was a simultaneous recording with the pulmonary wedge pressure against the left ventricular end diastolic pressure (LVEDP). With the data on the diseased bicuspid valve, he derived another quotient between the “p” wave width and the “a-v” wave width. 

Between 1986 and 2003, he tracked data on patients who had undergone right and left cardiac catheterizations for aortic valve stenosis, pulmonic stenosis, and mitral stenosis. He recorded measurements on 135 patients with stenosis of these three cardiac valves. Embil asked Dr. Hooshang Bolooki, an attending cardiothoracic surgeon, to measure the orifices of the valves of these symptomatic patients prior to valve replacement in a surgical setting. The values that Dr. Bolooki obtained correlated with a 1:1 ratio to Embil’s calculations. 

Embil realized that placing a catheter across a stenotic aortic valve was no longer necessary since the aortic pressure, if recorded above the aortic valve, could be used to calculate the area of the valve with greater accuracy than the Gorlin formula, which has been the gold standard since the early 50’s. This meant that the data that was needed to calculate valve areas with the Gorlin formula was no longer needed information: oxygen consumption, oxygen saturations, a hemoglobin value, arterial carrying capacity, and arterial and mixed venous oxygen content.

In recording the pressures, we must note that the standard use of disposable transducers produces innate moderate dampening of the waveforms compared to the previously used reusable transducers when sterile domes were changed between patients. Since the introduction of disposable transducers, the crispness of the waveforms has been lost due to the use of the disposable transducers that contain small transducer faces (versus the larger faces used in the larger research transducers), along with the use of smaller inner diameter pressure tubing that varies in length due to lack of standardization of basic instrumentation. These factors, among others, contribute to the loss of valuable data. 

Thousands of patients with aortic and mitral valve stenosis may have been medically treated for long periods before their conditions were declared critical, when areas of their aortic or mitral valves were calculated to be at 1.0 cm² or less. These plans for continuity of care gradually lead to other cardiac events such as congestive heart failure caused by right and left cardiac failure related to elevated right and left heart pressures. With the Embil Stenotic Valve Formula, patients with aortic valve stenosis could be treated with surgical valve replacement or with percutaneous aortic valve replacement before further impairment of the critical organ occurs, potentially removing years of palliative therapy for trisucpid, pulmonic, and mitral valve stenosis.