A method for the measurement of left ventricular overload for aortic valve insufficiency.

BACKGROUND: The degree of left ventricular overload in patients with aortic valve insufficiency (AI) plays an important role in determining the need and timing of surgical intervention. Because hemodynamic evaluation of AI may potentially predict the effects of an insufficient valve on the ventricle before they occur, it would be useful to guide valve surgery with such a diagnostic tool. The purpose of this study was to test the performance of a new hemodynamic index based on mechanical energy loss for the measurement of the effects of insufficiency on ventricular workload. METHODS AND RESULTS: An intact and subsequently perforated aortic bioprosthesis was tested within an in vitro model of the left heart, varying cardiac output, diastolic aortic pressure, and the size of perforation. Regurgitant orifice area (ROA), regurgitant volume (RV), regurgitant fraction (RF), and energy loss index (ELI) were measured for each experimental condition and plotted against the increase in workload per unit volume net forward flow (DeltaWPV) due to perforation. ROA, RV, and RF showed good correlations with DeltaWPV, but the relationship between these variables and DeltaWPV became ambiguous as their magnitudes increased. ELI had a near perfect linear relationship with DeltaWPV (slope=1.00, r(2)=0.98) independent of the experimental condition. CONCLUSIONS: RV, RF, and ROA do not by themselves fully describe the increase in difficulty the ventricle has in moving the blood across an insufficient valve. ELI, in contrast, was found to be a very good measure of the decrease in pump efficiency due to aortic valve insufficiency.

A method for the measurement of left ventricular overload for combined aortic valve pathology.

BACKGROUND AND AIM OF THE STUDY: Patients with combined aortic valve pathology (stenosis and insufficiency) are often evaluated as if they had only a single pathology, because a means of evaluating the detrimental effects of combined insufficiency and stenosis does not yet exist. The study aim was to test the performance of a new hemodynamic index based on mechanical energy loss to measure the effects of combined valve disease on ventricular workload. METHODS: An intact and subsequently perforated and sutured aortic bioprosthesis was tested in an in vitro model of the left heart, varying cardiac output, average diastolic aortic pressure, and the type and combination of valve lesion. The regurgitant fraction (RF), systolic transvalvular pressure gradient (Deltaps), and energy loss indices of forward flow (LPVf), regurgitant flow (LPVr), and the sum of the two (LPVc), were measured for each experimental condition and compared with the increase in work per unit volume net forward flow (DeltaWPV) due to perforation and suturing. RESULTS: Deltaps was found to underestimate LPVf when the valve was perforated. LPVc had an excellent linear relationship with DeltaWPV (slope = 0.98, r2 = 0.97) that was independent of valve lesion or flow and pressure conditions. CONCLUSION: Deltaps does not describe the increase in ventricular workload, or even the forward flow portion of it, when valve insufficiency is present. LPVc was found to be a very good measure of the decrease in pump effectiveness due to aortic valve insufficiency or combined valve pathology.

Aortic root dilatation may alter the dimensions of the valve leaflets.

OBJECTIVE: Valve-sparing surgery can be used in patients with dilated aortic roots and aortic insufficiency (AI) but has not become a common practice, in part because the spared valve may be incompetent. Our goal was to study how the dimensions of the aortic root and leaflets have changed in such patients. METHODS: Fourteen patients with dilated aortic root and AI were examined by transesophageal echocardiography. The annulus diameter, sinotubular junction (STJ) diameter, sinus height, leaflet free-edge length, and leaflet height were measured. Correlations among these dimensions and with the AI grades were explored. Measurements were also made in 19 normal human aortic valves from silicone molds. RESULTS: There was no evident change in the average diameter of the annulus between the normal valves and those in the dilated aortic roots. The STJ diameter was obviously increased in the dilated aortic roots; the aortic sinuses also appeared to be taller and the leaflets larger than normal. The leaflet free-edge length, the leaflet height, and the sinus height were found to increase with the dilated STJ diameter. The degree of AI was not found to correlate well with any of the dimensions measured. CONCLUSIONS: The dimensions of the leaflets may change parallel to aortic root dilatation with AI. Therefore, during valve sparing, it may be necessary to correct both the dilatation of the root and the leaflet free-edge length to achieve a competent valve.

Does post-stenotic dilatation enhance collateral flow?

Our goal was to investigate whether post-stenotic dilatation (PSD) enhances collateral blood flow. In vitro experiments and computer modeling analysis were used to study the flow through stenotic segments and through collateral channels in the presence and absence of PSD. Pulsatile blood flow was provided by a left heart simulator primed with glycerol or normal saline. Pressure gradients across the stenosis were measured at different "cardiac" outputs. Computer models were constructed to simulate the experiments. Flow patterns and pressure drop across the stenosis were determined for a steady flow of 3 L/min. We observed that PSD was associated with a larger pressure drop across the stenosis than the absence of PSD when the flow was occurring through the stenosis only. There was, however, no difference in the pressure drop between the two geometries when the flow was occurring through both the stenotic orifice and the collateral channels when saline solution was used, but a small pressure difference prevailed for glycerol. At all different geometries there was considerable turbulence at PSD, and PSD geometry was found to be either at a disadvantage or at no advantage when compared to the tapered geometry for the total flow past the stenosis. The PSD geometry, however, enhanced the flow through the collateral while the flow through the orifice decreased concomitantly, resulting in no net increase in the total flow. This was true for any proportion of the total flow going through the collateral channels. For the total flow past the stenosis, PSD does not offer a benefit over tapered geometry.