In vitro study of the pressure-velocity relation across stenotic orifices

Multimodality imaging derived energy loss index and outcome after transcatheter aortic valve replacement

Aims 

To assess whether the combination of transthoracic echocardiography (TTE) and multidetector computed tomography (MDCT) data affects the grading of aortic stenosis (AS) severity under consideration of the energy loss index (ELI) in patients undergoing transcatheter aortic valve replacement (TAVR).

Methods and results 

Multimodality imaging was performed in 197 patients with symptomatic severe AS undergoing TAVR at the University Hospital Zurich, Switzerland. Fusion aortic valve area index (fusion AVAi) assessed by integrating MDCT derived planimetric left ventricular outflow tract area into the continuity equation was significantly larger as compared to conventional AVAi (0.41 ± 0.1 vs. 0.51 ± 0.1 cm2/m2; P < 0.01). A total of 62 patients (31.4%) were reclassified from severe to moderate AS with fusion AVAi being >0.6 cm2/m2. ELI was obtained for conventional AVAi and fusion AVAi based on sinotubular junction area determined by TTE (ELILTL 0.47 ± 0.1 cm2/m2; fusion ELILTL 0.60 ± 0.1 cm2/m2) and MDCT (ELIMDCT 0.48 ± 0.1 cm2/m2; fusion ELIMDCT 0.61 ± 0.05 cm2/m2). When ELI was calculated with fusion AVAi the effective orifice area was >0.6 cm2/m2 in 85 patients (43.1%). Survival rate 3 years after TAVR was higher in patients reclassified to moderate AS according to multimodality imaging derived ELI (78.8% vs. 67%; P = 0.01).

Conclusion 

Multimodality imaging derived ELI reclassifies AS severity in 43% undergoing TAVR and predicts mid-term outcome.

Doppler-derived rate of left ventricular pressure rise. Its correlation with the postoperative left ventricular function in mitral regurgitation

A new Doppler-derived index of the rate of left ventricular (LV) pressure rise (delta P/delta t) was evaluated for the prognostic stratification of patients with chronic mitral regurgitation. The index is derived from the continuous wave Doppler mitral regurgitation signal by dividing magnitude of LV-left atrial pressure gradient rise (delta p) between 1 and 3 m/sec of the mitral regurgitation velocity signal by the time taken (delta t) for this change. We studied the LV delta P/delta t and other echocardiographic indexes of LV function before and after mitral valve surgery in 25 patients with chronic, severe mitral regurgitation in the absence of significant coronary artery disease. There was a good correlation between postoperative ejection fraction (EF) and the derived LV delta P/delta t (r = 0.75, p less than 0.001). The other echocardiographic parameters that correlated with postoperative EF were LV end-systolic dimension (r = -0.7, p less than 0.001), end-systolic volume (r = -0.69, p less than 0.001), end-diastolic dimension (r = -0.58, p less than 0.01), end-diastolic volume (r = -0.57, p less than 0.01), preoperative EF (r = 0.69, p less than 0.001), end-systolic wall stress (r = -0.61, p less than 0.01), and end-systolic wall stress normalized for end-systolic volume index (r = -0.45, p less than 0.05). With multiple regression, the LV delta P/delta t and LV end-systolic dimension (ESD) were shown to be independent predictors of postoperative EF. The postoperative EF could defined by the equation: 43 + 0.8 square root delta P/delta t--0.53 ESD (mm) (r = 0.86).(ABSTRACT TRUNCATED AT 250 WORDS)

Lessons from in vitro models of small, irregular, multiple and tunnel-like stenoses relevant to clinical stenoses of valves and small vessels

This review examines data on the accuracy of the simplified Bernoulli equation for quantitation of pressure drops across small, irregular, multiple and tunnel-like stenoses. This information is drawn from in vitro models of such cardiovascular stenoses and explores the limits of this simplification as they affect accuracy in special situations. Within the physiologic range, discrete small and irregular stenoses present no problems for the measurement of pressure drops using the simplified Bernoulli equation. Multiple side by side orifices of different dimension also give reasonable data using this approach. Tunnel-like stenoses of very small diameter and finite length produce underestimation of the true pressure drop through the stenosis when the simplified Bernouli equation is used. This underestimation is primarily due to neglect of the energy consumed by viscous friction in this situation. These considerations are especially pertinent to the problem of measuring pressure gradients across coronary vessels to assess their clinical significance as well as the adequacy of angioplasty and other intravascular interventional techniques. Because this area needs further exploration, some discussion of in vitro models as such as included.

Quantitative applications of Doppler cardiography in congenital heart disease

Doppler ultrasound has rapidly become a valuable tool in the noninvasive investigation of cardiac hemodynamics. Although based on secure principles, accurate application of this methodology to quantitative measurements necessitates a thorough understanding of both Doppler physics and instrumentation. Over the past several years a large body of clinical and animal data verifying the accuracy of Doppler determination of pressure and flow data at various sites in the cardiovascular system, as well as the potential sources of error in acquisition and interpretation of blood velocity recordings, has been published. Quantitative use of Doppler in congenital heart disease, with emphasis on limitations of existing studies and issues particular to this patient population, is reviewed.

Determination of right ventricular pressure in the presence of a ventricular septal defect using continuous wave Doppler ultrasound

Continuous wave Doppler ultrasound was employed in 38 patients with ventricular septal defects, many with associated lesions, to measure the velocity (V) of the shunted blood. Using the modified Bernoulli equation (delta P = 4V2) the pressure difference (delta P) between the ventricles was determined. In 22 patients both right ventricular and either left ventricular or ascending aortic pressure were measured at the time shunt velocity was determined. In another 16 patients these measurements were not obtained simultaneously but in most they were done within 24 hours of each other. In the entire group, measured pressure differences between the ventricles (or aorta and right ventricle) ranged from 0 to 97 mm Hg (mean 52 +/- 24). On the basis of velocity measurements the pressure difference ranged from 7 to 112 mm Hg (mean 51 +/- 24). A close correlation was found between the two methods (r = 0.95, SEE = 7.8 mm Hg). This accuracy was not altered by associated lesions. These findings indicate that by the use of continuous wave Doppler interrogation right ventricular pressure can be accurately measured in the presence of a ventricular septal defect.