Evaluation of the significance of a transvalvular catheter on aortic valve gradient in aortic stenosis: a direct hemodynamic and Doppler echocardiographic study

Phasic pressure measurements for coronary and valvular interventions using fluid-filled catheters: Errors, automated correction, and clinical implications

Objectives

We sought to develop an automatic method for correcting common errors in phasic pressure tracings for physiology‐guided interventions on coronary and valvular stenosis.

Background

Effective coronary and valvular interventions rely on accurate hemodynamic assessment. Phasic (subcycle) indexes remain intrinsic to valvular stenosis and are emerging for coronary stenosis. Errors, corrections, and clinical implications of fluid‐filled catheter phasic pressure assessments have not been assessed in the current era of ubiquitous, high‐fidelity pressure wire sensors.

Methods

We recruited patients undergoing invasive coronary physiology assessment. Phasic aortic pressure signals were recorded simultaneously using a fluid‐filled guide catheter and 0.014″ pressure wire before and after standard calibration as well as after pullback. We included additional subjects undergoing hemodynamic assessment before and after transcatheter aortic valve implantation. Using the pressure wire as reference standard, we developed an automatic algorithm to match phasic pressures.

Results

Removing pressure offset and temporal shift produced the largest improvements in root mean square (RMS) error between catheter and pressure wire signals. However, further optimization <1 mmHg RMS error was possible by accounting for differential gain and the oscillatory behavior of the fluid‐filled guide. The impact of correction was larger for subcycle (like systole or diastole) versus whole‐cycle metrics, indicating a key role for valvular stenosis and emerging coronary pressure ratios.

Conclusions

When calibrating phasic aortic pressure signals using a pressure wire, correction requires these parameters: offset, timing, gain, and oscillations (frequency and damping factor). Automatically eliminating common errors may improve some clinical decisions regarding physiology‐based intervention.

Pressure gradient vs. flow relationships to characterize the physiology of a severely stenotic aortic valve before and after transcatheter valve implantation

Aims

Echocardiography and tomographic imaging have documented dynamic changes in aortic stenosis (AS) geometry and severity during both the cardiac cycle and stress-induced increases in cardiac output. However, corresponding pressure gradient vs. flow relationships have not been described.

Methods and results

We recruited 16 routine transcatheter aortic valve implantations (TAVI’s) for graded dobutamine infusions both before and after implantation; 0.014″ pressure wires in the aorta and left ventricle (LV) continuously measured the transvalvular pressure gradient (ΔP) while a pulmonary artery catheter regularly assessed cardiac output by thermodilution. Before TAVI, ΔP did not display a consistent relationship with transvalvular flow (Q). Neither linear resistor (median R² 0.16) nor quadratic orifice (median R² < 0.01) models at rest predicted stress observations; the severely stenotic valve behaved like a combination. The unitless ratio of aortic to left ventricular pressures during systolic ejection under stress conditions correlated best with post-TAVI flow improvement. After TAVI, a highly linear relationship (median R² 0.96) indicated a valid valve resistance.

Conclusion

Pressure loss vs. flow curves offer a fundamental fluid dynamic synthesis for describing aortic valve pathophysiology. Severe AS does not consistently behave like an orifice (as suggested by Gorlin) or a resistor, whereas TAVI devices behave like a pure resistor. During peak dobutamine, the ratio of aortic to left ventricular pressures during systolic ejection provides a ‘fractional flow reserve’ of the aortic valve that closely approximates the complex, changing fluid dynamics. Because resting assessment cannot reliably predict stress haemodynamics, ‘valvular fractional flow’ warrants study to explain exertional symptoms in patients with only moderate AS at rest.

Supra-annular structure assessment for self-expanding transcatheter heart valve size selection in patients with bicuspid aortic valve

Objectives

To explore assessment of supra‐annular structure for self‐expanding transcatheter heart valve (THV) size selection in patients with bicuspid aortic stenosis (AS).

Background

Annulus‐based device selection from CT measurement is the standard sizing strategy for tricuspid aortic valve before transcatheter aortic valve replacement (TAVR). Because of supra‐annular deformity, device selection for bicuspid AS has not been systemically studied.

Methods

Twelve patients with bicuspid AS who underwent TAVR with self‐expanding THVs were included in this study. To assess supra‐annular structure, sequential balloon aortic valvuloplasty was performed in every 2 mm increments until waist sign occurred with less than mild regurgitation. Procedural results and 30 day follow‐up outcomes were analyzed.

Results

Seven patients (58.3%) with 18 mm; three patients (25%) with sequential 18 mm, 20 mm; and only two patients (16.7%) with sequential 18 mm, 20 mm, and 22 mm balloon sizing were performed, respectively. According to the results of supra‐annular assessment, a smaller device size (91.7%) was selected in all but one patient compared with annulus based sizing strategy, and the outcomes were satisfactory with 100% procedural success. No mortality and 1 minor stroke were observed at 30 d follow‐up. The percentage of NYHA III/IV decreased from 83.3% (9/12) to 16.7% (2/12). No new permanent pacemaker implantation and no moderate or severe paravalvular leakage were found.

Conclusions

A supra‐annular structure based sizing strategy is feasible for TAVR in patients with bicuspid AS.

Discrepancies between direct catheter and echocardiography-based values in aortic stenosis

OBJECTIVES

The goal of this article is to examine the correlation of catheter (cath) based and echocardiographic assessment of aortic stenosis (AS) in a community-based academic hospital setting, particularly in the degree that decision to refer for surgery is altered.

BACKGROUND

Current guidelines discourage AS evaluation by invasive pressure measurement if echocardiography (echo) is adequate, but several studies show sizable differences between echo and cardiac catheterization lab (CCL) measurements. We examine this correlation using high quality CCL techniques.

METHODS

Sequential patients with suspected AS by echo (n = 40) aged 61-94 underwent catheterization with pressure gradients via left ventricular pressure wire and ascending aorta catheter. The echos leading to the catheterization were independently reviewed by an expert panel to assess the quality of community-based readings.

RESULTS

CCL changed assessment of severity of aortic valve area (AVA) by more than 0.3 cm(2) in 25% and 0.5 cm(2) in 8%. Values changed to over or under the surgical threshold of AVA < 1 cm(2) in 30% of the patients. Pearson correlation of 0.35 between measurements of AVA by echo and CCL is lower than earlier studies, which often reported correlation values of 0.90 or greater. Echo expert reviews provided minimal improvement in discrepancies (Pearson correlation of 0.46), suggesting quality of initial interpretation was not the issue.

CONCLUSIONS

Cath-echo correlation of AS severity is lower in contemporaneous practice than previously assumed. This can alter the decision for aortic valve replacement. Sole reliance on echo-derived assessment of AS may at times be problematic.

Comparison of Invasive and Noninvasive Assessment of Aortic Stenosis Severity in the Elderly

Background—

Aortic valve area (AVA) in aortic stenosis (AS) can be assessed noninvasively or invasively, typically with similar results. These techniques have not been validated in elderly patients, where common assumptions make them most prone to error. Accurate assessment of AVA is crucial to determine which patients are appropriate candidates for aortic valve replacement.

Methods and Results—

Fifty elderly patients (mean 86 years, 46% female) referred for cardiac catheterization to evaluate AS also underwent transthoracic echocardiography within 24 hours. To minimize assumptions all patients had 3-dimensional echocardiography (Echo-3D), and at catheterization using directly measured oxygen consumption (Cath-mVo 2 ) and thermodilution cardiac output (Cath-TD). Correlation between Cath-mVo 2 and Echo-3D AVA was poor ( r =0.41). Cath-TD AVA had a moderate correlation with Echo-3D AVA ( r =0.59). Cath-mVo 2 (AVA=0.69 cm 2 ) and Cath-TD (AVA=0.66 cm 2 ) underestimated AVA compared with Echo-3D (AVA=0.76 cm 2; P =0.08 for comparison with Cath-mVo 2 ; P =0.001 for Cath-TD). Compared with Echo-3D, the sensitivity and specificity for determining critical disease (AVA <0.8 cm 2 ) were 81% and 42% for Cath-mVo 2 , and 97% and 53% for Cath-TD. The only independent predictor of the difference between noninvasive and invasive AVA was stroke volume index ( P <0.01). Resistance, a less flow-dependent measure, showed a stronger correlation between Echo-3D and Cath-mVo 2 ( r =0.69), and Echo-3D and Cath-TD ( r =0.77).

Conclusions—

Standard techniques of AVA assessment for AS show poor correlation in elderly patients, with frequent misclassification of critical AS. Less flow-dependent measures, such as resistance, should be considered to ensure that only appropriate patients are treated with aortic valve replacement.

Imaging spectrum of sudden athlete cardiac death

Sudden athlete death (SAD) is a widely publicized and increasingly reported phenomenon. For many, the athlete population epitomize human physical endeavour and achievement and their unexpected death comes with a significant emotional impact on the public. Sudden deaths within this group are often without prior warning. Preceding symptoms of exertional syncope and chest pain do, however, occur and warrant investigation. Similarly, a positive family history of sudden death in a young person or a known family history of a condition associated with SAD necessitates further tests. Screening programmes aimed at detecting those at risk individuals also exist with the aim of reducing fatalities. In this paper we review the topic of SAD and discuss the epidemiology, aetiology, and clinical presentations. We then proceed to discuss each underlying cause, in turn discussing the pathophysiology of each condition. This is followed by a discussion of useful imaging methods with an emphasis on cardiac magnetic resonance and cardiac computed tomography and how these address the various issues raised by the pathophysiology of each entity. We conclude by proposing imaging algorithms for the investigation of patients considered at risk for these conditions and discuss the various issues raised in screening.

Adult Echocardiography and Doppler

One of the first reports of cardiac ultrasound imaging occurred in 1954 by Elder and Hertz. They described the use of ultrasound imaging for displaying continuous recording of movement of heart walls. This was displayed by the use of A-mode and B-mode methods. In the late 1950s, continuous-wave Doppler was used in cardiac imaging. By the late 1960s, two-dimensional real-time B-mode imaging was performed using mechanical head transducers. In the mid-1970s, phased array transducers were being utilized. Also in the late 1970s, transesophageal echo was being tested. The 1980s have seen advances in computer technology that have made color flow Doppler imaging possible, along with better image quality through scan conversion and image processing. In the 1990s developing techniques included stress echocardiography, intravascular ultrasound, contrast echocardiography, digital acquisition, second harmonic imaging, ultrasonic tissue characterization, and three-dimensional echocardiography. More recently, echocardiography has seen advances in real-time 3D imaging, handheld echocardiography, and myocardial perfusion. Advances in technology, along with improved understanding of the equipment, have made the availability and demand of echocardiography invaluable.

Jet eccentricity: a misleading source of agreement between Doppler/catheter pressure gradients in aortic stenosis

Characterization of the severity of aortic stenosis relies on accurate measurement of the pressure gradient across the valve and the valve area. Pressure gradients measured by Doppler ultrasound based on the clinical form of the Bernoulli equation often overestimate pressure gradients by catheter as the result of pressure recovery. Doppler techniques measure the velocity of the vena contracta of the stenotic jet. This corresponds to the maximal pressure gradient and the minimal effective valve area. Pressure recovery can be characterized by analysis of the spread of the stenotic jet downstream of the valve as it fills the aorta and should be influenced by the shape of the velocity profile of the decaying jet. In this study, we addressed the hypothesis that the site of complete pressure recovery (the point at which the jet fully expands to the size of the aorta), the effective valve area, and the maximal pressure gradient are affected by jet eccentricity. To accomplish this, we developed a computational model of aortic stenosis that provides detailed velocity and pressure information in the vicinity of the valve. The results show that the width of the eccentric wall jet decreased and maximal velocity increased with greater jet eccentricity. Furthermore, for a constant anatomic area, the effective valve area decreased, the distance to complete pressure recovery increased, and the maximal pressure gradient increased with the degree of eccentricity. Failure to take this into account could fortuitously drive Doppler and catheter measurements toward agreement because the distal pressure sensor will not record the fully recovered pressure. Therefore the pressure gradient across a stenotic valve depends on jet eccentricity. The spread of the wall jet after attachment must be characterized to develop a robust method for the prediction of pressure recovery.

Accuracy of computer-based quantification of aortic valve stenosis

In patients with aortic valve stenosis, the quantification of stenosis is usually performed using fluid-filled catheters and a computerized calculation program. The aim of this study was to determine the accuracy of this technique in comparison to the manual planimetry of the area between the curves of a simultaneous registration, using a multitip micromanometer catheter. The study was performed in 19 patients, in whom left and right heart catheterization was warranted. Systolic left ventricular and aortic peak pressures were significantly overestimated using a fluid-filled catheter (206 +/- 35 vs. 199 +/- 37 mm Hg, P = 0.0003, and 148 +/- 18 vs. 143 +/- 21 mm Hg, P = 0.0052). However, peak-to-peak pressure gradients were identical comparing both techniques (58 +/- 31 vs. 56 +/- 32 mm Hg, r = 0.983). The mean pressure gradients and aortic valve areas based on simultaneous measurements of left ventricular and aortic pressures by micromanometer catheters were identical to the values determined by a computer-based program using fluid-filled catheters (54 +/- 21 vs. 52 +/- 21 mm Hg, r = 0.923, P < 0.05, and 0.75 +/- 0.25 vs. 0.77 +/- 0.25 cm2, r = 0.935). Thus, the conventional use of fluid-filled catheters and of a computerized calculation of aortic valve area is valid for quantification of aortic stenosis in patients with sinus rhythm and without significant aortic regurgitation.