Patient Population

A total of 116 patients with severe symptomatic aortic stenosis (aortic valve area [AVA] < 1.0 cm ² or transaortic mean pressure gradient ≥ 40 mm Hg) who underwent TAVI at two centers (84 patients at Leiden University Medical Center, Leiden, The Netherlands; 32 patients at the Québec Heart and Lung Institute, Department of Medicine, Laval University, Québec, Canada) were included in the present study. Patients who underwent transcatheter valve-in-valve procedures or in whom baseline Z _va could not be derived were excluded. On the basis of evaluation by a multidisciplinary team, patients were considered for TAVI because of high predicted operative risk or contraindications to conventional surgical aortic valve replacement. According to institutional protocols, patients underwent comprehensive clinical and echocardiographic evaluation before TAVI. In addition, invasive coronary angiography was performed to rule out significant coronary artery disease amenable to percutaneous intervention.

Clinical and echocardiographic data were retrospectively analyzed. Clinical parameters included demographics, cardiovascular risk factors, clinical symptoms, medications, and operative mortality risk calculated according to the logistic European System for Cardiac Operative Risk Evaluation. Noninvasive parameters of aortic stenosis severity and vascular resistance, including Z _va and systemic arterial compliance, were measured, and the changes in these parameters at short-term and midterm follow-up after TAVI were evaluated. In addition, the independent associations of these parameters with TAVI outcomes were investigated.

Echocardiography

Transthoracic echocardiography was performed at baseline with commercially available ultrasound systems (Vivid 7 and E9, GE Vingmed Ultrasound AS, Horten, Norway; iE33, Phillips Medical Systems, Best, The Netherlands). Aortic valve anatomy (bicuspid or tricuspid) was evaluated in the parasternal short-axis view. Aortic jet velocity was evaluated in multiple acoustic windows, adjusting gain, wall filter, baseline, and scale of continuous-wave Doppler recordings to optimize the signal. LV outflow tract velocity was measured in the apical long-axis or five-chamber view from the pulsed-wave Doppler spectral signal. AVA was calculated using the continuity equation. Severe aortic stenosis was considered present when AVA was <1.0 cm ² and/or the transaortic mean gradient was ≥40 mm Hg. LV end-diastolic volume and end-systolic volume were measured using the biplane Simpson’s method, and these measures were used to calculate the LV ejection fraction (LVEF). Standard LV linear dimensions and LV mass were also measured according to current recommendations. Finally, LV stroke volume was measured in the LV outflow tract from the pulsed-wave Doppler recordings and indexed to body surface area (stroke volume index [SVi]).

Measurement of Systemic Arterial Compliance, Z _va , and Systemic Vascular Resistance

Systemic arterial compliance was calculated as the ratio of LV SVi to pulse pressure, as previously described. Systemic arterial pressure was measured using an arm-cuff sphygmomanometer at the time of echocardiography, and pulse pressure was calculated from the difference between systolic and diastolic arterial pressures. In addition, global LV hemodynamic load was estimated using Z _va calculated as (systolic arterial pressure + transaortic mean gradient)/SVi. On the basis of previous studies, LV global load was considered to be severely increased when Z _va was ≥5 mm Hg/mL/m ² . Moreover, systemic vascular resistance was calculated as (80 × mean arterial pressure)/cardiac output.

TAVI Procedure

In the catheterization laboratory or hybrid operating room, an Edwards SAPIEN prosthetic valve (Edwards Lifesciences, Irvine, CA) of either 23 or 26 mm in size was implanted under general anesthesia. Prosthesis size selection was based on the dimensions of the aortic valve annulus as assessed using transesophageal echocardiography or multidetector row computed tomography, if available. Either a transapical or a transfemoral approach was used, on the basis of the peripheral artery anatomy as assessed using imaging of the iliofemoral arteries and aorta. The technique included rapid ventricular pacing during balloon dilatation of the native aortic valve and deployment of the balloon-expandable prosthetic valve. Transesophageal echocardiography complemented fluoroscopy for better guidance of the procedure. Procedural success was defined as the successful implantation of a functioning aortic prosthesis without intraprocedural mortality.

Follow-Up

Clinical and echocardiographic follow-up was scheduled at 1 and 12 months after TAVI. Clinical evaluation included New York Heart Association functional class, and complete transthoracic echocardiography was performed to assess prosthetic valve hemodynamics, LV dimensions and function, Z _va , systemic arterial compliance, and systemic vascular resistance. Paravalvular aortic regurgitation was evaluated at 1-month follow-up and was graded none or trivial (0 or 1), mild (2+), moderate (3+), or severe (4+), according to recommendations. In addition, all-cause mortality was recorded during follow-up.

Statistical Analysis

Statistical analyses were performed using SPSS version 17 (SPSS, Inc., Chicago, IL) and Stata version 11 (StataCorp LP, College Station, TX). Continuous variables are presented as mean ± SD if normally distributed, as determined by visual inspection of their histograms, or as medians and interquartile ranges otherwise. Categorical variables are presented as frequencies and percentages. Continuous variables were compared using unpaired Student’s t tests or Mann-Whitney tests as appropriate, whereas categorical variables were compared using χ ² tests or Fisher’s exact tests, as appropriate. Changes in continuous variables in the overall population from baseline to follow-up were analyzed using repeated-measures analysis of variance, and Bonferroni’s correction was used for post hoc analysis of significant results. In addition, patients were dichotomized according to a baseline value of Z _va ≥5 or <5 mm Hg/mL/m ² . One-way analysis of variance analysis for repeated measures was used to compare echocardiographic changes between groups. Cumulative event rates were calculated using the Kaplan-Meier method for patients with Z _va ≥ 5 mm Hg/mL/m ² and those with Z _va < 5 mm Hg/mL/m ² at baseline. The log-rank test for time-to-event data with respect to all-cause mortality was used for statistical comparison between two patient groups. Additionally, univariate and multivariate Cox proportional-hazards models were performed to identify independent determinants of all-cause mortality. Estimated hazard ratios and their 95% confidence intervals were obtained. Univariate variables with P values <.20 were included in the multivariate model. Two-sided P values <.05 were considered statistically significant.

Patient Characteristics

A total of 116 patients with severe symptomatic aortic stenosis (mean age, 81 ± 8 years; 49% men) were evaluated. All patients underwent successful TAVI using a transfemoral ( n = 48 [41%]) or transapical ( n = 68 [59%]) approach. Thirty-five patients (30%) received 23-mm valve prostheses, and 81 (70%) received 26-mm valves. Clinical and procedural characteristics are outlined in Table 1 .

Changes in Aortic Valve Hemodynamics and Global LV Load after TAVI

During the first postoperative month, seven patients (6%) died, and three additional patients died within the first postoperative year. Overall, 21 patients died during a median follow-up period of 25 months (interquartile range, 13–45 months), and no patients were lost to follow-up. Echocardiographic assessment was available in 109 patients at 1-month follow-up, and complete data (baseline and 1 and 12 months after TAVI) were available for 100 patients. Six patients had been followed for <12 months.

Table 2 summarizes the changes in aortic valve hemodynamics, LV dimensions and function, Z _va , systemic arterial compliance, and vascular resistance. As expected, AVA significantly increased (from 0.67 ± 0.17 to 1.86 ± 0.49 cm ² at 1-month follow-up, remaining stable at 12-month follow-up [1.81 ± 0.61 cm ² ], P < .001), and transaortic mean pressure gradient significantly decreased after TAVI (from 42 ± 15 mm Hg at baseline to 8 ± 3 and 9 ± 5 mm Hg at 1 and 12 months, respectively, P < .001). LVEF increased slightly from 54 ± 14% to 55 ± 13% at 1 month and to 56 ± 11% at 12 months ( P = .051). There was a significant reduction in Z _va (from 5.40 ± 1.52 to 4.13 ± 1.17 mm Hg/mL/m ² at 1-month follow-up, remaining stable at 12 months [4.35 ± 1.38 mm Hg/mL/m ² ], P < .001; Figure 1 ). In contrast, systemic arterial compliance did not change significantly (from 0.57 ± 0.27 to 0.57 ± 0.28 and 0.53 ± 0.27 mL/m ² /mm Hg, P = .408; Table 2 ). Similarly, systemic vascular resistance did not change over time (from 1,938 ± 669 to 1,856 ± 888 and 1,871 ± 767 dyne·s·cm ⁻⁵ , P = .697).

Mean values of global LV afterload ( Z _va ) at baseline and 1-month and 12-month follow-up.

In addition, the incidence of paravalvular aortic regurgitation was evaluated at 1-month follow-up. No or trivial paravalvular aortic regurgitation was observed in 82%, mild regurgitation in 17 (16%), and severe regurgitation in two (2%) patients.

Changes in Symptoms and Global LV Load after TAVI according to Baseline Z _va

At baseline, 68 patients (57%) had Z _va ≥ 5 mm Hg/mL/m ² . Table 3 outlines the differences in clinical and echocardiographic parameters between patients with baseline Z _va ≥ 5 mm Hg/mL/m ² and those with Z _va < 5 mm Hg/mL/m ² . Patients with baseline Z _va ≥ 5 mm Hg/mL/m ² had smaller AVA (0.65 ± 0.18 vs 0.73 ± 0.18 cm ² , P = .020), lower systemic arterial compliance (0.45 ± 0.15 vs 0.72 ± 0.29 mL/m ² /mm Hg, P < .001), smaller LV end-diastolic volume (105 ± 34 vs 133 ± 50 mL, P = .001), lower SVi (28 ± 6 vs 41 ± 9 mL/m ² , P < .001), and higher systemic vascular resistance (2,192 ± 709 vs 1,579 ± 455 dyne·s·cm ⁻⁵ , P = .005) compared with those with Z _va < 5 mm Hg/mL/m ² . The percentage of patients with low-gradient aortic stenosis (mean gradient < 40 mm Hg) was similar in patients with Z _va ≥ 5 mm Hg/mL/m ² and those with Z _va < 5 mm Hg/mL/m ² (33 [48%] vs 23 [48%], respectively, P = .948). The percentage of patients with low-gradient aortic stenosis and preserved LVEF (≥50%) was also similar between groups (17 [25%] in patients with Z _va ≥ 5 mm Hg/mL/m ² vs 16 [33%] in those with Z _va < 5 mm Hg/mL/m ² , P = .327).

Overall, 86 patients (86%) who were followed up at 12 months had improved their functional capacity by at least one grade. There was no difference in the proportion of patients who improved clinically between the group of patients with baseline Z _va ≥ 5 mm Hg/mL/m ² and patients with Z _va < 5 mm Hg/mL/m ² (50 [85%] vs 36 [86%]), respectively, P = .944).

In terms of echocardiographic outcomes, patients with baseline Z _va < 5 mm Hg/mL/m ² showed a significant reduction in LV end-diastolic volume compared with those with Z _va ≥ 5 mm Hg/mL/m ² (from 133 ± 52 to 122 ± 55 and 111 ± 50 mL at 1 and 12 months vs 104 ± 32 to 113 ± 35 and 109 ± 32 mL, respectively, P = .001). Interestingly, patients with baseline Z _va ≥ 5 mm Hg/mL/m ² showed a significant improvement in LVEF (from 52 ± 14% to 54 ± 13% and to 57 ± 11% at 1 and 12 months vs 55 ± 13% to 56 ± 13% and 55 ± 11%, respectively, P = .037) and SVi (from 28 ± 6 to 33 ± 9 and 35 ± 8 mL/m ² at 1 and 12 months vs 41 ± 9 to 37 ± 7 and 36 ± 10 mL/m ² , respectively, P < .001) ( Table 4 ). A subanalysis focused on 72 patients with baseline SVi ≤ 35 mL/ m ² showed no differences in remodeling between groups ( Table 5 ).

Table 4

Changes in echocardiographic parameters according to Z _va values

Variable	Z va ≥ 5 mm Hg/mL/m 2 ( n = 58)			Z va < 5 mm Hg/mL/m 2 ( n = 42)			P between groups	P for interaction of group and time
	Baseline	1 mo	12 mo	Baseline	1 mo	12 mo
LVEDV (mL)	104 ± 32	113 ± 35	109 ± 32	133 ± 52	122 ± 55	111 ± 50	.089	.001
LVESV (mL)	52 ± 32	51 ± 32	44 ± 24	60 ± 44	58 ± 47	51 ± 32	.306	.065
LVEF (%)	52 ± 14	54 ± 13	57 ± 11	55 ± 13	56 ± 13	55 ± 11	.740	.037
LV mass (g)	228 ± 71	219 ± 62	200 ± 49	237 ± 72	231 ± 71	203 ± 55	.510	.562
SVi (mL/m 2 )	28 ± 6	33 ± 9	35 ± 8	41 ± 9	37 ± 7	36 ± 10	.001	.001
SAC (mL/m 2 /mm Hg)	0.45 ± 0.16	0.51 ± 0.24	0.52 ± 0.21	0.73 ± 0.29	0.65 ± 0.30	0.52 ± 21	.356	.002
SVR (dyne·s·cm −5 )	2,194 ± 689	1,971 ± 899	1,937 ± 822	1,605 ± 469	1,707 ± 861	1,785 ± 690	.001	.087
SBP (mm Hg)	137 ± 26	135 ± 18	140 ± 24	126 ± 28	130 ± 29	139 ± 28	.470	.442
Cardiac output (L/min)	3.6 ± 0.9	4.3 ± 1.4	4.5 ± 1.5	4.6 ± 1.38	4.7 ± 1.2	4.5 ± 1.3	.015	.007

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