Choosing transcatheter aortic valve replacement in porcelain aorta: outcomes versus surgical replacement

Abstract

Objectives: Porcelain aorta complicates aortic valve replacement and is an indication for transcatheter approaches. No study has compared surgical and transcatheter valve replacement in the setting of porcelain aorta. We characterize porcelain aorta patients undergoing aortic valve replacement and the association of aortic calcification and outcomes.

Methods: Patients undergoing aortic valve replacement with porcelain aorta were identified. Aortic calcium volume was determined using 3D computed tomography thresholding techniques. Propensity scoring was performed to assess the effect of surgical versus transcatheter approaches. Risk factors for composite major hospital complications (death, stroke and dialysis) were identified using random forest machine learning.

Results: From January 2006 to January 2015, 164 patients with porcelain aorta underwent aortic valve replacement [105 (64%) surgical replacement, 59 (36%) transcatheter replacement]. Propensity scoring matched 29 pairs (49% of transcatheter patients). Before matching, 5-year survival was 41% [(43% surgical, 35% transcatheter, P(log-rank) = 0.9]. After matching, mortality for surgical versus transcatheter replacement was 3.4% (n = 1) vs 10% (n = 3), stroke 14% (n = 4) vs 3.4% (n = 1) and dialysis 6.9% (n = 2) versus 11% (n = 3). Matched 5-year survival was 40% after surgical replacement and 29% after transcatheter replacement [P(log-rank) = 0.4]. Total aortic calcium volume was greater in transcatheter than surgical patients [18 (8.0) vs 17 (7.7) ml] and was associated with more major hospital complications after either approach.

Conclusions: Surgical and transcatheter approaches are complementary options for aortic stenosis with porcelain aorta. Surgical valve replacement remains an effective treatment for patients requiring concomitant procedures. Quantifying aortic calcium volume is a helpful risk predictor in all patients with porcelain aorta.

Keywords: Aortic stenosis; Calcium volume quantification; Operative approach.

Figure 1:

Study design and porcelain aorta. (A) Patients undergoing aortic valve replacement with a diagnosis of porcelain aorta. A total of 105 patients underwent surgical valve replacement and 59 underwent transcatheter valve replacement. Propensity score matching identified 29 pairs (29% of the surgical group, 49% of the transcatheter group). SAVR: surgical aortic valve replacement; TAVR: transcatheter aortic valve replacement. (B) Porcelain aorta is defined as the circumferential, or near circumferential, deposition of calcium within the ascending aorta. Subcategories, types IA and IB, can be defined based on ‘clampability’ of the aorta. Left panel: 3D reconstruction of an unclampable, type IA. Right panel: 3D reconstruction of a clampable, type IB.

Figure 2:

Modified calcium thresholding technique for determining quantitative aortic calcium volume. (A) Calcified structures were initially isolated by setting a lower threshold ranging from 300–700 Hounsfield units and an upper threshold of 2000 Hounsfield units to isolate areas of interest. (B) The lower threshold was selected by visual examination in 25-unit increments to ensure only calcified structures were selected. (C) Region tools were used to manually select high-density calcium within the aortic wall. (D) 3D reconstruction was implemented, and calcium volume measured using volumetric analysis.

Figure 3:

Propensity score matching results for comparing outcomes of SAVR versus TAVR. AV: aortic valve; BMI: body mass index; Hx: history; NYHA: New York Heart Association Symptom Class; SAVR: surgical aortic valve replacement; TAVR: transcatheter aortic valve replacement. (A) Covariable balance for selected variables before (triangles) and after (squares) matching, contrasting characteristics of patients undergoing SAVR and TAVR. Values on the horizontal axis represent standardized difference. Triangles to the left of zero (negative) represent TAVR-like characteristics; triangles to the right of zero (positive) represent SAVR-like characteristics. (B) Mirror histogram of the distribution of propensity scores for SAVR (bars above zero line) and TAVR (bars below zero line) approaches. Shaded areas represent 29 matched patient pairs. Unshaded areas represent unmatched patients (SAVR, N = 76; TAVR, N = 30).

Figure 4:

Representative risk of major hospital complication is associated with aortic calcium volume and regionality. (A) Variable of importance plot. Variables with larger values are more important to the random forest model in predicting a major hospital complication. Variable acronyms/names are available in Supplementary Material, Table S8. (B) Partial-dependence risk-adjusted graph of association between total calcium score and predicted probabilities of composite major hospital complication (death, stroke, renal failure requiring dialysis). Risk-adjusted estimates are based on random forest classification. Symbols represent ensemble averages (probabilities) across total calcium volume, and solid line depicts smoothing spline curves of these probabilities. AV: aortic valve; BMI: body mass index; Hx: history; NYHA: New York Heart Association Symptom Class; SAVR: surgical aortic valve replacement; TAVR: transcatheter aortic valve replacement.

Figure 5:

Overall and matched survival following valve replacement in the setting of porcelain aorta. (A) Survival by surgical approaches [SAVR (blue) versus TAVR (red)] in the overall cohort. (B) Survival by surgical approaches [SAVR (blue) versus TAVR (red)] in the matched cohort. Each symbol represents a death, and vertical bars are asymmetric 68% confidence limits equivalent to ±1 standard error. Solid line depicts the parametric estimates of survival enclosed within dashed 68% confidence bands. SAVR: surgical aortic valve replacement; TAVR: transcatheter aortic valve replacement.