Abstract
Currently percutaneous aortic valve replacement (PAVR) is indicated for patients at high surgical risk or for inoperable patients. Preprocedural evaluation is crucial to select the patients who will benefit the most and have the procedure done safely. This review will focus on risk assessment and the value of the available risk score systems, and on the screening process, which is the key for success in PAVR. Because of the large delivery system, careful evaluation of iliofemoral vessels is crucial. It is important to know the amount of atherosclerosis and plaque in the aortic arch and ascending aorta for potential risk for neurological events. Accurate measurement of aortic annulus diameter and coronary arteries origin before the procedure is important. Specific coexistent conditions can influence the procedure, such as left ventricular function or left ventricular hypertrophy with narrow outflow tract. Assessment of all these components is necessary for procedural planning of access approach, valve sizing, and deployment.
1
Introduction
Preprocedural evaluation of patients for percutaneous aortic valve replacement (PAVR) is crucial to select the patients who will benefit the most and have the procedure done safely. Currently PAVR is indicated for patients at high risk for surgery and for inoperable patients. This review will focus on risk assessment and evaluation of patients with severe aortic stenosis being considered for PAVR. After determining appropriate operative risk, one needs to determine the anatomical suitability. At our center, patients coming for evaluation for the PARTNER trial spend a full day at the hospital; they start with a complete echocardiogram, followed by cardiac catheterization and angiography of the coronaries, left ventricle (LV), and aorta. A 4F catheter is left in the abdominal aorta, and the patient is then taken to the 64/256 computer tomography (CT) suite for a noncontrast CT of the chest and abdomen followed by a contrast CT of the abdominal aorta and iliacs with 10–12 cc injected in the abdominal aorta ( Fig. 1 A and B ).
Because the most common complication after PAVR is access complication, detailed and precise analysis of the iliofemoral vessels is conducted.
2
Patient selection and risk assessment
The percutaneous aortic valve is intended for use in symptomatic patients with severe calcific aortic stenosis requiring aortic valve replacement, who are at high risk for open chest surgery due to comorbid conditions or patients who are inoperable. This is a prerequisite for inclusion into one of the approved PAVR trials. Defining high-risk surgical patients is not simple. An STS risk score >10 and/or a Logistic EuroSCORE >20 are most often used to define high risk ( http://209.220.160.181/STSWebRiskCalc261/de.aspx , http://www.euroscore.org ). The STS predicted risk of mortality most accurately predicts perioperative and long-term mortality for the highest-risk patients having aortic valve replacement . The EuroSCORE overestimates the mortality risk of aortic valve replacement , and this overestimation is greatest in high-risk patients .
Patients can be at very high operative mortality risk but yet have low scores. There are numerous comorbidities not captured in either the Euro SCORE or the STS scoring systems such as porcelain aorta, chest wall radiation, chest wall deformity, highly compromised respiratory function, frailty, and others. There have been attempts to quantify frailty index and correlate frailty index with outcome ; however, the analysis of frailty is particularly difficult and is often no quantifiable. Clinical judgment of experienced cardiac surgeons has a key role in assessing operative mortality in these cases.
The currently available validated risk score systems have not captured the “non-operable” patients. The definition of “inoperability” is difficult and often requires the consensus of several surgeons. It is important to emphasize that those scoring systems are not intended to be used as substitutes for clinical decision making.
Many of these patients have decreased renal function. This is not a contraindication for the percutaneous valve procedure. We use contrast that is diluted 50% with normal saline, and we hydrate the patient before the percutaneous valve procedure. This has effectively prevented further deterioration of renal function post procedure.
2
Patient selection and risk assessment
The percutaneous aortic valve is intended for use in symptomatic patients with severe calcific aortic stenosis requiring aortic valve replacement, who are at high risk for open chest surgery due to comorbid conditions or patients who are inoperable. This is a prerequisite for inclusion into one of the approved PAVR trials. Defining high-risk surgical patients is not simple. An STS risk score >10 and/or a Logistic EuroSCORE >20 are most often used to define high risk ( http://209.220.160.181/STSWebRiskCalc261/de.aspx , http://www.euroscore.org ). The STS predicted risk of mortality most accurately predicts perioperative and long-term mortality for the highest-risk patients having aortic valve replacement . The EuroSCORE overestimates the mortality risk of aortic valve replacement , and this overestimation is greatest in high-risk patients .
Patients can be at very high operative mortality risk but yet have low scores. There are numerous comorbidities not captured in either the Euro SCORE or the STS scoring systems such as porcelain aorta, chest wall radiation, chest wall deformity, highly compromised respiratory function, frailty, and others. There have been attempts to quantify frailty index and correlate frailty index with outcome ; however, the analysis of frailty is particularly difficult and is often no quantifiable. Clinical judgment of experienced cardiac surgeons has a key role in assessing operative mortality in these cases.
The currently available validated risk score systems have not captured the “non-operable” patients. The definition of “inoperability” is difficult and often requires the consensus of several surgeons. It is important to emphasize that those scoring systems are not intended to be used as substitutes for clinical decision making.
Many of these patients have decreased renal function. This is not a contraindication for the percutaneous valve procedure. We use contrast that is diluted 50% with normal saline, and we hydrate the patient before the percutaneous valve procedure. This has effectively prevented further deterioration of renal function post procedure.
3
Access site peripheral anatomy
Adequate vascular access is one of the most important determinants of procedural success and/or complications. The 22F and 24F sheath used for delivery of the 23- and 26-mm valves require a minimum vessel diameter of 7 and 8 mm, respectively. Three imaging modalities are available to evaluate the access vessels: angiography, contrast CT, and intravascular ultrasound. Often there is discrepancy in the results obtained by these techniques. We find that high-quality CT is the most accurate and provides the most useful information to predict feasibility of transfemoral approach.
3.1
Angiography
Abdominal aortography gives excellent images. Digital subtraction allows for same or better images with smaller amount of contrast (10–15 cc). Vessel diameters are measured with QCA and a reference marker pigtail ( Fig. 2 ).
Precise vessel measurements are performed in multiple sites in the common femoral, superficial femoral, external, and common iliac arteries. A minimal diameter of 7 mm for the 23-mm valve and 8 mm for 26-mm valve is required.
Excess vessel tortuosity can prevent the large 22F or 24F sheath from advancing to the abdominal aorta, like the left iliac in Fig. 3 .
Tortuosity with large lumen and no calcification is no problem for use of the large sheaths. Tortuosity without calcification that is straightened by a wire does not preclude the procedure ( Fig. 4 ). Tortuosity with marked calcification does not allow the advancement of the large sheaths.
Calcification is often not well appreciated by angiography. We have seen many cases where the iliofemoral angiography showed adequate vessels for percutaneous access, and the CT revealed severe calcification making us reject the patient for transfemoral access ( Fig. 5 A–F ).
3.2
Computed tomography
A detailed CT analysis is very important and can predict possible access problems. The CT images are displayed in longitudinal, 3D, and axial views.
The vessel diameter is carefully assessed in longitudinal and axial views. We place the cursor in the abdominal aorta and bring it down millimeter by millimeter to get exact measurements in the entire length of the vessel considered for access. Examples of these measurements are given in Fig. 6 A and B ). Occasionally the longitudinal images appear to have and adequate minimum diameter but the axial views do not: the real cross-sectional diameters are smaller than required for the large sheaths.
