Multi-slice CT in trans-catheter aortic valve implantation planning
Transcatheter Aortic Valve Implantation (TAVI) is a technique to replace the aortic valve through a transvascular or transapical approach. Compared to traditional open aortic valve replacement with sternotomy and a heart-lung bypass machine, the TAVI technique is less invasive and can be performed on the beating heart. Thus, this technique may be beneficial for patients with symptomatic aortic stenosis.
Pre-operative assessment before TAVI includes CT angiography that is performed to evaluate the current vascular status, potential anatomic problems (e.g. severe iliac calcifications) and best surgical approach.
CT angiography
Aortic annulus diameters can be accurately measured during the cardiac cycle by ECG-gated CTA. This way, the TAVI implanter can select the most suitable-sized prosthesis and therefore reduce the possibility of complications, namely para-valvular regurgitation. It is crucial to measure the distance between the coronary ostia and the aortic annulus to allow for safe placement of the valve replacement (usually greater than 10 mm). Furthermore, CT angiography of the abdominal aorta and ilio-femoral vessels is performed for vascular access for pre-procedural planning.
We are sharing our experience of work on the basis of the patients who were examined in preoperative assessment for TAVI procedure till now using a 256 slice Computed Tomography scanner in the department of radio-diagnosis of Max Super specialty hospital Saket.
CT scan was done for these patients using the following protocol (Table 1), CT parameters and measurements (Table 2).
CT scan aortic root recommendation parameters
| IV IODINE CONTRAST. RATE | 80-100ML 4-6ML/SEC. |
| BOLUS TRACKING | CONCENTRATION IN ASCENDING. AORTA |
| ECG GATING | REQUIRED |
| SCAN DIRECTION | CRANIO-CAUDAL |
| SCAN COVERAGE | FROM AORTIC ARCH TO CARDIAC APEX |
| DTECTOR COLLIMATION | 0.4-0.6MM |
| PITCH | 0.2-0.4 |
| SLICE THICKNESS | 0.8MM |
| SLICE OVERLAP | 0.4MM |
| RECONSTRUCTION KERNEL | MEDIUM SMOOTH |
| POST PROCESSING | SYSTOLIC PHASE AND RECONSTUCTION THICKNESS <1MM |
CT parameters – measurements in pre-TAVI screening
| Aortic annulus (AA) — AA short and long diameters, AA perimeter and AA area.
Aortic valve–Pattern and extent of calcifications, presence of calcified cusps and uspidity. Aortic root–Height and width of sinus of Valsalva, Distance from the AA plane to the coronary artery ostia and Sino-tubular junction diameter. Aorta—Anatomy, Tortuosity and elongation, intraluminal calcification, thrombi, and dissections, Ascending aorta, aortic arch, and descending aorta diameters. Iliofemoral arteries- Minimal luminal diameters bilaterally, tortuosity, and angulation and calcifications.
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Figure 1
Indications of CT angiography
Indications of CT scan were to find out vascular status, anatomical problems (e.g. severe iliac calcifications), best surgical approach and aortic root assessment for TAVI. The aortic root also contains the aortic valve within the aortic sinus .Three distinct aortic valve leaflets can be visualized, (Fig 1)
CT image of the aortic root showing aortic valve, consisting of left coronary (green), right coronary (red), and non-coronary (yellow) cusps.
Imaging of the aortic root is performed with the goals of: 1) measuring aortic annulus size and perimeter; 2) measuring leaflet length and calcification; 3) locating the coronary ostia. Fig 2 and 3.
CT image at the level of the aortic root shows
Figure 2
distance (white double-headed arrow) between the annular plane and the nearest coronary ostium and length of the aortic valve leaflets (black double-headed arrow)
A minimum distance of 10 mm is recommended between the annular plane and the nearest coronary ostium. It is also recommended that this distance be greater than the length of the aortic valve leaflets (black double-headed arrow).
CT image (axial reformat) showing measurements of aortic annulus .AA short and long diameters (green), AA perimeter (pink).
Operative techniques
Figure 3
We did CT angiography for TAVI which were planned through trans-femoral route. In only one TAVI procedure trans-subclavian approach was selected due to severe peripheral vascular disease.
Conclusion
Multi-detector computed tomography (MDCT) has assumed an increasingly important, complementary role before and after TAVI, and provides detailed anatomic assessment of the aortic root structures and ilio-femoral access, adding to the information obtained with echocardiography and angiography.
