CT transcatheter aortic valve implantation planning (protocol)

The transcatheter aortic valve implantation or TAVI planning CT protocol is used to plan for transcatheter aortic valve implantation. CT allows for the assessment of the aortic root and valve annulus in order to select an appropriate valve size and location specific to the patient. An aortic angiogram is also performed in order to determine the suitability of iliofemoral access ¹.

NB: This article is intended to outline some general principles. Protocol specifics especially medications, contrast doses and decisions vs other cardiac acquisitions will vary subject to institutional protocols and patient factors as well as CT hardware and software.

The medication and contrast doses apply for cardiac CT examinations in adults.

Indications

The main indication for TAVI CT is severe aortic stenosis ². This can present as:

• rapid or irregular heartbeat

• chest pain

• shortness of breath

• heart palpitations

Purpose

The purpose of TAVI CT is to demonstrate the aortic valve filled with contrast without motion or step artefacts. The origins of the coronary arteries and entire aorta down to the femoral arteries should be opacified to allow for planning and measurements to be made. 

This examination requires patients to maintain long breath holds and follow breathing instructions. A stable heart rate of around 60 bpm is ideal for capturing a motionless aortic valve.

Technical requirements

The minimal technical requirements for TAVI CT are the following ²:

• 64-slice scanner

• detector element width ≤0.625 mm

• option of cardiac CT and ECG-gated triggering

Patient preparation

• patients should take their cardiac medications as usual

• no food 3-4 hours before the scan

• no caffeine for 12 hours

• instructions on how to breathe

• electrocardiogram signal need to be acquired

Technique

• patient position

  • supine with both arms above their head (as comfortable as possible)

  • ECG placement

• tube potential

  • ​100 kVp if patient’s weight ≤100 kg or BMI <30 kg/m²

• tube current

  • ​ use automated current adjustment mode

• scout

  • aortic arch to femoral arteries

• scan range

  • ​calcium score to include valve only

  • TAVI to include the entire heart

  • aortogram to include aortic arch to the femoral arteries

• scan direction

  • craniocaudal

• contrast injection considerations

  • contrast agents with high iodine concentrations (270-400 mg iodine/mL)

  • contrast timing

    • monitoring: ascending aorta

    • test bolus (test volume 10-20 mL at the same flow as the cardiac scan e.g. 5.0-6.0 mL/s)

    • bolus tracking

  • contrast volume

    • 50-70 mL contrast media at 5-7 mL/s

    • 30-40 mL contrast media at 4-5 mL/s (for longer bolus)

    • 50-80 mL saline chaser at 4-5 mL/s

• respiration phase

  • inspiration

  • for breath-hold consistency, a medium-sized breath is easier to reproduce throughout the examination compared to sharp deep breaths

  • if the aortogram and TAVI scan are performed in one breath-hold, instruct the patient to let their breath out slowly if they run out of breath

Practical points

• setting the estimated heart rate as the patient's lowest heart rate will ensure the pitch is appropriate for imaging the patient's heart

• calculating scan delay for a test bolus

  • as the time-enhancement curve will only begin recording after the scan delay.

  • the widely accepted formula for calculating the scan delay is ³: peak contrast enhancement (time-enhancement curve) + scanner's diagnostic scan delay

TAVI work up

The workup is performed by either the radiographer, cardiologist, radiologist or a combination. Measurements are made for:

• valve plane

  • the plane just inferior to the coronary cusps

• annulus diameter

  • the diameter of the aorta one slice below the valve plane

• annulus size

  • the circular diameter of the aorta one slice below the valve plane

• right coronary artery height

  • from the origin of the right coronary artery to the valve plane

• left main coronary artery height

  • from the origin of the left main coronary artery to the valve plane

• sinus of Valsalva diameter

  • the diameter of the aortic valve leaflets

  • the largest point of the aortic bulge

• sinotubular junction diameter

  • one slice superior to the left and right sinus heights

  • just superior to the left and right coronary artery origins

  • where the aorta transitions to a straight wall

• left sinus height

  • from the top of the left sinus to the valve plane

  • gives rise to the left main coronary artery

• right sinus height

  • from the top of the right sinus to the valve plane

  • gives rise to the right coronary artery