Imaging to Select and Guide TAVI
Imaging to Select and Guide TAVI
During TAVI, fluoroscopy is the basis for procedure guidance. Nevertheless, the combination of other imaging techniques, particularly TOE may overcome the lower soft tissue contrast resolution of fluoroscopy, particularly in less significant calcified valves. The use of 3D, by its larger spatial resolution, compared with 2D TEE allows a better visualization of the guide wire path and permits a better evaluation of the prosthesis position on the balloon, relative to the native valve annulus and surrounding structures. The mid-oesophagus long-axis view enables visualization of the guide wire through the aortic valve that might be delivered retrogradely (transfemoral, transubclavian or transaortic) or anterogradely (transapical). Using the 3D probe, it is possible to obtain simultaneous visualization of orthogonal planes, the long-axis and short-axis views of the aortic valve in real-time. Aortic valve crossing, balloon dilatation, and prosthesis deployment are key steps during TAVI. Peri-procedural TOE can contribute for these steps guidance and to confirm prosthesis function and potential complications, immediately after implantation. It can be used to confirm a secure position for inflation and to monitor the behaviour of the balloon and its effect on the calcified aortic cusps during inflation, as it may accidentally migrate (Figure 9). During prosthesis deployment, TOE gives support to confirm the correct position of the valve in conjunction with fluoroscopy. The Edwards SAPIEN valve optimal position is with the ventricular side of the prosthesis located 2–4 mm below the annulus, while the CoreValve is recommended to have the ventricular edge of the prosthesis placed 5–10 mm below the aortic valve annular plane. After the deployment, it is important to confirm that all the prosthetic cusps are moving well, the valve stent has a circular configuration and to exclude significant valvular or paravalvular AR. Mild AR through the prosthesis, until the guidewire is removed and at the next few minutes after deployment is common. Small jets of paravalvular AR are frequent and it may occur even in a successful procedure. However, severe AR is a serious complication and additional balloon inflation may be required in spite of the increased risk of cerebrovascular events.
(Enlarge Image)
Figure 9.
Three-dimensional transoesophageal echocardiography showing the catheter and the prosthesis through the native aortic valve while being deployed.
There is growing interest in fusion imaging modalities (echocardiography, MSCT, or CMR with fluoroscopy) for procedure guidance, providing supplementary data to fluoroscopy. The Syngo DynaCT system acquired volumetric reconstructions similar to MSCT images intra-operatively with the angiography C-arm. The resulting images are not comparable with modern cardiac CT images, but it has been shown that when acquired under rapid pacing, they are sufficient for pre-operative implant selection and automatic generation of a 3D model, containing all relevant anatomical landmarks. Moreover the optimal perpendicular view onto the aortic root can be identified and a 3D model extracted from the DynaCT can be superimposed on the angiography images to guide catheter placement.
Real-time CMR was shown to be feasible in CoreValve prosthesis implantation is animal model, allowing improved procedural guidance, immediate detection of complications and direct functional assessment with reduction of radiation and omission of contrast media. Nevertheless, further studies on these techniques for validation and clinical use assessment are still needed.
Aortic Regurgitation. Aortic regurgitation is the most common complication after TAVI and it is associated with short- and long-term mortality. It may occur as a consequence of incomplete expansion, incorrect positioning, restricted cusp motion, or inappropriate prosthetic size. An undersized prosthesis may result in paravalvular AR (Figure 10), while an oversized prosthesis has the risk of under expansion and central AR. Moreover, as well as the previous mentioned aortic valve calcification or larger size annulus, the higher cover/non-coaptation/mismatch indexes are associated with the occurrence of AR.
(Enlarge Image)
Figure 10.
Two-dimensional transoesophageal echocardiography showing paravalvular aortic regurgitation.
The regurgitation evaluation should include an assessment of both central and paravalvular components, combining the measurements for total AR estimation, using quantitative and semi-quantitative data. Paravalvular jets colour Doppler evaluation must be performed just below the valve and for central regurgitation at the coaptation point. The VARC recommendations suggest that for paravalvular jets, the proportion of the circumference of the sewing ring occupied by the jet gives a semi-quantitative guide to severity: <10% of the sewing ring suggests mild, 10–29% suggests moderate, and ≥30% suggests severe. For the quantitative approach, the width of the vena contracta is a robust estimate of regurgitant severity, but in the setting of prostheses, portions of the sewing ring may not be imaged due to acoustic shadowing. In addition, there has been no validation for adding the vena contracta widths of multiple jets as it may be encountered post-TAVI. Three-dimensional vena contracta planimetry might be an alternative for quantitative evaluation and moderate AR recognition of paravalvular AR after TAVI. However, it is challenging at the acute setting and it requires 3D echocardiography on site. In consequence, the final interpretation should follow the principle of a comprehensive evaluation and integrated approach. Additionally, using blood pressure and end-diastolic LV pressure, the index calculated as the ratio of the gradient between diastolic blood pressure (DBP) and left ventricular end-diastolic pressure (LVEDP) to systolic blood pressure (SBP): [(DBP − LVEDP)/SBP] × 100 was shown to independently predict 1-year mortality after TAVI, and to provide additional prognostic information, complementary to the echocardiographically assessed severity of paravalvular AR. Its use can be considered for the complementary evaluation of AR.
Transcatheter Aortic Valve Implantation Migration or Displacement. Prosthetic embolism can occur towards the aorta or the left ventricle and it might require surgical removal if transcatheter repositioning reveals impossible. Besides, the prosthesis displacement towards the LVOT can result in worsening of MR by anterior mitral leaflet restriction or even direct damage or distortion of the subvalvular apparatus. The displacement towards the aorta can cause coronary ostial occlusion by an obstructive portion of the valve frame and consequent anew LV dysfunction.
Additional Complications. Exceptional complications already experienced are the cardiac tamponade, secondary to wire perforation of the left or right ventricle and tear or ruptures of the aortic root. The later has been observed after balloon valvuloplasty or prosthesis deployment, especially in the presence of extensive annular calcification or prosthesis oversizing ( Table 3 ).
Comparing both valves, the main difference is the higher incidence of permanent pacemaker requirement using the Corevalve device (15–47%) vs. 4–21% with Edwards SAPIEN implantation. As Corevalve is self-expandable, it can lead to conduction disturbances following implantation, mainly in patients who had peri-procedural atrioventricular block, larger interventricular septum diameter, and a prolonged QRS duration. Patients having balloon pre-dilatation, or implantation of larger devices are also more likely to require a pacemaker. However, new pacemaker implant does not appear to be associated with long-term mortality, thus the decision should be based on operators experience, devices availability, and anatomic specifications.
Transoesophageal echocardiography is not mandatory during TAVI, as it usually requires general anaesthesia and the probe may also partially obstruct the optimal fluoroscopic view. However, it is the main technique for procedure guidance and assessment of complications, particularly in patients with limited native valve calcification. The intracardiac ultrasound catheter provides high-quality, ultrasound images, and Doppler blood flow information and it does not require transoesophageal intubation. It has been, recently, released with 3D capabilities and although the image has limitations compared with 3D TOE forthcoming experience will evaluate its part as an alternative for procedure guidance.
Role of Imaging: Guiding the Procedure
During TAVI, fluoroscopy is the basis for procedure guidance. Nevertheless, the combination of other imaging techniques, particularly TOE may overcome the lower soft tissue contrast resolution of fluoroscopy, particularly in less significant calcified valves. The use of 3D, by its larger spatial resolution, compared with 2D TEE allows a better visualization of the guide wire path and permits a better evaluation of the prosthesis position on the balloon, relative to the native valve annulus and surrounding structures. The mid-oesophagus long-axis view enables visualization of the guide wire through the aortic valve that might be delivered retrogradely (transfemoral, transubclavian or transaortic) or anterogradely (transapical). Using the 3D probe, it is possible to obtain simultaneous visualization of orthogonal planes, the long-axis and short-axis views of the aortic valve in real-time. Aortic valve crossing, balloon dilatation, and prosthesis deployment are key steps during TAVI. Peri-procedural TOE can contribute for these steps guidance and to confirm prosthesis function and potential complications, immediately after implantation. It can be used to confirm a secure position for inflation and to monitor the behaviour of the balloon and its effect on the calcified aortic cusps during inflation, as it may accidentally migrate (Figure 9). During prosthesis deployment, TOE gives support to confirm the correct position of the valve in conjunction with fluoroscopy. The Edwards SAPIEN valve optimal position is with the ventricular side of the prosthesis located 2–4 mm below the annulus, while the CoreValve is recommended to have the ventricular edge of the prosthesis placed 5–10 mm below the aortic valve annular plane. After the deployment, it is important to confirm that all the prosthetic cusps are moving well, the valve stent has a circular configuration and to exclude significant valvular or paravalvular AR. Mild AR through the prosthesis, until the guidewire is removed and at the next few minutes after deployment is common. Small jets of paravalvular AR are frequent and it may occur even in a successful procedure. However, severe AR is a serious complication and additional balloon inflation may be required in spite of the increased risk of cerebrovascular events.
(Enlarge Image)
Figure 9.
Three-dimensional transoesophageal echocardiography showing the catheter and the prosthesis through the native aortic valve while being deployed.
There is growing interest in fusion imaging modalities (echocardiography, MSCT, or CMR with fluoroscopy) for procedure guidance, providing supplementary data to fluoroscopy. The Syngo DynaCT system acquired volumetric reconstructions similar to MSCT images intra-operatively with the angiography C-arm. The resulting images are not comparable with modern cardiac CT images, but it has been shown that when acquired under rapid pacing, they are sufficient for pre-operative implant selection and automatic generation of a 3D model, containing all relevant anatomical landmarks. Moreover the optimal perpendicular view onto the aortic root can be identified and a 3D model extracted from the DynaCT can be superimposed on the angiography images to guide catheter placement.
Real-time CMR was shown to be feasible in CoreValve prosthesis implantation is animal model, allowing improved procedural guidance, immediate detection of complications and direct functional assessment with reduction of radiation and omission of contrast media. Nevertheless, further studies on these techniques for validation and clinical use assessment are still needed.
Assessment of Complications
Aortic Regurgitation. Aortic regurgitation is the most common complication after TAVI and it is associated with short- and long-term mortality. It may occur as a consequence of incomplete expansion, incorrect positioning, restricted cusp motion, or inappropriate prosthetic size. An undersized prosthesis may result in paravalvular AR (Figure 10), while an oversized prosthesis has the risk of under expansion and central AR. Moreover, as well as the previous mentioned aortic valve calcification or larger size annulus, the higher cover/non-coaptation/mismatch indexes are associated with the occurrence of AR.
(Enlarge Image)
Figure 10.
Two-dimensional transoesophageal echocardiography showing paravalvular aortic regurgitation.
The regurgitation evaluation should include an assessment of both central and paravalvular components, combining the measurements for total AR estimation, using quantitative and semi-quantitative data. Paravalvular jets colour Doppler evaluation must be performed just below the valve and for central regurgitation at the coaptation point. The VARC recommendations suggest that for paravalvular jets, the proportion of the circumference of the sewing ring occupied by the jet gives a semi-quantitative guide to severity: <10% of the sewing ring suggests mild, 10–29% suggests moderate, and ≥30% suggests severe. For the quantitative approach, the width of the vena contracta is a robust estimate of regurgitant severity, but in the setting of prostheses, portions of the sewing ring may not be imaged due to acoustic shadowing. In addition, there has been no validation for adding the vena contracta widths of multiple jets as it may be encountered post-TAVI. Three-dimensional vena contracta planimetry might be an alternative for quantitative evaluation and moderate AR recognition of paravalvular AR after TAVI. However, it is challenging at the acute setting and it requires 3D echocardiography on site. In consequence, the final interpretation should follow the principle of a comprehensive evaluation and integrated approach. Additionally, using blood pressure and end-diastolic LV pressure, the index calculated as the ratio of the gradient between diastolic blood pressure (DBP) and left ventricular end-diastolic pressure (LVEDP) to systolic blood pressure (SBP): [(DBP − LVEDP)/SBP] × 100 was shown to independently predict 1-year mortality after TAVI, and to provide additional prognostic information, complementary to the echocardiographically assessed severity of paravalvular AR. Its use can be considered for the complementary evaluation of AR.
Transcatheter Aortic Valve Implantation Migration or Displacement. Prosthetic embolism can occur towards the aorta or the left ventricle and it might require surgical removal if transcatheter repositioning reveals impossible. Besides, the prosthesis displacement towards the LVOT can result in worsening of MR by anterior mitral leaflet restriction or even direct damage or distortion of the subvalvular apparatus. The displacement towards the aorta can cause coronary ostial occlusion by an obstructive portion of the valve frame and consequent anew LV dysfunction.
Additional Complications. Exceptional complications already experienced are the cardiac tamponade, secondary to wire perforation of the left or right ventricle and tear or ruptures of the aortic root. The later has been observed after balloon valvuloplasty or prosthesis deployment, especially in the presence of extensive annular calcification or prosthesis oversizing ( Table 3 ).
Comparing both valves, the main difference is the higher incidence of permanent pacemaker requirement using the Corevalve device (15–47%) vs. 4–21% with Edwards SAPIEN implantation. As Corevalve is self-expandable, it can lead to conduction disturbances following implantation, mainly in patients who had peri-procedural atrioventricular block, larger interventricular septum diameter, and a prolonged QRS duration. Patients having balloon pre-dilatation, or implantation of larger devices are also more likely to require a pacemaker. However, new pacemaker implant does not appear to be associated with long-term mortality, thus the decision should be based on operators experience, devices availability, and anatomic specifications.
Transoesophageal echocardiography is not mandatory during TAVI, as it usually requires general anaesthesia and the probe may also partially obstruct the optimal fluoroscopic view. However, it is the main technique for procedure guidance and assessment of complications, particularly in patients with limited native valve calcification. The intracardiac ultrasound catheter provides high-quality, ultrasound images, and Doppler blood flow information and it does not require transoesophageal intubation. It has been, recently, released with 3D capabilities and although the image has limitations compared with 3D TOE forthcoming experience will evaluate its part as an alternative for procedure guidance.
