Intra-cardiac echocardiography in alcohol septal ablation: a prospective comparative study against trans-thoracic echocardiography

Abstract

Alcohol septal ablation (ASA) in hypertrophic obstructive cardiomyopathy reduces left ventricular outflow tract gradients. A third of patients do not respond; inaccurate localisation of the iatrogenic infarct can be responsible. Transthoracic echocardiography (TTE) using myocardial contrast can be difficult in the laboratory environment. Intra-cardiac echocardiography (ICE) provides high-quality images. We aimed to assess ICE against TTE in ASA. The ability of ICE and TTE to assess three key domains (mitral valve (MV) anatomy and systolic anterior motion, visualisation of target septum, adjacent structures) was evaluated in 20 consecutive patients undergoing ASA. Two independent experts scored paired TTE and ICE images off line for each domain in both groups. The ability to see myocardial contrast following septal arterial injection was also assessed by the cardiologist performing ASA. In patients undergoing ASA, ICE was superior in viewing MV anatomy (P=0.02). TTE was superior in assessing adjacent structures (P=0.002). There was no difference in assessing target septum. Myocardial contrast: ICE did not clearly identify the area of contrast in 17/19 patients due to dense acoustic shadowing (8/19) and inadequate opacification of the myocardium (6/19). ICE only clearly localised contrast in 2/19 cases. ICE does not visualise myocardial contrast well and therefore cannot be used to guide ASA. TTE was substantially better at viewing myocardial contrast. There was no significant difference between ICE and TTE in the overall ability to comment on cardiac anatomy relevant to ASA.

Keywords: alcohol septal ablation; hypertrophic obstructive cardiomyopathy; non-surgical septal reduction therapy.

Figure 1

Flow chart describing method of analysis for ICE and TTE in phases 1 and 2 respectively.

Figure 2

(A) and (B) show ICE images. (C) and (D) show paired TTE images. (B) and (D) are simultaneous images taken with myocardial contrast injection. The contrast is much more vivid in TTE (D) than ICE (B).

Figure 3

(A) and (B) show ICE images. (C) and (D) show paired TTE images. (B) and (D) are simultaneous images taken with myocardial contrast injection. There is significant acoustic shadowing seen following contrast injection in the ICE image (B). There is minimal shadowing seen on TTE (D).

Figure 4

(A) shows a long-axis ICE view of the left ventricle using a frequency of 11 MHz. (B) shows the same transducer position with a frequency of 5 MHz. (C) shows a myocardial contrast injection at a frequency of 5 MHz. Myocardial contrast is visible in the basal septum in (C), but to allow the operator to see this a reduction in frequencies is required. This degrades the image to the extent that it cannot be relied upon to accurately comment on cardiac anatomy.

Figure 5

(A) shows a typical TTE PLAX echo image, the papillary muscle in view is the posterior muscle. (B) shows a typical ICE long-axis view of the left ventricle, with both heads of the posterior muscle visible. (C) shows a three-chamber CMR still with a papillary muscle labelled. Relational short axis CMR images show this to be the posterior muscle (PP), the blue line represents the plane displayed in the three chamber view in (C). The anterior muscle (AP) is out of shot and would be very difficult to see in the same plane as the LVOT. The same perspectives are displayed in the non-HCM heart in (E) and (F).

Figure 6

(A) shows a typical ICE image taken from phase 1. It is similar projection to a TTE four-chamber view taken from inside the RV. (C) shows a typical four chamber view In CMR. (E) shows a short-axis cut of the same heart. The blue line represents the cut of the LV that is shown in (C). The shaded area is the target for ASA. The blue line clearly passes through the inferior septum, missing the target area. (B) shows an ICE image with the true LVOT in view. This is represented in the three-chamber cardiac magnetic resonance (CMR) image in (D). The shaded area is the target for ASA. (F) shows the corresponding short-axis view, the blue line this time passes through the target myocardium in the true septum.

Figure 7

Both (A) and (B) show ICE images in systole with SAM-septal contact. In each example, the AMVL is folded back and has a bend of nearly 90. In (B), an area of iatrogenic infarct in the mid-septum from previous ASA is seen. The contact area for the AMVL is further basal, there is viable, contracting myocardium in this area.

Figure 8

The arrow points towards the coronary wire. Acoustic shadowing is also seen. This is in the target myocardium.