CASES FROM ANZ

Members from Australian and New Zealand (and regional affiliates) are invited to submit cases for consideration for publication on the ANZCMR website. This is your chance to showcase your best and most interesting cases to your colleagues thoughout out region! 

"One-Stop-Shop with CMR in ASD Assessment "

This months case has been submitted from:

Dr Andrew Li, Dr Shah M Azarisman and Dr Karen SL Teo, Royal Adelaide Hospital, South Australia.

Introduction:

In these days majority of secundum ASD are closed by transcatheter approach. The size of device is chosen based on ASD geometry and the type of device.

For a stenting device (e.g. Amplatzer), a device size 2-4mm larger than the ASD is generally recommended. CMR is an accurate non-invasive alternative to trans-esophageal echo in pre-operative assessment for the eligibility, which includes ASD size less than 40mm in diameter, and length of rim around ASD more than 4mm, depending on operation experience.For non-stenting device (e.g. Starflex, Helix), size is usually twice the size of ASD.

CMR can also excludes contra-indications for transcatheter closure, such as non-secundum ASD or anomalous pulmonary venous drainage which are better treated by open surgery. 

Case 1:

A 41-year-old woman underwent CMR after echocardiography demonstrated a secundum atrial septal defect to evaluate for the suitability of transcatheter closure. She was in sinus rhythm. There was a significant left to right shunt with a Qp/Qs ratio of 1.7 to 1. Operation was indicated to reduce future probability of atrial fibrillation and stroke. 

Figure 1 - In the workup for suitability of transcatheter approach, the rims around ASD were measured in TEE as shown.  In the bicaval view the SVC rim was located postero-superiorly and the IVC rim postero-inferiorly. The mitral rim was located antero-inferiorly in the 4-chamber view. The measurements closely correlated with that in cardiac MR, except that the SVC rim was better seen in CMR. 


 

Movie 1 - In-plane velocity encoded image demonstrated left-to-right shunt across the ASD. 

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Figure 2 - (Left) The size of the defect measured 12 x 14mm in the CMR en face view. (Middle) Similar measurements of ASD (10 x 13mm in diameter) were obtained in trans-esophageal echocardiography. (Right) Stop-flow diameter measured intra-operatively was 16mm. 

Figure 3 - Successful percutaneous closure with a 18mm Amplatzer occluder. 

Case 2:

A 63-year-old woman was evaluated with CMR for right heart size and function after transthoracic echocardiogaphy demonstrated a primum atrial septal defect. 

Movie 1 - SSFP cine in HLA view showing primum ASD and right ventricular dilatation.

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Movie 2 - Axial SSFP stack demonstrated normal drainage of superior vena cava and pulmonary veins. The interventricular septum was intact.

Movie 3 - SSFP cine in short axis view showing preserved biventricular systolic function.

Summary of findings:

Primum ASD measuring 42 x 16mm (en face view not shown) with significant left to right shunt (Qp:Qs 2.8 : 1). Right ventriular volume and function was quantified on short axis stack and showed moderate right ventricular dilatation (indexed RV EDV 150ml/m2) with normal RVEF (63%).

Discussion:

How reliable is CMR in shunt assessment compared with the traditional method of catheterization? K Debla and colleagues [1] compared CMR with invasive oximetry for the measurement of shunt volumes in a group of patients comprising different kinds of left-to-right shunts. The shunt ratio was defined as significant in catheterization using the conventional cut-off of 1.5. The result showed a that a Qp/Qs ratios of 1.75 to 1 in CMR correlated strongly with a significant shunt in catheterization. This cutoff has a 93% sensitivity and 100% specificity in ROC analysis.

Why is measurement of rim important? The device may erode into the surroundings if the aortic rim is deficient. IVC rim deficiency is contra-indicated for transcatheter approach because of risk of device embolization after deployment. 

How about the measurement of defect size? It’s demonstrated that size of ASD measured in CMR fall within 1-2mm difference with that of transesophageal echocardiography and surgery, in both paediatric and adult populations [2, 3].

CMR measurement requires no geometric assumption and has become the gold standard in the assessment of volume and function of right heart. Normalization of right ventricular and atrial volumes post-ASD closure has been documented with CMR [4].

Conclusion:

CMR is a suitable one-stop shop to precisely assess ASD and suitability of a percutaneous approach including assessment of:

  • Shunt size and right heart volume
  • Location and size of ASD
  • Rims around ASD
  • Exclude contra-indications for percutaneous closure
  • Non-secundum type ASD
  • Anomalous pulmonary venous drainage

References:

  1. Debl K, Djavidani B, Buchner S, et al. Quantification of left-to-right shunting in adult congenital heart disease: phase-contrast cine MRI compared with invasive oximetry. Br J Radiol 2009; 82:386-91
  2. Beerbaum P, Korperich H, Esdorn H, et al. Atrial septal defects I pediatric patients: non-invasive sizing with cardiovascular MR imaging. Radiology 2003;228: 361-9
  3. Weber C, Weber M, Ekinci O, et al. Atrial septal defects type II: noninvasive evaluation of patients before implantation of an Amplatzer Septal Occluder and on follow-up by magnetic resonance imaging compared with TEE and invasive measurement. Eur Radiol 2008;18: 2406- 13
  4. Teo KSL, Dundon BK, Molaee P, et al. Percutaneous closure of atrial septal defects leads to normalisation of atrial and ventricular volumes. JCMR 2008;10:55