Keywords:
Cardiac, Cardiovascular system, MR, MR-Angiography, Ablation procedures, Computer Applications-Virtual imaging, Imaging sequences, Dilatation, Image verification
Authors:
C. Casella, C. Bogetti, F. Misischi, A. Rapellino, R. Faletti, F. Barisone, P. Fonio, G. Gandini; Turin/IT
Conclusion
Left atrial maximum volume (LAMV) has already been confirmed as the most reliable predictor of AF recurrences after AF transcatheter ablation1 and this is the reason why its exact quantification is still now a theme of crucial importance.
To date LAMV is routinely assessed by MRA and at the same time furnish precious information also on the morphology of auricle and PVs.
Unfortunately,
MRA,
in not synchronized with the diastole phase,
and thus targeted at the maximum atrium volume,
yields LA volume values consists about 15-18 complete cardiac cycles,
hence averaging over all atrium volumes from the diastolic (maximum) to the systolic (minimum). These discrepancies make hard to reach a coherent conclusion on the actual LAMV value of a patient,
on the key value to predict the feasibility and the probability of success of the AF transcatheter ablation.
In the ongoing strive to create the best and safest environment for AF patients,
we have devised a study based on a comparison of MRA with the synchronized 3D Steady State Free Procession Whole Heart technique.
The contraction of the heart muscle is a major determining factor in the image quality of cardiac MR images,
so different method and systems are currently available to perform ECG gating in an MRI environment: Patel et al.2 in their study demonstrate that LA volume changes significantly during the cardiac cycle,
and substantial regional variation in LA motion exists so standard measurements of LA volume with MRA significantly underestimate LA max compared to the gold standard measure of 2D ECG-gated SSFP sequences.
In this study we used the 3D SSFP-WH technique instead than the 2D SSFP sequences for two reasons: provides remarkable definition of LA anatomy,
it is synchronized with atrial diastole, can be matched to the electro-anatomic non fluoroscopic mapping used during ablation.
The LAMV dimension results obtained by MRA was lower than SSFP-WH according to the correlation SSFP-WH volume=MRA volume+24 ml (R=0.97) in agreement with this study.
The good agreement obtained among the two Operators confirms the accuracy of the measures.
The wide range of disagreement of the two Operators using SSFP-WH for the evaluation of PVs anatomy and LAA morphology reflects the limited use by this technique utilized for these measurements because,
as describe by Krishnam et al.3,
the SSFP technique suffers from limitations such as the low contrast blood and adjacent tissues and flow- artifact witch may result in signal loss.
SSFP-WH has longer execution time (average acquisition time: 14.54 min) than MRA (18 s).
However,
the application of 24 ml on MRA to calculate LAMV allows an evaluation in excellent agreement with SSFP-WH.
MRA was more accurate for PVs anatomy and LAA morphology study.