By Eleanor McDermid
Cardiac magnetic resonance (CMR) can potentially be used to detect thrombi at the same time as being used for pulmonary venous anatomy mapping, say researchers.
Compared with the more invasive gold standard of transesophageal echocardiogram (TEE), CMR was more than 99% accurate for detecting thrombi in the left atrium and the left atrial appendage (LAA), report Dipan Shah (Houston Methodist DeBakey Heart & Vascular Center, Texas, USA) and study co-authors.
The team tested three CMR sequences in the 261 patients referred for pulmonary vein isolation (PVI): cine-CMR; contrast-enhanced magnetic resonance angiography (MRA); and equilibrium phase delayed enhancement CMR with a long inversion time of 600 ms (long TI DE-CMR).
They found the long TI DE-CMR to be the best sequence. It detected all of the nine thrombi found on TEE (seven in the LAA; two in the left atrium) giving a sensitivity of 100%, although it was unable to definitively exclude thrombus in two cases, giving a specificity and overall accuracy of 99.2%. In addition, the interobserver agreement was highest for this sequence.
Accuracy was lower for the other two sequences, at 94.3% for contrast-enhanced MRA and 91.6% for cine-CMR. Both were only 66.7% sensitive, although they both had high negative predictive values (>98%).
Cardiac computed tomography can also be used for thrombus detection, but "CMR could provide valuable data for PVI procedures without exposure to radiation", write Shah et al in JACC Cardiovascular Imaging.
"This scenario might be even more important in certain patients who are expected to have a long PVI procedure time or a repeat procedure in the future."
In an accompanying editorial, Warren Manning and Aferdita Spahillari, both from Beth Israel Deaconess Medical Center and Harvard Medical School in Boston, Massachusetts, USA, highlight the fact that the long TI DE-CMR sequence proved feasible in patients with irregular heart rhythms (41.8% were in atrial fibrillation during CMR).
The editorialists say: "A diagnostic study that confidently answers 2 clinical questions is appealing from a practical and financial point of view. However, for this approach to become incorporated into clinical practice, the optimal timing for exclusion of [left atrial]/LAA thrombus in patients referred for PVI should be determined."
They add that this is especially important for atrial fibrillation patients who are taking oral anticoagulation but discontinue it between CMR and PVI.
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JACC Cardiovasc Imaging 2016; Advance online publication