The majority of left atrial thrombi involve the left atrial appendage. The surface ECG may not always reflect underlying left atrial appendage mechanical function, rather surface ECG p-wave reflects atrial body activation. Transesophageal echocardiography has the ability to record left atrial appendage pulse wave Doppler and determine weather flow pattern corresponds to the mechanical function of the sinus rhythm of atrial fibrillation. 

In this retrospective trial, a total of 208 consecutive patients with available TEE were screened, for which TEE LAA data were available on 201 (96%) patients. Discordance between the ECG/mitral valve motion rhythm and the LAA PWD phenotype was noted in 15 (7.5%) patient with 7 (3.5%) demonstrating AF discordance (SR on ECG/MVM and AF phenotype on LAA PWD) and 8 (4.0%) demonstrated SR discordance (AF ECG/MVM and SR LAA PWD).

The AF discordance group had significantly higher prevalence of LAA SEC, larger LAA area, longer length, lower LAA ejection velocity, and higher CHADS2-VASc. LAA thrombus was noted in 6 patients, all of whom had AF concordance.

Prothrombotic AF phenotype persists in the majority of the paroxysmal AF patients despite SR on the surface ECG recording. The authors are advocating use of anticoagulation in AF phenotype patients independent of the surface ECG. I agree that assessment of LAA phenotype in all patients undergoing TEE is warranted, but I would take a step back and rethink their suggestion for use of anticoagulation. In the post CRYSTAL-AF era, left atrial appendage pulse wave Doppler phenotyping could help in better selection of the patients that would benefit from the anticoagulation, but this would need to be answered in the prospective randomized trial.