Pranav Bhagirath

30 Chapter 2 environment may prove to be a great advantage for electrophysiologists who can work outside the dangers of ionizing radiation. It also enables an enhanced visualization of anatomic structures and provides the unique ability to instantly adjust the ablation strategy based on tissue characteristics (edema and necrosis). POST-PROCEDURAL IMAGING Assessment of PV stenosis PV stenosis is a complication which may occur after ablation and can be treated with balloon dilatation and stent placement (39) . The requirement for intervention depends upon presence and severity of symptoms (1;39) . Evaluation of the PV anatomy at follow-up can be performed with CT or CMR. PV flow data can be acquired reliably and reproducibly using a CMR flow map study ( figure 4 ) (40;41) . Comparison of flow before and after ablation allows a more functional assessment to be conducted regarding severity of the stenosis and interventional indication. Assessment of post-ablation scar The ability to perform tissue characterization is restricted to CT and CMR. So far, CT has been used in a limited number of trials focused on scar in the ventricles and considering its low sensitivity, should be conceived as a developing technique (42;43) . CMR on the other hand is the gold standard for detection of infarcted myocardium and assessment of viability (44) . Recent progress in 3D late gadolinium enhanced (LGE) imaging sequences enables identification and quantification of structural remodeling in cardiac tissue as thin as the atrial wall (7;45) . Acute atrial injury Acute injury is characterized by presence of both necrosis (fibrosis) and edema. Cardiac MRI allows for discrimination between edema and fibrosis. A combination of LGE, defining necrosis, and Short Tau Inversion Recovery (STIR), targeted at edema, need to be performed. These images, once merged, show the distribution of edema and necrosis on an anatomic shell which can be used to predict arrhythmia recurrence and may guide redo ablation strategies ( figure 2 ) (28) .