Three- and four-dimensional reconstruction of intra-cardiac anatomy from two-dimensional magnetic resonance images.

The present study was designed to evaluate the feasibility and clinical usefulness of three-dimensional (3D) reconstruction of intra-cardiac anatomy from a series of two-dimensional (2D) MR images using commercially available software. Sixteen patients (eight with structurally normal hearts but due to have catheter radio-frequency ablation of atrial tachyarrhythmias and eight with atrial septal defects (ASD) due for trans-catheter closure) and two volunteers were imaged at 1T. For each patient, a series of ECG-triggered images (5 mm thick slices, 2-3 mm apart) were acquired during breath holding. Depending on image quality, T1- or T2-weighted spin-echo images or gradient-echo cine images were used. The 3D reconstruction was performed off-line: the blood pools within cardiac chambers and great vessels were semi-automatically segmented, their outer surface was extracted using a marching cube algorithm and rendered. Intra- and inter-observer variability, effect of breath-hold position and differences between pulse sequences were assessed by imaging a volunteer. The 3D reconstructions were assessed by three cardiologists and compared with the 2D MR images and with 2D and 3D trans-esophagal and intra-cardiac echocardiography obtained during interventions. In every case, an anatomically detailed 3D volume was obtained. In the two patients where a 3 mm interval between slices was used, the resolution was not as good but it was still possible to visualize all the major anatomical structures. Spin-echo images lead to reconstructions more detailed than those obtained from gradient-echo images. However, gradient-echo images are easier to segment due to their greater contrast. Furthermore, because images were acquired at least at ten points in the cardiac cycles for every slice it was possible to reconstruct a cine loop and, for example, to visualize the evolution of the size and margins of the ASD during the cardiac cycle. 3D reconstruction proved to be an effective way to assess the relationship between the different parts of the cardiac anatomy. The technique was useful in planning interventions in these patients.

Atrial fibrillation current and future treatments: radiofrequency ablation and novel pacing techniques.

Atrial fibrillation (AF) is a common clinical arrhythmia with significant symptomatology and is associated with an increased risk of systemic embolic events. Until recently, the treatment options for AF were essentially pharmacological. Recent developments in the understanding of the mechanisms of AF have resulted in a series of non-pharmacological treatments becoming available. Such treatments include surgical 'maze' procedures and, more recently, the introduction of radiofrequency ablation techniques within the atria to prevent fibrillation. Complex pacing procedures, including multisite and biatrial pacing, have been used to treat AF. Tailoring treatment for individual patients is a complex task and this review will attempt to rationalise the non-pharmacological treatment paths for individual patients with AF.