Real-Time Cardiac MR Anatomy and Dyssynchrony Overlay for Guidance of Cardiac Resynchronization Therapy Procedures: Clinical Results Update
Optimal left ventricular (LV) lead placement via the coronary sinus (CS) is a critical factor in defining response to cardiac resynchronization therapy (CRT). Using novel MR image acquisition, segmentation, overlay and registration software we set out to guide lead placement by avoiding scar and targeting the LV region with the latest mechanical activation. We previously reported clinical results for 7 patients and now present updated results. 17 patients underwent cardiac magnetic resonance (CMR) scans. 3D whole heart images were segmented to produce high-fidelity anatomical models of the cardiac chambers and coronary veins. Four-chamber and short-axis cine images were processed using Tomtec software to give a 16-segment time volume-dyssynchrony map. In patients with myocardial scar, the Gadolinium late enhancement images were manually segmented and registered to the anatomical model along with the dyssynchrony map. The 3 latest mechanically acti- vated segments with <50% scar were identified and this information was overlaid at CRT implant on to live X-ray fluoroscopic images using a prototype version of the Philips EP Navigator software (see figure). Subsequently, the X-ray C-arm and table could be moved freely whilst automatically maintaining a registered roadmap. We used a high-fidelity pressure wire to assess the acute haemodynamic response to pacing in different regions of the overlaid 16 segment model. 15 of the 17 patients underwent successful placement of a LV pacing lead via the CS with satisfactory pacing parameters and no phrenic nerve stimulation at implant. In 2 patients we were unable to place a LV lead successfully in any branch of the CS. We paced in at least one of our 3 target segments in 11 patients. 67% of patients were responders as defined by a 10% increase in +dP/dt over baseline. In conclusion, CMR-guided CRT allowed left lead placement in 15/17 patients with approximately 2/3 patients being acute responders. Furthermore, specific targeting was successful in 11/15 patients using the image-guidance system. Following this successful pilot study, we will commence a randomized control study to examine if image-guided implantation improves patient response to CRT.