Computed tomography imaging of the coronary sinus: a valuable preoperative screen for resynchronization therapy?

The study by Mlynarska et al. [1] expands upon two previous studies [2, 3] evaluating the ability of multi-detector computed tomography (MDCT) imaging to visualize the coronary sinus (CS) and its branches in patients undergoing placement of a cardiac resynchronization therapy (CRT) system. As previously observed, the main body of the CS could be reasonably well visualized, whereas the lateral coronary veins were less well visualized. In general, successful endovascular implantation of a CRT device can be accomplished in 90–97% of cases [4, 5]. Following implantation, approximately two thirds of patients will improve clinically, with the remaining third being described as ‘non-responders’. In order for MDCT image reconstruction to be of value, it must provide information that will lead either to an increase in the success rate for implantation, an improvement in the efficiency of the procedure, or provide information leading to the identification of a means of addressing non-responders. There can be several explanations for a failure to successfully implant a CS lead. These include failure to engage and cannulate the ostium of the CS, failure to advance sheaths into the CS due to proximal tortuosity of the vessel, acute angle takeoffs of the target venous branches, venous stenosis, complete lack of suitable veins, and the relative proximity of the target vessel to the phrenic nerve leading to diaphragmatic pacing. Imaging techniques would specifically need to identify the location of the CS ostium and visualize the proximal 2 to 3 cm of the CS, rather than the main body of the CS. Beyond this, imaging of the origin and extent of the lateral veins are more important. Improvements in sheath design, lead size, and venoplasty techniques address many of these obstacles. The incremental benefit that would be provided by pre-procedural CT imaging of the CS anatomy is unclear and was not tested in the current study. Indeed, as the authors point out, CT imaging comes at the expense of approximately 120 mL contrast agent and exposure to radiation. Nor does it obviate the need for X-rays and contrast use during the actual procedure. Current procedure times for resynchronization device implantation range from just over one hour to more than three hours for difficult cases. Road mapping techniques using standard fluoroscopy in orthogonal views provide information. Newer techniques such as high speed rotational angiography [6–8] allow for three-dimensional reconstruction of the CS in real time. In some laboratories, this technique can be combined with the use of remote magnetic navigation to direct a magnetic guidewire to a distal coronary sinus branch through areas of tortuosity [9, 10]. New echocardiographic techniques can identify regions of delayed left ventricular activation. Correlation between lead position and the area of most delayed activation may predict the greatest response to resynchronization therapy [11]. Provided the location, size and extent of the target branches can be identified with MDCT, coupling this with an echocardiogram in order to identify target regions of dyssynchrony could begin to address the third of patients who do not respond to