Cardiac resynchronization therapy (CRT) is now an accepted treatment for patients with drug-refractory congestive heart failure, severe left ventricular (LV) systolic dysfunction, and an interventricular conduction delay. Clinical trials of CRT have consistently demonstrated improvement in functional class, exercise capacity, and quality of life and a reduction of recurrent hospitalizations for exacerbation of heart failure [1, 2, 3]. CRT has been shown to decrease ventricular volumes and improve left ventricular ejection fraction . Early attempts at pacing from the coronary veins used unipolar, standard endocardial leads that were modified for coronary venous placement by removing the tines and subsequently used leads specially designed for left ventricular pacing the coronary venous system [5,6]. Initially, these were leads dedicated to left atrial pacing, and subsequently these leads were specially designed for left ventricular pacing, which resulted in a higher success rate at implantation . The development of the over-the-wire pacing lead technology increased the likelihood of a successful CRT implantation. The coronary sinus ostium lies at the base of the triangle of Koch, whose dimensions have been reported to vary considerably, even in the absence of heart failure [8, 9, 10]. In patients undergoing CRT, cannulation of coronary sinus may occasionally be extremely difficult. The right atrial anatomy may be considerably distorted and the tricuspid valve as well the various fossae extremely dilated. Moreover, the failing heart is associated with right ventricular and left atrial enlargement, upward rotation of the long axis, posterior rotation of the short axis of the heart and mitral annulus dilatation. All these abnormalities change the relative position of the Coronary Sinus (CS) ostium within the right atrium and the orientation of the CS relative to normal fluoroscopic landmark. The CS takes a more vertical and posterior location requiring the guiding catheter to engage the ostium from a location more inferiorly in the right atrium. Variations in coronary sinus shape, diameter, angulation, and branches anatomy increase the difficulty of the insertion of permanent pacing leads [11, 12, 13]. The analysis of the outcomes of transvenous CRT system implantation in 4,844 patients from MIRACLE, MIRACLE ICD, InSync III, CONTAK CD, COMPANION, and CARE-HF studies indicates that the implant attempt succeeded in 4,386 of 4,844 (90.5%) patients. A total of 20 deaths were procedure related. A total of 74 patients experienced coronary sinus complications (dissections, perforations). A total of 256 LV lead dislodgments was reported [14, 15] (Table 14.1).
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