An appreciation of some timing functions of a cardiac resynchronization device capable of left ventricular sensing.

Some systems for cardiac resynchronization therapy (CRT) offer left ventricular sensing. This discussion with an illustrative case demonstrates that timing cycles in these devices may sometimes be difficult to understand because of left ventricular sensing. Programming of the left ventricular upper rate interval is crucial to optimize the resynchronization ability of the system. Interactions with the maximum sensor rate, the right ventricular upper rate interval, the left ventricular T wave protection algorithm, and the minimum ventricular tachycardia detection rate have to be considered.