Apparatus and methods for automatic adjustment of av interval to ensure delivery of cardiac resynchronization therapy

A method of left ventricular pacing including automated adjustment of a atrio-ventricular (AV) pacing delay interval and intrinsic AV nodal conduction testing comprising—upon expiration or reset of a programmable AV Evaluation Interval (AVEI)—performing the following steps:

• temporarily increasing a paced AV (PAV) interval and a sensed AV (SAV) interval and a. testing for adequate AV conduction and b. measuring a median intrinsic atrio-ventricular (PR) interval for a first-to-depolarize ventricular chamber for at least three consecutive cardiac cycles, storing:
• in the event that the AV conduction test reveals a physiologically acceptable intrinsic PR interval for said ventricular chamber then storing the physiologically acceptable median PR interval in a memory structure;
• subtracting approximately 30 milliseconds from the median PR interval to define a pre-excitation interval (PEI);
• in the event that the AV conduction test reveals unacceptably long PR intervals then:
• 1. performing a pacing mode-switch to a bi-ventricular (Bi-V) pacing mode and 2. increasing the magnitude of the AVEI;
• and
• delivering a pacing stimulus to the last to depolarize ventricle approximately at the expiration of the PEI.