Systems and methods for selecting a cardiac resynchronization therapy (CRT) mode involve sensing electrocardiogram (ECG) data for a patient, identifying a PR interval from the sensed ECG data, comparing the PR interval to a threshold, and selecting a CRT mode by selecting between a synchrony optimization mode and a preload optimization mode, the selection based on the comparison of the PR interval to the threshold. A synchrony optimization mode may be selected if the parameter is less than the threshold, and may optimize CRT for fusion between a left ventricular pulse and an intrinsic wavefront. The preload optimization mode may be selected if the parameter is greater than the threshold, and may optimize CRT for fusion between respective wavefronts of the left ventricular pace and a right ventricular pace.
