The Application of Negative Atrioventricular Hysteresis in Cardiac Resynchronization Therapy

Inclusion Criteria: * Implanted with a functioning SJM Quadripolar CRT Pacing System * QRS duration \> 140 ms * Left bundle branch block documented * Ability to provide informed consent for study participation * Willing to comply with the study evaluation requirements * At least 18 years of age Exclusion Criteria: * CRT Pacing System implanted less than 1 week at time of enrollment * CRT Pacing System implanted more than 24 months at time of enrollment * CRT Pacing System implanted more than 90 days at time of enrollment AND intrinsic QRS duration is shorter than pre-implant intrinsic QRS duration by more than 10 ms * Resting ventricular rate \>100 bpm * Intrinsic PR interval \> 300 ms * Paroxysmal or persistent atrial tachycardia or atrial fibrillation documented * A recent myocardial infarction, ablation, drug intoxication, electrolyte imbalance, or any condition within the last 90 days that would be contraindicated for CRT programming changes in the opinion of the investigator * Women who are pregnant or who plan to become pregnant during the study