The purpose of primary endpoint 1 is to evaluate the Sentus QP related complication-free rate through 6 months post-implant. This is evaluated as a percentage of participants without a complication.

All participants in the Pre-Market cohort, defined as the study participants who were consented and implanted with a Sentus QP LV lead on or before January 29, 2016.

The purpose of primary endpoint 2 is to evaluate the LV lead pacing threshold for the permanently programmed pacing vector at 3 months post-implant.This was evaluated by performing an exact, binomial test comparing the percentage of participants with acceptable pacing thresholds to a performance goal of 88%. LV threshold values of less than or equal to 2.5 V at 0.4 ms in the permanently programmed vector are considered acceptable.

All participants in the Pre-Market cohort, defined as the study participants who were consented and implanted with a Sentus QP LV lead on or before January 29, 2016, and with completed threshold testing at 3 months post-implant or with available data from remote monitoring or next visits (as pre-specified in the protocol).

The purpose of primary endpoint 3 is to evaluate the Sentus QP related complication-free rate through study termination (post approval phase). This is evaluated as a percentage of participants without a complication.

All participants in the Post-Market cohort, which included all participants who were enrolled with planned 5 year follow-up and were successfully implanted with a Sentus QP left ventricular lead.

The purpose of the secondary endpoint is to evaluate the LV lead pacing threshold for the permanently programmed pacing vector at 3 months post-implantation in the two different lead types, Sentus OTW QP L and Sentus OTW QP S. This was evaluated as the number of participants with an acceptable pacing threshold out of the total number of patients for each lead model. LV threshold values of less than or equal to 2.5 V at 0.4 ms in the permanently programmed vector is considered acceptable.

All participants in the Pre-Market cohort, defined as the study participants who were consented and implanted with a Sentus QP LV lead on or before January 29, 2016, and with completed threshold testing at 3 months post-implant.

The purpose of this secondary endpoint is to evaluate the number of participants with at least one acceptable LV lead pacing threshold in a novel pacing vector at 3 months post-implantation. This was evaluated as the number of participants with at least one acceptable LV pacing threshold in a novel pacing vector out of the total number of participants with completed novel pacing threshold testing. LV threshold values of less than or equal to 2.5 V at 0.4 ms in a novel pacing vector is considered acceptable.

All participants in the Pre-Market cohort, defined as the study participants who were consented and implanted with a Sentus QP LV lead on or before January 29, 2016, and with completed novel vector threshold testing at 3 months post-implant.

The purpose of this secondary endpoint is to evaluate acceptable LV lead sensing amplitude at 3 months post-implantation. This was evaluated as the number of participants with an acceptable LV sensing amplitude out of the total number of participants. R-wave sensed mean amplitude of greater than or equal to 2 mV is considered acceptable.

All participants in the Pre-Market cohort, defined as the study participants who were consented and implanted with a Sentus QP LV lead on or before January 29, 2016, and with completed sensing test at 3 months post-implant.

The purpose of this secondary endpoint is to evaluate the acceptable LV lead pacing impedance at 3 months post-implantation. This was evaluated as the number of participants with an acceptable LV pacing impedance out of the total participants. LV impedance values of greater than 200 Ohms and less than 2000 Ohms is considered acceptable.

All participants in the Pre-Market cohort, defined as the study participants who were consented and implanted with a Sentus QP LV lead on or before January 29, 2016, and with completed impedance testing at 3 months post-implant.

The purpose of this secondary is to evaluate the Sentus related complication-free rate through 6 months post-implant by the Kaplan-Meier method. The below table shows Kaplan-Meier estimates of the estimated freedom from Sentus related complications at 180 days.

All participants in the Pre-Market cohort, defined as the study participants who were consented and implanted with a Sentus QP LV lead on or before January 29, 2016.

The purpose of secondary endpoint 7 is to evaluate the Sentus QP related complication-free rate through study termination (post approval phase). This is evaluated as percentage of participants without a complication per lead model.

All participants in the Post-Market cohort, which included all participants who were enrolled with planned 5 year follow-up and were successfully implanted with a Sentus QP left ventricular lead.

The purpose of secondary endpoint 8 is to evaluate the rate of individual types of adverse events related to the Sentus QP lead through study termination (post approval phase). This is evaluated as the percentage of participants with a specific adverse event out of the total participants.

All participants in the Post-Market cohort, which included all participants who were enrolled with planned 5 year follow-up and were successfully implanted with a Sentus QP left ventricular lead.

The purpose of this secondary endpoint is to evaluate the number of participants in whom phrenic nerve stimulation or high LV pacing threshold was be successfully resolved by reprogramming of the LV pacing vector. This is evaluated as the number of participants with successful reprogramming out of all participants experiencing phrenic nerve stimulation or high LV pacing threshold. LV pacing threshold resulting in invasive intervention, or, in the absence of intervention, a lead threshold that has increased two fold from the chronic threshold value, and is unable to achieve a 2:1 safety margin at follow-up is considered a high LV pacing threshold.

All participants in the Pre-Market cohort, defined as the study participants who were consented and implanted with a Sentus QP LV lead on or before January 29, 2016, and whom experienced phrenic nerve stimulation or high LV pacing threshold.