Post-Operative Anticoagulation and the Incidence of Left Ventricular Assist Device Thrombosis

Introduction

Anticoagulation is critical for patients with durable left ventricular assist devices (LVADs) in order to protect against life threatening thromboembolic events. An increase in the incidence of pump thrombosis between 2009 and 2014 prompted examination of our anticoagulation practices following device implants. As the majority of pump thromboses occurred within six months of implant, we hypothesized that anticoagulation strategies employed immediately after implant might play a role. We describe the initial post-operative anticoagulation management of 105 patients implanted with a Heart Mate II (HM II) LVAD by a single surgeon at our academic center. Although patients with more severe clinical compromise were more likely to be bridged, we found no difference in overall pump thrombosis incidence based on the use of a post-operative parenteral anticoagulation bridge compared to unopposed warfarin.

Methods

We performed a retrospective review of 105 patients undergoing primary implant of a HM II LVAD at our center from 2009 through 2014 with follow up through May 31, 2015. Data included demographics, clinical status at time of implant, intra-operative practices, and initial post-operative anticoagulation management. A parenteral bridge was defined as initiation of a parenteral anticoagulant prior to achieving an INR ≥2.0. A parenteral bridge was further defined as early if initiated within ≤3 days of device implant and therapeutic if a goal PTT was achieved during each of the first 0-24, 24-48, and 48-72 hours of the bridge duration. A parenteral bridge was considered sub-therapeutic if at least one but not all PTT measurements were at goal and non-therapeutic if no PTT measurements were at goal. Unopposed warfarin was defined as initiation to reach a therapeutic INR without the use of parenteral anticoagulants. Pump thrombosis was defined as detection within the device, inflow cannula, or outflow conduit at the time of pump replacement, pump explantation, heart transplantation, or autopsy. Pump thrombosis within 186 days of implant was defined as early. Fisher's exact test and the Wilcoxon rank-sum test were used to compare categorical and continuous variables between groups. Cumulative incidence of pump thrombosis was compared using the Gray test with reimplantation, explantation, transplantation, or death as a competing risk.

Results

Among 105 HM II implants, 73 (70%) were treated with any parenteral bridge, 50 (48%) with an early bridge, and 29 (28%) with an early therapeutic bridge. Median time to bridge initiation was 3 days (range 1 to 7) and median bridge duration was 6 days (range 1 to 45). A total of 32 patients (30%) received unopposed warfarin. Time to warfarin initiation and therapeutic INR were shorter in patients who received unopposed warfarin compared to a parenteral bridge, with median values of 1 vs. 2 days and 5 vs. 8 days, respectively (p<0.001 for both). Patients who received a parenteral bridge had more severe preoperative clinical compromise (p=0.039) and longer intensive care unit length of stay (p=0.005).

Pump thrombosis occurred in 25 patients (24%) and 14 (13%) were early. Hypertension was the only clinical variable that differed by group (p=0.012) and was more prevalent in patients with pump thrombosis.

Cumulative incidence analyses showed no significant difference in the incidence of pump thrombosis between patients who did and did not receive a parenteral bridge (p = 0.25), an early parenteral bridge (p=0.37), or a therapeutic parenteral bridge (p=0.87) (Figure 1). At 6 months the cumulative incidence (95% confidence interval) of pump thrombosis was 7.9% (2.0, 19.3) for those who received a therapeutic bridge and 16.4% (8.7, 26.3) for those who did not. At 24 months these values were 22.7% (9.4, 39.5) and 24.3% (14.6, 35.3), respectively.

Among patients who did not receive a parenteral bridge, there was no difference in the time to initiation of warfarin (p=0.23) or therapeutic INR (p=0.13) according to the outcome of pump thrombosis.

Conclusions

Post-operative parenteral bridging was more common than initiation of unopposed warfarin. Indices of more severe clinical compromise were associated with the use of a parenteral bridge. Our data suggest that post-implant bridging does not affect overall incidence of LVAD thrombosis. Further analysis will be performed to determine if parenteral bridging prevents early pump thrombosis.

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