Temporary biventricular pacing decreases the vasoactive-inotropic score after cardiac surgery: a substudy of a randomized clinical trial

Abstract

Objective: Vasoactive medications improve hemodynamics after cardiac surgery but are associated with high metabolic and arrhythmic burdens. The vasoactive-inotropic score was developed to quantify vasoactive and inotropic support after cardiac surgery in pediatric patients but may be useful in adults as well. Accordingly, we examined the time course of this score in a substudy of the Biventricular Pacing After Cardiac Surgery trial. We hypothesized that the score would be lower in patients randomized to biventricular pacing.

Methods: Fifty patients selected for increased risk of left ventricular dysfunction after cardiac surgery and randomized to temporary biventricular pacing or standard of care (no pacing) after cardiopulmonary bypass were studied in a clinical trial between April 2007 and June 2011. Vasoactive agents were assessed after cardiopulmonary bypass, after sternal closure, and 0 to 7 hours after admission to the intensive care unit.

Results: Over the initial 3 collection points after cardiopulmonary bypass (mean duration, 131 minutes), the mean vasoactive-inotropic score decreased in the biventricular pacing group from 12.0 ± 1.5 to 10.5 ± 2.0 and increased in the standard of care group from 12.5 ± 1.9 to 15.5 ± 2.9. By using a linear mixed-effects model, the slopes of the time courses were significantly different (P = .02) and remained so for the first hour in the intensive care unit. However, the difference was no longer significant beyond this point (P = .26).

Conclusions: The vasoactive-inotropic score decreases in patients undergoing temporary biventricular pacing in the early postoperative period. Future studies are required to assess the impact of this effect on arrhythmogenesis, morbidity, mortality, and hospital costs.

Keywords: 16; 17; 21; 31; BiPACS; BiVP; Biventricular Pacing After Cardiac Surgery; CPB; ICU; MVO2; SOC; VIS; VIS(max); biventricular pacing; cardiopulmonary bypass; intensive care unit; maximum vasoactive-inotropic score; myocardial oxygen consumption; standard of care; vasoactive-inotropic score.

Figure 1. Time Course of BiPACS Protocol

During Phase I, after weaning from cardiopulmonary bypass (CPB), the protocol maximizing cardiac output was performed. The optimal paced setting, as determined by Phase I optimization, was designated P1. Patients were randomized after Phase I into either the BiVP arm or the standard of care arm. Patients in the BiVP arm were paced under P1 until Phase II. During Phase II, after sternal closure (SC), the protocol maximizing mean arterial pressure was determined and designated P2. Pacing was then resumed using P2 in the BiVP arm until Phase III optimization, at which point the study period was concluded. VIS was calculated before randomization (VIS₁), before Phase II (VIS₂), upon relocation from the operating room to the ICU (VIS₃), and hourly when the patient was in the ICU (VIS₄ – VIS₁₀).

Figure 2. Diverging time course from randomization to ICU admission in the standard of care (SOC, n=26) and biventricular pacing groups (BiVP, n=24)

VIS increased from 12.5±1.9 at randomization to 15.5±2.9 at ICU entry in the SOC group but decreased from 12.0±1.5 to 10.5±2.0 in the BiVP group. The slopes of these VIS-time relations are significantly different by linear mixed effects analysis (p=0.02). The time between Phase I and Phase II averaged 66±30 minutes and 65±35 minutes between Phase II and ICU entry. Pacing was optimized at time points VIS₁ and VIS₂.

Figure 3. VIS from randomization until 7 hours after ICU entry

Hourly averages of VIS are shown for the standard of care (SoC, n=26) and biventricular pacing (BiVP, n=24) groups. The slopes of the ViS-time relations are significantly different through the first hour in the ICU by linear mixed effects analysis (p=0.0015). Pacing was optimized at time points VIS₁ and VIS₂. Data collection was limited to 7 hours because premature Swann-Ganz catheter removal disqualified one patient from continuing study.