Background
Thoracic paravertebral block (TPVB) has been shown to provide excellent postoperative analgesia after minimally invasive cardiac surgery with lateral thoracotomy. Supraventricular arrhythmias (SVAs), including atrial fibrillation are a common complication after cardiac surgery and are associated with increased morbidity and mortality. Both postoperative pain and sympathetic nerve hyperactivity contribute to the development of SVAs. We hypothesized that continuous TPBV could reduce the occurrence of postoperative SVAs by inhibiting of both components. We evaluated the effect of continuous TPVB and other possible risk factors on the occurrence of postoperative SVAs in patients undergoing minimally invasive mitral valve repair at our institution.

Materials and Methods
After institutional review board approval, we performed a retrospective record based review of all patients who underwent minimally invasive mitral valve repair at our center between March 2011 and October 2016. Supraventricular arrhythmia was defined as at least 1 hour-duration of either atrial fibrillation, junctional rhythm, or atrial premature complex. We investigated the relationship between the incidence of SVAs with continuous TPVB, age, sex, and duration of aortic cross clamp time. A multivariate analysis was performed to identify independent risk factors.

Results
We included a total of 73 patients. A TPVB catheter was placed under ultrasonic guidance prior to surgery and a continuous dose of levobupivacaine (6.7 mg/h) was administered post operatively (54 cases). Fourty-two patients were diagnosed with SVA (57.5%) and commonly occurred on the first postoperative day. Catecholamines were either discontinued or maintained at very low doses in all cases. In the multivariate analysis, the risk of SVAs was decreased with continuous TPVB (odds ratio [OR] 0.24; 95% confidence interval [CI] 0.06-0.85, p=0.03). Duration of aortic cross clamp time (OR per min 1.02, 95%CI 1.01-1.03, p<0.01), and female gender (OR 4.64, 95%CI 1.55-15.49, p<0.01) were independent risk factors of SVAs. Increased age was not a significant factor.

Conclusion
The use of continuous TPVB was significantly related with a decreased incidence of postoperative SVAs. Duration of aortic cross clamp time and female gender were also significant risk factors. In addition to excellent postoperative pain control, continuous TPVB reduces the risk of SVAs in patients undergoing minimally invasive mitral valve repair.

Continuous thoracic paravertebral block reduces the risk of supraventricular arrhythmias after minimally invasive mitral valve repair