Minimally Invasive AVR vs AVR Through Full Sternotomy
Minimally Invasive AVR vs AVR Through Full Sternotomy
Although the benefits of mini AVR surgery have been widely reported, widespread adoption has not occurred and some skeptics are calling for additional evidence. We present a robust, propensity-matched comparison of aortic valve replacement via HS and FS approaches from our institution since 2002. The major findings in our study are that patients undergoing isolated AVR via HS had less time on the ventilator, shorter ICU and hospital length of stays with comparable short and long-term survival compared to the FS group. These findings corroborate other reports demonstrating similar in-hospital benefits of mini AVR. Numerous studies have shown that these improved in-hospital outcomes likely result from decreased post-operative pain, facilitating quicker return of pulmonary function and mobilization.
Another major advantage promoted by champions of minimally invasive surgery is the decreased transfusion requirements compared with FS. In our study, we found a decreased rate of transfusion in the HS group. These results are consistent with prior meta-analyses, as well as another recent propensity-matched study by Gilmanov and colleagues, which reported half as many units transfused per patient in the minimally invasive AVR group compared to FS patients. Interestingly, Gilmanov and colleagues reported no difference in reoperations for bleeding, a finding consistent with our own results (Table 4). Along with increased transfusion requirements, blood loss in the first 24 h after surgery is higher with FS.
The simple principle that less dissection yields less chance for bleeding and therefore minimizes transfusion requirements may also extend to reoperative surgery. In a report of our early experience with reoperative partial upper HS, we showed decreased operative and post-operative transfusions, as well as less chest tube drainage in the first 24 h. Our current investigation did not corroborate these initial transfusion findings, consistent with our recent report that octogenarians undergoing reoperative AVR have no difference in bleeding and transfusion requirements. Detailed data on chest tube drainage was not available.
Another important difference seen in the HS group was the decreased incidence of new onset atrial fibrillation during the post-operative period (HS: 17.6% vs. FS: 25.4%). While the etiology of atrial fibrillation remains complex and multi-factorial, similar findings have been reported, though pooled data remains inconclusive. Differences in new onset atrial fibrillation have also been observed with other minimally invasive approaches such as the right anterior minithoractomy. Recent studies comparing ministernotomy and right minithoracotomy for AVR also show possible advantages to the minithoracotomy, including less transfusion and hospital length of stay. Additional studies and data pooled from multiple institutions are needed to confirm these findings.
The HS affords the surgeon a "familiar exposure" and does not require special instruments. This may minimize the learning curve compared to a mini-thoracotomy approach and may ultimately facilitate faster cardiopulmonary bypass and aortic cross clamp times as reported in our cohort. Brown and colleagues performed a meta-analysis of 26 studies and concluded that differences in operative times were not significant, but many of these studies reported data from early surgical experiences with minimally invasive sternotomy prior to 2002. An important advantage of the HS is the option for conversion to conventional, FS. We have previously published data on the conversion rate from our first 10 years of mini AVR experience, reporting an incidence of 4%, with poor exposure being the most common reason for conversion. Pooled data now estimate a conversion rate of 3% (95% confidence interval 1.8-4%).
Our long term clinical outcomes confirm the safety and efficacy of valves placed through a HS approach. No differences were seen in overall survival or time to aortic valve re-intervention for any cause (Figures 2, 3).
This study represents a retrospective, single center experience and is therefore subject to all limitations inherent to such a design. While the propensity matching technique used has been well validated, a limitation of the methodology is that it cannot address bias introduced by unmeasured variables, thus it is possible our results reflect the influence of unknown factors other than the effect of the treatment on the treated. However, this design does allow us to evaluate a patient sample that is representative of the isolated AVR population at our institution, and our sample size was robust. We chose to begin our study period in 2002 for two reasons: (I) this is approximately 5 years after the commencement of routine mini AVRs and, therefore, represents a period after the learning curve; and (II) completeness of data available in our electronic records. While this may be a limitation in the sense that we excluded patients undergoing mini AVR, it represents a truer comparison of surgical expertise in the two techniques.
Discussion
Although the benefits of mini AVR surgery have been widely reported, widespread adoption has not occurred and some skeptics are calling for additional evidence. We present a robust, propensity-matched comparison of aortic valve replacement via HS and FS approaches from our institution since 2002. The major findings in our study are that patients undergoing isolated AVR via HS had less time on the ventilator, shorter ICU and hospital length of stays with comparable short and long-term survival compared to the FS group. These findings corroborate other reports demonstrating similar in-hospital benefits of mini AVR. Numerous studies have shown that these improved in-hospital outcomes likely result from decreased post-operative pain, facilitating quicker return of pulmonary function and mobilization.
Another major advantage promoted by champions of minimally invasive surgery is the decreased transfusion requirements compared with FS. In our study, we found a decreased rate of transfusion in the HS group. These results are consistent with prior meta-analyses, as well as another recent propensity-matched study by Gilmanov and colleagues, which reported half as many units transfused per patient in the minimally invasive AVR group compared to FS patients. Interestingly, Gilmanov and colleagues reported no difference in reoperations for bleeding, a finding consistent with our own results (Table 4). Along with increased transfusion requirements, blood loss in the first 24 h after surgery is higher with FS.
The simple principle that less dissection yields less chance for bleeding and therefore minimizes transfusion requirements may also extend to reoperative surgery. In a report of our early experience with reoperative partial upper HS, we showed decreased operative and post-operative transfusions, as well as less chest tube drainage in the first 24 h. Our current investigation did not corroborate these initial transfusion findings, consistent with our recent report that octogenarians undergoing reoperative AVR have no difference in bleeding and transfusion requirements. Detailed data on chest tube drainage was not available.
Another important difference seen in the HS group was the decreased incidence of new onset atrial fibrillation during the post-operative period (HS: 17.6% vs. FS: 25.4%). While the etiology of atrial fibrillation remains complex and multi-factorial, similar findings have been reported, though pooled data remains inconclusive. Differences in new onset atrial fibrillation have also been observed with other minimally invasive approaches such as the right anterior minithoractomy. Recent studies comparing ministernotomy and right minithoracotomy for AVR also show possible advantages to the minithoracotomy, including less transfusion and hospital length of stay. Additional studies and data pooled from multiple institutions are needed to confirm these findings.
The HS affords the surgeon a "familiar exposure" and does not require special instruments. This may minimize the learning curve compared to a mini-thoracotomy approach and may ultimately facilitate faster cardiopulmonary bypass and aortic cross clamp times as reported in our cohort. Brown and colleagues performed a meta-analysis of 26 studies and concluded that differences in operative times were not significant, but many of these studies reported data from early surgical experiences with minimally invasive sternotomy prior to 2002. An important advantage of the HS is the option for conversion to conventional, FS. We have previously published data on the conversion rate from our first 10 years of mini AVR experience, reporting an incidence of 4%, with poor exposure being the most common reason for conversion. Pooled data now estimate a conversion rate of 3% (95% confidence interval 1.8-4%).
Our long term clinical outcomes confirm the safety and efficacy of valves placed through a HS approach. No differences were seen in overall survival or time to aortic valve re-intervention for any cause (Figures 2, 3).
Study Limitations
This study represents a retrospective, single center experience and is therefore subject to all limitations inherent to such a design. While the propensity matching technique used has been well validated, a limitation of the methodology is that it cannot address bias introduced by unmeasured variables, thus it is possible our results reflect the influence of unknown factors other than the effect of the treatment on the treated. However, this design does allow us to evaluate a patient sample that is representative of the isolated AVR population at our institution, and our sample size was robust. We chose to begin our study period in 2002 for two reasons: (I) this is approximately 5 years after the commencement of routine mini AVRs and, therefore, represents a period after the learning curve; and (II) completeness of data available in our electronic records. While this may be a limitation in the sense that we excluded patients undergoing mini AVR, it represents a truer comparison of surgical expertise in the two techniques.
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