Utilization of Minimally Invasive Approaches
MIAVS was introduced to the Cleveland Clinic in 1996 by Cosgrove. In that year, these operations comprised 89 of a total of 718 aortic valve operations (12.4%), of which 66 (74.2%) were isolated aortic valves. The incision of choice for these early procedures was a right parasternal approach with peripheral cannulation. Despite a high rate of technical success, this approach was unsatisfactory secondary to a number of lung herniations requiring reoperation, and a stroke rate of 3%, which was attributed by the authors to the use of peripheral cannulation in atherosclerotic aortas. Over the next few years, surgeon preference combined with an evaluation of early and late outcome data evolved toward an upper hemisternotomy approach. With this, there was an increasing adoption of MIAVS as the preferred approach for isolated valve operations, and the advent of transcatheter valve replacement has not impacted the valve surgery volume (Table 1). In recent years, the number of combined operations has increased significantly, reflecting the increasing adoption of concomitant aortic procedures in particular.
Overall, the trend for both isolated aortic and mitral valve operations has been moving away from sternotomy and more toward less invasive approaches, with sternotomy now the incision of choice in the minority of isolated valve cases (Figure 2). The two greatest growth areas for the valve practice at present are primary and reoperative isolated aortic valves (data not shown). Since 2011, right anterior thoracotomy approaches have been used for a selected group of patients with aortic valve disease. To date, 48 of these operations have been performed with no hospital or 30-day mortality. Surgeon preference has been for routine preoperative three-dimensional (3D) imaging in these patients, and use of direct aortic cannulation where possible. Recently, this approach has also been used for sutureless valve replacement.
Concomitant Procedures and Standardized Approach
Operations performed in the early cohort of patients undergoing MIAVS included bioprosthetic AVRs, homograft aortic root replacements, and aortic valve repairs. With increasing experience, a large number of concomitant operations have been performed via MIAVS approaches. Currently, ascending aortoplasties, aortic root enlargements, aortic root replacements, ascending aortic replacements (with a cross-clamp) and hemiarch replacements (with circulatory arrest) are routinely performed in addition to aortic valve surgery via the upper hemisternotomy. AVR and root enlargement are performed via right anterior thoracotomy. To date, ascending aortic procedures, except for aortic endarterectomy for calcium, have not been performed via the anterior thoracotomy approach. While choice of incision is still dependent on surgeon preference, rough guidelines have evolved over time to govern incision selection (Table 2).
Mortality and MIAVS
Cosgrove and Sabik reported no mortality in the first small series of parasternal aortic valve surgery, setting the standard that minimally invasive approaches should maintain the same safety profile as conventional operation. Over the period of the study, operative mortality for isolated aortic valve surgery has remained low, and declined gradually to 0.5% in 2013. Routine surveillance of aortic valve outcomes has been part of the practice at the Cleveland Clinic and continues to inform procedure and incision selection in these patients. In isolated aortic valve patients, overall mortality is higher for sternotomy than for MIAVS, reflecting patient selection. In a subset of propensity matched patients, early mortality was low (0.7%) and equivalent for both groups, and long term survival was identical (Figure 3).
Survival after less invasive and full sternotomy aortic valve surgery among propensity-matched patients. Each symbol represents a death, positioned actuarially, vertical bars of 68% confidence limits, and numbers in parentheses patients remaining at risk. Solid lines are parametric estimates enclosed within dashed 68% confidence limits (equivalent to one standard error). Reproduced with permission (4).
Benefits of MIAVS
MIAVS patients report less pain after surgery, an effect that is sustained, though not dramatic (Figure 4). In addition, there is less utilization of narcotic pain medication in the first 2–3 days following surgery. MIAVS patients receive fewer blood and blood product transfusions, and are discharged from the hospital earlier than those with sternotomy. Of note, there is also a significant benefit in terms of pulmonary function as measured by bedside spirometry in the first 24–48 hours after surgery in MIAVS patients. This benefit in terms of early lung function may be one reason why patients with worse preoperative pulmonary function gain the most from MIAVS in comparison to sternotomy (Figure 5).
Temporal pattern of patients without pain (pain score category 0) after less invasive versus full sternotomy aortic valve surgery among propensity-matched patients. Adapted from reference (4).
Predicted 1-year risk-adjusted mortality according to preoperative FEV1% stratified by approach. FEV1, forced expiratory volume in 1 second. Adapted from reference (6).
Pitfalls of MIAVS
Complications related to the minimally invasive approach are related to the particularities of the incision itself, the lack of visualization of the entire heart and mediastinum and the increased challenge of navigating with decreased visibility. Lung herniation occurred in a subset of patients with parasternal approaches, requiring reoperation. Of the upper hemisternotomy patients, overall complication rates were not different compared with full sternotomy; however, in an analysis of 1,193 patients treated between 1995 and 2004, 34 (2.8%) patients underwent conversion to full sternotomy. Reasons for conversion included inadequate visualization (preclamp) and bleeding (postclamp). Of the patients with bleeding requiring conversion, the majority were related to coronary sinus injuries from placement of the retrograde cardioplegia cannula. An additional pitfall, which is not immediately apparent from the raw data, involves the frequency with which staff or trainee performs the procedure. Cross clamp times were shorter for upper hemisternotomy operations compared to full sternotomy for equivalent procedures, likely reflecting a tendency for the full sternotomy cases to be "teaching cases".
Ann Cardiothorac Surg. 2015;4(2):140-147. © 2015 AME Publishing Company