This study demonstrates that MIAVR has comparable outcomes with those of CAVR with regard to in-hospital mortality and midterm survival when analyzed at 1 and 5 years. Small increases in cross-clamp and CPB times for MIAVR were demonstrated, but these are unlikely to have impact on outcomes. A statistically significant shorter PLOS was present in the MIAVR group. The strength of this study is the propensity-matched comparative analysis of MIAVR outcomes. This study combines contemporary national MIAVR experience to CAVR experience at the same cardiac centers and thus provides accurate real-world outcome data for MIAVR.
We wrote to all centers in the UK to invite them to participate in this study. Nine enthusiastic centers responded, and seven are included where the data collected were robust and complete; other units did not participate, and therefore, this work represents a snapshot of contemporary practice in the UK. The data demonstrates that MIAVRs are increasingly performed, with an increase in numbers as a total percentage of AVRs. The proportion doubles during the study period.
Based on the results of this study, MIAVR is a safe alternative to CAVR, with 98.6% of patients surviving to hospital discharge. The reduction in PLOS in the MIAVR group may be a surrogate marker for reduced postoperative complications. Survival at 1 year exceeds 94% for both MIAVR and CAVR, and there is no difference in midterm survival.
Although the percentage of MIAVRs increased during the study period, MIAVR still represents a small proportion of total caseload even at the enthusiastic centers participating in this study. There are wide variations in the number of centers undertaking MIAVR and the number of surgeons involved at those centers. Practice is known to range between surgeons who have a default minimally invasive approach where all first-time isolated AVRs are performed as minimally invasive operations to those who exclusively perform CAVR.
There are areas of concern for cardiothoracic surgeons regarding technique for CPB during MIAVR. These pertain to the limited cardiac exposure that has numerous theoretical risks (including placement of cannulae, adequate cardioplegia, and cardiac venting). Limited exposure might limit assessment of volume-loaded ventricles, deairing of the heart, placement of pacing wires, or a retrograde cardioplegia cannula. Transesophageal echocardiogram mitigates some of these problems, as well as instillation of CO2 into the operative field, anterior placement of pacing wires, and manipulation of empty ventricles on CPB to avoid right ventricular injury. The data do not allow us to comment on the conversion rate to full sternotomy for technical difficulties. Published data on conversions show it to be in the region of 1% to 3%.13 In the presence of similar CPB and cross-clamp times in our cohort, it is likely that the surgeons undertaking the procedure have achieved the learning curve for the techniques.
There is apparent clinical equipoise between the two techniques. Minimally invasive AVR is safe, and multiple benefits have been reported in retrospective, propensity-matched, and randomized prospective studies. Previous studies of MIAVR have demonstrated reduced length of stay, with no change in mortality or operative times.12,27 The meta-analyses of multiple randomized trials have demonstrated decreased length of ITU stay and hospital stay,11,12 ventilation times,10 blood loss,10,11 and incidence of arrhythmias10 as well as improvement in pulmonary spirometry, sternal stability, and wound pain.15,28 However, a need remains for large adequately powered study to conclusively determine the advantages of MIAVR and in which patient population these benefits apply to.
Intuitively, these advantages might specially apply to higher-risk elderly patients with poorer physiological reserves and who might tolerate minimally invasive procedure better with a quicker recovery.29 The reasons for these reported benefits could be the maintenance of the bony continuity of the ribcage with preservation of respiratory dynamics, improved sternal stability, reduced pain, and less risk of chest and sternal infections. There might also be a reduction in bleeding as less bone marrow and periosteum are exposed with reduced cardiac dissection during surgical access.
The role of minimally invasive techniques in surgical AVR within the setting of sutureless valve technology and TAVI needs to be defined. Surgical AVR remains the criterion standard for patients requiring AVR. At present, although TAVI is only recommended for patients who are high-risk for surgical AVR, data from German registries have begun to demonstrate that “risk creep” is already occurring in transcatheter aortic valve procedures with some centers advocating expanding TAVI to younger lower-risk groups.30 In addition, a number of TAVI studies on intermediate-risk patients are on the way. The PARTNER II trial seeks to evaluate outcomes in patients with aortic stenosis and The Society of Thoracic Surgeons (STS) score of 4% to 6% and compare patients to CAVR. Patients with concomitant coronary artery disease will be randomized to percutaneous coronary intervention plus TAVI versus coronary artery bypass graft surgery plus AVR. As a noninferiority study, it will directly compare CAVR with transaortic (TAo) TAVI, transapical (TA) TAVI, or transfemoral-TAVI. Additional nested registries will also analyze outcomes in patients who are unsuitable for femoral access that are randomized to TA-TAVI or transaortic TAVI versus surgery. This strategy will seek to marry the advantages of the miniAVR access approach with balloon deployed TAVI device. Similarly, the Surgical Replacement and Transcatheter Aortic Valve Implantation (SURTAVI) trial will include patients older than 70 years with an STS score of 3% to 8%.
The stent valve evolution will deliver a greater range of sizes of prosthesis through smaller totally percutaneous delivery systems. Novel valve designs are currently in early human studies to improve the incidence of paravalvular leak, for instance, with the addition of sealing cuffs to variations of nitinol frames.31 Numerous cerebral embolic protection devices aim to catch debris from the aorta and reduce the neurological morbidity from the procedure.32 Percutaneous closure devices for femoral access vessels are being routinely used with smaller delivery sheaths, and percutaneous left ventricular apex closure is in animal testing stages.33
If surgeons are to remain actively engaged in the heart valve team driving technical improvements in TAo and TA techniques, this is likely to begin with assessing the impact of MIAVR for surgical cases and likely to evolve into completely minimally invasive/port access implantation of transcatheter devices for high/intermediate-risk patients. One of the centers involved in this study has an active TAo-TAVI program, and it is likely that these techniques will develop in parallel.34 The presence of the heart team at units undertaking transcatheter valve procedures is increasing referrals of elderly comorbid patients now undergoing open AVR.2,35–37 However, a recent decline in CAVR work has been observed with up to 40% of aortic valve operations being performed by TAVI in 2012.37,38
Other authors have commented on the fact that although TAVI is an attractive and viable treatment for selected high-risk patients (eg, porcelain aorta, truly frail patients, previous cardiac surgery, patient grafts), surgical minimally invasive access AVR should be regarded as a criterion standard for all the rest of the patients. The functional outcomes are excellent, including valve durability, low incidence of stroke, and no paravalvular leak, which are of paramount importance. For octogenarians, the results of MIAVR are better than often assumed.29,38 Even when MIAVR is performed in patients with mean logistic EuroSCOREs of 17% (leading into the accepted TAVI range), the midterm survival is good, with in-hospital mortality of 7.8% and freedom from all-cause death at 5 years at 72.4%.2,39 Outcomes in 175 octogenarians from a cohort of more than 1000 MIAVR patients demonstrated an operative mortality of 2%.13
Minimally invasive AVR might offer additional advantages to the sutureless valve technologies that are perceived to be an alternative treatment for high surgical risk patients with severe aortic stenosis. Sutureless valves aim to minimize CPB and cross-clamp times by using novel rapid valve deployment techniques. One-year outcomes for the Edwards INTUITY Valve System as part of the TRITON trial report MIAVR in 48.8% of cases with overall cumulative survival of 92.5% at 9.8 months. The CPB and cross-clamp times are reported as 75 minutes and 46.6 minutes with 54% of cases being isolated AVRs.2,5 There are other INTUITY studies that are planned; with CADENCE-MIS, the benefits of MIAVR coupled with rapid deployment valves will be studied versus CAVR and standard valves. The use of Perceval S and ATS 3f Enable has demonstrated similar reduction in bypass times of less than 30 minutes.3,40 Comparison with STS data show 60% decrease in operative time, which might reduce the effects on myocardial ischemia and hypoxia.27
There seems to be genuine clinical equipoise between MIAVR and CAVR. Before widespread adoption of MIAVR can be recommended, there is a need for a well-constructed, adequately powered prospective randomized controlled study comparing MIAVR with CAVR. To demonstrate differences in mortality, the study would need to be powered to include very large number of patients. Pragmatic approach would involve high-risk patients in whom the clinical benefits would be more pronounced for the minimally invasive techniques. The benefits in terms of reduced ITU and hospital stay need to be balanced against the costs of mini techniques. Although majority of the procedure is performed using standard AVR equipment and valves, trials are already underway to compare the impact of sutureless valves. It is likely that the most benefit from these procedures will be in higher-risk elderly patients with limited physiological reserves. Increased patient preference for minimally invasive techniques and improvement in quality-of-life surveys are also important end points that will need to be considered in the randomized trials.
This propensity-matched study of minimally invasive aortic valve surgery is based on multicenter, “real-world” experience and shows that MIAVR is a safe and feasible procedure with excellent early and midterm outcomes for patients with aortic valve disease. In line with other authors, we have shown benefits in shorter hospital stay that might lead to more widespread use.
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This study evaluated the outcomes of isolated minimally invasive aortic valve replacement (MIAVR) compared with conventional aortic valve replacement (CAVR) by performing a propensity-matched study from the UK National Database. Data were analyzed from seven volunteer centers from 2006 to 2012. Three hundred seven consecutive MIAVR patients were matched in a 1:1 ratio with CAVR patients. There was no statistically significant difference in the in-hospital mortality or 1-year survival. Although there was a significantly longer cross-clamp time in the MIAVR group, median postoperative length of stay was lower in the MIAVR patients by 1 day. The authors concluded that MIAVR was a safe alternative to CAVR with a shorter postoperative length of stay.
This is an excellent multicenter study evaluating MIAVR. The propensity matching is a strength of this article but does not fully compensate for selection bias. The authors recommended that a prospective, randomized study is needed to better evaluate MIAVR. Although this is true, unfortunately, it will be difficult for surgeons experienced in the minimally invasive technique and for patients to be randomized between MIAVR and CAVR.