Diabetes mellitus is an increasingly prevalent disease afflicting nearly 27% of persons older than age 65, and the prevalence of diabetes is estimated to grow to 1 in 3 adults in the US by the year 2050.¹ Diabetes is highly prevalent among patients with cardiovascular disease, particularly in patients with severe aortic stenosis. The SURTAVI (Surgical Replacement and Transcatheter Aortic Valve Implantation) trial showed a diabetes prevalence of 34% among its study population.² The negative impacts of diabetes on cardiac surgery including aortic valve replacement have been well described and include the increased risks of sternal wound infections, post-operative respiratory failure, post-operative renal failure, need for blood transfusions, and in-hospital mortality.^3,4 Considering the invasive nature of surgical aortic valve replacement (SAVR), including the need for intubation, sternotomy, and cardiopulmonary bypass, it is intuitive that patients with diabetes mellitus undergoing SAVR would have worse outcomes compared to transcatheter aortic valve replacement (TAVR) given the less invasive nature of TAVR.

Multiple prior randomized trials and post-hoc analyses of these trials have demonstrated a benefit of transfemoral TAVR versus SAVR among patients at high and intermediate surgical risk with regards to mortality as well as complications including atrial fibrillation, bleeding, and renal failure.^2,5,8,9 In a recent paper, Ando et al. have now expanded on this evidence base by comparing the outcomes of TAVR versus SAVR in patients with diabetes undergoing aortic valve replacement between 2011 and 2013 using the Nationwide Inpatient Sample database (NIS).⁶ This study included a much larger patient population with sampling of 1,151 TAVR patients and 13,390 SAVR patients included in the analysis, comprising a weighted sampling representing 5,719 TAVR patients and 65,096 SAVR patients with diabetes over the study period. The authors demonstrated a significantly lower odds of the primary outcome of inpatient all-cause mortality in the TAVR group compared to SAVR (OR 0.63, 95% confidence interval [CI] 0.42 to 0.91, p = 0.02). This was despite the fact that the TAVR group was older (80 vs. 70 years, p < 0.001) and had more comorbid conditions. In addition to lower inpatient mortality, the TAVR group demonstrated less bleeding requiring transfusion (OR 0.43, 95% CI 0.34 to 0.53, p < 0.01), cardiac procedural complications (OR 0.34, 95% CI 0.27 to 0.45, p < 0.01), respiratory complications (OR 0.26, 95% CI 0.15 to 0.45, p < 0.01), postoperative sepsis (OR 0.45, 95% CI 0.27 to 0.77, p = 0.03), and acute myocardial infarction (OR 0.62, 95% CI 0.49 to 0.79, p < 0.01). The TAVR group had a higher rate of vascular complications (OR 1.5, 95% CI 1.1 to 2.0, p < 0.01) and new pacemaker implantation (OR 1.5, 95% CI 1.2 to 1.9, p <0.01) compared to SAVR consistent with all randomized trials of TAVR versus SAVR to date and with large registry studies.^2,5,7-9 Finally, Ando et al. showed that TAVR resulted in a modest reduction in hospital length of stay (median 6 vs. 8 days, p < 0.001) and overall cost ($58,878 vs. $63,869, p = 0.003) compared to SAVR among diabetic patients.

It is important to take into account that the data included in the study by Ando et al. were collected between 2011 and 2013, when earlier generation TAVR devices necessitating larger delivery sheaths and associated with high rates of pacemaker implantation and paravalvular leak were in use. It is also important to note that despite the increased vascular complication rate reported in the TAVR group, these patients demonstrated less bleeding than the SAVR cohort.

As the authors note, a strength of this study is that the NIS database is more representative of real world clinical practice as compared to randomized trials, hence making it generalizable. Indeed, the outcomes reported in this study are comparable to those recently reported for TAVR from the ACC/STS Transcatheter Valve Therapies (TVT) registry, which included overall 54,000 TAVR procedures performed in the US between 2012 and 2015 with an inpatient mortality rate ranging from from 5.7% in 2012 to 2.9% in 2015.⁷

There are several limitations to this study by Ando et al., most inherent to any retrospective database analysis utilizing administrative claims data. These include: selection bias, unmeasured and residual confounders, potential coding errors, and lack of detail in coding covariates (including a lack of data regarding diabetes severity and the types of TAVR devices implanted). Finally, since only inpatient mortality was studied, the impact of TAVR versus SAVR with regard to mortality among diabetics over longer periods of follow-up is unknown.

While these data add to a growing literature demonstrating a benefit for TAVR (and in particular transfemoral TAVR) versus SAVR in patients with elevated surgical risk, the study by Ando et al. underscores diabetes as an important surgical risk factor and a modulator of treatment effect among patients with severe aortic stenosis. As previously mentioned, diabetes is already widely recognized as a risk factor for cardiac surgical mortality and complications, and the Society for Thoracic Surgeon (STS) risk calculator incorporates detailed information regards diabetic status and treatment in risk estimation for SAVR. The recent study by Ando et al. reaffirms the benefit of transfemoral TAVR over SAVR among diabetic patients as was previously shown for all patients with at least intermediate surgical risk. These data should stimulate inquiry into whether diabetes may comprise of marker of incremental surgical risk favoring TAVR in patients deemed low or standard risk by current risk estimation algorithms.

References

1. American Diabetes Association. Economic costs of diabetes in the U.S. in 2007. Diabetes Care 2008;31:596-615.
2. Reardon MJ, Van Mieghem NM, Popma JJ, et al. Surgical or transcatheter aortic-valve replacement in intermediate-risk patients. N Engl J Med 2017;376:1321-31.
3. Bucerius J, Gummert JF, Walther T, et al. Impact of diabetes mellitus on cardiac surgery outcome. Thorac Cardiovasc Surg 2003;51:11-6.
4. Halkos ME, Kilgo P, Lattouf OM, et al. The effect of diabetes mellitus on in-hospital and long-term outcomes after heart valve operations. Ann Thorac Surg 2010;90:124-30.
5. Lindman BR, Pibarot P, Arnold SV, et al. Transcatheter versus surgical aortic valve replacement in patients with diabetes and severe aortic stenosis at high risk for surgery: an analysis of the PARTNER trial (Placement of Aortic Transcatheter Valve). J Am Coll Cardiol 2014;63:1090-9.
6. Abdo T, Akintoye E, Telila T, et al. Comparison of hospital outcome of transcatheter versus surgical aortic valve replacement in patients with diabetes mellitus (from the Nationwide Inpatient Sample). Am J Cardiol 2017;119:1250-4.
7. Grover FL, Vemalupalli S, Carroll JD, et al. 2016 annual report of the Society of Thoracic Surgeons/American College of Cardiology Transcatheter Valve Therapy Registry. J Am Coll Cardiol 2017;69:1215-30.
8. Adams DH, Popma JJ, Reardon MJ, et al. Transcatheter aortic-valve replacement with a self-expanding prosthesis. N Engl J Med 2014;370:1790-8.
9. Leon MB, Smith CR, Mack MJ, et al. Transcatheter or surgical aortic-valve replacement in intermediate-risk patients. N Engl J Med 2016;374:1609-20.

Keywords: Transcatheter Aortic Valve Replacement, Aortic Valve, Risk Factors, Hospital Mortality, Retrospective Studies, Sternotomy, Prevalence, Cardiopulmonary Bypass, Confidence Intervals, Atrial Fibrillation, Selection Bias, Inpatients, Length of Stay, Aortic Valve Stenosis, Heart Valve Prosthesis, Registries, Myocardial Infarction, Blood Transfusion, Diabetes Mellitus, Renal Insufficiency, Intubation, Wound Infection, Respiratory Insufficiency, Surgeons, Sepsis, Metabolic Syndrome

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