Abstract: Objectives. To evaluate the long-term outcomes of self-expandable nitinol stent implantation with intraluminal angioplasty for chronic total occlusion (CTO) in the superficial femoral artery (SFA) of patients with TransAtlantic Inter-Society Consensus (TASC) D lesions. Methods. From 2004 to 2011, self-expandable nitinol stent implantation in SFA was performed successfully in 72 consecutive limbs of 68 patients with TASC D lesions. These patients were assessed for an average of 38.8 ± 25.6 months. The procedure was performed using a 0.014˝ or 0.018˝ guidewire and intraluminal angioplasty. Results. Patients with hemodialysis constituted 20.6% of cases. The mean occlusion length was 244.6 ± 34.1 mm. A bidirectional approach was performed in 69.4% of cases. Primary patency rates were 77.9%, 71.9%, 67.2%, and 51.5% at 1 year, 2 years, 3 years, and 5 years, respectively. Secondary patency rates were 88.6%, 78.7%, 71.1%, and 56.0% at 1 year, 2 years, 3 years, and 5 years, respectively. Cox regression multivariate analysis for hemodialysis pertaining to loss of primary and secondary patency resulted in hazard ratio = 2.555 (95% confidence interval, 1.108-5.891; P=.03) for loss of primary patency and hazard ratio = 3.615 (95% confidence interval, 1.380-9.471; P=.01) for loss of secondary patency. Conclusion. Long-term patency of self-expandable nitinol intraluminal stent implantation with intraluminal angioplasty to treat CTO (TASC D) in SFA is promising. Hemodialysis was the only independent predictor for loss of primary and secondary patency.
J INVASIVE CARDIOL 2016;28(2):58-64
Key words: long-term outcomes, superficial femoral artery, self-expandable nitinol stent, TASC D, CTO
The second report of the TransAtlantic Inter-Society Consensus (TASC II) recommends femoropopliteal (FP) bypass surgery as the first-line therapy for patients with chronic total occlusion (CTO) in the superficial femoral artery (SFA). Such type D lesions can result in life-limiting claudication or critical limb ischemia (CLI).1 However, it remains controversial whether endovascular therapy (EVT) or FP bypass surgery should be performed for SFA in TASC D lesions in patients with comorbidity or high surgical risk.2 Long-term outcomes from subintimal angioplasty using a 0.035˝ looped guidewire with back-up support of a 4 Fr or 5 Fr diagnostic catheter have been reported previously;3-6 however, there are few reports on intraluminal angioplasty using 0.014˝ or 0.018˝ guidewires.5 Implantation of self-expandable nitinol stents produces favorable patency in SFA compared with balloon angioplasty.7 However, the long-term outcomes of SFA implantation of self-expandable nitinol stents via intraluminal angioplasty in TASC D lesions remain unknown. Moreover, a bidirectional approach can be applied in cases where an antegrade approach fails.8,9 Here, we report the long-term outcomes of self-expandable nitinol stent implantation via intraluminal angioplasty to treat TASC D lesions in the SFA, including bidirectional approaches.
From 2004 to 2011, self-expandable nitinol stents were successfully implanted in 72 consecutive limbs of 68 patients with TASC D lesions in the SFA. Results were analyzed in these patients for an average of 38.8 ± 25.6 months. Inclusion criteria of this study were as follows: (1) symptomatic lower-limb ischemia (Rutherford classification 2 to 6); and (2) de novo TASC D lesions in the SFA. We excluded patients with acute or subacute lower-limb ischemia in the SFA. We developed the study protocol in accordance with the Declaration of Helsinki, and it was approved by the ethics committee. Written informed consent was obtained from all patients.
Procedure. All patients were prescribed dual-antiplatelet therapy (ticlopidine 200 mg/day or clopidogrel 75 mg/day with aspirin 100 mg/day) for at least 3 days before EVT. After EVT, patients were prescribed ticlopidine or clopidogrel for at least 1 month and aspirin lifelong. The approach site was chosen at the physician’s discretion. If an antegrade approach was used, a 6 Fr sheathless guiding catheter or a 6 Fr sheath was inserted in the contralateral or ipsilateral groin, respectively. The popliteal artery was used if a retrograde approach was required. If the retrograde route needed to be established from the beginning of the EVT procedure, the popliteal artery was punctured with an 18 gauge needle under the guidance of ultrasonography with the patient in the prone position, followed by 3 or 4 Fr sheath insertion. If the retrograde approach was needed after a failed attempt at an antegrade approach, the popliteal artery was punctured with an 18 gauge needle with the patient in the supine position under guidance from a contrast dye injection, followed by the insertion of a microcatheter over a 0.014˝ floppy guidewire. Unfractionated heparin (5000-10,000 U) was administered via the guiding sheath. During the EVT procedure, intraluminal angioplasty was performed, in which a 0.014˝ or 0.018˝ guidewire with a microcatheter for support was manipulated with the intention of crossing the guidewire within the true lumen as much as possible;5 a 0.035˝ looped guidewire was not used for crossing the occlusion. The use of intravascular ultrasound (IVUS) was at physician discretion. After the guidewire successfully crossed the occluded lesion, the vessel diameter was assessed by predilating the lesion with a 3-4 mm balloon catheter. After predilation, self-expandable nitinol stents (Smart [Cordis Corporation], Luminexx or e-Luminexx [Bard PV], Wall [Boston Scientific], or Zilver [Cook Medical]) were implanted to fully cover the extent of the lesion. A stent was implanted in all cases, and was chosen at physician discretion. No atherectomy device, specialized crossing CTO catheter, or reentry device was used because these devices were not available in Japan during the study period. After stent implantation, postdilation was performed in all cases. Hemostasis was performed by hand compression for groin sites and by external compression devices (Tometa or balloon tamponade) for popliteal puncture sites.
Follow-up. Follow-up was performed during patient visits to the outpatient clinic. The lower extremity was imaged with ultrasonography, the ankle-brachial pressure index (ABI) test was performed, and the patient was asked about claudication of the lower extremity. Angiography of the lower extremity was performed if significant stenosis was suspected on ultrasonography, if the ABI had decreased by more than 0.15 with claudication, or if claudication had worsened to more than stage 1 Rutherford classification.
Definitions. Restenosis was defined as a peak systolic velocity rate of >2.5 in a duplex ultrasound examination or of >50% stenosis in an angiogram. Target-lesion revascularization (TLR) was defined as repeated vascularization of the stented segment within 5 mm proximal or distal to the stent. Clinically driven TLR was defined as TLR for patients with ischemic symptoms in a lower limb. Major amputation was defined as amputation above the foot joint. Primary patency was defined as a treated vessel without restenosis or revascularization. Secondary patency was defined as patency after TLR to the restenosis or occlusion in a treated vessel.
Endpoints. The primary endpoint was primary patency, and the secondary endpoint was secondary patency.
Statistics. Continuous variables are expressed as mean ± standard deviation. Differences between continuous variables were assessed with Student’s t-test. Differences between categorical variables were assessed with χ2 tests. Tests were two-tailed and P-values <.05 were considered to be statistically significant. Kaplan-Meier curves for time-to-event were plotted. A univariate analysis of lesions with and without restenosis was used to evaluate the following predictors for loss of primary and secondary patency: age, gender, hemodialysis, diabetes mellitus, hypertension, hypercholesterolemia, history of smoking, family history of ischemic heart disease, history of cerebrovascular disease, old myocardial infarction, angina pectoris, previous EVT, previous percutaneous coronary intervention (PCI), previous coronary artery bypass surgery (CABG), presence of CLI, preprocedural ABI, medication at baseline (cilostazol, thienopyridine, aspirin, calcium-channel blocker, angiotensin-converting enzyme inhibitor/angiotensin-receptor blocker [ACE/ARB], β-blocker, statins), number of stents implanted, reference vessel diameter, lesion length, number of below-the-knee (BTK) run-offs, lesion with calcification, inflow procedure, outflow procedure, use of IVUS, and application of a bidirectional approach. Factors with a P-value <.20 in the univariate analysis were included as a covariate in a multivariate analysis (Cox proportional hazard model). The results are presented as hazard ratios (HRs) with 95% confidence intervals (CIs). All analyses were performed with SPSS version 21 (IBM).
The present study included 72 limbs (lesions) of 68 consecutive patients. The mean follow-up period was 38.8 ± 25.6 months. The baseline characteristics and medical treatments at baseline are shown in Table 1 and Table 2, respectively. The mean age was 72.5 ± 7.3 years and 51.5% of patients had diabetes mellitus, 20.8% had CLI, and 20.6% were on hemodialysis. Lesion characteristics and procedural results are shown in Table 3. The mean occlusion length was 244 ± 34.1 mm and mean number of stents implanted per lesion was 3.1 ± 0.5. The target lesion showed moderate calcification in 8.3% of cases and severe calcification in 8.3% of cases. There were no BTK run-offs in 6.9% of lesions and 1 BTK run-off in 51.4% of lesions. An adjunctive inflow procedure (EVT for the iliac lesion) was performed for 15.3% and an outflow procedure (EVT for the BTK lesion) for 2.8% of lesions. The approach site is also shown in Table 3. In the present study, a bidirectional approach was employed in 50 cases (69.4%).
Procedural complications occurred in 3 cases (4.2%) (Table 3). Pseudoaneurysm at the puncture site in the popliteal artery developed in 1 case (1.4%), and was treated by external hand compression under the ultrasound guidance. Stent occlusion developed the day after the procedure in 1 case (1.4%), and was treated by balloon dilation with thrombus aspiration. Cholesterol embolization was observed in 1 case (1.4%), and was treated by low-density lipoprotein apheresis.
There were no procedure-related deaths or amputations. The long-term outcomes are shown in Table 4. During the follow-up period, death occurred in 13 cases (19.1%), while restenosis, including occlusion, occurred in 25 lesions (34.7%), occlusion occurred in 14 lesions (19.4%), and major amputation was required for 1 limb (1.4%). TLR was required in 17 lesions (23.6%), clinically driven TLR in 15 lesions (20.8%), and FP bypass surgery in 3 lesions (4.2%).
Primary and secondary patency rates are plotted as Kaplan-Meier curves in Figure 1. The estimated primary patency rates at 1 year, 2 years, 3 years, 5 years, and 7 years were 77.9%, 71.9%, 67.2%, 51.5%, and 51.5%, and the secondary patency rates at the same time points were 88.6%, 78.7%, 71.1%, 56.0%, and 56.0%, respectively. To determine the predictors for loss of primary and secondary patency, we compared the factors between lesions with and without restenosis, and included factors with P<.20 in a multivariate analysis. Therefore, hemodialysis, CLI, and ACE/ARB were included in the multivariate Cox proportional hazard model (Table 5). The HR of hemodialysis for loss of primary patency was 2.555 (95% CI, 1.108-5.891; P=.03), while HR for loss of secondary patency was 3.615 (95% CI, 1.380-9.471; P=.01). Hemodialysis was the only independent predictor for loss of primary and secondary patency in the present study. Clinical measurement over time is shown in Table 6. The number of limbs lost to follow-up at 1, 2, 3, and 5 years after the procedure was 5 (6.9%), 20 (27.8%), 29 (40.3%), and 42 (58.3%), respectively. At these times, the restenosis rate was 16.9%, 21.7%, 27.0%, and 40.0%, respectively. The mean Rutherford classification post EVT and at 1, 2, 3, and 5 years after the EVT procedure was 1.3 ± 1.1, 1.4 ± 1.0, 1.6 ± 1.1, 1.7 ± 1.1, and 2.1 ± 1.2, and the mean ABI was 0.92 ± 0.16, 0.87 ± 0.16, 0.82 ± 0.20, 0.78 ± 0.27, and 0.74 ± 0.25, respectively.
Patients with TASC D lesion in the SFA and life-limiting claudication or CLI are recommended to undergo FP bypass surgery rather than EVT because of the superiority of FP bypass surgery for long-term patency.1 However, it remains controversial whether EVT or FP bypass surgery should be performed for those patients with comorbidity or a high surgical risk.2 In such cases, EVT would be a promising procedure for recanalization of the CTO lesion. Implantation of full-metal, self-expandable nitinol stents is required to achieve successful revascularization in these patients.3,5,6,10-13 The long-term outcomes of such stent implantations have not been fully elucidated in previous studies. To achieve a successful stent implantation, it is necessary to cross the guidewire through the CTO lesion. In general, the wire manipulation follows one of the following two approaches.
The first approach is subintimal angioplasty, in which a looped 0.035˝ guidewire with the back-up support of a 4 Fr or 5 Fr diagnostic catheter is simply pushed forward within the CTO lesion,3-6,13 while the other is intraluminal angioplasty, in which a 0.014˝ or 0.018˝ guidewire with a microcatheter for support is manipulated with the intention of crossing the guidewire within the true lumen. However, with the latter method, the guidewire does not always cross the true lumen and it cannot always be assured that it is within the true lumen.5 Most previous data regarding the long-term outcomes of such cases was based on subintimal angioplasty with 0.035˝ looped guidewire and the back-up support of a 4 Fr or 5 Fr diagnostic catheter;3-6,13 there have been only limited studies on intraluminal angioplasty with 0.014˝ or 0.018˝ guidewires,5 and few studies that assess the effects of a bidirectional approach. The present study included long-term outcomes after a bidirectional approach, performed in 50 cases (69.4%). Thus, in the present study, the primary patency rate, including the bidirectional approach, was superior compared with previous reports.3-6,13 There are two possible reasons for this superiority. First, the procedure was performed with intraluminal angioplasty using a 0.014˝ or 0.018˝ guidewire in all cases. The STELLA registry, as reported by Davine et al, showed primary patency rates of 66.0% at 12 months and 62.2% at 30 months after implantation of self-expandable nitinol stents (LifeStent; Bard PV) via subintimal angioplasty in patients with long CTO lesions (TASC C/D) in the SFA. However, TASC D lesions in the SFA constituted only 23 cases (37.1%) in the STELLA registry6 and 72 (100%) in the present study. Moreover, the prevalence of patients with hemodialysis was 1.7% in the STELLA registry and 20.6% in the present study. In the present study, primary patency rates were 77.9% at 1 year, 71.9% at 2 years, and 67.2% at 3 years. Thus, the results of the present study suggest that further investigation by randomized studies or meta-analysis of the intraluminal approach vs the subintimal approach will be needed to estimate the effect of intimal angioplasty on long-term outcomes. Conversely, a limitation pertaining to ensuring that the guidewire passed entirely through the true lumen existed because the IVUS catheter could not always pass through the entire long and hard CTO lesion. As previous studies have described, the difference between intraluminal and subintimal angioplasty not only involves which lumen the guidewire is passed through, but also a difference in how to manipulate the guidewire and which guidewire (0.014˝/0.018˝ or looped 0.035˝ guidewire) is used to cross the CTO lesion.3,5 Intraluminal angioplasty did not always result in the guidewire passing entirely through the true lumen. Conversely, subintimal angioplasty occasionally resulted in the guidewire passing through the true lumen.
Second, the bidirectional approach was performed frequently in the present study (69.4% of cases). Soga et al previously reported primary patency rates of 72% at 1 year and 55% at 3 years after self-expandable nitinol stent implantation via intraluminal angioplasty for treatment of CTO lesions.5 In the present study, the primary patency rate was 77.9% at 1 year and 67.2% at 3 years. The mean occluded lesion length was 24.4 cm in our study, vs 15.1 cm in the study by Soga et al, but a bidirectional approach was used more frequently in our study (69.4% vs 34.0%). Therefore, the 1-year and 3-year primary patency rates were better in the present study than in the study by Soga et al, despite the longer occlusion length and a higher prevalence of patients with hemodialysis (20.6% vs 17.0%) in the present study. It is possible that the bidirectional approach produced favorable results for long-term patency. However, further study would be needed to examine this issue. Although we could not always ensure the guidewire passed through the whole true lumen, a bidirectional approach could theoretically enable the guidewire to more frequently penetrate the true lumen compared with a unidirectional approach. Although the selection of a bidirectional or unidirectional approach was at the physician’s discretion in the present study, a bidirectional approach was applied in cases with a failed attempt to cross the guidewire antegradely with a unidirectional approach or cases in which a bidirectional approach was required from the outset of the procedure because of a severely calcified lesion. A possible disadvantage of the bidirectional approach is a potential increase in complications at the puncture site in the popliteal artery. However, there was only 1 case (1.4%) of pseudoaneurysm at the popliteal puncture site. It may be important not to restrict directional approaches to unidirectional and switch to a bidirectional approach in cases in which it would be difficult to cross the guidewire through the lesion antegradely even with the use of a stiff guidewire.
In the present study, hemodialysis was the only independent predictor for loss of primary and secondary patency, with more than double the risk of patency loss. The risk of restenosis or loss of patency in patients with hemodialysis during EVT of SFA has not been fully elucidated. Previous studies reported that patients with hemodialysis had an increased risk for restenosis or loss of primary patency after stent implantation in the SFA.14,15 The results of the present study are consistent with previous studies. Because perioperative mortality rates pertaining to the surgical revascularization of lower limbs are higher in patients with hemodialysis (10%) than in patients with normal renal function (2%),2 discussion is needed to assess whether FP bypass surgery or EVT is more appropriate for TASC D patients with hemodialysis. In the present study, the procedural mortality rate was 0%, despite 20.6% of patients having hemodialysis, although hemodialysis was an independent predictor for loss of primary and secondary patency.
Further studies are needed to determine the best revascularization strategy for SFA in TASC D patients with hemodialysis or comorbidity, taking the mortality rate of lower-extremity surgical revascularization into consideration. In the present study, a self-expandable nitinol stent was used for the treatment of EVT in the SFA. Recently, drug-eluting balloons have been reported to be promising for EVT in the SFA without stent implantation or with minimized provisional stent implantation.16 It would be more important to cross the guidewire within the true lumen for an optimal result after drug-eluting balloon treatment with the implantation of fewer or no stents because in comparison with using intraluminal angioplasty, the creation of a more subintimal space using subintimal angioplasty could possibly require the implantation of a greater number of stents. Further study would be needed to examine the effectiveness of the drug-eluting balloon treatment with the implantation of fewer or no stents in SFA TASC-D lesions.
Although we have described intraluminal angioplasty and a bidirectional approach for the treatment of TASC D lesions in SFA in the present study, other devices specifically designed for crossing complex CTO lesions, including the Frontrunner (LuMend), Crosser system (Bard PV), and MultiCross catheter (Roxwood Medical, Inc), have been reported to be promising in previous studies.17-21 These devices were not available in Japan during this study period, but would have been useful for the intraluminal approach. In addition, pedal access has been reported to be a useful technique for the intraluminal procedure.22 Further studies would be needed to examine the feasibility of these devices and techniques for treating TASC-D lesions in the SFA.
Study limitations. There were some limitations to the present study. First, this was a retrospective, single-center study with a small sample size. Second, some patients were lost to follow-up. Third, TLR was not performed in asymptomatic patients or in patients who did not hope to receive TLR. This may have affected the secondary patency rate because secondary patency was lost automatically in these patients. Fourth, there was a limitation in ensuring that the guidewire was within the whole true lumen.
Long-term outcomes are promising after SFA implantation of self-expandable nitinol stents via unidirectional and bidirectional intraluminal angioplasty for the treatment of TASC D lesions. Hemodialysis was the only independent predictor for loss of primary and secondary patency. Further registries and trials are needed to examine long-term outcomes of EVT with intraluminal crossing in TASC D SFA lesions, particularly in the era of drug-coated balloon angioplasty.
1. Norgren L, Hiatt WR, Dormandy JA, Nehler MR, Harris KA, Fowkes FG. Inter-society consensus for the management of peripheral arterial disease (TASC II). J Vasc Surg. 2007;45:S5-S67.
2. O’Hare AM, Feinglass J, Sidawy AN, et al. Impact of renal insufficiency on short-term morbidity and mortality after lower extremity revascularization: data from the Department of Veterans Affairs’ National Surgical Quality Improvement Program. J Am Soc Nephrol. 2003;14:1287-1295.
3. Ko YG, Kim JS, Choi DH, Jang Y, Shim WH. Improved technical success and midterm patency with subintimal angioplasty compared to intraluminal angioplasty in long femoropopliteal occlusions. J Endovasc Ther. 2007;14:374-381.
4. Baril DT, Chaer RA, Rhee RY, Makaroun MS, Marone LK. Endovascular interventions for TASC II D femoropopliteal lesions. J Vasc Surg. 2010;51:1406-1412.
5. Soga Y, Iida O, Suzuki K, et al. Initial and 3-year results after subintimal versus intraluminal approach for long femoropopliteal occlusion treated with a self-expandable nitinol stent. J Vasc Surg. 2013;58:1547-1555.
6. Davaine JM, Querat J, Guyomarch B, et al. Primary stenting of TASC C and D femoropopliteal lesions: results of the STELLA register at 30 months. Ann Vasc Surg. 2014;28:1686-1696.
7. Laird JR, Katzen BT, Scheinert D, et al. Nitinol stent implantation versus balloon angioplasty for lesions in the superficial femoral artery and proximal popliteal artery: twelve-month results from the RESILIENT randomized trial. Circ Cardiovasc Interv. 2010;3:267-276.
8. Schmidt A, Bausback Y, Piorkowski M, et al. Retrograde recanalization technique for use after failed antegrade angioplasty in chronic femoral artery occlusions. J Endovasc Ther. 2012;19:23-29.
9. Fanelli F, Lucatelli P, Allegritti M, Corona M, Rossi P, Passariello R. Retrograde popliteal access in the supine patient for recanalization of the superficial femoral artery: initial results. J Endovasc Ther. 2011;18:503-509.
10. Ferreira M, Lanziotti L, Monteiro M, et al. Superficial femoral artery recanalization with self-expanding nitinol stents: long-term follow-up results. Eur J Vasc Endovasc Surg. 2007;34:702-708.
11. Dippel E, Shammas N, Takes V, Coyne L, Lemke J. Twelve-month results of percutaneous endovascular reconstruction for chronically occluded superficial femoral arteries: a quality-of-life assessment. J Invasive Cardiol. 2006;18:316-321.
12. Dosluoglu HH, Cherr GS, Lall P, Harris LM, Dryjski ML. Stenting vs above knee polytetrafluoroethylene bypass for TransAtlantic Inter-Society Consensus-II C and D superficial femoral artery disease. J Vasc Surg. 2008;48:1166-1174.
13. Davaine JM, Azema L, Guyomarch B, et al. One-year clinical outcome after primary stenting for Trans-Atlantic Inter-Society Consensus (TASC) C and D femoropopliteal lesions (the STELLA “STEnting Long de L’Artere femorale superficielle” cohort). Eur J Vasc Endovasc Surg. 2012;44:432-441.
14. Ishii H, Kumada Y, Toriyama T, Aoyama T, Takahashi H, Murohara T. Prognostic values of C-reactive protein levels on clinical outcome after endovascular therapy in hemodialysis patients with peripheral artery disease. J Vasc Surg. 2010;52:854-859.
15. Soga Y, Iida O, Hirano K, et al. Utility of new classification based on clinical and lesional factors after self-expandable nitinol stenting in the superficial femoral artery. J Vasc Surg. 2011;54:1058-1066.
16. Tepe G, Laird J, Schneider P, et al. Drug-coated balloon versus standard percutaneous transluminal angioplasty for the treatment of superficial femoral and popliteal peripheral artery disease: 12-month results from the IN.PACT SFA randomized trial. Circulation. 2015;131:495-502.
17. Charalambous N, Schafer PJ, Trentmann J, et al. Percutaneous intraluminal recanalization of long, chronic superficial femoral and popliteal occlusions using the Frontrunner XP CTO device: a single-center experience. Cardiovasc Intervent Radiol. 2010;33:25-33.
18. Shetty R, Vivek G, Thakkar A, Prasad R, Pai U, Nayak K. Safety and efficacy of the Frontrunner XP catheter for recanalization of chronic total occlusion of the femoropopliteal arteries. J Invasive Cardiol. 2013;25:344-347.
19. Laird J, Joye J, Sachdev N, et al. Recanalization of infrainguinal chronic total occlusions with the Crosser system: results of the PATRIOT trial. J Invasive Cardiol. 2014;26:497-504.
20. Staniloae CS, Mody KP, Yadav SS, Han SY, Korabathina R. Endoluminal treatment of peripheral chronic total occlusions using the Crosser® recanalization catheter. J Invasive Cardiol. 2011;23:359-362.
21. Mitsutake Y, Ebner A, Yeung AC, Taber MD, Davidson CJ, Ikeno F. Efficacy and safety of novel multi-lumen catheter for chronic total occlusions: from preclinical study to first-in-man experience. Catheter Cardiovasc Interv. 2015;85:E70-E75.
22. Fanelli F, Cannavale A. Retrograde recanalization of complex SFA lesions indications and techniques. J Cardiovasc Surg (Torino). 2014;55:465-471.
From the Department of Cardiology and Catheterization, Laboratory and Cardiovascular R&D Center, Shonan Kamakura General Hospital, Kamakura, Japan.
Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.
Manuscript submitted August 10, 2015, provisional acceptance given November 2, 2015, final version accepted December 7, 2015.
Address for correspondence: Junya Matsumi, MD, Department of Cardiology, Shonan Kamakura General Hospital, 1370-1 Okamoto, Kamakura, Kanagawa 247-0072, Japan. Email: email@example.com