Methods

The CREDO-Kyoto (Coronary REvascularization Demonstrating Outcome Study in Kyoto) Registry Cohort-2 is a physician-initiated, non–company-sponsored, multicenter registry that enrolled consecutive patients who underwent first coronary revascularization in 26 centers in Japan from January 2005 through December 2007. The relevant ethics committees in all 26 participating centers ( Supplementary Data A ) approved the research protocol. Because of retrospective enrollment, written informed consent from the patients was waived. However, patients who refused participation in the study when contacted for follow-up were excluded.

The study design and patient enrollment in the registry have been previously described in detail. Of 15,939 patients enrolled in the registry, patients who refused study participation (n = 99), had concomitant noncoronary surgery (n = 609), had acute myocardial infarction (MI; n = 4892), and had percutaneous coronary intervention (n = 8337) were excluded. For the comparison of outcomes after CABG stratified by HF status, we excluded 125 patients (6%) without LVEF data. The present study population consisted of 1,877 patients who underwent CABG with known LVEF. HF was clinically diagnosed with the definition of American College of Cardiology Foundation/American Heart Association HF stage C or D according to the admitting physician. There were 1,489 patients (79%) with normal LV function, defined as an LVEF of >50% without a history of HF (Normal group), 236 patients (13%) with HF with reduced LVEF (≤50%, HFrEF group), and 152 patients (8%) with HF with preserved LVEF (>50%, HFpEF group).

LVEF was measured by echocardiography or LV cine angiography. M-mode and/or 2-dimensional echocardiography was performed by experienced operators in each institution. M-mode LVEF was calculated using the Teichholz correction. Two-dimensional echocardiographic LVEF was also evaluated by the Simpson biplane method of discs with manual planimetry of the endocardial border in end-diastolic (largest) and end-systolic (smallest) frames. LV cine angiography was obtained in either a single-plane right anterior oblique view or biplane right and left anterior oblique views. LVEF was calculated using the built-in programs.

Demographic, angiographic, and procedural data were collected from hospital charts according to the prespecified definitions by experienced research coordinators in an independent research organization (Research Institute for Production Development, Kyoto, Japan; Supplementary Data B ). Definitions for clinical characteristics are described in the Supplementary Data C .

The Synergy between Percutaneous Coronary Intervention with TAXus and Cardiac Surgery (SYNTAX) scores were available in 1,503 patients (80%). The SYNTAX score was calculated using the SYNTAX score calculator (available at http://www.syntaxscore.com ) by a dedicated SYNTAX score committee ( Supplementary Data D ) in a blinded fashion to the clinical data. Intraobserver and interobserver variabilities of the SYNTAX score calculation in our group were previously reported. Cutoff values for SYNTAX score tertiles (low <23, intermediate 23 to 33, and high ≥33) were defined according to the analysis in the SYNTAX trial.

Collection of follow-up information was conducted mainly through review of inpatient and outpatient hospital charts by clinical research coordinators in the independent research organization. Additional follow-up information was collected through contact with patients, relatives, and/or referring physicians by sending mail with questions on vital status, additional hospitalizations, and antiplatelet medications. Death, MI, and stroke were adjudicated by the clinical event committee (see Supplementary Data E ).

The outcome measurements evaluated in the present analysis included all-cause death, cardiac death, sudden death, stroke, MI, and any coronary revascularization. Death was regarded as cardiac in origin unless obvious noncardiac causes could be identified. Any death during the index hospitalization for coronary revascularization was regarded as cardiac death. Sudden death was defined as unexpected death in previously stable patients. MI was defined according to the definition in the Arterial Revascularization Therapy Study. Stroke during follow-up was defined as ischemic or hemorrhagic stroke requiring hospitalization with symptoms lasting >24 hours. Scheduled staged coronary revascularization procedures performed within 3 months of the initial procedure were not regarded as follow-up events but were included in the index procedure.

All continuous variables are expressed as the mean ± standard deviation. Differences in baseline characteristics across the 3 groups were examined by analysis of variance. Categorical variables were presented as number and percentage and were compared with chi-square tests. Cumulative incidence was estimated by the Kaplan–Meier method, and differences were assessed using log-rank test. Outcomes after CABG by the stratification of HF status were compared by Cox proportional hazards models. Cox proportional hazards models were adjusted for the following confounders: age, gender, body mass index, hypertension, diabetes mellitus, current smoker, mitral regurgitation grade 3 or 4, previous MI, previous stroke, peripheral arterial disease, atrial fibrillation, chronic kidney disease, hemodialysis, anemia, platelet count, chronic obstructive lung disease, liver cirrhosis, malignancy, emergency procedure, on- or off-pump surgery, left or right internal thoracic artery use, right gastroepiploic artery use, radial artery use, saphenous vein use, 3 vessel disease, left main disease, chronic total occlusion, proximal left anterior descending coronary artery, and treatment with aspirin, statins, angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, β blockers, calcium channel blockers, nitrates, and warfarin. These variables were consistent with previous reports from the current registry. Continuous variables except age and body mass index were dichotomized using clinically meaningful reference values or median values. Unadjusted variables with p <0.05 were included in the adjusted model. All reported p values were 2 sided, and p values <0.05 were regarded as statistically significant.

All analyses were conducted by a statistician (ST) with the use of SAS version 9.2 (SAS Institute Inc., Cary, North Carolina) and S-Plus version 7.0 (Insightful Corp., Seattle, Washington). The investigators had full access to the data and take responsibility for its integrity. All investigators have read and agreed to the manuscript as written.

Results

Age was the highest in the HFpEF group ( Table 1 ). Patients in the HFrEF group had the highest prevalence of previous MI, mitral regurgitation grade 3 or 4, and diabetes mellitus. Patients in the HFpEF group had the highest prevalence of hypertension, atrial fibrillation, peripheral artery disease, hemodialysis, and malignancy. Estimated glomerular filtration rate was the lowest in the HFpEF group. SYNTAX score was the highest in the HFrEF group. Number of target coronary anastomosis was not different among the 3 groups ( Table 2 ). Off-pump surgery was applied most common in the HFpEF group.

Median follow-up duration for the surviving patients was 1,895 days. Unadjusted 30-day mortality rate was the highest in the HFrEF group (p = 0.003, Table 3 ). Thirty-day incidences of nonfatal stroke and MI were not different among the 3 groups.

Cumulative 5-year incidence of all-cause death was significantly different among the 3 groups (p <0.001; Figure 1 ). After adjusting confounders, the excess mortality risk of the HFpEF group relative to the Normal was significant ( Tables 4 and 5 ). The mortality risk was not different between the HFrEF and the HFpEF groups. Cumulative 5-year incidences of cardiac death, sudden death, and readmission for HF were significantly different among the 3 groups ( Figure 1 ). After adjusting confounders, the excess risks of the HFpEF group relative to the Normal for cardiac death, sudden death, and readmission for HF were significant ( Table 5 ). Adjusted risks for stroke, MI, and any coronary revascularization were not different between the HFpEF and the Normal groups. Adjusted risks for cardiac death, sudden death, readmission for HF, stroke, MI, and any coronary revascularization were not different between the HFpEF and the HFrEF groups.

Kaplan–Meier curves for each end points in patients with normal left ventricular function, HFrEF, and HFpEF. (A) All-cause death. (B) Cardiac death. (C) Sudden death. (D) Readmission for heart failure. HFpEF = heart failure with preserved ejection fraction; HFrEF = heart failure with reduced ejection fraction; Normal = preserved ejection fraction without heart failure.

Table 4

Risk factors and unadjusted and adjusted hazard ratios for all-cause death undergoing coronary artery bypass grafting

Variable	Unadjusted			Adjusted
	Hazard ratio	chi-square	P value	Hazard ratio	95% confidence interval		P value
Age (years)	1.06	71.14	<0.001	1.05	1.03	1.07	<0.001
Men	1.18	1.60	0.21
Previous myocardial infarction	1.61	16.04	<0.001	1.31	1.02	1.67	0.03
Atrial fibrillation	1.47	8.85	0.003	1.11	0.85	1.43	0.44
Mitral regurgitation grade 3/4	3.60	37.85	<0.001	2.20	1.43	3.37	<0.001
Body mass index (kg/m 2 )	0.90	33.72	<0.001	0.98	0.94	1.02	0.29
Hypertension	1.17	1.00	0.32
Diabetes mellitus	1.23	3.45	0.06
Current smoker	1.02	0.03	0.86
Previous stroke	1.27	2.71	0.10
Peripheral artery disease	2.46	49.96	<0.001	1.87	1.45	2.42	<0.001
Estimated glomerular filtration rate < 30 ml/min/1.73 m 2	2.70	44.15	<0.001	2.09	1.50	2.90	<0.001
Hemodialysis	4.23	103.43	<0.001	3.76	2.72	5.18	<0.001
Anemia (hemoglobin <11.0 g/dl)	2.85	85.21	<0.001	1.17	0.90	1.52	0.26
Platelet count < 100 x 10 9 /L)	3.19	24.13	<0.001	2.14	1.32	3.46	0.002
Chronic obstructive pulmonary disease	0.93	0.03	0.86
Liver cirrhosis	1.15	0.23	0.63
Malignancy	1.63	10.57	0.001	1.19	0.88	1.61	0.27
3 (without left main disease)	1.20	2.06	0.15
Left main	1.00	0.00	0.98
Proximal left anterior descending artery	1.12	0.47	0.50
Chronic total occlusion	1.06	0.27	0.60
On-pump surgery	0.70	8.52	0.004	0.75	0.59	0.96	0.02
Left internal thoracic artery use	0.71	1.86	0.17
Right internal thoracic artery use	0.94	0.26	0.61
Right gastroepiploic artery use	1.11	0.66	0.42
Radial artery graft use	0.38	31.25	<0.001	0.71	0.49	1.01	0.06
Saphenous vein graft use	0.92	0.51	0.48
Aspirin	0.30	18.42	<0.001	0.42	0.24	0.75	0.003
Statins	0.60	15.96	<0.001	0.77	0.59	0.99	0.05
Beta-blockers	0.97	0.06	0.81
Angiotensin-converting enzyme inhibitor/angiotensin receptor blocker	1.14	1.24	0.27
Nitrates	1.12	1.02	0.31
Calcium channel blockers	0.81	3.70	0.05
Warfarin	0.95	0.24	0.62
HFpEF vs. Normal	2.34	55.94	<0.001	1.42	1.02	1.97	0.04
HFpEF vs. HFrEF	0.50	26.19	<0.001	0.88	0.61	1.29	0.52

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