Table 3.
Evaluation of the prognostic value of aortic systolic BP as compared with office systolic BP
| Stroke,all patients (N = 37,316) | |||
| Cox regression with both BPvariables in the same model | HR (95% CI) | P-value | |
| Adjusted | office BP | 1.06 (1.03–1.10) | <0.001 |
| aortic BP | 1.03 (1.01–1.06) | 0.02 | |
| C-statistics | Harrel’s C (95% CI) | ||
| Cox regression with office BP versus Cox regression with aortic BP | office BP | aortic BP | |
| Adjusted | 0.70 | 0.70 | |
| Difference | 0.003 (-0.005 to 0.006) | 0.10 | |
| Reclassification (aortic BP added to model with office BP) | continuous net reclassification index (95% CI) | ||
| Adjusted | 4.78 (-8.4 to 10.41) % | 0.10 | |
| Likelihood ratio test (model with office BP vs. model with aortic BP and office BP) for goodness-of-fit | |||
| Adjusted | 0.02 | ||
| Stroke, nonrenal patients (eGFR ≥60 ml/min per 1.73 m2) (n = 31,306) | |||
| Cox regression with both BP variables in the same model | HR (95% CI) | P-value | |
| Crude | office BP | 1.11 (1.07–1.15) | <0.001 |
| aortic BP | 1.05 (1.02–1.08) | 0.001 | |
| Adjusted | office BP | 1.07 (1.03–1.11) | <0.001 |
| aortic BP | 1.031 (0.999–1.065) | 0.06 | |
| C-statistics | Harrel's C (95% CI) | ||
| Cox model with office BP versus Cox model with aortic BP | office BP | aortic BP | |
| Crude | 0.58 | 0.56 | |
| Difference | 0.013 (−0.007 to 0.032) | 0.21 | |
| Adjusted | 0.70 | 0.70 | |
| Difference | 0.0030 (−0.0003 to 0.0064) | 0.07 | |
| Reclassification (aortic BP added to model with office BP) | continuous net reclassification index (95% CI) | ||
| Crude | 8.64 (2.38–14.89) % | 0.007 | |
| Adjusted | 6.90 (0.44–13.36) % | 0.04 | |
| Likelihood ratio test (model with office BP vs. model with aortic BP and office BP) for goodness-of-fit | |||
| Crude | 0.001 | ||
| Adjusted | 0.06 | ||
| Stroke, patients with CKD (eGFR <60 ml/min per 1.73 m2) (n = 6010) | |||
| Cox regression with both BP variables in the same model | HR (95% CI) | P-value | |
| Adjusted | office BP | 1.04 (0.98–1.11) | 0.20 |
| aortic BP | 1.03 (0.98–1.09) | 0.21 | |
| C-statistics | Harrel’s C (95% CI) | ||
| Cox model with office BP vs. Cox model with aortic BP | office BP | aortic BP | |
| Adjusted | 0.64 | 0.64 | |
| Difference | 0.002 (−0.005 to 0.010) | 0.55 | |
| Reclassification (aortic BP added to model with office BP) | continuous net reclassification index (95% CI) | ||
| Adjusted | −2.07 (−13.56 to 9.41) % | 1.28 | |
| Likelihood ratio test (model with office BP vs. model with aortic BP and office BP) for goodness-of-fit | |||
| Adjusted | 0.21 | ||
| MI, patients with CKD (eGFR <60 ml/min per 1.73 m2) (n = 6010) | |||
| Cox regression with both BP variables in the same model | HR (95% CI) | P-value | |
| Crude | office BP | 1.07 (1.02–1.12) | 0.01 |
| aortic BP | 1.06 (1.01–1.11) | 0.01 | |
| Adjusted | office BP | 1.052 (0.999–1.109) | 0.06 |
| aortic BP | 1.051 (1.004–1.100) | 0.03 | |
| C-statistics | Harrel's C (95% CI) | ||
| Cox model with office BP vs. Cox model with aortic BP | office BP | aortic BP | |
| Crude | 0.54 | 0.55 | |
| Difference | −0.0017 (−0.044 to 0.009) | 0.20 | |
| Adjusted | 0.72 | 0.72 | |
| Difference | −0.0006 (−0.0045 to 0.0033) | 0.77 | |
| Reclassification (aortic BP added to model with office BP) | continuous net reclassification index (95% CI) | ||
| Crude | 10.45 (0.84–20.06) % | 0.03 | |
| Adjusted | 5.43 (−4.72 to 15.59) | 0.29 | |
| Likelihood ratio test (model with office BP vs. model with aortic BP and office BP) for goodness-of-fit | |||
| Crude | 0.01 | ||
| Adjusted | 0.03 | ||
BMI, body mass index; BP, blood pressure; CKD, chronic kidney disease; HR, hazard ratio; MI, myocardial infarction; 95% CI, 95% confidence interval.
HR results for stroke and MI are presented per 10 mm Hg difference. Evaluation of aortic versus office systolic BP was only performed in the subgroups in which both BP indices were associated with the outcome (stroke and MI) when tested in separate Cox models, using patients with complete data (n = 37,316 hereof n = 6010 with eGFR <60 ml/min per 1.73 m2 due to missing covariate values for BMI and smoking) (Supplementary Table S4).
The prognostic contribution of aortic and office systolic BP was assessed using complementary statistical strategies as follows: (i) by simultaneously including both BP indices in the same Cox models (crude and adjusted), (ii) discrimination was assessed based on Harrell’s C calculated for Cox models (crude and adjusted) fitted with either aortic systolic BP or office systolic BP, (iii) improvement in reclassification by adding aortic systolic BP to models with office systolic BP (crude and adjusted) was assessed by the continuous net reclassification index, and (iv) the incremental value of adding aortic systolic BP to a model with brachial systolic BP was tested with a likelihood ratio test for goodness-of-fit of the model with or without aortic systolic BP in the model.
Adjusted models for stroke includes: age, sex, smoking (never, former, and active), number of diseased vessels (none, diffuse coronary atherosclerosis without significant [>50%] stenosis/1, 2, or 3 vessel disease), atrial fibrillation (yes/no), diabetes (yes/no), statin treatment (yes/no), antiplatelet treatment (yes/no), antihypertensive drugs prescribed (0, 1, 2, or >2), and BMI category (kg/m2): (<18.5 [underweight], 18.5–24.9 [normal], 25–29.9 [overweight], 30–34.9 [class 1 obesity], 35–39.9 [class 2 obesity], ≥40 [class 3 obesity]).
Adjusted models for MI includes: age, sex, smoking (never, former, and active), number of diseased vessels (none, diffuse coronary atherosclerosis without significant [>50%] stenosis/1, 2, or 3 vessel disease), diabetes (yes/no), hypertension (yes/no), statin treatment (yes/no), antiplatelet treatment (yes/no), BMI category (kg/m2): (<18.5 [underweight], 18.5–24.9 [normal], 25–29.9 [overweight], 30–34.9 [class 1 obesity], 35–39.9 [class 2 obesity], ≥40 [class 3 obesity]).