A total of 78,812 patients fulfilling the inclusion criteria were identified from the CDARS of HAHK during the study period. Among the randomly sampled 682 HT patients, 144 (21.1%) were excluded due to the following reasons: 1 due to misdiagnosed HT, 17 due to FU in specialist out-patient clinics, 46 due to £1 attendance during the study period, 2 due to no documented BP and 78 due to no annual blood and urine done within the study period. No case of HT with a secondary cause was identified. Clinical data of the remaining 538 cases were collected from the CMS and entered into data analysis (Figure 1).
Table 1 summarized the demographics and characteristics of all included HT patients. Their mean age was 67.4 ± 11.5 years, and 51.9% were female. 14.3% of patients were current smoker, 5.6% were current drinker, while 57.6% were obese. Majority of patients had associated comorbidities, including 40.1% had DM, 80.1% had hyperlipidaemia, 15.4% had CKD, 12.6% had stroke and 10.2% had IHD. The mean duration of HT was 10.1 ± 6.4 years, and the mean systolic and diastolic BP were 128 ± 12.3 and 74 ± 10.8 mmHg respectively. Among them, 40 cases were identified to have RHT, giving a prevalence of 7.43%.
Table 1: Demographics and Characteristics of All Included Patients (Total number = 538)
Variables
|
Number (% out of total) or #Mean + SD
|
Age (years)
|
67.4 + 11.5#
|
Female
|
279 (51.9)
|
Male
|
259 (48.1)
|
Current smoker
|
77 (14.3)
|
Current drinker
|
30 (5.6)
|
Body mass index, BMI (kg/m2)
Underweight (<18.5)
Normal (18.5 – 22.9)
Overweight (23 – 24.9)
Obesity (>/=25)
|
11 (2.1)
114 (21.2)
103 (19.1)
310 (57.6)
|
Duration of hypertension (years)
|
10.1 + 6.4#
|
Systolic blood pressure (mmHg)
|
128 + 12.3#
|
Diastolic blood pressure (mmHg)
|
74 + 10.8#
|
Resistant hypertension (RHT)
|
40 (7.43)
|
Diabetes mellitus
|
216 (40.1)
|
Hyperlipidaemia
|
431 (80.1)
|
Chronic kidney disease
|
83 (15.4)
|
Microalbuminuria
|
86 (16.0)
|
Stroke
|
68 (12.6)
|
Ischaemia heart disease
|
55 (10.2)
|
Left ventricular hypertrophy
|
29 (5.4)
|
Congestive heart failure
|
12 (2.2)
|
Atrial fibrillation
|
21 (3.9)
|
Peripheral vascular disease
|
1 (0.2)
|
Gout
|
34 (6.3)
|
Obstructive sleep apnea
|
27 (5.0)
|
Benign prostatic hypertrophy
|
60 (23.2 in male)
|
Table 2 compared the demographic and clinical parameters in patients with and without RHT. There were statistically more male patients (67.5% versus 32.5%) in the RHT group (p=0.011). RHT patients were found to have longer duration of HT than non-RHT patients (13.7 ± 7.4 years versus 9.8 ± 6.2 years, p=0.0002). Patients with RHT had statistically higher proportions of comorbidities: DM (65.0% versus 38.2%, p=0.001); CKD (32.5% versus 14.1%, p=0.002); microalbuminuria (30.0% versus 14.9%, p=0.012); CHF (10.0% versus 1.6%, p=0.008); and gout (15.0% versus 5.6%, p=0.032).
Table 2. Association between Clinical Variables of Patients With and Without RHT
Variables
|
Number (% out of total or #Mean + SD
|
p-value
|
|
Non-RHT (n =498)
|
RHT (n = 40)
|
|
Demographics
|
Age (years)
|
67.4 + 11.6#
|
69.9 +10.5#
|
0.820
|
Female
|
266 (53.4)
|
13 (32.5)
|
-
|
Male
|
132 (46.6)
|
27 (67.5)
|
0.011
|
Current smoker
|
72 (14.5)
|
5 (12.5)
|
0.734
|
Current drinker
|
26 (5.2)
|
4 (10.0)
|
0.268
|
Clinical Parameters
|
Body mass index, BMI (kg/m2)
Underweight (<18.5)
Normal (18.5 – 22.9)
Overweight (23 – 24.9)
Obesity (>/=25)
|
10 (2.0)
110 (22.1)
96 (19.3)
282 (56.6)
|
1 (2.5)
4 (10.0)
7 (17.5)
28 (70.0)
|
0.283
|
Duration of hypertension (years)
|
9.8 + 6.2#
|
13.7 + 7.4#
|
0.0002
|
Comorbidities
|
|
|
|
Diabetes mellitus
|
190 (38.2)
|
26 (65.0)
|
0.001
|
Hyperlipidaemia
|
397 (79.7)
|
34 (85.0)
|
0.434
|
Chronic kidney disease
|
70 (14.1)
|
13 (32.5)
|
0.002
|
Microalbuminuria
|
74 (14.9)
|
12 (30.0)
|
0.012
|
Stroke
|
59 (11.8)
|
9 (22.5)
|
0.051
|
Ischaemia heart disease
|
48 (9.6)
|
7 (17.5)
|
0.167
|
Left ventricular hypertrophy
|
24 (4.8)
|
5 (12.5)
|
0.055
|
Congestive heart failure
|
8 (1.6)
|
4 (10.0)
|
0.008
|
Atrial fibrillation
|
19 (3.8)
|
2 (5.0)
|
0.664
|
Peripheral vascular disease
|
1 (0.2)
|
0 (0.0)
|
1.000
|
Gout
|
28 (5.6)
|
6 (15.0)
|
0.032
|
Obstructive sleep apnea
|
25 (5.6)
|
2 (5.0)
|
1.000
|
Benign prostatic hypertrophy
|
61 (26.3, male=232)
|
5 (18.5, male=27)
|
0.380
|
In addition to the seven statistically significant variables associated with RHT, stroke and LVH also had p <0.1 and were hence entered into multivariate logistic regression to identify associated risk factors of RHT, as shown in Table 3. Adjusting all nine variables forward stepwise in the model, increased risk of RHT were statistically associated with four factors, in ascending order of odds ratio: duration of HT (OR 1.08, 95%CI 1.03-1.14), male gender (OR 2.72, 95%CI 1.33-5.56), comorbid with type 2 DM (T2DM) (OR 2.99, 95%CI 1.49-6.00), and CHF (OR 5.39, 95%CI 1.41-20.69).
Table 3: Associated Risk Factors of Resistant Hypertension
Variables
|
Adjusted OR
|
95% C.I.
|
p-value
|
Male gender
|
2.72
|
1.33 - 5.56
|
0.005
|
Duration of hypertension
|
1.08
|
1.03 - 1.14
|
0.001
|
Diabetes mellitus
|
2.99
|
1.49 - 6.00
|
0.002
|
Chronic kidney disease
|
1.56
|
0.68 - 3.61
|
0.297
|
Microalbuminuria
|
1.04
|
0.45 - 2.40
|
0.924
|
Stroke
|
1.38
|
0.56 - 3.40
|
0.481
|
Left ventricular hypertrophy
|
2.24
|
0.71 - 7.05
|
0.168
|
Congestive heart failure
|
5.39
|
1.41 - 20.69
|
0.014
|
Gout
|
1.34
|
0.45 - 4.00
|
0.595
|
The duration of HT as an associated risk factor was further analysed as shown in Figure 2. Patients with HT over 10 years were nearly twice more likely to have RHT compared to those diagnosed within 10 years, and nearly four times more likely when the duration is over 15 years (p=0.0007).
Figure 3 demonstrates the interactions among the other three risk factors associated with RHT. One in ten male HT patients had RHT and this ratio increased to one in six if they were also diabetic. One-third of male HT patients with CHF had RHT, and the risk increased to one in half if the male HT patients had both T2DM and CHF concomitantly (p=0.003).