Supplementary Table 1. Study population and quality assessment of included studies

First Author / Study population / Selection / Comparability / Outcome
Brandt / Older than 18 years and had an office BP of 160 mm Hg (150 mm Hg for type 2 diabetes patients) or more, despite treatment with at least 3antihypertensive drugs (including a diuretic), with no changesin medication for a minimum of 3 months before enrollment. / ★★★★ / ★★ / ★★★
Doltra / Office systolic blood pressure (SBP) above the target (≥140 mm Hg) or mean ambulatory 24-hour SBP >135 mm Hg despite the use of ≥3 antihypertensive agents（including a diuretic）of different classes. A stable antihypertensive medication regimen (>3-monthtreatment on stable dosing) / ★★★★ / ★★ / ★★★
Kiuchi / Patients with resistant hypertension and chronic kidney disease. / ★★★ / ★ / ★★★
Mahfoud / aged ≥18 years with an office SBP above goal (≥140 mmHg) or mean ambulatory 24h SBP 135 mmHg despite the use of ≥3 antihypertensive agents of different classes, including a diuretic at maximum or highest tolerateddoses. / ★★★★ / ★★ / ★★★
Tsioufis / 18 to 80 years of age and had an office SBP remained at least 160mmHg (150mmHg for patients with type 2 diabetes) despite the stable use of atleast three antihypertensive medications concurrently atmaximally tolerated doses（including a diuretic）. Drug regimen was to remain stable for a minimum of 14 days prior to enrolment. / ★★★★ / ★★ / ★★★
Dores / Patients with essential resistant hypertension. / ★★★ / ★★★
Carvalho / Patients with essential resistant hypertension. / ★★★ / ★★★
Schirmer / Resistant arterial hypertension (office SBP 140 mm Hg), in sinus rhythm and did not suffer from systolicheart failure (ejection fraction <50%) or severe renaldysfunction (estimated glomerular filtration rate <45 ml/min/1.73 m2 as measured by cystatin C). / ★★★ / ★★★
McLellan / ≤75 years; Treatment-resistant hypertension. / ★★★ / ★★★
Palionis / Patients with resistant arterial hypertension / ★★★ / ★★★
Tsioufis / Patients with resistant hypertension / ★★★ / ★★★
Verloop / Both patients with resistant hypertension (defined as a SBP≥160mm Hg, despite use of ≥3anti-hypertensive drugs) as well as patients fulfilling the sameBP criteria, but without optimal pharmacological treatment due to intolerance for antihypertensive drugs. / ★★★ / ★★★

A maximum of 4 stars for selection, 2 for comparability and 3 for outcome.

NEWCASTLE - OTTAWA QUALITY ASSESSMENT SCALE

COHORT STUDIES

Note: A study can be awarded a maximum of one star for each numbered item within the Selection and Outcome categories. A maximum of two stars can be given for Comparability

Selection

1) Representativeness of the exposed cohort

a) truly representative of the average ______(describe) in the community 

b) somewhat representative of the average ______in the community 

c) selected group of users eg nurses, volunteers

d) no description of the derivation of the cohort

2) Selection of the non exposed cohort

a) drawn from the same community as the exposed cohort 

b) drawn from a different source

c) no description of the derivation of the non exposed cohort

3) Ascertainment of exposure

a) secure record (eg surgical records) 

b) structured interview 

c) written self report

d) no description

4) Demonstration that outcome of interest was not present at start of study

a) yes 

b) no

Comparability

1) Comparability of cohorts on the basis of the design or analysis

a) study controls for ______(select the most important factor) 

b) study controls for any additional factor  (This criteria could be modified to indicate specific control for a second important factor.)

Outcome

1) Assessment of outcome

a) independent blind assessment 

b) record linkage 

c) self report

d) no description

2) Was follow-up long enough for outcomes to occur

a) yes (select an adequate follow up period for outcome of interest) 

b) no

3) Adequacy of follow up of cohorts

a) complete follow up - all subjects accounted for 

b) subjects lost to follow up unlikely to introduce bias - small number lost - > ____ % (select an adequate %) follow up, or description provided of those lost) 

c) follow up rate < ____% (select an adequate %) and no description of those lost

d) no statement