What is the clinical evidence from this study?

Study design: Systematic Review. Population: Primary hypertension (n=33611). Intervention: Thiazide diuretics vs. Placebo or untreated controls. Primary outcome: Coefficient of variation of systolic blood pressure at end of treatment (p=not significant).

May 21, 2009Open Access

Factors Affecting Blood Pressure Variability: Lessons Learned from Two Systematic Reviews of Randomized Controlled Trials

Key Result

Treatment with a thiazide diuretic does not significantly affect blood pressure variability compared to placebo, as the coefficient of variation of systolic and diastolic blood pressure did not differ at end of treatment.

Study Design

Type

Systematic Review (n=33,611)

Structured PICO

Do thiazide diuretics affect blood pressure variability in adult patients with primary hypertension?

Population

33,611 adult patients with primary hypertension included in two systematic reviews of randomized controlled trials evaluating the blood pressure lowering efficacy of thiazide diuretics.

Intervention

Thiazide diuretics (monotherapy for 3-12 weeks in Review 1; first-line therapy for at least 1 year in Review 2)

Comparator

Placebo or untreated controls

Outcome

Blood pressure variability, assessed by the standard deviation (SD) and coefficient of variation (CV) of resting systolic and diastolic blood pressuresurrogate

Thiazide diuretics do not significantly affect blood pressure variability, and using specific blood pressure thresholds for trial entry artificially reduces baseline variability.

Main Result

Absolute Event Rate: 9.9% vs 9.4%

p-value: p=not significant

Limitations

Analysis based on standard deviation reported in trials rather than individual patient data.
Potential measurement bias due to clustering of BP measurements at threshold entry criterion levels.
Lack of power to definitively rule out small differences in BP variability between treated and control groups.
Difference in variability between SBP and DBP may be an artifact of the auscultatory measurement method.

Abstract

Systematic reviews can often reveal much more than the original objective of the work. The objectives of this retrospective analysis were to answer three basic questions about blood pressure variability: 1) Does blood pressure entry criterion have an effect on baseline blood pressure variability? 2) Do thiazide diuretics have a significant effect on blood pressure variability? and 3) Does systolic blood pressure vary to the same degree as diastolic blood pressure? This analysis of blood pressure variability is based on resting standardized research setting BP readings from two systematic reviews evaluating blood pressure lowering efficacy of thiazide diuretics from double blind randomized controlled trials in 33,611 patients with primary hypertension. The standard deviation reported in trials was the focus of the research and the unit of analysis. When a threshold systolic or diastolic blood pressure value is used to determine entry into a trial, baseline variability is significantly decreased, systolic from 14.0 to 9.3 mmHg and diastolic from 8.4 to 5.3 mmHg. Thiazides do not change BP variability as the standard deviation and coefficient of variation of systolic blood pressure and diastolic blood pressure did not differ between thiazide and placebo groups at end of treatment. The coefficient of variation of systolic blood pressure was significantly greater than the coefficient of variation of diastolic blood pressure. Entry criterion decreases the baseline blood pressure variability. Treatment with a thiazide diuretic does not affect blood pressure variability. Systolic blood pressure varies to a greater degree than diastolic blood pressure.

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