Prior studies have established that Calcium channel blockers and Thiazide diuretics have maximum impact on the Systolic Blood Pressure (SBP) and the variability in blood pressure thereby decreasing primary and recurrent stroke risk. The authors of this study investigated the impact of several antihypertensive class medications on home blood pressure variability and if the effect was greater at a certain time of the day. Five hundred and thirty six patients were recruited from the Oxford Vascular Study’s TIA and Stroke clinic. At the first ascertainment visit, one month after the index event, patients underwent BP monitoring in the clinic. BP was measured in the non-dominant arm in a sitting position 5 minutes after rest and two separate readings 5 minutes apart were recorded. The patients were instructed to monitor their BP at home at the first opportunity after discharge which could be before or at the one month visit.
Three sets of home measurements were taken utilizing a pre specified equipment type upon waking, at mid-morning and before bed. These measurements recorded by a Bluetooth-enabled, regularly-calibrated, telemetric BP monitor were then transmitted by a Bluetooth radio to a mobile phone, for secure transmission to a server hosting a password-protected website for review and download of readings. Goal mean BP was 130/80 mm Hg and medications to achieve this goal were started either in clinic or after one week of home monitoring. A standardized protocol utilizing a combination of thiazide diuretics (TI) , calcium channel blockers (CCB) and renin angiotensin inhibitors (RASi) was most commonly used, however medications could be altered based on adverse reactions and physician discretion. Mean, minimum and maximum SBP and DBP were assessed and compared between two periods- 3-10 days prior to intervention and 8-15 days after. Diurnal variability in SBP was measured as the coefficient of variation of the cluster averages for each day and Day-to-day variability in SBP and DBP was measured as the residual CV about a moving average over 5 days. Multivariate linear regression and Chi-square tests were used for analysis of data.
The authors report a significant reduction in home SBP variability following treatment with CCBs or Tis as compared with RASis. Differences in change in SBP variability persisted after adjustment for age, gender and cardiovascular risk factors and baseline mean and variability in SBP (CCB/diuretic vs combination vs RASi p=0.005). The reduction in day to day SBP variability was greatest for early morning readings and there was no significant impact observed on DBP variability or on mean SBP.
How can we translate these results to general practice? And what does this mean for our patients? The lack of outcome data, rate of recurrent ischemia etc. makes it difficult to apply these findings in clinical practice. Although the SBP variability was decreased on home BP monitoring by Calcium channel blockers and thiazide diuretics, did these patients benefit from this reduction in variability? Additionally only a few medications from each class were used and some like Indapamide are not widely prescribed in the US. BP was recorded only three times a day which may be too few to measure an actual effect on variability, another alternative would be to use ambulatory BP monitors. Well, in my mind this study is useful in understanding that CCB’s and TI’s reduced SBP variability in TIA and stroke measurements even when BP is recorded in the home setting, BUT I am left asking for more clinically significant outcome data.