Blood pressure in ambulatory monitoring after transient ischaemic attack (BAT24 study)

Abstract

Background: Circadian blood pressure (BP) variation patterns have been defined by day and night BP changes measured by 24-hour ambulatory BP monitoring. Abnormal circadian BP patterns include non-dipper, reverse dipper, and extreme dipper patterns due to their association with cardiovascular/cerebrovascular risk and worse prognosis. Impaired autonomic nervous system function has been considered to be related to abnormal BP dipping profiles. People with abnormal circadian BP variation have a high risk of developing stroke and patients with stroke tend to have more prevalent abnormal circadian BP patterns. However, there are no data concerning circadian BP patterns in patients with transient ischaemic attack (TIA) or minor stroke.

Aims: The aims of the present study were to demonstrate the distribution of circadian BP patterns in patients with TIA or minor stroke in comparison to controls, and to investigate their association with autonomic nervous system function.

Methods: This was a cross-sectional comparison study, with a prospective, observational sub-study following up patients with TIA or minor stroke for three months after the initial event. Patients with TIA or minor stroke and no previous stroke history were approached and recruited within seven days after their initial event at the Austin Hospital or the Northern Hospital TIA Clinic, both located in Melbourne, Australia. Control participants were age and gender group-matched, and recruited from among family members, friends of recruited patients, patients from the Austin Hospital Stroke Prevention Clinic, or the Hypertension Clinic. Volunteers from the local community were also recruited as control participants via newspaper advertisement.

A face-to-face interview, clinic BP measurement, 24-hour ambulatory BP monitoring, and a 15 minute electrocardiogram-based heart rate variability (HRV) for autonomic nervous system function assessment were conducted for all participants. These tests were repeated at a three-month follow-up assessment for the TIA/minor stroke participants. The primary outcome of the study was recurrent stroke/TIA during the follow-up period.

Blood pressure patterns were classified into dipper, non-dipper, reverse dipper, and extreme dipper based on published criteria. Statistical analyses were performed using Stata version 10 software.

Results: There were 158 participants, including 76 patients (mean age 67.2 years, male 58%) and 82 controls (mean age 65.6 years, male 55%). There were 47 patients with TIA and 29 patients with minor stroke. There were no significant differences for age, gender and most risk factors between patients and controls. Patients had a higher mean body mass index (28.7 kg/ m2 versus 26.9 kg/ m2), greater prevalence of hypertension (72% versus 49%) and atrial fibrillation (17% versus 1%) than controls. Fifty-eight patients (76.3%) returned to the clinic for a face-to-face follow-up interview, and had a second 24-hour period of ambulatory BP monitoring.

Blood pressure measured by ambulatory BP monitoring was shown to be well controlled (24-hour ambulatory BP < 130/80 mm Hg) in patients within seven days, and at three-months after the initial TIA/minor stroke event. Although not significant, the average clinic BP was higher than the average daytime BP (net difference in systolic BP: 13 mm Hg for patients, 8 mm Hg for controls; net difference in diastolic BP: 5 mm Hg for patients, 2 mm Hg for controls) and 24-hour ambulatory BP (net difference in systolic BP: 16 mm Hg for patients, 10 mm Hg for controls; net difference in diastolic BP: 7 mm Hg for patients, 4 mm Hg for controls) for both patients and controls. There was poor agreement between ambulatory BP and clinic BP measurements, for example, concordance correlation coefficient, r = 0.5 (95% CI: 0.4 to 0.6) for agreement between the average clinic systolic BP, and the average 24-hour systolic BP.

A systolic dipper pattern was found in 31.6% of patients with TIA or minor stroke. However, the prevalence of abnormal circadian BP patterns in patients was not significantly different to that among controls. Heart rate variability did not differ significantly between patients and controls, for example, the standard deviation of the average normal-to-normal QRS intervals (Standard Deviation of Normal to Normal [SDNN], one of the parameters in the HRV analysis) was 43.1 ms (95% CI: 37.0 to 49.2) for patients, and 42.2 ms (95% CI: 37.6 to 46.8) for controls (p = 0.8).

During the three-month follow-up period, there were 26 recurrent TIA events identified in 15 patients (TIA risk 19.7%), and four stroke events occurred in four patients (stroke risk 5.3%). There was no association between circadian BP patterns and risk of recurrent stroke/TIA.

Conclusion: Patients with TIA or minor stroke had no more prevalent abnormal circadian BP patterns and no greater impairment of autonomic nervous system function when compared to controls. These findings differ from the existing evidence for patients with stroke.