Blood Pressure in Patients With Atrial Fibrillation: Part 1––Measurement

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and is an important risk factor for stroke.1 AF is estimated to be present in 1% to 2% of the general population, with an increasing prevalence with age, and is present in approximately 5% of adults older than 65 years.1, 2 Hypertension and AF commonly coexist.1 AF is usually diagnosed with opportunistic screening using pulse palpation while measuring blood pressure (BP) using the auscultatory method and is recommended in patients 65 years and older.3 Current guidelines for BP measurement in AF recommend using the auscultatory method with repeated BP measurements to compensate for the increased beat-to-beat BP variability. The accuracy of BP measurement using the oscillometric BP method may be inaccurate in patients with AF.4, 5 Although automated oscillometric BP measurement is not recommended in patients with AF, this method is most frequently used for home BP monitoring and is increasingly being used in clinical practice because mercury sphygmomanometers are being progressively eliminated from clinical use and, in many circumstances, are being replaced by automated electronic BP monitors. Few studies have evaluated the accuracy of automated BP monitors in AF, and, therefore, the accuracy of BP measurement using oscillometric devices in AF remains controversial. In the presence of AF, variations in ventricular filling time, stroke volume, and contractility may lead to increased beat-to beat BP variability, which may affect BP estimation using both the auscultatory and oscillometric methods.6 Using the auscultatory method there is often failure to accurately interpret the Korotkoff sounds as a result of muffled sounds and confusion of the auditory and visual signals, leading to large intra-observer and inter-observer variability of BP measurement in patients with AF, particularly for diastolic BP measurements.7 Another issue regarding BP measurement in AF using the auscultatory method is related to the deflation rate, and, particularly in patients with bradyarrhythmias, it is important that the deflation rate is less than the heart rate, because too rapid deflation will lead to underestimation of systolic BP and overestimation of diastolic BP.1 The oscillometric BP measurement method is not dependent on the user but the beat-to-beat changes in mean pressure and pulse pressure may distort the relationship between cuff pressure and oscillometric wave amplitude in AF, thereby affecting the accuracy of the automated BP measurement. Some automated electronic BP devices can provide valid readings in patients with AF resulting in valid BP readings in greater than 90% of patients.7 However, established validation criteria, such as the American Association for the Advancement of Medical Instrumentation validation protocol and the European Society of Hypertension International Protocol have not been consistently applied in most studies. Automated BP measurement in AF is reasonably accurate for systolic BP, but overestimates diastolic BP, although systolic hypertension is more likely to be the relevant predictor of cardiovascular risk since AF is more common in older patients. Limited data also exist with the use of ambulatory BP monitoring (ABPM) in AF. Three studies using the Spacelabs 90207 ABPM device (Spacelabs Healthcare, Snoqualmie, WA) in patients with AF obtained BP readings in 80% to 93% of attempts.8-10 Using R-wave gating for Korotkoff sounds, the Accutracker 1 BP (Suntech Medical Instruments, Raleigh, NC) monitor showed an overall 86% rate of successful readings.8 However, these are small studies with limited data. Use of automated BP monitors to detect AF has been reported with good diagnostic accuracy, which appears to be a useful screening tool in elderly hypertensive patients where AF is often asymptomatic or intermittent.1, 11-16 A review and meta-analysis of six studies (n=2332) was performed, which assessed the diagnostic accuracy of the Microlife BP monitor algorithm (Widnau, Switzerland) and demonstrated a pooled sensitivity of 98% and specificity of 92%.17 Analysis of four of the studies (n=1126) showed that more readings improved specificity and sensitivity further and taking three sequential readings with at least two detecting AF gave the highest diagnostic accuracy. In another recent study, two different home BP monitors were evaluated in 503 patients with simultaneous measurements (Omron M6 and Microlife BPA200 Plus devices). The sensitivity for detecting AF was 100% and the specificity was 94% for the Omron M6 device, compared with 92% and 97%, respectively, for the Microlife BPA200 Plus device.18 These results demonstrate satisfactory diagnostic accuracy of home BP monitors, which appear to be an efficient screening tool for the early detection and management of asymptomatic AF among elderly hypertensive patients. Along these lines, the National Institute for Health and Care Excellence (NICE) in the United Kingdom recommends the WatchBP Home A (Microlife) for BP measurement in patients 65 years and older in the primary care setting19 given its accuracy for AF detection. NICE anticipates that this will lead to a reduction in strokes with additional cost savings due to lower hospital costs associated with stroke admissions.20 The assessment of BP in AF is challenging and current guidelines question the accuracy of automated BP measurement and recommend repeated measurements using the auscultatory method. Until more evidence becomes available, the auscultatory method remains the reference method for office BP measurement in AF. Out-of-office BP measurement (ambulatory and home) in AF remains challenging; however, automated BP monitors with AF detection capability represent an enhanced opportunity to detect asymptomatic AF and possibly reduce the incidence of stoke. None.