Should Oscillometric Blood Pressure Monitors Be Used in Patients With Atrial Fibrillation?

Despite the widespread use of electronic oscillometric sphygmomanometers, there continues to be concern about the accuracy of these devices in patients with arrhythmias, especially atrial fibrillation. Guidelines in North America and Europe1-3 now recommend oscillometric devices for all types of blood pressure (BP) measurement, including office BP, home BP, and 24-hour ambulatory BP monitoring. These guidelines also state a preference for fully automated oscillometric office BP monitors, which are capable of taking multiple readings with the patient resting quietly alone, a procedure known as automated office BP (AOBP), which provides a more reliable evaluation of BP than semi-automated devices.4 In patients with arrhythmias such as atrial fibrillation, the European guidelines2 recommend that repeated BP measurements be taken in order to improve accuracy. However, these guidelines do not specify which type of sphygmomanometer should be used in this situation. A European Society of Hypertension statement on requirements for professional office BP monitors5 noted that oscillometric devices may not record BP accurately in patients with arrhythmias and that further studies are needed to clarify this issue, with the implication being that the presence of an arrhythmia may be one reason for retaining access to auscultatory BP measurement in the office. What is the evidence favoring manual BP in atrial fibrillation over readings taken with an oscillometric device? In a systematic review and meta-analysis, Stergiou and colleagues6 examined the literature comparing readings taken with oscillometric recorders with readings obtained using manual sphygmomanometers, mostly the standard mercury device. The authors found significant heterogeneity in methodology and measurement protocols with most studies not following established guidelines for evaluating the accuracy of individual sphygmomanometers. By performing a meta-analysis of studies on oscillometric sphygmomanometers used for ambulatory, home, and office BP recordings, the authors concluded that these monitors "appear to be accurate for systolic but not diastolic BP." It should be noted that none of the devices tested in these studies would currently be considered appropriate for use in office practice. The present study by Maselli and colleagues7 is unique in that it examines the agreement between manual and oscillometric BP readings recorded in the same patients with and without atrial fibrillation. In this study, manual BP was obtained using a conventional mercury sphygmomanometer and oscillometric readings were taken using a validated oscillometric device (A&D TM-2430, Tokyo, Japan) designed for 24-hour ambulatory BP monitoring. By recording sets of three manual BP and three automated BP readings in patients in atrial fibrillation and then in sinus rhythm after DC-cardioversion, the authors were able to show that both methods recorded similar mean systolic and diastolic BP readings with and without the arrhythmia being present. An advantage of this study is that triplicate measurements were obtained using each method, as currently recommended in atrial fibrillation,2 in order to account for the increased beat-to-beat variability caused by variations in ventricular filling time, stroke volume, and contractility. However, their study is not without methodological limitations. Contrary to what was stated in the article, the procedure for the BP measurements did not follow any of the established protocols for the validation of BP monitors.8, 9 The reference manual BP was taken by a single observer, instead of two observers performing readings simultaneously and blinded to each other's measurements. In addition, there were no repeated sequential BP measurements alternating the reference and the test devices. Instead, a single set of triplicate reference manual BP readings were taken and followed by triplicate oscillometric measurements. As noted by the authors, these deficiencies did affect the BP readings. The reduced variability of the manual readings as determined by the standard deviation was almost certainly the result of "recall bias" with the observers aware of previous readings when recording the next one. Also, the mean oscillometric BPs were consistently, albeit only slightly, lower than the mean manual BP readings as a result of an "order effect," with the manual readings always being taken first, and a longer period of rest with accommodation to the BP measurements affecting the oscillometric BPs. The variability of both the manual and oscillometric readings was higher with atrial fibrillation than with sinus rhythm, which would be expected because of the variable R-R interval associated with the arrhythmia. Despite these shortcomings, the findings of Maselli and colleagues7 do have some relevance to office practice. The mean of three manual BP readings was similar to the oscillometric BP measurements in both atrial fibrillation and sinus rhythm in the same patients. Given the variability in BP readings in the presence of atrial fibrillation, regardless of which type of sphygmomanometer is used, multiple readings should be performed in order to obtain a more accurate estimate of an individual's BP.2 There are now at least three oscillometric sphygmomanometers specifically designed for AOBP that automatically record three to five BP measurements over several minutes with the patient resting alone.4 Although none of these AOBP devices has been specifically evaluated in patients with atrial fibrillation, at least one, the Microlife WatchBP Office (Microlife Corporation, Widnau, Switzerland),10 uses the same diagnostic algorithm as another device used for home BP, the Microlife BPA 100 Plus,11 which has been tested in atrial fibrillation. In the latter study, which followed proper validation procedures for device accuracy evaluation in the presence of atrial fibrillation, the oscillometric home BP recorder met accuracy criteria for systolic but not diastolic BP, which is consistent with the overall findings in the meta-analysis of oscillometric sphygmomanometers.6 There is no reason to expect that the other two oscillometric AOBP devices, the BpTRU (Coquitlam, British Columbia, Canada)12 and Omron HEM-907 (Omron Healthcare, Inc, Lake Forest, IL),13 would record BP in patients with atrial fibrillation any differently. Considering that systolic BP is a stronger predictor of cardiovascular risk than diastolic BP in most hypertensive patients and particularly in the elderly, who are those most affected by atrial fibrillation, the possible diminished accuracy in diastolic BP with oscillometric sphygmomanometers is of less concern in clinical practical. Clearly, more research using proper validation methodology is needed to assess the accuracy of all types of oscillometric sphygmomanometers, including AOBP devices, in patients with atrial fibrillation. Meanwhile, how should BP be recorded in patients with atrial fibrillation in routine practice? For long-term home BP monitoring by patients with atrial fibrillation, many of whom are elderly hypertensives, auscultatory self-measurement is usually not feasible and repeated automated measurement should be recommended.6 Ambulatory BP monitors are almost exclusively oscillometric; therefore, auscultatory devices are not an option. Studies in patients with atrial fibrillation have shown that the 24-hour recordings with these devices are not only valid but also correlate with preclinical target organ damage.14, 15 With regard to routine office practice, current guidelines1-3 generally recommend oscillometric devices for office BP because of improved accuracy in primary care. Paradoxically, manual BP measurement is still considered somewhat better for patients with atrial fibrillation.5 Although this preference might be valid for BP readings performed according to guidelines in a research setting, manual BP readings are still subject to numerous sources of error and bias in routine clinical practice. Thus, in office practice, the choice will frequently be either a mean of three oscillometric BP readings recorded automatically, preferably without human involvement (AOBP), or one (possibly two or three) manual BP measurement rounded off to the nearest zero value taken without any antecedent rest and with the patient and observer talking. For the same reasons oscillometric devices are now recommended for general use in the office, it would seem preferable to accept a small degree of inaccuracy in diastolic BP and use the same oscillometric device in all patients in the office, including those with atrial fibrillation. Needless to say, this practical approach to office BP measurement should be validated by properly conducted studies relevant to office practice in the community. Moreover, further technological improvements to achieve more accurate oscillometric BP measurement in atrial fibrillation for all types of devices would be welcomed. MGM: Nothing to declare. GSS: Received honoraria for educational lectures from Omron and consultation fees from Microlife.