From the Guidelines
Automatic blood pressure machines provide inaccurate readings in patients with irregular cardiac rhythms, particularly atrial fibrillation, frequent premature beats, and significant bradycardia or tachyarrhythmias. These devices rely on oscillometric technology that detects regular arterial wall oscillations during cuff deflation, which becomes unreliable when the cardiac rhythm is irregular 1. In atrial fibrillation, the varying stroke volumes and irregular intervals between beats cause inconsistent arterial pressure waves, leading to measurement errors, as noted in a statement from the American Heart Association Council on High Blood Pressure Research 1. Similarly, frequent ectopic beats disrupt the pattern of oscillations the device is programmed to detect, and significant bradycardia provides too few data points for accurate measurement, while tachyarrhythmias create rapid, inconsistent pressure waves. Some key rhythms that may lead to inaccurate blood pressure measurements include:
- Atrial fibrillation
- Frequent premature beats (PVCs or PACs)
- Significant bradycardia (heart rate below 40 beats per minute)
- Tachyarrhythmias (rapid irregular rhythms) For patients with these rhythms, manual auscultatory blood pressure measurement using a sphygmomanometer and stethoscope remains the gold standard, as a trained clinician can account for beat-to-beat variability and identify true systolic and diastolic pressures by listening for Korotkoff sounds, and this approach is supported by guidelines on blood pressure measurement 1.
From the Research
Cardiac Rhythms Affecting Blood Pressure Measurement
The following cardiac rhythms can provide inaccurate blood pressure readings when using an automatic blood pressure machine:
- Atrial fibrillation: Studies have shown that automated blood pressure monitors may not be accurate in measuring diastolic blood pressure (DBP) in patients with atrial fibrillation, although they may be accurate in measuring systolic blood pressure (SBP) 2, 3.
- Premature ventricular contractions (PVCs): PVCs can affect the accuracy of non-invasive blood pressure monitors, with some studies showing that SBP may be overestimated during PVCs 4.
- Missed beats: Missed beats can prolong signal response times in non-invasive blood pressure monitors, potentially affecting the accuracy of blood pressure readings 4.
- Nonsustained ventricular tachycardia (NSVT): While there is limited research on the specific effect of NSVT on blood pressure measurement, it is a type of ventricular arrhythmia that can be detected during ECG screening 5.
Factors Influencing Blood Pressure Measurement Accuracy
Several factors can influence the accuracy of blood pressure measurement in patients with cardiac arrhythmias, including:
- Heart rate: Some studies have shown that heart rate can affect the accuracy of automated blood pressure monitors, although this is not always the case 2, 4.
- Beat-to-beat blood pressure variability: Increased beat-to-beat blood pressure variability, such as that seen in atrial fibrillation, can make blood pressure measurement more challenging and prone to error 3.
- Type of blood pressure monitor: Different types of blood pressure monitors, such as auscultatory or oscillometric devices, may have varying degrees of accuracy in patients with cardiac arrhythmias 2, 4, 3.