Ankle - Brachial Index Measurement in Atrial Fibrillation

Consecutive patients with atrial fibrillation will be admitted to the hospital for electrical cardioversion. Ankle brachial index will be measured three times with oscillometric method and three times with doppler method. Two study sessions will be performed: the first before and the second after electrical cardioversion. The first session will be ended before anesthesia. The second session will be started before a conscious patient will be transported from intensive care unit to general ward.

All the measurements will be taken in the intensive care unit at an ambient temperature of 21° C, after patients will give their written informed consent to participate in the study. All patients will be awake, fasting and in the supine position. ABI will be measured according to the guidelines issued by AHA. Systolic blood pressure will be measured using a Doppler device (Echo Sounder ES-101EX, Hadeco, Japan) and a validated and calibrated aneroid sphygmomanometer (Minimus II, Rister, Germany). Measurement of ABI using oscillometric method will be performed using WatchBP Office ABI system (Microlife WatchBP AG, Widnau, Switzerland). The appropriate cuff size will be used with the width of the cuff being at least 40% of the limb circumference. The arm with higher systolic blood pressure will be used to calculate the ABI. Higher systolic blood pressure measured on the posterior tibial or dorsalis pedis artery will be used to calculate the ABI. During both study sessions ABI measurements will be repeated 3 times with each method in the reverse order of the preceding measurement e.g., in the case of the initial counterclockwise sequence: right arm, right popliteal, right dorsalis pedis, left popliteal, left dorsalis pedis, left arm, right arm, the clockwise sequence will be used, starting and ending with the left arm. The same sequence of limb pressure measurements will be used used during the study.

A sample size calculation was based on the preliminary observations made by the study team. It was calculated that the study sample size of 79 subjects would be needed to detect a difference of 0.1 in the ABI measured in sinus rhythm and during atrial fibrillation, with a two-tailed α of 0.05 and a (1-β) of 0.90. The investigators initial estimate of sample size of 115 patients incorporated an assumption of dropout due to non-effective electrical cardioversion, patient decision to quit study or failure to obtain adequate ABI.

The measurements will be repeated three times with each method and for the each method the mean will be used for the calculations. Investigator - study nurse, trained at the vascular department, will perform all ABI measurements.