Factors affecting the validity of the oscillometric Ankle Brachial Index to detect peripheral arterial disease

A randomized cross-over trial in patients suspected of PAD on diagnostic accuracy of ankle-brachial index by Doppler-based versus four-point oscillometry based measurements

Summary. Background: For diagnosis of peripheral arterial occlusive disease (PAD), a Doppler-based ankle-brachial-index (dABI) is recommended as the first non-invasive measurement. Due to limitations of dABI, oscillometry might be used as an alternative. The aim of our study was to investigate whether a semi-automatic, four-point oscillometric device provides comparable diagnostic accuracy. Furthermore, time requirements and patient preferences were evaluated. Patients and methods: 286 patients were recruited for the study; 140 without and 146 with PAD. The Doppler-based (dABI) and oscillometric (oABI and pulse wave index – PWI) measurements were performed on the same day in a randomized cross-over design. Specificity and sensitivity against verified PAD diagnosis were computed and compared by McNemar tests. ROC analyses were performed and areas under the curve were compared by non-parametric methods. Results: oABI had significantly lower sensitivity (65.8%, 95% CI: 59.2%–71.9%) compared to dABI (87.3%, CI: 81.9–91.3%) but significantly higher specificity (79.7%, 74.7–83.9% vs. 67.0%, 61.3–72.2%). PWI had a comparable sensitivity to dABI. The combination of oABI and PWI had the highest sensitivity (88.8%, 85.7–91.4%). ROC analysis revealed that PWI had the largest area under the curve, but no significant differences between oABI and dABI were observed. Time requirement for oABI was significantly shorter by about 5 min and significantly more patients would prefer oABI for future testing. Conclusions: Semi-automatic oABI measurements using the AngER-device provide comparable diagnostic results to the conventional Doppler method while PWI performed best. The time saved by oscillometry could be important, especially in high volume centers and epidemiologic studies.

Oscillometric and Doppler Ankle Brachial Indexes as predictors of all-cause mortality in a Primary Care population

BACKGROUND

Doppler Ankle Brachial Index (ABI), the non-invasive reference standard for peripheral arterial disease (PAD) in Primary Care, has proved good capacity to predict all-cause mortality. However, the role of oscillometric ABI is uncertain. This study aims to evaluate the ability of oscillometric and Doppler ABI to predict all-cause mortality in a Primary Care population.

METHODS

Oscillometric and Doppler ABI were measured in 203 consecutive subjects with ≥1 cardiovascular risk factors or intermittent claudication. Pathologic ABI was defined when ABI was ≤0.9 or ≥1.4, and when the oscillometer was unable to record a value (oscillometric error). All-cause mortality was ascertained through examination of electronic medical records or telephone contact.

RESULTS

After analyzing 602.9 subjects/year, all-cause mortality was recorded in 17 (8.4%) patients. Kaplan-Meier survival curves for oscillometric (Log-Rank test χ2=66.02, P<0.001) and Doppler ABI (Log-Rank test χ2=42.30, P<0.001) showed that a pathologic ABI is associated with all-cause mortality. After adjusting for covariates, the hazard ratio in multivariable Cox regression were 4.52 (95% CI: 1.67-12.18, P=0.003) and 2.08 (95% CI: 0.83-5.18, P=0.117) for oscillometric and Doppler ABI models, respectively. When introducing oscillometric and Doppler ABI simultaneously in the Cox regression model, only oscillometric ABI was an independent predictor with a hazard ratio=7.90 (95% CI: 1.79-34.83, P=0.006). Regarding Doppler ABI, no significant differences were found in all-cause mortality between low ABI (≤0.9) and calcified ABI (≥1.4), (Log-Rank test χ2=0.98, P=0.322).

CONCLUSIONS

Oscillometric ABI predicted all-cause mortality in a Primary Care population even better than Doppler ABI, irrespective of cardiovascular risk factors. Oscillometric ABI, due to a high feasibility, could routinely identify high-risk patients to implement preventive measures.