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DO PATIENTS WITH AN ABNORMALLY HIGH ABI HAVE EVIDENCE OF OBSTRUCTIVE PAD?

DO PATIENTS WITH AN ABNORMALLY HIGH ABI HAVE EVIDENCE OF OBSTRUCTIVE PAD?
Authors JK Todd, DW Armstrong, D Brouillard, M Nault, MF Matangi
Kingston, Ontario

BACKGROUND: Epidemiological observational data indicates that a high ABI, >1.30, is associated with increased cardiovascular risk. It is our impression that most of the risk is in fact related to increasing age and that very few of these individuals actually have obstructive peripheral arterial disease. The pupose of our investigation is to use the Toe-Brachial Index (TBI), which is not affected by the presence of peripheral arterial calcification, as the gold standard as to whether obstructive PAD is present or not and to compare these patients with patients who do not have PAD using the traditional ABI range of 0.91-1.30.

METHODS: CARDIOfileTM our cardiology database was searched for all patients with abnormally high ABIs (>1.30) in both lower limbs. These patients were then compared to patients with a normal ABI (0.91-1.30) in both lower limbs. The TBI was measured in all patients. A TBI of <0.72 was considered abnormal. The unpaired t test was used to detect differences between the means and the Fisher's exact test was used to detect differences between proportions. The Bonferroni correction method was used to adjust the level of significance for multiple comparisons. As there were 9 statistical tests performed a p value of <0.0056 (0.05/9) was considered statistically significant.
RESULTS: The mean age was 68.2±8.3 years in the abnormal TBI group and 65.3±10.5 years in the normal ABI group (P value is not significant with the Bonferroni correction). For other results see Table 1. NB: For the TBI we have used total limbs rather than patients and therefore the denominator is doubled.
Table 1.
  ABI > 1.30 (n=66) ABI 0.91-1.30 (n=902) P value
R) ABI 1.41±0.10 1.14±0.09 <0.0001
L) ABI 1.41±0.13 1.13±0.09 <0.0001
R) TBI 0.93±0.24 0.88±0.19 NS
L) TBI 0.91±0.26 0.88±0.19 NS
TBI <0.72 (Y/N) 31/132 440/1804 NS
Smoker (Y/N) 6/60 220/682 <0.005
Hypertensive (Y/N) 23/43 589/313 <0.0001
Diabetes (Y/N) 42/24 652/250 NS
Dyslipidemia (Y/N) 52/14 641/261 NS

CONCLUSION: Patients with a high ABI (>1.30) had similar TBIs to patients with normal ABIs. The frequency of abnormal TBIs in both the normal ABI (24.4%) and high ABIs (23.5%) were very similar indicating a similar spectrum of TBI values. The high ABI group on average had slightly higher TBIs and were slightly older but neither of these reached statistical significance. The high ABI group were significantly less likely to be smokers or be treated for hypertension. There was no significant difference with respect to the frequency of dyslipidemia or diabetes. In summary most patients (76.5%) with a high ABI, >1.30, do not have evidence to support a diagnosis of obstructive PAD. Similar percentages of both groups (23.5% and 24.4%) have PAD by TBI criteria.