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Table 2

**Characteristics of Type A, B, and C Lesions**
Lesion-Specific Characteristics
Type A lesions (minimally complex)
Discrete (length <10 mm)
Concentric
Readily accessible
Nonangulated segment (<45°)
Smooth contour
Little or no calcification
Less than totally occlusive
Not ostial in location
No major side branch involvement
Absence of thrombus
Type B lesions (moderately complex)^∗
Tubular (length 10 to 20 mm)
Eccentric
Moderate tortuosity of proximal segment
Moderately angulated segment (>45°, <90°)
Irregular contour
Moderate or heavy calcification
Total occlusions <3 mo old
Ostial in location
Bifurcation lesions requiring double guide wires
Some thrombus present
Type C lesions (severely complex)
Diffuse (length >2 cm)
Excessive tortuosity of proximal segment
Extremely angulated segments >90°
Total occlusions >3 mo old and/or bridging collaterals
Inability to protect major side branches
Degenerated vein grafts with friable lesions
^∗ Although the risk of abrupt vessel closure may be moderately high with Type B lesions, the likelihood of a major complication may be low in certain instances such as in the dilation of total occlusions <3 mo old or when abundant collateral channels supply the distal vessel.