Intravascular ultrasound assessment of distal left main bifurcation disease: the importance of the polygon of confluence of the left main, left anterior descending, and left circumflex arteries.

BACKGROUND: The polygon of confluence (POC) represents the zone of confluence of the distal left main (LM), ostial left anterior descending (LAD), and ostial left circumflex (LCX) arteries. METHODS: We used intravascular ultrasound (IVUS) to assess the POC pre and post-drug-eluting stent implantation for unprotected distal LM disease. Four segments within 82 LM bifurcation lesions were defined by longitudinal IVUS reconstruction: (1) ostial LAD, (2) POC, and (3) distal LM (DLM)--from LAD-pullback, and (4) ostial LCX from LCX-pullback. RESULTS: Preprocedural minimum lumen area (MLA) and poststenting minimum stent area (MSA) within the LM were mainly located within the POC (51 and 71%). On ROC analysis, a cut-off of the MLA within the POC of 6.1 mm(2) predicted significant LCX carinal stenosis (85% sensitivity, 52% specificity, AUC = 0.7, 95% CI = 0.57-0.78, P < 0.01). Poststenting MSA within the distal LM proximal to the carina (to include DLM and POC) positively correlated with the preprocedural MLA within the POC (r = 0.283, P = 0.02); it was significantly smaller in 48 lesions with a pre-PCI MLA within the POC < 6.1 mm(2) versus 25 lesions with a pre-PCI MLA ≥6.1 mm(2) (7.5 ± 2.1 mm(2) vs. 8.6 ± 2.0 mm(2), P = 0.04). Independent predictors for poststenting LCX carinal MLA also included preprocedural MLA within the POC (ß = 0.240, 95% CI = 0.004-0.353, P = 0.04). CONCLUSION: The MLA within the POC was a good surrogate reflecting the overall severity of LM bifurcation disease including ostial LCX stenosis pre-PCI and the ability to expand a stent within the distal LM as well as final ostial LCX lumen area post-PCI.