Infrapopliteal calcification patterns in critical limb ischemia: diagnostic, pathologic and therapeutic implications in the search for the endovascular holy grail.

Critical limb ischemia (CLI) represents the terminal stage of peripheral arterial disease (PAD) and is characterized by multilevel and multivessel disease. Amongst patients with infrainguinal disease, approximately one third have predominantly isolated infrapopliteal disease and the remaining two thirds, a combination of femoropopliteal and infrapopliteal disease. Isolated infrapopliteal disease is mainly seen in the elderly, diabetic, or dialysis-dependent patients. These patients have higher risk of amputation and shorter amputation-free survival. Infrapopliteal disease presents with either complex high-grade calcified tandem lesions in multiple vessels or with long chronic total occlusion (CTO) segments with plaques characterized by higher calcium and lower fibro-fatty content than the inflow vessels, as arterial calcium deposition increases as we progress distally in the arterial tree. Vascular calcification occurs in both intima and media. Intimal calcification leads to development of calcified atheroma and occlusive lesions. Medial calcification leads to stiffening and decrease in arterial wall elasticity and compliance leading to atherosclerosis, reduced perfusion, and PAD, increasing cardiovascular mortality among patients with end-stage renal disease. This article attempts to review the implications of the diverse pathologic patterns of calcium distribution in infrapopliteal vessels of CLI patients, on the diagnostic modalities, technological developments, and the evolution of therapeutic approaches to improve outcomes among these patients. A critical analysis of the currently available data is provided, pointing to the surprising omission on the role of calcium on outcomes, and future directions are discussed. Is infrapopliteal calcium a roadblock or the avenue towards new paths? Necessity remains the mother of invention.