LAD

**1. Left Anterior Descending (LAD) artery (Cardiology/Anatomy)** - Anatomy: Arises from the left main coronary artery (LCA), which also gives rise to the left circumflex (LCx). The LAD runs in the anterior interventricular groove toward the apex. Branches: diagonal branches (anterolateral LV) and septal perforators (anterior 2/3 of the interventricular septum). - Supplies: Anterior wall of the LV, anterior 2/3 of the septum, the apex, the anterior papillary muscle, and (variably) the bundle branches (the right bundle and the left anterior fascicle). - Clinical significance: The most common site of coronary occlusion (about 40-50% of MIs), hence the "widow-maker" when the proximal segment is occluded. - ECG: Anterior STEMI shows ST elevation in V1-V4 (anteroseptal: V1-V2; anterior: V3-V4). Proximal LAD occlusion can also involve I and aVL (anterolateral). - Complications: LV failure/cardiogenic shock, anterior wall aneurysm, LV free wall rupture (days 3-14), septal rupture (VSD with a new holosystolic murmur and a step-up in O2 saturation in the RV), conduction block (Mobitz II, bundle branch block), ventricular arrhythmias, and mural thrombus/embolic stroke. - Management: Emergent reperfusion (PCI, or thrombolytics if PCI is unavailable). Also aspirin plus a P2Y12 inhibitor, anticoagulation, beta-blocker, high-intensity statin, and ACE inhibitor. CABG often uses the left internal mammary artery (LIMA) to graft the LAD, which has excellent long-term patency. - Other relevant points: The posterior descending artery (PDA) supplies the posterior 1/3 of the septum (from the RCA in right-dominant circulation, about 85%). Sudden onset of chest pain, a Q-wave anterior MI, and pulmonary edema are classic clues.

**2. Left Axis Deviation (LAD) (ECG)** - Mean QRS axis between -30° and -90°. Lead I positive, aVF negative (and lead II negative if more marked). - Causes: Left anterior fascicular block, inferior MI (Q waves in inferior leads), LVH, WPW (some), ventricular pacing/PVCs, and a high diaphragm (pregnancy, ascites, obesity).

**3. Leukocyte Adhesion Deficiency (LAD) (Immunology)** - Type 1: Defective CD18 (β2 integrin, ITGB2 mutation, AR). Neutrophils can't adhere or transmigrate. Features: delayed umbilical cord separation (>30 days), recurrent skin and mucosal infections without pus, a marked neutrophilia (leukocytosis), and impaired wound healing. The lack of pus is a classic clue. - Type 2: Defective fucosylated ligand for selectin (sialyl Lewis X; GDP-fucose transporter defect). Features: similar to type 1 plus the Bombay blood phenotype, with intellectual disability and short stature. CD18 is normal. - Treatment: Hematopoietic stem cell transplantation.

**Test tips:** If the stem describes chest pain with ST elevation in V1-V4, think LAD occlusion. If it describes a newborn with a late-falling umbilical stump and no pus, think LAD-1 (CD18).