Severe Aortic Stenosis for Non-Cardiac Surgery

Aortic stenosis is fixed obstruction at the LV outflow. Cardiac output becomes preload-dependent (failing LV needs full filling), rate-dependent (slow enough for filling, not so slow CO drops), and sinus-rhythm-dependent (LV needs the atrial kick — ~30% of stroke volume in severe AS). Coronary perfusion of the hypertrophied LV is precarious — diastolic perfusion only, low coronary reserve, easily ischemic if MAP drops. Severity grading: peak velocity, mean gradient, valve area (AVA), low-flow low-gradient subset.

Critical / severe AS: peak velocity ≥4 m/s, mean gradient ≥40 mmHg, AVA ≤1.0 cm² (or indexed AVA ≤0.6 cm²/m²). With symptoms (angina, syncope, heart failure) — pre-op TAVR or surgical AVR is standard for elective non-cardiac surgery. Asymptomatic severe AS: case-by-case, usually proceed with optimization. Moderate AS: usually fine with careful management. The 2014 ACC/AHA + 2020 ESC guidelines + 2024 update push this hard — most cardiology consults will recommend TAVR first.

AVOID spinal anesthesia in severe AS. Why: sudden loss of sympathetic tone → ↓ SVR → ↓ coronary perfusion of the hypertrophied LV → ischemia → spiral of decompensation. Death-on-the-table reports are well-documented. Epidural with slow titration is acceptable (gradual titration allows hemodynamic correction). General anesthesia with careful induction is standard for moderate-severe AS surgery. AVOID drugs that cause tachycardia (ketamine, ephedrine, anticholinergics + atropine — bradycardia is preferable to tachycardia). AVOID nitroglycerin (drops preload + SVR).

Induction: low-dose etomidate (preserves contractility) + low-dose fentanyl + slow titration of NMB. Avoid propofol bolus (drops SVR). Maintain SINUS RHYTHM aggressively — treat AFib early with cardioversion (loss of atrial kick = ↓ CO 30% in AS). Treat hypotension with PHENYLEPHRINE first (no tachycardia, raises SVR + coronary perfusion). Norepinephrine as second-line. Vasopressin for refractory. Maintain MAP within 10% of baseline (autoregulation impaired). Slow heart rate (60-80 bpm target) — esmolol if needed. Aggressive intra-arterial monitoring + consider TEE for severe.

First move: phenylephrine bolus 100-200 mcg + IV fluid. Don't waste time on inotropes — the LV is fine; what's failing is coronary perfusion. Ephedrine WORSENS the situation (tachycardia + drops CO further). If refractory: add vasopressin infusion + consider methylene blue if vasoplegic. New AFib: synchronized cardioversion (don't titrate amiodarone — drops SVR). Consider mechanical support (IABP, ECMO) if refractory shock — but TAVR-first patients have rescue options.

(1) Low-flow low-gradient AS is a separate pattern — patients have severe AS by area but low gradient because LV is failing. They look 'mild' on echo but are actually higher-risk. Dobutamine stress echo distinguishes. (2) Hypertrophic obstructive cardiomyopathy (HOCM) physiology is opposite for some elements: avoid inotropes (worsens dynamic obstruction), avoid Trendelenburg (decreases preload). (3) The murmur of AS goes AWAY in critical AS — when forward flow is so limited that turbulence is silent. New 'no murmur' in known AS = late-stage. (4) Pre-op echo within 12 months minimum; sooner if symptoms changing.