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12-Lead ECG Interpretation for the CRNA
TEXTMonitoring & Patient Safety V · 10 min read
Systematic 5-step reading, ischemia localization by lead, and the electrolyte/drug patterns that change anesthetic management.
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3 min read5 sectionsSystematic approach
Bundle branch blocks
Common, often benign — but masks RV strain and can be a new sign of acute PE.
Often CAD-related; NEW LBBB with ischemic chest pain is treated as STEMI-equivalent (Sgarbossa criteria for ischemia within LBBB).
LBBB obscures the standard STEMI diagnosis — RWMA on TEE becomes the intraop ischemia detector.
Bifascicular block (RBBB + LAFB or RBBB + LPFB) raises complete-heart-block risk during anesthesia.
Ischemia localization
STEMI = ST elevation ≥1 mm in two contiguous leads (≥2 mm V2–V3 in men, ≥1.5 mm women)RECIPROCAL ST DEPRESSION confirms.
STEMI requires urgent reperfusion (PCI within 90 min door-to-balloon); cancel elective anesthesia and transfer.
Electrolyte + drug effects
QT PROLONGATION drugs to know — ondansetron, droperidol, haloperidol, methadone, amiodarone, fluoroquinolones, macrolides, antifungals — additive when combined; check baseline QTc and avoid stacking in patients with congenital long-QT or hypokalemia/hypomagnesemia.
Intraoperative monitoring pearls
For high-risk cardiac patients, additional V3–V4 leads modestly improve sensitivity.
ST-SEGMENT TREND software (most modern monitors) auto-compares to baseline and triggers alarm at 1 mm change in 2 leads × 1 minute — calibrate to baseline at induction.
New ST elevation/depression in 2 contiguous leads, new RWMA on TEE, unexplained hemodynamic instability, or new arrhythmia in a high-risk patient should be treated as intraoperative ischemia until proven otherwise — increase FiO2, deepen anesthesia to reduce VO2, normalize MAP and HR, get an ABG + send troponin, and call cardiology.
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