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ONTARIO BASE HOSPITAL GROUP Chapter 10 for 12 Lead Training -12 Lead Interpretation – Part 2Ontario Base Hospital Group Education Subcommittee 2008 TIME IS MUSCLE 12 Lead Interpretation – Part 2 AUTHOR REVIEWERS/CONTRIBUTORS Greg Soto, BEd, BA, ACP Neil Freckleton, AEMCA, ACP Hamilton Base Hospital Niagara Base Hospital Jim Scott, AEMCA, PCP Sault Area Hospital Ed Ouston, AEMCA, ACP Ottawa Base Hospital Laura McCleary, AEMCA, ACP SOCPC Tim Dodd, AEMCA, ACP Hamilton Base Hospital 2008 Ontario Base Hospital Group Dr. Rick Verbeek, Medical Director SOCPC OBHG Education Subcommittee Chapter 10 - Objectives Recognize ST-depression and relate to the ACS patient Recognize Reciprocal Changes (RCs) and relate to the significance of STEMI Recognized Q-waves and relate to the ACS patient Discuss the evolution of an AMI Explain the reasons why a normal ECG does not rule out AMI OBHG Education Subcommittee Ischemia Epicardial Coronary Artery Septum Thrombus forming Left Ventricular Cavity Lateral Wall of LV Positive Electrode Inferior Wall of LV OBHG Education Subcommittee Ischemia Inadequate oxygen to tissue Subendocardial Represented by ST depression or T-wave inversion May or may not result in infarct OBHG Education Subcommittee ST depression OBHG Education Subcommittee T-wave Inversion OBHG Education Subcommittee Evolution of AMI • Hyperacute T Wave OBHG Education Subcommittee Evolution of AMI • Acute OBHG Education Subcommittee Evolution of AMI • Acute OBHG Education Subcommittee Evolution of AMI • Age undetermined OBHG Education Subcommittee Hyper-acute T-waves Earliest ECG sign of AMI Tall and peaked w/in minutes of blood flow interruption Differential Dx: hyperkalemia BER LVH OBHG Education Subcommittee Why hyper-acute T-wave are important to recognize OBHG Education Subcommittee AMI Recognition A “normal” 12-lead ECG DOES NOT rule out AMI Not all AMI have STE (approx. 50%) Early AMI may have no STE but may evolve over time Non STEMI AMI have non specific but abnormal ECGs OBHG Education Subcommittee Why can’t AMI be ruled out? PHECG has high specificity for STEMI = 97%* Meaning = when PHECG shows STEMI it almost always turns out to be an AMI. OBHG Education Subcommittee Why can’t AMI be ruled out? PHECG has only moderate sensitivity for AMI = 68% Meaning - when PHECG does not show STEMI only 68% of time does it turn out to NOT be an AMI. (over 30% of AMI patients do not have STE on PHECG) CAN’T RULE OUT AMI WITH NO STE on 12 LEAD ECG Source: Ioannides JA et al. Accuracy & clinical effect of out-of-hospital ECG in the diagnosis of acute cardiac ischemia: a meta-analysis. Annals of Emergency Medicine 2001;37. OBHG Education Subcommittee Practice OBHG Education Subcommittee Practice OBHG Education Subcommittee Practice OBHG Education Subcommittee QRS Q waves Physiologic Q waves < .04 sec (40ms) Pathologic Q waves >.04 sec (40 ms) OBHG Education Subcommittee Q-wave & Infarct represent irreversible necrosis – death of tissue may develop early (1st hour) but usually 8-12 hours post-AMI may persist permanently but some resolve regardless of reperfusion not all AMIs produce Q-waves OBHG Education Subcommittee QRS Q wave OBHG Education Subcommittee QS Complex OBHG Education Subcommittee Common Q-waves “age undetermined” Likely old septal MI ↑ index of suspicion not a bad idea Q-wave associated with an AMI = necrosis has likely begun ↑ severity/seriousness OBHG Education Subcommittee ONTARIO BASE HOSPITAL GROUP Sample ECGs with Q-waves Find them………. Septal – V1 to V3 (? – II, III, aVF ) OBHG Education Subcommittee Lateral - aVL OBHG Education Subcommittee aVL, V1 – V5 OBHG Education Subcommittee ONTARIO BASE HOSPITAL GROUP Reciprocal Changes Reciprocal Changes Occur in larger MI Able to “see” the MI on the opposite side because it is larger RC’s make the STE more likely to be due to AMI Don’t have to have RC’s but they make the diagnosis easier OBHG Education Subcommittee Reciprocal Changes OBHG Education Subcommittee Reciprocal Changes OBHG Education Subcommittee Reciprocal Changes II, III, aVF I, aVL, V leads OBHG Education Subcommittee Reciprocal Changes Anterior = Septal, Anterior and Lateral walls Inferior OBHG Education Subcommittee Practice OBHG Education Subcommittee Practice OBHG Education Subcommittee AMI Recognition OBHG Education Subcommittee AMI Recognition Imitators of infarct BBB LVH Ventricular beats Pericarditis Early Repolarization Others OBHG Education Subcommittee Summary AMI recognition Know what you are looking for > 1mm of ST elevation in limb leads > 2mm of ST elevation in chest leads Two contiguous leads Know where you are looking Positive electrode as an “eye” Memorize lead locations OBHG Education Subcommittee Summary Reciprocal Changes Not necessary to presume infarction Strong confirming evidence when present OBHG Education Subcommittee Summary ST segment elevation is presumptive evidence for AMI Other conditions may also cause ST elevation OBHG Education Subcommittee Summary NEVER FORGET: A normal 12-Lead ECG DOES NOT rule out AMI OBHG Education Subcommittee ONTARIO BASE HOSPITAL GROUP QUESTIONS? ONTARIO BASE HOSPITAL GROUP Well Done! Education Subcommittee START QUIT