Elderly patient found down. Better know this for the Boards!
- positive deflections at junction between the QRS complex and ST-segment
- repolarization abnormality caused by exaggerated outward K+ current
- usually observed in patients with hypothermia
- Osborn waves
- Sinus brady, junctional rhythm
- Prolongation of all intervals
- Slow irregular Afib
- Ventricular fibrillation
Paced rhythms cause ST-segment & T wave changes that can make the identification of acute MI difficult
Patients with paced rhythms can be expected to have ST segment & T wave changes that are discordant to the direction of the QRS complex
This is normal & referred to as the “Rule of Appropriate Discordance”
ST-segment deviations that are concordant (in same direction) to the QRS complex are abnormal
in the setting of both paced rhythms & LBBB
Here is what to look for:
1. Concordant ST elevation ≥ 1mm in any single lead
2. Concordant ST depression ≥ 1mm in either V1, V2, or V3
3. Excessively discordant ST elevation ≥ 5mm in any lead
Do you remember what the Modified Sgarbossa rule is & how to use it?
If not, check out …The Modified Sgarbossa Rule
Sgarbossa EB. Recent advances in the electrocardiographic diagnosis of myocardial infarction: left bundle branch block and pacing. Pacing Clin Electrophysiol. 1996;19(9):1370–1379. Pubmed Link
Sgarbossa EB, Pinski SL, Gates KB, Wagner GS. Early electrocardiographic diagnosis of acute myocardial infarction in the presence of ventricular paced rhythm. GUSTO-I investigators. Am J Cardiol. 1996;77(5):423–424. Pubmed Link
Maloy KR, Bhat R, Davis J, Reed K, Morrissey R. Sgarbossa Criteria are Highly Specific for Acute Myocardial Infarction with Pacemakers. West J Emerg Med. 2010;11(4):354–357. Pubmed Link
Should ST depression ever be treated like STE? Check out these two cases so you know!
- 1-3 mm of ST-depression upsloping at the J-point in the precordial leads, leading into tall symmetric T-waves
- High risk of acute anterior MI
- Suggestive of an acute proximal LAD occlusion (contrast to sub-acute occlusion of Wellens syndrome)
Want to learn more about T-waves in ischemia? Check these out…
Goebel M, Bledsoe J, Orford JL, et al. A new ST-segment elevation myocardial infarction equivalent pattern? Prominent T wave and J-point depression in the precordial leads associated with ST-segment elevation in lead aVr. American Journal of Emergency Medicine. In press.
- R wave in V5 or V6 + S wave in V1 > 35 mm
- Maximum amplitude R wave + max S wave in precordial leads > 45 mm
- R wave in aVL > 11 mm
- ST depression in any of: I, aVL, V4-V6 +/- II and aVF
- T wave inversions in same leads (asymmetric morphology)
- ST elevation in V1-V3 (& aVR)
- QRS widening (non-specific intraventricular conduction delay)
No reliable way to distinguish between STEMI vs. LVH with strain
Horizontal ST depression & symmetric T wave inversions are associated with ischemia
When in doubt…GET SERIAL &/or OLD ECGs!