ACS Flashcards
Discuss Hyperacute T-wave
The earliest ECG finding in STEMI is a hyperacute t-wave which can occur within minutes of interrupted blood flow. Usually broad based and assymetrical
ST segment elevation at the J point – typically hyperacute T will progress to elevation
Cause of hyperacute t-waves include
- STEMI
- hyerkalaemia
- pericarditis
- BER
- LBBB
Discuss ST segment
ST segment eleavtion usually progresses from flat to convex to domed or tombstoned
Concave morphology if noted in ST elevation is rare in STEMI and is more commonly due to other causes of ST elevation
ST depression generally reflex sub-endocardial ischaemia. Can be diffuse spanning multiple different regions of the heart – seen commonly in NSTEMI and unstable angina
DDX of ST depression include -Myocardial ishcaemia or infarction -repolarization abnormaility of left ventricular hypertrophy (strain) - BBB Ventricular paced rhythm -Digoxin - hyperkalemia, hypokalemia PE ICH Mycoarditis Post cardioversion
Discuss t-wave inversion
Can suggest chronic or acute ischaemia
best compared to previosu ECG to see if acute change
Classically narrow and symmetrical in ACS
Notable group of ishcaemic t-wave is assoicated with Wellens syndrome which classically mainfest with dep symmetrically t-wave or bisphase change in the anterior precordial leads.
Biphasic t-wave in general are suggestive of ishcaemic heart disease
DDX for t-wave inversion
1) ACS
2) Ventricular hypertrophy
3) PE
4) pnemothorax
5) BBB
6) CVA
7) WPW
8) persistant juvenile t-wave pattern
Discuss location of MI
Anterior - v1-4
Septal v1-2 externaion to the lateral wall is evident by extension into lateral leads
Inferior: 2,3 AVF
Right: inferior infarct + right sided leads
Posterior - reciprical change in precardium and ST elevation in posterior leads
Discuss posterior infarcts
Accompanies 10-15% of infract usually inferior or lateral
Occurs 5% isolated
Posterior extension of an inferior or lateral infarct suggest a much larger area of ischaemic damage and is associated with worse prongosis
Not visualised on a standard ECG look for reciprical changes in precordium (v1-3)
- Horizontal St depression
- upright t-waves
- Dominant r wave R/S ratio > 1
On posterior ECG
-St elevation and q-wave
ST elevation becomes depression, q-waves becomes r waves, terminal t-wave inversion become upright t
Posterior lead placement
V7: left posterior axillary line in the same plane as v6
V8: tip of scapula same plane
V9: para spinal same plane
Discuss right sided infarct
Right ventricular infarct accompanies approxiamtly 40% of inferior STEMI
Patient with RV infarction are very sensitive to preload (due to poor RV contractility). Can become markedly hypotensive if given nitrate
hypotension is treated with fluid and nitrate are contraindicated
Indications of RV infarct without right sided ECG include
1) ST eleavtion in V1 with interior infarct – looks directly at right heart
2) ST elevation V1, ST depression V2
3) ST elevation greater in 3 than 2
Right sided ECG mirror of left sided
Discuss AVR elevation
Can be seen in LMCA – classical finding are
- ST elevation in AVR >1mm,
- ST elevation AVR>V1,
- wide spread ST depression seen greatest 1,2 V4-6
ST elevation in AVR can also be seen with
- Proximal LAD
- Severe Tripple vessel disease
- Diffuse subendocardial o2 mismatch as is seen after cardiac arrest
2 causes of AVR eleavtion
1) diffuse subendocardial ischaemia leading to reciprical changes
2) Infarction of the basal septum – STEMI involving AVR
In the context of widespread ST depression + symptoms of myocardial ischaemia:
- STE in aVR ≥ 1mm indicates proximal LAD / LMCA occlusion or severe 3VD
- STE in aVR ≥ 1mm predicts the need for CABG
- STE in aVR ≥ V1 differentiates LMCA from proximal LAD occlusion
- Absence of ST elevation in aVR almost entirely excludes a significant LMCA lesion
Discuss Wellens syndrome
Wellens syndrome is deep t-wave inversion or biphasic t-waves in V2-3, highly specific for critical LAD stenosis
Type A Biphasic with initial positivity and terminal negativity
Type B Deeply and symmetrically inverted
Discuss the evolution of t-waves in Wellens Syndrome
Sudden occlusion of the LAD causes a STEMI and the patient has chest pain
- Re-perfusion of the LAD due to spont clot lysis or aspirin, ST elevation improves and t-wave become biphasic or inverted - identical to reperfusion after successful PCI
- If the artery remains open deep classic t-wave develop
- The coronary perfusion is however unstable and the LAD can re-occlude at any time. The first sign of this is pesudo normilsation of the t-wave – would normally be hyperactue t-wave
Can occur in cocaine induced vasospasm
Discuss De winter Twave
De-winter t-wave is a STEMI equivilent that presents without ST elevation
Characterised by ST depression and peaked t-wave in the precordial leads
Seen in around 2% of LAD occlusions
-Unfamiliarity with condition may lead to under treatment ( ie. failure to activate the cath lab)
Discuss scarbossi criteria
Used to define STEMI in LBBB or ventricular paced rhythms
Modified scarbosi criteria are
1) one or more leads with 1 or more mm of concordant ST elevation (5)
2) one or more leads with one or more mm of concordant ST depression in V1-3 (3)
3) Excessive discordant STE defined by > 25% of the depth of the preceeding s-wave (2)
Positive if any are met
Original sgarbossi criteria used 5mm of discordance and point system <3 consistent with MI. Modified +ve if any are met
Neither the modified or original criteria are sensitive enough to exclude MI in patient with LBBB they are however specific enough to rule them in
DIscuss DDX of LBB
Aortic stenosis IHD HTN DCMX Lenegre-lve disease (primary degnerative disease of the conducting system) TOX (digoxin toxicity) Hyperkalaemia
