ECG UPDATE

STEMI EQUIVALENTS

ST segment - flat, isoelectric section between the end of the S ( J point) and beginning T .

represents interval between ventricular depolarization and repolarization.

most important cause of ST segment abnormality (elevation or depression) is myocardial ischaemia or infarction

Standard STEMI criteria do miss a significant number of patients with obstructive lesions who would benefit from primary PCI

making the recognition of high-risk STEMI-equivalent patterns all the more necessary

A number of atypical and recently described ECG patterns that may signal risk of transmural myocardial infarction (“STEMI-equivalents”) are must-knows

1. ST depression or T wave changes

2. ST elevation

current guidelines identify at least two other clinical findings that should prompt Cath lab activation but may be overlooked

intractable ischemic chest pain despite medical management

New Regional Wall Motion Abnormalities (RWMA) on bedside Echocardiography

STEMI criteria ≥1 mm (0.1 mV) of ST segment elevation in the limb leads

≥ 2 mm elevation in the precordial leads and present in anatomically contiguous leads

IWMI

Part I: ST-Depressions and T-Wave Changes

Isolated Posterior Myocardial InfarctionWhile the posterior heart is

involved in up to 20% of all STEMIs,

isolated posterior STEMI is only found 5% of the time.

PWMI RCA (90%), LCA (10%)ST depression (horizontal >>

downsloping/upsloping)Prominent and broad R wave (>30ms)Relative tall R waves in precordial

leads (may find R = S amplitude in V1)

R/S wave ratio >1.0 in lead V2Prominent, upright T waveCombination of horizontal ST-segment

depression with upright T wave

Posterior ECG or 15-lead ECG may be helpful

V7: Left posterior axillary line along the 5th ICS

V8: Tip of the left scapula line along the 5th ICS

V9: Left paraspinal area line along the 5th ICS

Posterior ECG findings≥1 mm ST-segment elevation

Isolated ST-Depression in AVLReciprocal ST-depression (STD) in

lead aVL is seen in inferior STEMI, - as a STEMI equivalent.

STD may be apparent in the absence of clear-cut ST-elevation.

Reciprocal depression in aVL - high sensitivity for inferior STEMI in 2 largest series to date by Birnbaum and Smith et al.

Hyperacute T-waves (HATWs) broad based, taller than normal

T > 5mm in the limb > 10mm precordial leads may be symmetric or

asymmetricreciprocal changes in opposing

leads as well as increased R wave amplitude (if prior ECG is available).

most important ones to distinguish from HATWs are hyperkalemia, benign early repolarization (BER), and left ventricular hypertrophy (Box 1).13

Hyperkalemia: narrow-based, symmetric, and peaked (sharp); may have a widened QRS

BER: diffuse, peaked, associated with J-point elevation

LVH: look for voltage criteria and a strain pattern

Sovari et al.—looking for a T-wave to QRS ratio of > 75%–seems like a reasonable option

Collins et al,◦ST on/T amp of greater than 25%◦T amp/QRS amplitude (QRS amp) of

greater than 75%◦ST on of greater than 0.30 mV◦Patients older than 45 years

Wellens’ SyndromeECG findings in absence of chest pain, but

with recent cardiac chest pain symptoms critical stenosis of the LADNot necessarily STEMI equivalent but will

require PCI in the next 24-48hDeeply-inverted or biphasic T waves in

V2-3Isoelectric or minimally-elevated ST

segment (<1 mm)Absent precordial Q waves with preserved

R waves

Type A: Biphasic pattern - 25% - Biphasic T-waves (initial + deflection and terminal - deflection)

Type B: Inversion pattern - 75% - Deeply inverted and symmetric T-waves

De Winter PatternSuggestive of proximal LAD lesion

Precordial ST-segment depression at the J-point

Tall, peaked, symmetric T waves in the precordial leads

Lead aVR shows slight ST-segment elevation in most cases

Difference between hyperacute T waves and de Winter T waves

De winter are not transient findings

remain present in subsequent ECGs

Part II: ST-Segment Changes

ST Elevation (STE) in AVR

diffuse ST depression combined with STE in AVR may be indicative of “subendocardial ischemia” from significant left main coronary (LMCA) stenosis, left main equivalent disease (LMEQ, significant disease of the left anterior descending and left circumflex), or three-vessel disease(TVD).

LM/TVD subendocardial Ischemia

ST elevation in aVR ≥ 1mmST elevation in aVR ≥ V1ST depression typically seen in

lateral

Presumed New Left Bundle Branch Block

Historically, new or presumed new left bundle branch block identified in the setting of acute coronary syndrome was designated as a STEMI equivalent.

While that general sentiment remains prevalent, it is not in keeping with current evidence or guidelines.

LBBB findings12-Lead ECG findingsQRS > 0.12 in limb leadsLeadsLarge and wide R waves — leads

I, aVL, V5, and V6Small R wave followed by deep S

wave —leads II, III, aVF, V1–V3

Chang et al (2009) showed that patients with chest pain and (presumed) new LBBB (n= 55) were not more likely to have myocardial infarction (STEMI or non) than those with an old or without LBBB (n = 136 and 7746), nor were they more likely to die within 30 days.25

 A review of recent literature by Neeland et al. (2012) found that only about 40% (89/225) of patients with presumed new LBBB had a culprit lesion on angiography.26 

STEMI guidelines from 2013 have removed new or presumed new LBBB as diagnostic of myocardial infarction “in isolation.

LBBBNew or presumed new LBBB is

thus not sufficient to prompt STEMI activation in patients presenting with ACS.

exceptions unstable hemodynamics Positive Sgarbossa criteria Echo : RWMA , Reduced EF

STEMI Equivalent in Paced Rhythmsdepolarization is initiated from a

right ventricular lead, bypassing the Bundle of His and prolonging depolarization of the left ventricle.

morphology that mimics LBBB, with depolarization characterized by deep S-waves followed by ST-elevation and upright T-waves during repolarization (discordance).

Sgarbossa's Criteria≥3 points = 98% probability of STEMIST elevation ≥1 mm in a lead with upward (concordant) QRS complex - 5 pointsST depression ≥1 mm V1, V2, or V3 - 3 pointsST elevation ≥5 mm in a lead with downward (discordant) QRS complex - 2 pointsSmith's modificationChanges the 3rd rule of original Sgarbossa's Criteria to be ST depression OR elevation discordant with the QRS complex and with a magnitude of at least 25% of the QRS increases Sn from 52% to 91% at the expense of reducing Sp from 98% to 90%

we should be adept at recognizing the clinical STEMI equivalents of intractable symptoms and new wall motion abnormalities on bedside echocardiography