STEMI & STE-MimicsBy Adam Thompson

ST-Elevation

The most common cause of ST-elevation is not myocardial infarction.

Less than 50% of STEMI alerts called by paramedics are actually ACS patients

NERD ALERT!

The Research

902 patients were enrolled in the study. Of those, 202 patients (22.4%) had ST segment elevation on their initial 12 lead ECG. Of those, only 31 patients (15%) had a discharge diagnosis of STEMI. In other words, 171 patients (85%) had a non-AMI cause of ST segment elevation on their initial 12 lead ECG

Causes of ST-Elevation

Listed from most common to least: Left ventricular hypertrophy (LVH) Left bundle branch block (LBBB) Benign early repolarization (BER) Right bundle branch block (RBBB) Nonspecific BBB Ventricular Aneurysm Pericarditis Undefined or unknown cause

Causes of ST-Elevation

Easier way to remember:E - Electrolytes (hyperkalemia)

L - LBBB

E - Early repolarization (high take off)

V - Ventricular hypertrophy (LVH)

A - Aneurysm

T - Treatment (eg pericardiocentesis)

I - Injury (AMI, contusion)

O - Osborne waves (hypothermia)

N - Non-occlusive vasospasm

More Research

“Paramedics diagnosed over half of patients as having ST elevation AMI, when in fact they did not. One reason for this may be that the paramedics were concerned about missing patients with this condition.”

Also From The Research

The incidence of poor quality ECGs recorded by the paramedics was calculated to determine the paramedics performance in electrocardiographic acquisition.

In 13 of 124 patients (10.5%), the ECGs were characterized as poor quality..."

6 Steps of 12-Lead Interpretation

1.) Rate and rhythm 2.) Axis determination 3.) QRS duration (Intervals) 4.) Morphology 5.) STE-Mimics 6.) Ischemia, Injury, Infarct

Lead Placement

Poor ECG captures were noted as a common problem.

V3 is most often misplaced lead

Which Electrode is Causing Artifact?

Precordial leads are easy. V1 has artifact? Check V1 electrode.

If Leads I & III have artifact, check left shoulder.

If Leads I & II have artifact, check right shoulder.

Leads II & III? Check left leg electrode.

What are Contiguous Leads?

Reciprocal Changes

Disclaimer

NOTHING you learn here changes your protocol.

This is all in hopes of improving your assessment skills.

STE-Mimics

STE-Mimics are every cause of ST-elevation other than myocardial infarction.

The rest of this presentation will be dedicated to recognizing STE-Mimics

Left Ventricular Hypertrophy

The “Strain Pattern” is a repolarization abnormality associated with LVH and may cause ST-Segment changes.

STEMI is more difficult, but still possible to identify in the presence of LVH.

LVH Criteria

Deepest S wave in V1/V2 plus tallest R wave in V5/V6 > 35mm and/or R wave in aVL > 12mm

"Strain" is a pattern of asymmetric ST segment depression and T wave inversion. LV strain is most commonly seen in one or more leads that look at the left ventricle (leads I, aVL, V4, V5, V6); less commonly it can be seen in inferior leads.

LV Strain Pattern

STE-Mimic LVH Clues

QRS Duration < 120 ms (Not BBB) T wave Discordance (widened QRS/T angle) Concave ST-Segments with asymmetrical T waves The height of STE and T waves are directly

proportionate to the depth of the S waves. The taller the R wave the deeper the ST depression. STE in right precordial leads with depression in left

precordial leads due to “strain pattern”.

Deep narrow dagger-like Q waves have been noted in lateral leads with hypertrophic cardiomyopathy.

Left Bundle Branch Block

Delayed conduction due to a block of both the Left Anterior Fascicle & Left Posterior Fascicle.

Atrial rhythm with QRS duration > 120 ms and negatively deflected QRS complex in V1.

May cause ST-elevation, new LBBB = STEMI.

LBBB Research

The evidence shows that there is no correlation between a new LBBB and ACS despite what was previously believed.

This does not change the guideline. With new LBBB, contact medical control.

STE due to LBBB

Like LVH, STE may be caused by the T wave discordance normally found with a LBBB.

Acute Myocardial Infarction can still be diagnosed in the presence of LBBB.

An AMI can be diagnosed, but STEMI alert should not be called.

MI Criteria in LBBB

Sgarbossa’s criteria has 100% sensitivity to MI in LBBB. It is good, but a hard to use points system.

Easier method : STE > 0.25 (25%) of the preceding S wave in V1-V4 or concordant ST-elevation in any lead.

This is true due to the elevation being directly related to the depth of the S wave with T wave discordance(like LVH).

Once again, this is not enough to call STEMI. Transport to a cath-capable facility should be initiated.

QuickTimeª and a decompressor

are needed to see this picture.

Benign Early Repolarization (BER)

BER may present with an appearance of ST-elevation.

Notched J points are the most commonly taught indicator of “early repol”.

The ST-segment morphology is the easiest way to determine malignancy of the finding.

LOOK for reciprocal changes!!!

Anterior MI vs. BER

If mean amplitude of R wave in V2-V4 > 5mm than BER is more likely.

Consequently if the mean amplitude of V2-V4 is < 5 mm, the probability the patient is suffering from an MI is almost 99%.

An MI is still possible even if the above criteria does not indicate so.

Anterior MI vs. BER

Anterior MI vs. BER

BER

ST-Segment Morphology

Right Bundle Branch Block

A conduction delay due to blockage of the only right fascicle.

ST-segment usually not altered by the normal T wave discordance of RBBB.

QRS duration > 120 ms with positive QRS deflection in V1.

RBBB

Identify your J point Compare J point to leads above and

below to make certain you have the correct spot.

Identify Isoelectric line Compare J point to isoelectric line. STE > 1mm in limb leads or 2mm in

precordial leads = STEMI.

Left Ventricular Aneurysm

Localized area of infarcted myocardium that bulges outward during both systole and diastole.

LVAs most often are noted after large anterior wall events but may also be encountered status after inferior and posterior wall injuries.

May cause varying degrees of persistent STE < 4mm.

No reciprocal changes present. Deep Q waves in leads with STE. Most common in V1-V3.

Left Ventricular Aneurysm

Not expected to differentiate this presentation from STEMI on a normal basis.

If convex STE is present, err on the side of caution.

Acute Pericarditis

Inflammation of the pericardium (pericardial sac).

May present with global STE STE may appear pronounced due to PR-

depression. Tip - STE will be present in leads I & II,

even though these leads are reciprocal to each other in most patients.

aVR will present with ST-depression

QuickTimeª and a decompressor

are needed to see this picture.

Acute Pericarditis

Stage Ieverything is UP (ST elevation in almost all leads) Stage IITransition

("pseudonormalization"). Stage IIIEverything is DOWN

(inverted T waves). Stage IV Normalization.

Acute Pericarditis

Hyperkalemia

Peaked, usually narrow, symmetrical T waves

Severe hyperkalemia may present with straight line from tip of S wave (nadir) to peak of T wave, AKA Sine wave.

Sometimes presents with wide complexes, possibly lacking P waves. Z-Fold pattern is common with severe hyperkalemia.

Use medical history to help determine cause.

Hyperkalemia

Other STE-Mimics

Brugada Syndrome - AKA Sudden Unexpected Death Syndrome.

Takotsubo Cardiomyopathy - non-ischemic cardiomyopathy in which there is a sudden temporary weakening of the myocardium. Because this weakening can be triggered by emotional stress, such as the death of a loved one, the condition is also known as broken heart syndrome

Brugada Syndrome

ST Morphology found in V1-V3.

Not a STEMI, but this patient may be candidate for AICD.

Other MI Findings

If Zoll print out does not read ***Acute MI***, it is highly unlikely that the capture meets STEMI criteria. It is possible that the 12-lead is not a true STEMI even with the AMI reading, however.

Hyperacute T waves - Peaked, wide, asymmetrical T waves (Hyperkalemia T waves usually present symmetrically and narrow).

Wellen’s phenomenon - Biphasic T wave (sometimes inverted) in V2 & V3, precursor to AMI from LAD stenosis.

Pathological Q waves - Wide and deep Q waves.

Abnormal Q Waves

V2:  Any V3:  Almost any V4:  If more than 1mm deep or larger than Q in V5 or > .02 sec wide (0.5 mm)

aVL:  >.04 sec or >50% amplitude of the QRS

III:  Q wave >0.04 sec, depth in this lead is not [AS] important

Any Questions?