Look Behind You!

A 45 yo female with a history of cigarette smoking and tobacco abuse reports a sudden onset of severe, substernal chest discomfort. EMS providers perform a 12 lead ECG.

12 Lead ECG

12 Lead Discussion

ST elevation is noted in leads II, III, and aVF. Reciprocal changes are seen in leads I and aVL. Note ST elevation extends into the lateral precordial leads of V4, V5, and V6. Also of significance is the ST segment depression in leads V2 and V3. Though the R waves aren't especially tall, the ST depression and slightly positive R waves is consistent with extension of the infarction into the heart's posterior wall. A large obstructing lesion of the right coronary artery can affect these geographic areas of the heart. Posterior wall MIs usually do not occur in isolation. The "Life in the Fast Lane" blog has a good page on the interpretation of the posterior wall myocardial infarction. 

12 Lead Interpretation

Inferior lateral ST elevation myocardial infarction with extension into the posterior wall.

The Eclectic Equivalent

A 64 yo female calls 911 for chest discomfort. The patient reported chest pressure that waxed and waned in intensity. The discomfort was retrosternal and did not radiate. The patient compared the pressure to previous bouts of "indigestion." The patient experienced associated nausea. No LOC, no diaphoresis. Providers obtain a 12 lead ECG. Vital signs remained stable.

12 Lead ECG

12 Lead ECG Interpretation 

The rhythm is sinus and the rate is regular. ST depressions are present in leads II, III, and aVF. There are also ST depressions noted in the precordial leads V3-V6. R wave progression is preserved, and it appears that R waves reach their maximum amplitude in lead V4. There is no obvious ectopy.

ST elevation of > 1 mm is noted in aVR and V1.

Sinus rhythm, diffuse ST segment depression, ST segment elevation in aVR and V1.

Case Discussion

Providers correctly identify the ECG tracing as a potential STEMI equivalent. The STE in aVR and V1 is concerning for its association with acute left main occlusion. The patient was transported to the cardiac cath lab. Cardiologists discovered a near total occlusion of the left main coronary artery.

aVR has long been cast as the "forgotten lead" in electrocardiography. Studies link ST elevation in aVR to left main disease and cardiogenic shock. There is also data to suggest that patients with changes in aVR are more likely to require surgical intervention and progress into cardiogenic shock. Indeed, ST elevation in aVR is often considered a, "STEMI equivalent" due to its association with a poorer prognosis. Always scrutinize all leads of the electrocardiogram for abnormal ST segment morphology. In some studies, STE in aVR that is greater than the STE in V1 distinguishes left main disease from left anterior descending artery disease.

Findings such as STE in aVR are often labeled, "STEMI equivalents." Though not widely recognized as automatic triggers for cath lab activation, these concerning electrocardiographic findings represent time sensitive conditions that benefit from an early interventional approach. Other equivalents include:

• Posterior wall MI (ST depression anteriorly)
• New left bundle in association with chest pain/ACS history 
• Hyperacute T waves
• The deWinter ST/T complex
• Positive Sgarbossa criteria

References
1. Yamaji H, Iwasaki K, Kusachi S, et al. Prediction of acute left main coronary artery obstruction by 12 lead electrocardiography. ST segment elevation in lead aVR with less ST segment elevation in lead V1. J Am Coll Cardiol. 2001;38(5):1348-54

2. Nough H, Jorat MV, Varasteravan HR, et al. The value of ST segment elevation in lead aVR for predicting left main coronary artery lesion in patients suspected of acute coronary syndrome. Rom J Intern Med. 2012;50(2):159-64

3. Nikus KC, Eskola MJ. Electrocardiogram patterns in acute left main coronary artery occlusion. J Electrocardiol. 2008;41(6):626-9

"Abnormal ECG" and Bypass of the Closest Facility

So.. would you call this one and activate the cath lab from the prehospital ECG? The patient is a 72 year old female with severe uncontrolled hypertension. She called 911 for mild shortness of breath. Her blood pressure is over 200 mm Hg systolic. The patient is awake, alert, and oriented. The paramedic is bypassing a local facility in favor of the closest cardiac interventional center.

What's your analysis?

12 Lead ECG

 

12 Lead ECG Interpretation and Discussion

A baseline sinus rhythm is present. There is a significant amount of artifact that interferes with interpretation in the limb leads. A fusion beat is seen in the limb lead tracings. However, there is > 1mm of ST segment elevation in lead III. Lead aVF also has minimal ST segment elevation. Pathologic Q waves are present in contiguous leads (III and aVF). Though an isolated Q wave is common in limb lead III, the presence of Q waves in contiguous inferior leads (III and aVF) suggests ischemia. In addition, ST segment depression is present in the reciprocal leads of I and aVL. This finding further supports the presence of acute injury. ST segment elevations are also seen in leads aVR and V1. As discussed in a previous case, the presence of STE in leads aVR and V1 may predict obstruction of the left main coronary artery. Poor R wave progression is present across the precordial leads V2-V6. This finding  (the loss of R wave amplitude) is consistent with the machine generated diagnosis of "anterior infarct, age undetermined." These findings, when put together, reveal an inferior wall STEMI. This patient is best cared for at a facility capable of percutaneous cardiac intervention.

Final interpretation

Sinus rhythm, inferior wall STEMI. Anterior wall ischemia. Reciprocal changes in the form of ST depression present in the anterior-lateral limb leads.

LVH, Strain, Ischemia, or What?

A patient calls 911 for chest pain. The discomfort is desribed as a retrosternal pressure. It is worse with coughing and slightly improved with rest. The patient reports a productive cough and subjective fevers.  The patient is awake and alert. Past medical history is significant for COPD, asthma, and tobacco abuse.

BP: 180/100
P: 140
R: 16

Sp02: 92% on room air.

Prehospital 12 lead:

12 lead ECG interpretation:

Sinus tachycardia, left ventricular hypertrophy, diffuse ST segment depression and T wave inversion (inferior, anterior, lateral leads) consistent with strain, possible anterior-lateral ischemia

A baseline sinus tachycardia is present. There are diffuse and prominent ST segment changes. The ECG meets voltage criteria for the diagnosis of LVH. The S wave in V1 plus the R wave in V5/V6 is greater than 35 mm. ST segment depression and T wave inversion is most pronounced in the anterior precordial and lateral leads (V3-V6). This ECG illustrates an ischemic "mimic." Changes associated with high left ventricular voltage, by definition, include ST segment abnormalities. Repolarization abnormalities include ST segment depression, ST segment elevation, and T wave inversion.  The downsloping and depressed ST segment is also consistent with a condition called, "strain." Increases in heart rate can also cause "demand" related ischemia. As the heart rate accelerates, the myocardium's demand for oxygen increases. Tachycardia can therefore induce (and accentuate) ST segment changes such as T wave inversion and ST segment depression.

Left ventricular hypertrophy refers to an increase in heart muscle mass. This change is usually secondary to advanced and uncontrolled hypertension. Simply put, the ventricular muscle increases in order to pump against the increased (hypertension-mediated) afterload. Left ventricular hypertrophy manifests on the ECG as increased R wave amplitude (height). There are several scoring systems for LVH and some have rather poor sensitivity. The definitive diagnosis of LVH is by echocardiogram. The echocardiogram actually measures the thickness of the left ventricle.

General ECG features of LVH:

• Left axis deviation
• Repolarization changes (ST depression)
• Increased QRS amplitude (tall R waves, deep S waves)

Electrocardiographic voltage criteria for LVH:

• http://en.wikipedia.org/wiki/Left_ventricular_hypertrophy#ECG_criteria_for_LVH
• http://lifeinthefastlane.com/ecg-library/basics/left-ventricular-hypertrophy/

The STRAIN of hypertension:

Ventricular strain is usually associated with hypertensive heart disease and coronary artery disease. It is a type of ECG pattern seen in ECGs consistent with ventricular hypertrophy. It usually indicates a compensatory response to uncontrolled hypertension and may indicate underlying ischemia. Electrocardiographic criteria for ventricular strain includes:

• ST depression greater than or equal to 1mm in lateral leads I, aVL and V4-V6
• Direction of the T wave usually opposite an upright QRS complex
• Downsloping ST-T segment, rapid upslope

"Strain" of the ST segment:
http://www.medscape.com/viewarticle/504439_3

Case Resolution:

The patient was transported to a local emergency department. The tachycardia resolved following administration of intravenous fluids. Repeat ECGs showed some improvement of the ST segment abnormalities. Given the patient's hypertension and ECG changes, blood was also sent to the lab for cardiac enzyme analysis. Cardiac enzymes remained negative throughout the patient's hospital stay. The patient was diagnosed with bronchitis. The patient was admitted to the hospital for symptom management, blood pressure control, and cardiac stress testing.

EMS Pearls:

• Fix the rate first! Tachycardia, by itself, increases myocardial oxygen demand and produces ST segment changes
• Left ventricular hypertrophy causes ST segment changes that resemble ischemic patterns
• The "strain" pattern, characterized by ST sepression and T wave inverison, is associated with underlying coronary artery disease
• LVH is a common response to long standing and uncontrolled hypertension