12-lead ECG Monitoring
1. Lead Placement
a. Limb leads – I, II, III (bipolar- Einthoven’s triangle), aVR, aVL, aVF (unipolar).
b. Precordial leads (chest leads) - V1-V6.
2. Injury Patterns
a. Ischemia - ST segment depression and/or inverted or tall T waves.
b. Injury - ST segment elevation (STEMI), T wave may invert.
c. Infarction (old) - Abnormal (deep and wide) Q wave.
3. Contiguous Leads
a. STEMI – ST elevation in two or more contiguous leads.
b. Inferior MI – Leads II, III, aVF.
c. Anterior MI – Leads V1-V4 (Septal V1-V2).
d. Lateral MI – Leads I, aVL (high lateral), V5, V6 (low lateral).
4. Reciprocal Leads – leads that oppose contiguous leads.
a. ST segment depression in leads I and aVL with inferior MI.
b. ST segment depression in II, III, aVF in high lateral MI.
Acute Myocardial Infarction
1. Inferior MI
a. ST segment elevation in leads II, III, and aVF, with reciprocal changes in I and aVL.
b. Most commonly occludes the Right Coronary Artery (RCA.)
c. Common S/S: Epigastric and nausea, shoulder pain, dyspnea, chest pressure, diaphoresis.
d. Common Dysrhythmias: Bradycardias resulting in hypotension, second degree type 1 (Wenckebach). Ominous sign if inferior MI patient gets if tachycardic.
e. Complications: Risk of mitral regurgitation and papillary muscle rupture.
f. TX: Oxygen if O2 saturation < 94% or in respiratory distress, nitroglycerin, aspirin, morphine, cardiology consult. Use caution with preload-reducing agents such as NTG, diuretics, morphine, and beta-blockers since they decrease contractility.
g. Associated with right ventricular and posterior infarcts, so repeat ECG to include V4R and V7-V9.
2. Anterior MI
a. ST segment elevation in leads V1-V4.
b. Most commonly occludes the Left Anterior Descending (LAD).
c. Common S/S: Shortness of breath, feeling of impending doom, crackles in lungs, tachycardia.
d. Common Dysrhythmias: Tachycardia, ventricular dysrhythmia, bundle branch block.
e. Complications: Systolic murmur – ventricular septal defect.
f. TX: Oxygen if O2 saturation < 94% or in respiratory distress, nitroglycerin, aspirin, morphine, cardiology consult.
3. Right Ventricle MI
a. ST elevation at V4R (5th intercostal space, right mid-clavicular line).
b. Most commonly occludes the proximal right coronary artery.
c. Common S/S: Jugular vein distention, signs of shock, hypotension.
d. TX: Oxygen if O2 saturation < 94% or in respiratory distress, aspirin, cardiology consult, 250 cc isotonic crystalloid boluses and dobutamine to increase contractility. Avoid preload-reducing agents like nitrates, diuretics, and morphine.
4. Posterior MI
a. ST segment depression in leads V1 and V2 and/or elevation in V7-V9.
b. Commonly associated with inferior MI’s.