Published on March 7, 2014
ECG in Acute Coronary Syndrome Dr Awadhesh Kumar sharma Deptt of Cardiology
The Normal Conduction System
ECG Leads • The standard EKG has 12 leads: – 3 Standard Limb Leads – 3 Augmented Limb Leads – 6 Precordial Leads
ECG Limb Leads • Leads are electrodes which measure the difference in electrical potential between either: 1. Two different points on the body (bipolar leads) 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)
Recording of the ECG • Limb leads are I, II, II. • Each of the leads are bipolar; i.e., it requires two sensors on the skin to make a lead. • If one connects a line between two sensors, one has a vector. • There will be a positive end at one electrode and negative at the other. • The positioning for leads I, II, and III were first given by Einthoven (Einthoven’s triangle).
ECG Limb Leads
Standard Chest Lead Electrode Placement The Right-Sided 12-Lead ECG The 15-Lead ECG
Contiguous Leads • • • • • Lateral wall: I, aVL, V5, V6 Inferior wall: II, III, avF Septum: V1 and V2 Anterior wall: V3 and V4 Posterior wall: V7-V9 (leads placed on the patient’s back 5th intercostal space creating a 15 lead EKG)
Ctn. Electrocardiogram (ECG)
Coronary Circulation • Coronary arteries and veins • Myocardium extracts the largest amount of oxygen as blood moves into general circulation • Oxygen uptake by the myocardium can only improve by increasing blood flow through the coronary arteries • If the coronary arteries are blocked, they must be reopened if circulation is going to be restored to that area of tissue supplied
ST segment • Connects the QRS complex and T wave • Duration of 0.08-0.12 sec (80-120 msec)
S – T Segment I V1 Normal Elevated V3 Depressed 7
T waves • Represents repolarization or recovery of ventricles • Interval from beginning of QRS to apex of T is referred to as the absolute refractory period
T wave morphology AVR I Upright T 8 Inverted T
Acute Coronary Syndrome Definition: a constellation of symptoms related to obstruction of coronary arteries with chest pain being the most common symptom in addition to nausea, vomiting, diaphoresis etc. Chest pain concerned for ACS is often radiating to the left arm or angle of the jaw, pressure-like in character, and associated with nausea and sweating. Chest pain is often categorized into typical and atypical angina.
Acute coronary syndrome • Based on ECG and cardiac enzymes, ACS is classified into: – STEMI: ST elevation, elevated cardiac enzymes – NSTEMI: ST depression, T-wave inversion, elevated cardiac enzymes – Unstable Angina: Non specific EKG changes, normal cardiac enzymes
Unstable Angina • Occurs at rest and prolonged, usually lasting >20 minutes • New onset angina that limits activity • Increasing angina: Pain that occurs more frequently, lasts longer periods or is increasingly limiting the patients activity
ECG • First point of entry into ACS algorithm • Abnormal or normal • Neither 100% sensitive or 100% specific for AMI • Single ECG for AMI – sensitivity of 60%, specificity 90% • Represents single point in time –needs to be read in context • Normal ECG does not exclude ACS – 1-6% proven to have AMI, 4% unstable angina
• GUIDELINES: • Initial 12 lead ECG – goal door to ECG time 10min, read by experienced doctor (Class 1 B) • If ECG not diagnostic/high suspicion of ACS – serial ECGs initially 15 -30 min intervals (Class 1 B) • ECG adjuncts – leads V7 –V9, RV 4 (Class 2a B) • Continuous 12 lead ECG monitoring reasonable alternative to serial ECGs (Class 2a B)
Evaluating for ST Segment Elevation • Locate the J-point • Identify/estimate where the isoelectric line is noted to be • Compare the level of the ST segment to the isoelectric line • Elevation (or depression) is significant if more than 1 mm (one small box) is seen in 2 or more leads facing the same anatomical area of the heart
The J Point • J point – where the QRS complex and ST segment meet • ST segment elevation - evaluated 0.04 seconds (one small box) after J point
• Coved shape usually indicates acute injury • Concave shape is usually benign especially if patient is asymptomatic
Significant ST Elevation • ST segment elevation measurement – starts 0.04 seconds after J point • ST elevation – > 1mm (1 small box) in 2 or more contiguous chest leads (V1-V6) – >1mm (1 small box) in 2 or more anatomically contiguous leads (ie: II, III, aVF; I, aVL, V5, V6) • Contiguous lead – limb leads that “look” at the same area of the heart or are numerically consecutive chest leads (ie: V1 – V6)
EKG STEMI: Q waves , ST elevations, hyper acute T waves; followed by T wave inversions. Clinically significant ST segment elevations: > than 1 mm (0.1 mV) in at least two anatomical contiguous leads or 2 mm (0.2 mV) in two contiguous precordial leads (V2 and V3) Note: LBBB and pacemakers can interfere with diagnosis of MI on EKG
EKG • NSTEMI: – ST depressions (0.5 mm at least) or T wave inversions ( 1.0 mm at least) without Q waves in 2 contiguous leads with prominent R wave or R/S ratio >1. – Isolated T wave inversions: • can correlate with increased risk for MI • may represent Wellen’s syndrome: – critical LAD stenosis – >2mm inversions in anterior precordial leads • Unstable Angina: – May present with nonspecific or transient ST segment depressions or elevations
Evolution of AMI A - pre-infarct (normal) B - Tall T wave (first few minutes of infarct) C - Tall T wave and ST elevation (injury) D - Elevated ST (injury), inverted T wave (ischemia), Q wave (tissue death) E - Inverted T wave (ischemia), Q wave (tissue death) F - Q wave (permanent marking)
ST Segment Elevation
Lateral Wall MI: I, aVL, V5, V6 Source: The 12-Lead ECG in Acute Coronary Syndromes, MosbyJems, 2006.
Inferior Wall MI II, III, aVF Source: The 12-Lead ECG in Acute Coronary Syndromes, MosbyJems, 2006.
Septal MI: Leads V1 and V2 Source: The 12-Lead ECG in Acute Coronary Syndromes, MosbyJems, 2006.
Anterior Wall MI V3, V4 Source: The 12-Lead ECG in Acute Coronary Syndromes, MosbyJems, 2006.
Posterior MI – Reciprocal Changes ST Depression V1, V2, V3 Source: The 12-Lead ECG in Acute Coronary Syndromes, MosbyJems, 2006.
MI- Few ECGs
Evolution of acute anterior myocardial infarction at 3 hours
Lateral MI Reciprocal changes
Inferior wall MI
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