ECG BASICS

ECG Interpretation ECG Basics

The 12-LeadsThe 12-leads include:3 Limb leads (I, II, III)3 Augmented leads (aVR, aVL, aVF)6 Precordial leads (V1- V6)

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The ECG PaperHorizontallyOne small box - 0.04 sOne large box - 0.20 s VerticallyOne large box - 0.5 mV

The ECG Paper (cont)

Every 3 seconds (15 large boxes) is marked by a vertical line.This helps when calculating the heart rate.NOTE: the following strips are not marked but all are 6 seconds long.

3 sec3 sec

Learning ModulesECG BasicsHow to Analyze a RhythmNormal Sinus RhythmHeart ArrhythmiasDiagnosing a Myocardial InfarctionAdvanced 12-Lead Interpretation

Step 1: Calculate Rate

Option 1Count the # of R waves in a 6 second rhythm strip, then multiply by 10.Reminder: all rhythm strips in the Modules are 6 seconds in length.Interpretation?Option 2: 300/ No. of big squares between 2 successive Rs

9 x 10 = 90 bpm3 sec3 sec

Axis of the heartNormal axisLADRAD

IIII--++-+--+-++Normal range of heart axis: 30-90Axis of the heart1- Normal2- Hypertrophy3- BBB

HypertrophyLeft Ventricle: SV1+ RV5,6 > 7 big squaresRight Ventricle: R bigger than S in V1Left Atrium: Wide P wave bifid in Lead IIRight Atrium: Tall tented P in Lead IIRVHLVH

Diagnosing a MITo diagnose a myocardial infarction you need to go beyond looking at a rhythm strip and obtain a 12-Lead ECG.

Views of the HeartSome leads get a good view of the:

Anterior portion of the heartLateral portion of the heartInferior portion of the heart


ST ElevationOne way to diagnose an acute MI is to look for elevation of the ST segment.

ST Elevation (cont)Elevation of the ST segment (greater than 1 small box) in 2 leads is consistent with a myocardial infarction.

Anterior View of the HeartThe anterior portion of the heart is best viewed using leads V1- V4.If you see changes in leads V1 - V4 that are consistent with a myocardial infarction, you can conclude that it is an anterior wall myocardial infarction.


MI LocationsNow, using these 3 diagrams lets figure where to look for a lateral wall and inferior wall MI.Limb LeadsAugmented LeadsPrecordial LeadsAVLAVFAVRIIIIII

Other MI LocationsLimb LeadsAugmented LeadsPrecordial LeadsAVLAVFAVRRemember the anterior portion of the heart is best viewed using leads V1- V4.IIIIII

Other MI LocationsSo what leads do you think the lateral portion of the heart is best viewed? Limb LeadsAugmented LeadsPrecordial LeadsAVLAVFAVRLeads I, aVL, and V5- V6IIIIII

Other MI LocationsNow how about the inferior portion of the heart? Limb LeadsAugmented LeadsPrecordial LeadsAVLAVFAVRLeads II, III and aVFIIIIII

Putting it all TogetherHow about now?

Anterolateral MIThis persons MI involves both the anterior wall (V2-V4) and the lateral wall (V5-V6, I, and aVL)!

ST Elevation and non-ST Elevation MIsWhen myocardial blood supply is abruptly reduced or cut off to a region of the heart, a sequence of injurious events occur beginning with ischemia (inadequate tissue perfusion), followed by necrosis (infarction), and eventual fibrosis (scarring) if the blood supply isn't restored in an appropriate period of time.

The ECG changes over time with each of these events

ECG Changes & the Evolving MIThere are two distinct patterns of ECG change depending if the infarction is:

ST Elevation (Transmural or Q-wave), orNon-ST Elevation (Subendocardial or non-Q-wave)Non-ST ElevationST Elevation

ST Elevation InfarctionST depression, peaked T-waves, then T-wave inversionThe ECG changes seen with a ST elevation infarction are:Before injuryNormal ECGST elevation & appearance of Q-waves ST segments and T-waves return to normal, but Q-waves persist

ST Elevation InfarctionLook at the inferior leads (II, III, aVF). Heres an ECG of an inferior MI:Question: What ECG changes do you see?ST elevation and Q-wavesExtra credit: What is the rhythm?Atrial fibrillation (irregularly irregular with narrow QRS)!

IIIIIIaVRaVLaVFV1V2V3V4V5V6II

Anterior and anteroseptal MI= Main Left CALateral MI: Circumflex (branch of left CA)Anterior wall: LAD (left anterior descending or left ant interventricular br of Left Coronary Artery)Inferior Infarction: Right CA.MI resulting in rhythm abnormalities: Rt CA. Site of MI and the involved coronary artery branch

Subendocardial and Transmural infarctionsNon ST segment Elevation Infarction (NSTEMI)Partial occlusion of the coronary and less severe infarction (may be only subendocardia) not enough to produce ST changes. Cardiac markers are important in diagnosis.

Troponin12 Hrs

Cardiac markerHoursTroponin12Creatin-Kinase (CK-MB)10-24Lactate Dehydrogenase (LDH)72Myoglobin2Glycogen Phosphorylase Isoenzyme BB7

Localization of myocardial infarctionThe chest leads cluster around the heart in the horizontal plane and look in from the front (V1 to V4) and from the left (V5 and V6); leads I and aVL also look in from the left while leads II, III, and aVF look in at the under surface.Signs of anterior MI (grey area), territory supplied by the left anterior descending coronary artery (LAD), are seen in V1 to V4.

Signs of lateral MI (grey area), territory supplied by the left circumflex coronary artery (LC), are seen in leads I, aVL, V5 and V6.

Signs of inferior MI (grey area), territory supplied by the right coronary artery (RCA), are seen in leads II, III, and aVF.Pure posterior wall infarctions are rare. Most extend to involve the inferior wall or lateral wall. Signs of posterior MI on a 12-lead ECG are not the characteristic ST elevation and Q waves, which would be the case if there is a lead recording from the patients back. Since V1 and V2 are attached to the patients front, they will record changes reciprocal to changes seen from the back, which are ST depression and tall R waves. These uncharacteristic signs make the diagnosis of posterior MI difficult

ArrhythmiasSinus RhythmsPremature BeatsSupraventricular ArrhythmiasVentricular ArrhythmiasAV Junctional Blocks

Sinus RhythmsSinus Bradycardia

Sinus Tachycardia

Premature BeatsPremature Atrial Contractions (PACs)Premature Ventricular Contractions (PVCs)

Supraventricular ArrhythmiasAtrial FibrillationAtrial FlutterParoxysmal Supraventricular Tachycardia

Ventricular ArrhythmiasVentricular Tachycardia

Ventricular Fibrillation

ArrhythmiasSinus RhythmsPremature BeatsSupraventricular ArrhythmiasVentricular ArrhythmiasAV Junctional Blocks

AV Nodal Blocks1st Degree AV Block

2nd Degree AV Block, Type I

2nd Degree AV Block, Type II

3rd Degree AV Block

// 1st Degree AV Block // 2nd Degree AV Block, Type I// 2nd Degree AV Block, Type II // 3rd Degree AV Block

Bundle Branch BlocksRight BBB: M wave V1, V2 Left BBB: M wave V4,5,6

For more presentations www.medicalppt.blogspot.comHyperkalemia: Tall tented THypokalemia: Small, flat or inverted T.


As hyperkalaemia tends to cause bradycardia and eventually asystole, HYPOkalaemia tends to make the myocardium more irritable and prone to Ventricular Fibrillation (VF). Imagine the T waves are actually made of potassium they increase in size as potassium rises!

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ECG BASICS