Electrocardiogaram - ECG EKG

Electrocardiogram (ECG)

Dr. Fuad FarooqConsultant Cardiologist

Conduction System of the Heart

• Electrocardiogram (ECG) retains its central role – even though there continues to be new technologies developed for the diagnostic evaluation of patients with cardiovascular disease

• The most important test for interpretation of the cardiac rhythm, conduction system abnormalities and for the detection of myocardial ischemia

• Of great value in the evaluation of other types of cardiac abnormalities including valvular heart disease, cardiomyopathy, pericarditis, and hypertensive disease

• Finally, the ECG can be used to monitor drug treatment (specifically antiarrhythmic therapy) and to detect metabolic disturbances

Introduction

A systematic approach to interpretation of the ECG is important in order to avoid overlooking important abnormalities

Introduction

• Graphical record of electric potentials generated by myocytes during each cardiac cycle

• Detected on the body surface using electrodes attached to extremities and chest wall

• Amplified by the electrocardiograph machine and displayed on special graph paper

Electrodes and Leads

• Electrodes – Sites at which an electrical potential is measured

• ECG leads – Record the difference in potentials between two electrodes

Electrodes

Standard surface electrodes– Right and left arm– Right and left leg– Six precordial

electrodes

Leads

• Record differences in electrical potentials• Six extremity (limb) leads and six chest (precordial)

leads• Two types– Bipolar – between two surface electrodes

• Limb Leads I, II and III are bipolar leads

– Unipolar – between a surface electrode and the central terminal of Wilson• All leads except the bipolar limb leads are unipolar (aVR, aVL, aVF,

V1, V2, V3, V4, V5, and V6)

Leads Orientation – Limb Leads

• Lead I records potential difference between left arm (the +ve pole) and right arm (-ve pole)

• Lead II records between left leg (+ve) and right arm (-ve)

• Lead III records between left leg (+ve) and left arm (-ve)

• Lead aVR records right arm potentials

• Lead aVL records left arm potentials

• Lead aVF records left leg (foot) potentials

Leads Orientation – Precordial leads

• The six chest/precordial leads – represent the voltage difference between the central terminal and electrodes placed in the following positions

– V1 — 4th intercostal space (ICS), just to the right of the sternum– V2 — 4th ICS, just to the left of the sternum– V3 — midway between V2 and V4– V4 — 5th ICS in the mid-clavicular line– V5 — anterior axillary line, same level as V4– V6 — mid-axillary line, same level as V4 and V5

Leads

• 12-lead ECG provides spatial information about the heart's electrical activity in 3 approximately orthogonal directions: – Right Left⇔– Superior Inferior⇔– Anterior Posterior⇔

I and AVL

II, III and AVF

V3 & v4

V1 & v2

V5 & v6

Where the positive electrode is positioned, determines what part of the heart is seen!

• If an electrode is placed so that wave of depolarization spreads toward the recording electrode, the ECG records a positive (upward) deflection.

• If wave of depolarization spreads away from recording electrode, a negative (downward) deflection occurs.

Electrophysiology

Electrophysiology

ECG Grid

Voltage/amplitude in mvolt

Time in msec

Paper speed = 25mm/sec

Standardization

ECG Waves

Genesis of Normal ECG

• P wave – wave preceded by QRS complex• Q wave – first downward deflection after P wave– Signals start of ventricular depolarization

• R wave is positive deflection after Q wave

• S wave is negative deflection preceded by Q or R waves

• T wave follows QRS

Genesis of Normal ECG

Intervals and Segments

• Segments– ST segment– TP segment

• Intervals– PR interval– QRS interval– QT interval– RR interval

A systematic approach to interpreting an ECG is essential for correct diagnosis

Step 1: RateIs the rate between 60 and 100? Rates less than 60 is bradycardia and greater than

100 is tachycardia

Step 2: RhythmAre P waves present?

Is there a P wave before every QRS complex and a QRS complex after every P wave?

Are the P waves and QRS complexes regular? Is the PR interval constant?

Step 3: AxisIs there left or right axis deviation?

ECG Interpretation – Stepwise Approach

Step 4: Intervals

What is the PR interval?– Short PR interval is suggestive of Wolff-Parkinson-White (WPW)

syndrome– Long PR intervals are usually seen in first degree AV block

What is the QRS interval? – Long QRS intervals represent a bundle branch block, ventricular

preexcitation, ventricular pacing, or ventricular tachycardia

What is the QT interval? – Short and long QT intervals may be present


Step 5: P wave

– What is the shape and axis of the P wave?– The P wave morphology should be examined to determine

if the rhythm is sinus or from another atrial location– Amplitude and duration should also be analyzed to

determine left and right atrial enlargement


Step 6: QRS complex Is the QRS wide?

– If so, examination of the morphology can determine if there is left or right bundle branch block

– Increased voltage may indicate left or right ventricular hypertrophy

– Are Q waves present? – suggestive of infarction


Step 7: ST segment-T wave

– Is there ST elevation or depression?– Are the T waves inverted?– Abnormalities of the ST segment or T wave may represent myocardial

ischemia or infarction


Step 8: Overall interpretation

– Only after the prior steps have been completed should an overall interpretation and possible diagnoses be determined

– This ensures assimilation of all information in the ECG and that no detail will be overlooked


Step 1 - Heart Rate

Heart rate– Both atrial and ventricular rates - if different– Normal heart rate 60-100 beats per minute

>100 beats/min = tachycardia<60 beats/min = Bradycardia

Methods of measurement– 1500 divided by No. of small boxes in Inter R-R interval– 300 divided by No. of big boxes in Inter R-R interval– What if heart rate irregular?

Step 1 – Heart Rate

Interpreting the rhythm of the ECG is sometimes difficultLocate the P wave

– The most important and first step in rhythm interpretation is the identification of P waves and an analysis of their morphology

– Are P waves visible? Each lead needs to be examined for P waves– What is the rate of the P waves (i.e., the PP interval)? If the rate is less

than 60, then a bradycardia and if the atrial or P wave rate is over 100, then there is tachycardia

– What is the morphology and axis of the P waves? The normal sinus P wave is generally upright in leads I, II, aVF, and V4-V6. It will be negative in lead aVR

Step 2 – Rhythm Analysis

Establish the relationship between P waves and the QRS complex

• To determine the relationship between the P waves and the QRS complexes, addressing the following questions:– Are the P waves associated with QRS complexes in a 1:1

fashion?• If not, are there more or less P waves than QRS complexes

and what are the atrial and ventricular rates?– Do the P waves precede each QRS complex?– What is the PR interval, and is this interval fixed?


Analyze the QRS morphology• If the QRS complexes are of normal duration (<0.12 sec) and

morphology, then the rhythm is supraventricular

• It is essential to analyze the QRS in all 12 leads to be sure that it is normal

• If the QRS is wide (i.e., >0.12 sec), then the rhythm is either supraventricular with aberrant conduction, pre-excitation, or ventricular pacing, or it is of ventricular origin – take the widest QRS in the 12 lead ECG



• State the basic rhythm e.g., "normal sinus rhythm", "atrial fibrillation", etc.

• Identify additional rhythm events if present e.g., "PVC's", "PAC's", etc.

• Remember that arrhythmias may originate in the atria, AV junction, and ventricles

Step 3 – Axis

• PR interval includes the P wave as well as the PR segment

• Measured from the beginning of the P wave to the first part of the QRS complex (which may be Q wave or R wave)

• Includes time for atrial depolarization (the P wave) and conduction through the AV node and the His-Purkinje system (which constitute the PR segment)

• The length of the PR interval changes with heart rate, but is normally 0.12 to 0.20 sec (three to five small boxes)

Step 4 - Intervals

PR Interval

• Consists of the QRS complex, the ST segment, and T wave• Primarily a measure of ventricular repolarization• Depends upon the heart rate

– Shorter at faster heart rates and longer when the rate is slower– Need to be corrected for heart rate (QTc)

Step 4 - Intervals

QT interval

• The P wave represents atrial depolarization• The normal sinus P wave demonstrates right followed by left atrial

depolarization and is an initial low amplitude positive deflection preceding the QRS complex

• The duration is generally <0.12 sec (three small boxes) and the amplitude <0.25 mv (2.5 small boxes)

• Since right atrial depolarization precedes that of the left atrium (as the sinus node is in the high right atrium), the P wave is often notched in the limb leads and usually biphasic in lead V1– The initial positive deflection in V1 is due to right atrial depolarization

that is directed anteriorly, while the second negative deflection represents left atrial depolarization that is directed posteriorly.

Step 5 – P wave

• Represents the time for ventricular depolarization

• If the initial deflection is negative, it is termed a Q wave

• The first positive deflection of the QRS complex is called the R wave – represents depolarization of the left ventricular myocardium

• The negative deflection following the R wave is the S wave – represents terminal depolarization of the high lateral wall

• If there is a second positive deflection it is known as an R’

Step 6 – QRS complex

QRS complex

• Lower case letters (q, r, or s) are used for relatively small amplitude waves of less than 0.5 mV (less than 5 mm with standard calibration)

• An entirely negative QRS complex is called a QS wave

• The entire QRS duration normally lasts for 0.06 to 0.10 seconds (1½ to 2½ small boxes) and is not influenced by heart rate

• The R wave should progress in size across the precordial leads V1-V6. Normally there is a small R wave in lead V1 with a deep S wave. The R wave amplitude should increase in size until V4-V6, due to more left ventricular forces being seen, while the S wave becomes less deep. This is termed R wave progression across the precordium

• Occurs after ventricular depolarization has ended and before repolarization has begun

• Time of electrocardiographic silence

• Initial part of the ST segment is termed the J point

• The ST segment is usually isoelectric and has a slight upward concavity

• Depressed (below the isoelectric line) in Myocardial ischemia and infarction

• Elevated (above the isoelectric line) acute myocardial infarction and pericarditis

Step 7 – ST SegmentST segment

• T wave represents the period of ventricular repolarization• The rate of repolarization is slower than depolarization, the T

wave is broad, has a slow upstroke, and rapidly returns to the isoelectric line following its peak (i.e., slow upstroke, rapid downstroke)– Thus, the T wave is asymmetric and the amplitude is variable– In addition, the T wave is usually smooth up and down– If there is any irregularity on the T wave (bump, notch, rippled,

nipple, etc) a superimposed P wave should be considered

Step 7 –T wave

ECG Interpretation

• Conclusion of the above analyses

• Interpret the ECG as "Normal" or "Abnormal“

• Occasionally the term "borderline" is used if unsure about the significance of certain findings or for minor changes

• List all abnormalities

A systematic approach to interpretation of the ECG is critically important

• Rate — Is the rate between 60 and 100?• Rhythm — Is it normal sinus or other?• Axis — Is there axis deviation? • Intervals — Are all intervals normal? • P wave — What is its height, width, and axis?• QRS complex — Are there pathologic Q waves, bundle branch

block, or chamber hypertrophy? • ST-T waves — Is it isoelectric, elevated, or depressed relative to

the TP segment? • Overall interpretation — What is the diagnosis?

Summary

Myocardial Ischemia and Infarction

• T-wave inversion ( flipped T)• ST segment depression• T wave flattening• Biphasic T-waves

Baseline

ECG Changes : Ischemia

• ST segment elevation of greater than 1mm in at least 2 contiguous leads

• Heightened or peaked T waves• Directly related to portions of myocardium rendered

electrically inactive

Baseline

ECG Changes : Injury

ECG Changes: Infarct

• Significant Q-wave where none previously existed– Why?

• Impulse traveling away from the positive lead• Necrotic tissue is electrically dead

• No Q-wave in Subendocardial infarcts– Why?

• Not full thickness dead tissue• But will see a ST depression• Often a precursor to full thickness MI

• Criteria– Depth of Q wave should be 25% the height of the R wave– Width of Q wave is 0.04 secs– Diminished height of the R wave

ECG Changes : Infarct

1 year

Q wave

ST Elevation

T wave inversion

Evolving MI and Hallmark of AMI

A Normal 12 Lead ECGA Normal 12 Lead ECG

Anterior Myocardial Infarction

– Anterior infarct with ST elevation

– Left Anterior Descending Artery (LAD)

– V1 and V2 may also indicate septal involvement which extends from front to the back of the heart along the septum

Anterior Myocardial Infarction

Anterior MI Anterior Myocardial Infarction

– Inferior Infarct with ST elevations

– Right Coronary Artery (RCA)

Inferior Myocardial Infarction

Inferior MIInferior Myocardial Infarction

– Lateral Infarct with ST elevations

– Left Circumflex Artery– Rarely by itself– Usually in combo

Lateral Myocardial Infaction

Lateral MILateral Myocardial Infaction

– Posterior Infarct with ST Depressions and/ tall R wave in V1 and V2

– RCA and/or LCX Artery– Rarely by itself usually in

combo

Posterior Myocardial Infarction

Posterior MIPosterior Myocardial Infarction

Putting it All Together

• They are not transmural• Look for diffuse or

localized changes and non Q wave abnormalities– T-wave inversions– ST segment depression

Non ST Elevation Myocardial Infarction

Non ST Elevation Myocardial Infarction

Any Questions?

Electrocardiogaram - ECG EKG

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