ECG Basics

The Normal Conduction System

What is an ECG?

The electrocardiogram (ECG) is a The electrocardiogram (ECG) is a representation of the electrical events of the representation of the electrical events of the cardiac cycle.cardiac cycle.

Each event has a distinctive waveform, the Each event has a distinctive waveform, the study of which can lead to greater insight study of which can lead to greater insight into a patient’s cardiac pathophysiology.into a patient’s cardiac pathophysiology.

What types of pathology can we identify and study from ECGs?

ArrhythmiasArrhythmiasMyocardial ischemia and infarctionMyocardial ischemia and infarctionPericarditisPericarditisChamber hypertrophyChamber hypertrophyElectrolyte disturbances (i.e. Electrolyte disturbances (i.e. hyperkalemia, hypokalemia)hyperkalemia, hypokalemia)Drug toxicity (i.e. digoxin and drugs which Drug toxicity (i.e. digoxin and drugs which prolong the QT interval)prolong the QT interval)

Parts of the ECG (Waveforms and Intervals)

Parts of the ECG

ECG Leads

Leads are electrodes which measure the Leads are electrodes which measure the difference in electrical potential between difference in electrical potential between either:either:

1. Two different points on the body (bipolar leads)1. Two different points on the body (bipolar leads)

2. One point on the body and a virtual reference point 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of with zero electrical potential, located in the center of the heart (unipolar leads)the heart (unipolar leads)

ECG Leads

The standard EKG has 12 leads:The standard EKG has 12 leads: 3 Standard Limb Leads

3 Augmented Limb Leads

6 Precordial Leads

The axis of a particular lead represents the viewpoint from The axis of a particular lead represents the viewpoint from which it looks at the heart.which it looks at the heart.

The Standard Leads

Lead I is obtained by measuring the voltage between the left arm and right arm. The left arm is the positive pole. An electrical wave moving towards the left arm will cause an upward deflection of the ECG machine stylus on the paper.

Lead I is most useful for seeing electrical activity moving in a horizontal direction.

The Standard Leads

Lead II connects connects the right arm to the the right arm to the leg, and therefore leg, and therefore best sees electricity best sees electricity moving down and moving down and leftward.leftward.

The Standard Leads

Lead III compares compares voltage in left arm and voltage in left arm and the leg, and will the leg, and will measure electricity measure electricity moving down and moving down and rightward. rightward.

Lead II and Lead III are positive at the footare positive at the foot

Standard Limb Leads

The Augmented Leads

Three additional limb leads can be Three additional limb leads can be obtained by mixing combinations of obtained by mixing combinations of electrodes. These are electrodes. These are leads R, L, and F..To create these limb leads, two electrodes To create these limb leads, two electrodes are connected together to create an are connected together to create an “average” electrode, then connected “average” electrode, then connected through the ECG machine to the through the ECG machine to the remaining electrode.remaining electrode.

The Augmented Leads

Lead F is created by is created by connecting the two arms connecting the two arms together to create an together to create an “average” electrode. To “average” electrode. To the ECG machine, this the ECG machine, this combination looks like a combination looks like a single electrode midway single electrode midway between the two arms — between the two arms — directly in the center of directly in the center of the body above the heart. the body above the heart. This “average” electrode This “average” electrode is connected through the is connected through the ECG machine to the foot ECG machine to the foot electrodeelectrode

The Augmented Leads

Lead L is created by is created by connecting the right arm connecting the right arm and the leg together, then and the leg together, then comparing this “average” comparing this “average” electrode to the left arm electrode to the left arm electrode. The left arm electrode. The left arm electrode is positive, electrode is positive, meaning that electricity meaning that electricity moving to the left will moving to the left will cause an upward motion cause an upward motion of the ECG stylus.of the ECG stylus.

The Augmented Leads

To create To create lead R, the left arm , the left arm and the foot electrodes are and the foot electrodes are connected together, then the connected together, then the voltage of this “average” voltage of this “average” electrode is compared to the electrode is compared to the right arm lead. right arm lead. Because Because lead R “aims” in the “aims” in the opposite direction from the other opposite direction from the other limb leads, its ECG waveforms limb leads, its ECG waveforms will usually be “upside down” by will usually be “upside down” by comparisoncomparison. . This means that every electrical wave in lead R should have a net negative direction, unless pathology is present.

Augmented Limb Leads

All Limb Leads

The Chest (Precordial) Leads

Precordial LeadsThe precordial (chest) leads start with:The precordial (chest) leads start with:

Lead V1 is placed in the 4th intercostal space, near is placed in the 4th intercostal space, near by right edge of sternumby right edge of sternumLead V2 is opposite is opposite Lead V1V1 at the left side of the at the left side of the sternum. sternum. Lead V3 is halfway to is halfway to lead V4, which is placed , which is placed below rib 5 on the midbelow rib 5 on the midclavicular lineclavicular line. . Lead V5 is straight around the chest from is straight around the chest from Lead V4, on the anterior axillary , on the anterior axillary lineline. . Lead V6 is directly around from is directly around from Lead V5, straight , straight down from the middle of the armpit (the down from the middle of the armpit (the mid-axillary line)line)

Precordial Leads

Summary of Leads

Limb LeadsLimb Leads Precordial LeadsPrecordial Leads

BipolarBipolar I, II, IIII, II, III(standard limb leads)(standard limb leads)

--

UnipolarUnipolar aVR, aVL, aVF aVR, aVL, aVF (augmented limb leads)(augmented limb leads)

VV11-V-V66

Arrangement of Leads on the ECG

Anatomic Groups(Septum)

Anatomic Groups(Anterior Wall)

Anatomic Groups(Lateral Wall)

Anatomic Groups(Inferior Wall)

Anatomic Groups(Summary)

The ECG GridThe paper on which the The paper on which the ECG is drawn is divided up ECG is drawn is divided up into 1 millimeter lines into 1 millimeter lines horizontally and vertically. horizontally and vertically. The vertical lines represent passage of time. Because the paper . Because the paper moves at a rate of 25 mm moves at a rate of 25 mm per second, each 1 mm per second, each 1 mm line represents 0.04 line represents 0.04 seconds of time. Every fifth seconds of time. Every fifth line is darkened to help line is darkened to help with counting. with counting. The time The time between large boxes between large boxes (darkened lines) is 0.2 (darkened lines) is 0.2 seconds, and five large seconds, and five large boxes equals one boxes equals one secondsecond..

The ECG GridThe vertical direction represents the strength of electrical voltage. . Positive voltage moves the Positive voltage moves the stylus up, negative voltage stylus up, negative voltage moves it downward. moves it downward. Each millimeter vertically represents 0.1 millivolt. Ten vertical boxes is one millivolt. .

The horizontal direction represents passage of time

Parts of the ECG The P Wave

The The P waveP wave represents the spread of represents the spread of electrical activity over the atrium. The electrical activity over the atrium. The normal depolarization begins at the normal depolarization begins at the sinoatrial (SA) node near the top of the sinoatrial (SA) node near the top of the atrium. It’s normally atrium. It’s normally largest in lead IIlargest in lead II. The . The normal P wave is upright in all leads normal P wave is upright in all leads except R.except R.The P waveThe P wave normally normally lasts less than 0.11 lasts less than 0.11 secondsseconds (just less than three small (just less than three small boxes). An abnormally long P wave boxes). An abnormally long P wave occurs whenever it takes extra time for occurs whenever it takes extra time for the electrical wave to reach the entire the electrical wave to reach the entire atrium. This occurs in left atrial atrium. This occurs in left atrial enlargement.enlargement.The height of the PThe height of the P wavewave is normally is normally less less than 2.5 small boxes (less than 0.25 than 2.5 small boxes (less than 0.25 millivolts).millivolts). An abnormally tall P wave is An abnormally tall P wave is seen when larger amounts of electricity seen when larger amounts of electricity are moving over the atrium. This usually are moving over the atrium. This usually indicates hypertrophy of the right atrium. indicates hypertrophy of the right atrium. The P wave may be decreased in height The P wave may be decreased in height by hyperkalemia.  by hyperkalemia. 

Parts of the ECGThe PR Interval:

Following the P wave is the Following the P wave is the PR segmentPR segment. . (NOTE: the PR segment and the PR interval are (NOTE: the PR segment and the PR interval are NOT the same thing.) The PR segment is not NOT the same thing.) The PR segment is not routinely measured, but may be commented on if routinely measured, but may be commented on if it is depressed or elevated. During the PR it is depressed or elevated. During the PR segment, the electrical wave moves slowly segment, the electrical wave moves slowly through the atrioventricular (AV) node. This through the atrioventricular (AV) node. This activity is not seen on the ECG.activity is not seen on the ECG.The PR interval is the time from the beginning is the time from the beginning of the P wave until the beginning of the QRS of the P wave until the beginning of the QRS complex. It is normally complex. It is normally between 0.12 and 0.2 between 0.12 and 0.2 seconds (three to five small boxes) in lengthseconds (three to five small boxes) in length..The PR interval may be prolonged when The PR interval may be prolonged when conduction of the electrical wave through the AV conduction of the electrical wave through the AV node is slow. This may be seen with node is slow. This may be seen with degenerative disease of the node, or with degenerative disease of the node, or with digoxin, hyperkalemia, hypercalcemia, or digoxin, hyperkalemia, hypercalcemia, or hypothermia.hypothermia.The PR interval may be unusually short when The PR interval may be unusually short when conduction is rapid. A mildly short PR interval conduction is rapid. A mildly short PR interval may be seen with hypokalemia or hypocalcemia. may be seen with hypokalemia or hypocalcemia. An artificially-short PR interval occurs when the An artificially-short PR interval occurs when the QRS complex begins early, as happens with an QRS complex begins early, as happens with an extra conducting bundle — Wolff-Parkinson-extra conducting bundle — Wolff-Parkinson-White Syndrome (WPW).  White Syndrome (WPW). 

Parts of the ECGThe QRS Complex:

The QRS complex represents The QRS complex represents activation of the ventricle. activation of the ventricle. The QRS complex is is normally normally less than 0.10 seconds in less than 0.10 seconds in length — two and a half boxeslength — two and a half boxes. . Lengthening of the QRS Lengthening of the QRS indicates some blockage of the indicates some blockage of the electrical action in the electrical action in the conducting system. This may conducting system. This may be due to ischemia, necrosis of be due to ischemia, necrosis of the conducting tissue, the conducting tissue, electrolyte abnormality, or electrolyte abnormality, or hypothermia.hypothermia.

Parts of the ECGQ wave

If the first deflection of the QRS is If the first deflection of the QRS is downward, it’s called a downward, it’s called a Q waveQ wave. The Q . The Q wave represents activation of the wave represents activation of the ventricular septum. The electricity ventricular septum. The electricity spreads from right to left through the spreads from right to left through the septum.septum.Q waves may be normalQ waves may be normal. For example in . For example in lead I, a Q less than 1/4 of the R height, lead I, a Q less than 1/4 of the R height, and less than one box wide, is and less than one box wide, is considered normal. This is the early considered normal. This is the early activation of the septum. This activation activation of the septum. This activation goes left — away from lead I — and is goes left — away from lead I — and is therefore negative on the ECG. “Septal therefore negative on the ECG. “Septal Qs” are normal in I, F, V5 and V6. Qs are Qs” are normal in I, F, V5 and V6. Qs are also generally innocent in lead III and also generally innocent in lead III and lead V1 if no other abnormality is seen.lead V1 if no other abnormality is seen.Q waves are “significant” if they are Q waves are “significant” if they are greater than 1 box in width (longer than greater than 1 box in width (longer than 0.04 msec) OR are larger than 1/4 of the 0.04 msec) OR are larger than 1/4 of the R wave. Significant Q waves indicate R wave. Significant Q waves indicate either myocardial infarction or obstructive either myocardial infarction or obstructive septal hypertrophy (IHSS).septal hypertrophy (IHSS).

Parts of the ECG

R waveThe first upward The first upward deflection of the QRS is deflection of the QRS is called called the R wavethe R wave. Most . Most of the ventricle is of the ventricle is activated during the R activated during the R wave. The R wave may wave. The R wave may be prolonged if the be prolonged if the ventricle is enlarged, and ventricle is enlarged, and may be abnormally high may be abnormally high (indicating strong voltage) (indicating strong voltage) if the ventricular muscle if the ventricular muscle tissue is hypertrophied.tissue is hypertrophied.

Parts of the ECG

S waveThe S waveThe S wave is any is any downward deflection downward deflection following the R wave. following the R wave. Like the R wave, an Like the R wave, an abnormally large S abnormally large S wave may indicate wave may indicate hypertrophy of the hypertrophy of the ventricle.ventricle.

Parts of the ECGThe ST Segment

The ST segmentThe ST segment is the portion of the is the portion of the tracing falling between the QRS complex tracing falling between the QRS complex and the T wave. During this time, the and the T wave. During this time, the ventricle is contracting, but no electricity is ventricle is contracting, but no electricity is flowing. The ST segment is therefore flowing. The ST segment is therefore usually even with the baseline. usually even with the baseline. The length of the ST segmentThe length of the ST segment shortens shortens with increasing heart rate.with increasing heart rate. Abnormality of Abnormality of electrolytes may also affect the ST electrolytes may also affect the ST segment length, however measurement of segment length, however measurement of the length of the ST segment alone is the length of the ST segment alone is usually not of any clinical use.usually not of any clinical use.Upward or downward shifts in the ST Upward or downward shifts in the ST segment are extremely important.segment are extremely important. Deviation of the ST segment from Deviation of the ST segment from baseline can indicate infarction or baseline can indicate infarction or ischemia, pericarditis, electrolyte ischemia, pericarditis, electrolyte abnormality, or ventricular strain. ST abnormality, or ventricular strain. ST segment elevation or depression is segment elevation or depression is generally measured at a point two boxes generally measured at a point two boxes beyond the QRS complex.  beyond the QRS complex. 

Parts of the ECGThe T wave

The T waveThe T wave represents the wave of represents the wave of repolarization, as the ventricle prepares to fire repolarization, as the ventricle prepares to fire again. again. The T wave is normally upright in leads The T wave is normally upright in leads I, II, and V3-V6I, II, and V3-V6. It is normally inverted in lead . It is normally inverted in lead R. Ts are variable in the other leads (III, L, F, R. Ts are variable in the other leads (III, L, F, and V1-V2).and V1-V2).T wave abnormalities may be seen with, or T wave abnormalities may be seen with, or without ST segment abnormality. Tall T waves without ST segment abnormality. Tall T waves may be seen in hyperkalemia or very early may be seen in hyperkalemia or very early myocardial infarction. Flat T waves occur in myocardial infarction. Flat T waves occur in many conditions. Inverted T waves may be many conditions. Inverted T waves may be seen in both ischemia and infarction, late in seen in both ischemia and infarction, late in pericarditis, ventricular hypertrophy, bundle pericarditis, ventricular hypertrophy, bundle branch block, and cerebral disease.branch block, and cerebral disease.In young children, T waves may be inverted in In young children, T waves may be inverted in the right precordial leads (V1 to V3). the right precordial leads (V1 to V3). Occasionally, these T inversions persist in Occasionally, these T inversions persist in young adults. young adults. 

Parts of the ECG

The U Wave

A second wave A second wave following the T wave following the T wave is called a is called a U waveU wave. . Large U waves may Large U waves may be seen in electrolyte be seen in electrolyte abnormality (such as abnormality (such as hypokalemia), or with hypokalemia), or with drug effects. drug effects.

Parts of the ECGThe QT Interval

The QT intervalThe QT interval is the time from the is the time from the beginning of the QRS complex until the beginning of the QRS complex until the end of the T wave. The “normal” QT end of the T wave. The “normal” QT length varies with heart rate. Very fast length varies with heart rate. Very fast rates shorten the QT length. rates shorten the QT length. At normal heart rates, At normal heart rates, QT length is QT length is abnormal if it’s greater than 0.40 sec abnormal if it’s greater than 0.40 sec (10 boxes) for males and 0.44 sec (11 (10 boxes) for males and 0.44 sec (11 boxes) for femalesboxes) for females. Extreme QT . Extreme QT prolongations (greater than 0.60 sec — prolongations (greater than 0.60 sec — 15 small boxes) predispose the patient 15 small boxes) predispose the patient to arrhythmias.to arrhythmias.The QT interval may be prolonged with The QT interval may be prolonged with electrolyte abnormality, such as electrolyte abnormality, such as hypokalemia, hypocalcemia, or hypokalemia, hypocalcemia, or hypomagnesemia. Myocardial hypomagnesemia. Myocardial ischemia may also prolong the QT ischemia may also prolong the QT interval.  interval. 

Sequence of ECG analysis1.1. EExclusion xclusion of of technical faulttechnical faultss

2.2. EstimationEstimation: : the strength of electrical voltagethe strength of electrical voltage

3.3. What is the rhythm? Is the rhythmWhat is the rhythm? Is the rhythm regular or irregular regular or irregular ??

6.6. What is the rate?What is the rate?

7. Determining QRS axis.

7.7. Check the waves, intervals, complexesCheck the waves, intervals, complexes

9.9. ECG conclusionECG conclusion

10.10. CCompare ompare ECG data ECG data withwith- age and body habitus of patient- age and body habitus of patient

- physiologic- physiologic featuresfeatures (e.g. pregnancy) (e.g. pregnancy)

- - clinical clinical findingfindingss

- - treatmenttreatment

Where to lookLook for P waves. Are they all the same shape? Are there any Look for P waves. Are they all the same shape? Are there any inverted Ps other than in lead R? Does the PR interval vary? Are inverted Ps other than in lead R? Does the PR interval vary? Are there any non-conducted P waves? Is the P wave abnormally wide there any non-conducted P waves? Is the P wave abnormally wide or high?or high?Check the PR interval. Is there first degree AV block? Is the PR Check the PR interval. Is there first degree AV block? Is the PR abnormally short?abnormally short?Look at the QRS complex in each lead. Is the QRS axis normal? Is Look at the QRS complex in each lead. Is the QRS axis normal? Is the QRS width normal? Do the wave forms suggest conduction the QRS width normal? Do the wave forms suggest conduction block? Are there significant Q waves? Is the precordial R wave block? Are there significant Q waves? Is the precordial R wave pattern normal? Are the QRS complexes too small or too large?pattern normal? Are the QRS complexes too small or too large?Look at the ST segments. Is there an abnormality? Is the Look at the ST segments. Is there an abnormality? Is the abnormality diagnostic of ischemia, infarction, or ventricular strain?abnormality diagnostic of ischemia, infarction, or ventricular strain?Check the T waves. Is the shape normal? Are there inverted Ts in I, Check the T waves. Is the shape normal? Are there inverted Ts in I, II, or V3-V6?II, or V3-V6?Look at the QT interval. Is it over half the R-R distance, or over 10 Look at the QT interval. Is it over half the R-R distance, or over 10 boxes in length?boxes in length?

Once you spot an abnormality, check for other findings that firm up Once you spot an abnormality, check for other findings that firm up the diagnosis. For example, when you spot a large R in V1, you the diagnosis. For example, when you spot a large R in V1, you check for axis deviation, ST depression, and the orientation of the P check for axis deviation, ST depression, and the orientation of the P wave in V1.  wave in V1. 

The sinus rhythm

P-wave precedes QRS complex

The regular rhythmRR intervals are

equal

Determining the Heart Rate

Rule of 300Rule of 300

10 Second Rule10 Second Rule

Cardio- tables

Cardio- tables

Cardio-ruler

Rule of 300

Take the number of “big boxes” between Take the number of “big boxes” between neighboring QRS complexes, and divide this neighboring QRS complexes, and divide this into 300. The result will be approximately into 300. The result will be approximately equal to the rateequal to the rate

Although fast, this method only works for Although fast, this method only works for regular rhythms.regular rhythms.

What is the heart rate?

(300 / 6) = 50 bpm

What is the heart rate?

(300 / ~ 4) = ~ 75 bpm

What is the heart rate?

(300 / 1.5) = 200 bpm

The Rule of 300

It may be easiest to memorize the following table:It may be easiest to memorize the following table:

# of big # of big boxesboxes

RateRate

11 300300

22 150150

33 100100

44 7575

55 6060

66 5050

10 Second Rule

As most ECGs record 10 seconds of rhythm per As most ECGs record 10 seconds of rhythm per page, one can simply count the number of beats page, one can simply count the number of beats present on the ECG and multiply by 6 to get the present on the ECG and multiply by 6 to get the number of beats per 60 seconds.number of beats per 60 seconds.

This method works well for irregular rhythms.This method works well for irregular rhythms.

What is the heart rate?

33 x 6 = 198 bpm

The QRS Axis

The QRS axis represents the net overall The QRS axis represents the net overall direction of the heart’s electrical activity.direction of the heart’s electrical activity.

Abnormalities of axis can hint at:Abnormalities of axis can hint at:

Ventricular enlargementVentricular enlargement

Conduction blocks (i.e. hemiblocks)Conduction blocks (i.e. hemiblocks)

Axis Deviation

Normal QRS axis is from is from around -30 to +90 degrees. around -30 to +90 degrees.

More negative than -30 is More negative than -30 is called called left axis deviation. .

More positive than +90 is More positive than +90 is called called right axis deviation. .

Axis DeviationRight axis deviation is seen on the ECG when more electrical is seen on the ECG when more electrical forces are moving to the right than normal. This is usually due to forces are moving to the right than normal. This is usually due to hypertrophy of the right ventricle (RVH). Causes of right axis deviation hypertrophy of the right ventricle (RVH). Causes of right axis deviation include COPD, pulmonary emboli, valvular disease, septal defects, and include COPD, pulmonary emboli, valvular disease, septal defects, and pulmonary hypertension.pulmonary hypertension.An axis of +90 is common in persons with emphysema. This so-called An axis of +90 is common in persons with emphysema. This so-called “vertical heart” reflects both the rotation of the heart downward as the “vertical heart” reflects both the rotation of the heart downward as the diaphragm position drops due to air trapping, and some degree of diaphragm position drops due to air trapping, and some degree of hypertrophy of the right ventricle.hypertrophy of the right ventricle.Left axis deviation occurs when additional electrical forces move to occurs when additional electrical forces move to the left (hypertrophy), or when the time required for the electrical activity the left (hypertrophy), or when the time required for the electrical activity to move over the ventricle is prolonged (LBBB, left ventricular dilation).to move over the ventricle is prolonged (LBBB, left ventricular dilation).Causes of left axis deviation include hypertension, aortic stenosis or Causes of left axis deviation include hypertension, aortic stenosis or regurgitation, subaortic stenosis, mitral regurgitation, and left ventricular regurgitation, subaortic stenosis, mitral regurgitation, and left ventricular conduction defects.conduction defects.The QRS axis may shift during the respiratory cycle if elevation of the The QRS axis may shift during the respiratory cycle if elevation of the diaphragm changes the physical position of the heart. Beat-to-beat diaphragm changes the physical position of the heart. Beat-to-beat variation in QRS axis (an every-other-beat change in QRS shape) is variation in QRS axis (an every-other-beat change in QRS shape) is called “electrical alternans.” This is thought to be caused by the heart called “electrical alternans.” This is thought to be caused by the heart physically swinging back and forth in a pericardial effusion.  physically swinging back and forth in a pericardial effusion. 

Determining QRS axis by inspection

lead I positive, lead III positive = normal axis

lead I negative (+/- R positive) = RIGHT axis

lead III negative, lead II negative = LEFT axis

Determining QRS axis by inspection

Normal axis

Determining QRS axis by inspection

Vertical axis

Determining QRS axis by inspection

Horizontal axis

Determining QRS axis by inspection

Right axis deviation

Determining QRS axis by inspection

Left axis deviation

The QRS Axis

By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°.

-30° to -90° is referred to as a left axis deviation (LAD)

+90° to +180° is referred to as a right axis deviation (RAD)

Chamber EnlargementRight atrial enlargement

Right atrial enlargement (RAE) is Right atrial enlargement (RAE) is diagnosed by the presence of a diagnosed by the presence of a P P wave 2.5 millimeters or greater in wave 2.5 millimeters or greater in heightheight ( (often called “P often called “P pulmonale.” pulmonale.” )). The P wave often . The P wave often has a sharp, peaked appearance. has a sharp, peaked appearance. This increased voltage is caused This increased voltage is caused by hypertrophy or acute strain of by hypertrophy or acute strain of right atrial tissue.right atrial tissue.

Causes of right atrial enlargementCauses of right atrial enlargement include COPD, mitral stenosis, include COPD, mitral stenosis, mitral regurgitation, or pulmonary mitral regurgitation, or pulmonary emboli. emboli.

Chamber Enlargement

Left atrial enlargementDilation or hypertrophy of the

left atrium may increase the DURATION of the P wave.

P wave longer than 0.11 P wave longer than 0.11 milliseconds (called “P milliseconds (called “P mitrale”)mitrale”) is diagnostic of left is diagnostic of left atrial enlargement (LAE).atrial enlargement (LAE).

LAELAE often occurs in often occurs in mitral mitral valve diseasevalve disease (either (either stenosis or insufficiency). stenosis or insufficiency).

Chamber EnlargementRight ventricular hypertrophy

RVH CriteriaRVH CriteriaR in V1 > 7 mm or > S waveR in V1 > 7 mm or > S waveT in V1 invertedT in V1 invertedRight axis deviationRight axis deviationS waves in V5-V6S waves in V5-V6

Chamber EnlargementLeft ventricular hypertrophy

Summary of LVH Criteria1) R-I + S-III >25 mm 2) S-V1 + R-V5 >35 mm 3) ST-Ts in left leads 4) R-L >11 mm 5) LAE + other criteria Positive Criteria: 1=possible 2=probable 3=definite