[Os 213] Ws 02 Ecg Reading

OS 213: Human Disease and Treatment 3 (Circulation and Respiration)WS 02: E.C.G. READING

Exam 1 | Dr. Felix Eduardo Punzalan| August 9, 2012

OUTLINE I. The Normal ECGII. Guide in Reading ECGs

A. Standardization and TechniqueB. RhythmC. RateD. P WaveE. PR Interval

F. QRS IntervalG. ST SegmentH. QT IntervalI. T WaveJ. Normal Rate, Segment,

Duration, and AxisK. Obtaining the Axis

I. THE NORMAL ECGParts of the ECG

P wave QRS Complex T wave U wave P-R Interval P-R Segment S-T Segment S-T Interval Q-T Interval

Figure 1. The Normal ECG.

II. GUIDE IN READING ECG’SA. Standardization and Technique

This is done to ensure that the ECG machine is calibrated. In cases of decreased conduction of impulses (i.e., obese/fat

patients), the ECG waves are shown twice its normal size to clearly show the wave morphology.

Figure 2. Calibrated ECG-doubled. The height of the R wave measures approximately 4 big boxes. Divide 4 by 2 (since this is doubled). Hence its height is actually 2 big boxes. To convert this to millivolts , multiply it by 0.5 mV [since 1 big box=0.5mV] resulting to 1 mV as the actual R wave reading of the patient.

In cases of high intensity impulses (i.e., hypertrophy) the ECG scaling is lowered so that the drawn waves will not exceed the paper.

Figure 3. Calibrated ECG-half. The height of the R wave measures approximately 3 big boxes. Multiply this by 2 (since this is calibrated to 1/2). Therefore the R wave (peak) is actually 6 big boxes= [6 big box x 0.5mV]=3 mV. (This will be helpful in determining presence of hypertrophy when adding actual R and S waves).

B. RhythmRegularity Regular = if R-R interval is the same every cardiac cycle Irregular

a. Regularly irregular - there is a pattern in being irregular. (e.g. 1st RR interval=0.8, 2nd RR interval= 0.4, 3rd RR interval=

0.1; then the same 0.8. 0.4 and 0.1 RR intervals repeats for the succeeding RR-intervals.

Figure 4. Regularly Irregular. RR interval is alternately 0.4 and 0.8

b. Irregularly irregular- total absence of any discernible pattern in the durations of succeeding R-R intervals

Figure 5. Irregularly Irregular. No pattern of RR intervals.

Examples of Irregular Heart RhythmsFor more information, check this site: http://pediatriccardiology.uchicago.edu

1. Premature atrial contraction (PAC): The atria fire an early impulse which causes the heart to beat earlier, causing irregularity in the heart rhythm.

Figure 6. Premature Atrial Contraction. Note the shorter PR interval and the RR distance, different p wave shape (not always present) and the longer RR after the PAC. The QRS complex is narrow as the ventricles are activated at an ectopic origin near the AV node & His-Purkinje system. Also note presence of a prolonged R to R distance after the premature contraction, w/ is the compensatory pause.

2. Premature ventricular contraction (PVC): caused by an ectopic pacemaker in the ventricle

Figure 7. Premature Ventricular Contraction. Characterized by premature and bizarrely shaped QRS complex not preceded by a P wave and with inverted, large T wave. A shorter R to R interval (A) precedes the PVC with a longer RR interval (B). In contrast to the PAC the ectopic beat is a broad complex confirming its ventricular origin.

3. Atrial fibrillationo most common irregular heart rhythm o is a result of many sites, instead of SA node, within the atria

firing electrical impulses rapidly and in an irregular fashiono The atria then cannot push blood effectively into the ventricleo Unusual in children (S4 absent in patients with atrial fibrillation

because S4 is an atrial event)

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http://pediatriccardiology.uchicago.edu/



Figure 8. Atrial Fibrillation. Note the absence of P waves and presence of high frequency wavy records. QRS complex with irregular timing but otherwise normal.

Check Sinus Rhythm If it is in sinus rhythm, determine if it is normal sinus, sinus

bradycardia, or sinus tachycardia o Normal sinus - Regular, 60-100 BPM; P waves normal and

upright, one before each QRSo Sinus bradycardia – Regular, <60 BPM (may be caused by

medications with beta blockers)

Figure 9. Sinus Bradycardia. Through inspection/estimation it is indicated by

R-R intervals reaching more than 5 big boxes.

o Sinus tachycardia – Regular, >100 BPM; the impulse generating the heart are normal but at a faster pace (during exercise or excitement)

Figure 10. Sinus tachycardia. Through inspection estimation it is indicated

by R-R intervals not reaching 3 big boxes.

Non-sinus rhythm

Figure 11. Absent P Wave.A sinus rhythm is a normal beating from the SA node.

Determine Fast Or Slow Heart RateFast sinus rhythmo Supraventricular tachycardia

Abnormal heart rhythm The impulse stimulating the heart is not generated by the sinus node,

but instead comes from a collection of tissue around and involving the atrioventricular (AV) node.

Figure 12. Supraventricular Tachycardia.

o Atrial Flutter

Figure 13. Atrial flutter. The abnormal tissue generating the rapid heart rate is in the atria. Note the difference with atrial fibrillation, which is the presence of multiple p waves (in a 2:1 or 3:1 rhythm

with the QRS/ventricular contraction)

Slow Sinus Rhythmo Atrioventricular block

The sinus node may be generating heart beats causing the atria to contract at a normal rate

However, not every electrical impulse coming from the atria is being passed down the AV bundle (of His) to the ventricles by the atrioventricular node due to a block in conduction.

Figure 14. Atrioventricular block.

Check Other AbnormalitiesObserve for the different waves, segments and intervals, determine

abnormalitites (if present).

Tall P waves - peaked P waves (P pulmonale) suggests right atrial hypertrophy (e.g.: pulmonary hypertension or tricuspid stenosis)

Figure 15. Tall P wave.

Bifid P waves (P mitrale) - suggests left atrial hypertrophy (eg. mitral stenosis)

Figure 16. Bifid P Wave.

The PR interval is measured from the beginning of the P wave to the R wave and is usually 1 large square in duration (0.2 s)

Short PR intervalo represents rapid conduction across the AV node, usually through

an accessory pathway (e.g. Wolff–Parkinson–White syndrome). o Note for the delta wave.


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C. RATE: ATRIAL AND VENTRICULAR

D. P WAVE: MORPHOLOGY AND DURATION

E. PR INTERVAL



Figure 17. Delta Wave. A “shark” like wave characteristic of Wolff–Parkinson–White syndrome.

First-degree AV BlockA long PR interval (>1 large square) preceding every QRS complex

by the same distance is first degree AV block (see fig Figure 18). This is usually not significant, though it is worth checking the

patient’s drug history for beta-blockers or rate limiting calcium antagonists, e.g. verapamil and diltiazem.

Figure 18. First-degree AV block.Second-degree AV BlockSecond-degree AV Block Mobitz I (Wenckebach’s)o A PR interval that lengthens with each consecutive QRS complex,

followed by a p wave which has no QRS complex and then by a p wave with a short PR interval

o Problem mainly in AV node

Figure 19. Second-degree AV Block Mobitz I. Note the absent QRS complex/”dropped beat” (arrow).

Second-degree AV Block Mobitz IIo If the P waves that are followed by a QRS complex have a normal

PR interval, with the occasional non-conducted P wave – i.e. a P wave with no subsequent QRS complex (a “dropped beat”)

o Problem mainly in AV bundle (of His).

Figure 20. Second-degree AV Block Mobitz II. Note absence of QRS complex (arrow). Difference with Mobitz I is lack of progressive increases in PR intervals (PR intervals

equal) prior to the “dropped beat”.

Third-degree AV Block/ Complete Heart BlockWhen P waves are regular (usually about 90 bpm) and the QRS

complexes are regular (about 40 bpm), but there is no association between the two (Fig. 21). e.g. hypotensive, will need insertion of a temporary pacing wire.

Figure 21. Third-degree AV Block. Note dissociation of the QRS complexes and the P waves, indicating an “escape” of ventricular

control.

F. QRS Interval Check If QRS width (normally < 3 small squares or 0.12 s) and

morphology is normal. If wider than normal, this could indicate:a. the beat is ventricular in origin, e.g. an ectopic beat; or

b. there is a bundle branch block.

Figure 22. Wide QRS. General indicator of bundle branch block.

1. A broad QRS complex with an RSR pattern in V1 represents right bundle branch block. LOOK FOR THE “M” shaped QRSIf it is found in V1, it is Right bundle branch block (Fig 23)

Figure 23. Right Bundle Branch Block.

2. A broad QRS with an ‘M’ pattern in lead V6 represents left bundle branch block

Figure 24. Left Bundle Branch Block.

Check the depth of the Q wave. The first negative deflection of a QRS complex is the Q wave. If the Q wave is > 2 mm (two small squares), it is considered pathological.

Figure 25. Deep Q Wave.

G. ST Segment It is important to note that ST segments are abnormal and cannot

be interpreted in patients with bundle branch block, especially LBBB.o ST Depression – could indicate cardiac ischemia.


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M-shaped

M-shaped



Figure 26. ST Depression.

o ST Elevation – suggestive of infarction.

Figure 27. ST Elevation.

o Saddle-shaped concave - usually seen across all the ECG, suggesting a diagnosis of pericarditis.

Figure 28. Saddle-shaped Concave.

H. QT Interval The QT interval is usually about 0.4 s (two large squares) long. It is important as prolongation can lead to serious ventricular

arrhythmias such as torsades de pointes. It can be prolonged for several reasons – including drugs such as

amiodarone, sotalol and some anti-histamines A family history of sudden cardiac death is also important as a

congenital long QT syndrome may be present.

Figure 29. Prolonged QT Interval.

I. T Wave T waves should be upright in all leads other than leads III and V1

where an inverted T wave can be a normal variant. o Tall tented T waves could represent hyperkalaemiao T wave inversion can represent coronary ischaemia, previous

infarction or electrolyte abnormality such as hypokalaemia

Figure 30. T Wave Abnormalities.

J. Normal Rate, Segment Duration, and AxisTable 1. Normal Values of Heart Rate, Segment Duration, and Axis Deviation.

Normal Heart rate 60 - 100 beats/min (bpm)Bradycardia < 60 bpmTachycardia > 100

PR interval 0.12 – 0.20 secQRS < 0.12 secQRS axis - 30º to + 110ºQTc < 0.45 sec

K. Obtaining the Axis Step 1. Orient yourself. o For determining Left, Right or inferior abnormalities of the

heart (I.e., hypertrophy/ enlargement), Leads I, II, III, aVR

(Right), aVL (Left), aVF (Foot) are used.

Figure 31. Determining the Axis.

Step2: For determining if the heart damage is anterior or lateral.o Take note of the proximity of leads in the drawing: V1 (Right

atrium), V2 and V3 (right ventricle), V4, V5 and V6 (left ventricle). You would expect that a deviation from the normal (ie increase in height of QRS) in a lead would indicate abnormality in the area of the heart close to it.

END


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[Os 213] Ws 02 Ecg Reading