ECG Interpretation

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ECG - is a series of waves and deflections recording the hearts electrical activity from a certain view.

Heart Conduction

Electrical Conduction Rate SA node

Rate: 60 100 bpm AV node

act as back-up

pacemaker Rate: 40 60 bpm Purkinje Fiber can act as back-up pacemaker Rate: 20 40 bpm

Breakdown of ECG strip

Components of the Cardiac CycleP wave: (SA node fires) Atrial depolarization Normal shape:

upright & round


P-R interval (PRI) impulse travels from

the SA node to the atria P wave followed by

isoelectric line From the beginning of

P wave to the beginning of Q wave

QRS Complex ventricular depolarization Impulse from the Bundle

of HIS throughout the ventricular muscles

T wave Ventricular

repolarization Resting phase of the

cardiac cycle upright & round

U wave Purkenji fiber

repolarization Etiology: hypokalemia

Electrode application White to right Red to ribs Black over the red.


Produces positive deflection Commonly used for routine



Step I: rhythm Regular


Step II:


Normal: 60 100 bpm Bradycardia: < 60 bpm Tachycardia: > 100 bpm


Method I For regular rhythm: Count the number of large boxes between

2 R waves and that number is divided into 300. Remember:

.20 sec/large box = 5 large boxes/sec. 60 sec/min x 5 = 300 large boxes/min.

What is the rate?

Rate: 300 / 4 = 75 bpm

Method II For fast heart rate: count the number of small boxes between two

R waves and that number is divided into 1500

Remember: 5 small boxes/large box 300 large boxes/min

300 x 5 = 1500

What is the rate?

Rate: 1500 / 10 = 150 bpm

Method III For irregular rhythm:

Count the R waves in 6 sec strip (between 3

hash marks) and multiply it by 10. Remember: 5 large boxes / sec

Method IV:

Find the R wave that fall on a large box line. Level the next large box line a rate of 300 150 100 75 60 50 43 37 33 & 30, until the next R wave.

Step 3 P wave configuration: round and upright

Location: precedes QRS complex Duration: .06 -.11 sec. (1.5 2.5 small boxes) Amplitude: up to 2.5mm

To ask: Are P wave present? Do they look the same? Is there P before every QRS?

Other P wave configurations

Step 4: PR interval From the start of Atrial depolarization to the beginning of

ventricular depolarization Location: beginning of P wave to beginning of Q wave Duration: .12 - .20 sec Amplitude: not measured Configuration: P wave followed by isoelectric line To ask? Are all P-R intervals consistent?

P-R interval (PRI)

Step 5: QRS complex Ventricular depolarization / atrial repolarization

Location: follows P-R interval Amplitude: varies with lead Duration: .04 -.12 (1-3 small boxes) Configuration: varies with lead

to ask? Are there QRS? Do they look the same? Do they come after the P wave? Are the R R intervals equal?


T wave Ventricular repolarization

Location: after S wave Amplitude: 5 mm or less Duration: not measured Configuration: Normal: rounded & upright Inverted Flat Peaked

ST segment End of ventricular depolarization to the beginning of

ventricular repolarization Location: end of S wave to beginning of T wave Amplitude: isoelectric Duration: not measured Configuration: nearly isoelectric

Configuration Isoelectric

Elevated (> 1 2 mm) Sign of acute MI Depressed (> .5 mm) Sign of ischemia

QT interval Location: beginning of Q wave to end of T wave

Amplitude: not measured Duration: < the distance of the R-R interval Configuration: not measured

U wave Purkinje fiber repolarization

Location: follows T wave or may not be present Amplitude: not measured Duration: not measured Configuration: rounded & upright

First Rhythm Strip to Identify



ARTIFACTSFour Common Causes: Patient Movement Loose or defective electrodes Improper grounding Faulty ECG apparatus


Mechanism: Rhythm originates in the SA node


ECG characteristics

Rhythm: regular Rate: normal (60 100 bpm) P wave: normal / 1 per QRS complex PR interval: normal (.12 - .20 sec) QRS complex: normal (.04 - .12 sec) ST segment: not elevated or depressed T wave: normal

Normal sinus rhythm Etiology: Normal cardiac function Clinical Tip: A normal ECG does not exclude heart



depressed automaticity of the SA node with normal

conduction 2.

ECG characteristics: all normal rate - < 60

Sinus BradycardiaEtiology: sleeping; young, athletic individuals Excessive vagal tone (straining, vomiting, intubation) Sick sinus syndrome, MI Digoxin toxicity, Sedative Hyperkalemia Trauma to conductive system

Clinical signs: low CO low perfusion lethargy, mental status change, anxiety, poor capillary refill, mottled skin, low UO syncope

BradycardiaNursing action: (if symptomatic) Document rhythm & notify MD Apply O2 & consider atropine Prepare for external pacing If with PVCs dont treat with lidocaine (this is the hearts

attempt to improve perfusion) Atropine SO4 0.5 mg IV (may repeat in 3-5 min)

Maximum dose: 3 mg Do not give < 0.5 mg may worsen the bradycardia Do not push slow

Mechanism: increased automaticity of the SA node with normal conduction3.

ECG characteristics: all normal Rate: 101 160 bpm P wave: normal or merge to T wave

Sinus tachycardiaEtiology: a natural response to environmental stimuli pain, fever, exercise, emotion, dehydration Drugs, caffeine, alcohol, Hyperthyroidism, shock, CHF, hypoxia Clinical signs: Increased workload of the heart decrease CO low perfusion angina, SOB, anxiety, hypotension, low UO Nursing action: if symptomatic Document rhythm & notify MD Apply O2 Treat underlying cause May consider vagal maneuver cough, bear down, blow through straw try blowing plunger off the syringe

Mechanism: reflux vagal tone inhibition associated with respiration. (rate increases with inspiration & drops with exhalation) 4.

ECG characteristics: Rhythm: irregular Others: All normal

Sinus ArrhythmiaEtiology: Normal phenomenon with inspiration (esp, in infant) Digitalis toxicity, MI, increased ICP Fever, anxiety, shock Nursing action: Document rhythm & notify MD if symptomatic No treatment

Mechanism: Signal to SA node is not generated or it fails to leave the SA node5.

Sinus pause / block - Basic rhythm resumes after a pause ECG Characteristics: Rhythm: irreg Rate: normal or < 60 Other waves: Normal except during pause or arrest

Sinus arrest basic rhythm does not resume after a pause6.

Sinus pause/arrest/block Etiology: High vagal tone or increased vagal stimulation Drug toxicity (esp. digoxin) MI, s/p cardiac surgery, SA node trauma lupus, metabolic disorders Clinical signs: If HR is 10 PACs = CHF Palpitations

Nursing Action: Document Treat underlying cause

AF Mechanism: Atrial quiver with ventricular response (> 100 = RVR (rapid) / 60 =100 CVR (controlled)) blood clots


ECG Characteristics: Rhythm: irreg Rate: Atria: 350-600 / Ventricle: varies P wave: none ( F wave) QRS comp: Normal Others: not measurable

Atrial Fibrillation Etiology: Atrial enlargement due to AV valve disorders Hpn, CAD, COPD, CHF, MI Hypoxia, drugs, digitoxicity, tobacco Clinical signs: Irregular pulse, palpitation, anxiety, SOB CHF

shock Nursing Action: Document rhythm & inform MD Apply O2 Possible Synchronize cardioversion Anticoagulant therapy

Mechanism: Extremely rapid atrial rate (saw-tooth configuration)9.

ECG characteristics: Rhythm: irreg / regular Rate: Atria: 250-350 / ventricle: varies QRS comp: Normal Others: not measurable

Atrial Flutter Etiology: Related to underlying heart disease Hyperthyroidism, alcoholism Clinical signs: decreased CO hypotension, mental status change,

fatigue, CHF, SOB Nursing Action if symptomatic: Document rhythm & notify MD Apply O2 Vagal maneuver If tachycardic consider synchronize cardioversion

PAT / SVT Mechanism: impulse originate above the ventricle, due to rapid

rate loss of atrial kick


ECG characteristics: Rhythm: regular Rate: 140 250 bpm P wave: hidden in T wave QRS comp: normal PRI: not measurable

Paroxysmal Atrial tachycardia (PAT) / Supraventricular tachycardia Etiology

Heart diseases, emotional stress Regular atrial rhythm Digitalis toxicity Clinical sign: loss of atrial kick decrease CO

decreased perfusion myocardia ischemia Nursing Action: Treat the cause Valsalva maneuver or carotid massage


Junctional rhythm / junctional escape rhythm Mechanism: Rhythm originate from AV junctional tissue (maybe an escape rhythm, enhanced automaticity of the AV node that override the SA node)


ECG characteristics: Rate: 40 60 bpm P wave: inverted or none or retrograde PRI: shortened QRS comp: normal Others normal unless distorted by the P wave

Accelerated junctional rhythm:12.

Rate: 61 100 bpm Nursing action: same as junctional rhytm

Junctional tachycardia13.

Rate: 101 180 bpm