Normal measurements:PR Interval: 0.12 – 0.20 sec.QRS complex: less than 0.12 sec.QT interval: less than ½ the distance between two consecutive R waves

Representation of cardiac activity on the ECG:P wave = atrial depolarizationQRS complex= ventricular depolarizationST segment = early repolarization of the ventriclesT wave = later stages of ventricular repolarization.

Label ECG tracing w/P,Q,R, S, T and U

Cardiac Conduction Pathway

Label SA node, AV node, bundle of His, bundle branches and Purkinje fibers

SA node= 60-100 beats/minAV node= 40-60 beats/minBundle of His= 40-60 beats/minPurkinje fibers= 20-40 beats/min

The ECG Tracing

label PR Inteval, QRS complex, ST segment and QT interval

ECG Monitoring – Reference Guide

Location Inscription Color

Right Arm RA White Left Arm LA Black Right Leg RL Green Left Leg LL Red

Chest V1 Brown

Lead placement mnemonic:White is right.Snow over trees (white over green).Smoke over fire (black over red).Chocolate (brown) is close to the heart.

Area LeadLateral I, AVL (high lateral)

V5, V6 (low lateral)

Inferior Wall II, III, AVF.Anterior Wall V1-V4/ V2-V4Septum V1, V2.

View of the heart provided by each lead:264

Lead placement for 5 lead ECGs

American Heart Association’s standard color coding for ECG leads

ECG Monitoring – Guide to Leads

The Six-Second MethodThis method can be used to easily measure the heart rate in non-regular rhythms. To calculate the ventricular rate, simply count the number of QRS complexes in a 6 second strip and multiply by 10. To calculate the atrial rate, count the P waves instead of the QRS complexes.

The Small Box MethodCount the small boxes between two sequential R waves (for the ventricular rate) or two sequential P waves (for the atrial rate). Divide this number into 1500 to obtain the rate.

The Square Counting, or Sequence, MethodThe square counting method can be used for regular heart rhythms. First, find an R wave that falls on a thick line. The next thick lines will be counted as follows: 300, 150, 100, 75, 60, 50, 43, 37. Stop the sequence at the next R wave. If the second R wave falls between two thick lines, use the mean of the two numbers (for example, if the R wave falls between 150 and 100, the rate would be 125)

The Large Box MethodFor this method, count the number of large boxes between two sequential R or P waves. Divide this number into 300 to obtain the rate.

ECG Monitoring – 5 Step Analysis

Step 2: Calculating the heart rate

Step 1: Assess the regularity of the rhythm

Are the P waves (for atrial rhythm) or the R waves (for ventricular rhythm) consistently equidistant from each other?

If there is a variation of more than 3 small boxes (0.12 seconds), the rhythm is considered irregular.

The P wave represents atrial depolarization. An absent P wave indicates that the electrical impulse is being generated from somewhere other than the SA node. An inverted P wave can be seen with ectopic atrial and junctional rhythms.

Peaked P waves may be seen with right atrial enlargement, usually due to pulmonary hypertension

Notched P waves can be seen with left atrial enlargement, usually due to mitral stenosis. (#2b) Variable P waves are indicative of multifocal atrial rhythms (meaning multiple sites within the atrium or AV junction are acting as ectopic pacemakers).

The PR interval reflects the total time it takes for the electrical impulse to travel from the SA node through the AV node into the ventricles. A shortened PR interval (> 0.12 seconds) can indicate a junctional rhythm where the impulse originates in the AV junction, or an abnormal conduction pathway. A prolonged PR interval indicates that the impulse is being delayed before entering the ventricles. This is called first degree block and can be caused by myocarditis, acute myocardial infarction, hyperkalemia, medication effects, AV septal defects and enhanced vagal tone. A variable PR interval can indicate a wandering atrial pacemaker, Wenckebach rhythm (2nd degree Mobitz Type I), 3rd degree (complete ) AV block.

The fifth step is to assess the QRS complex. The QRS complex represents ventricular depolarization.As with the PR interval, the QRS complex needs to be assessed for both duration (width) and consistency. The QRS can be classified as narrow (<0.10 sec) or wide (>0.12 sec). An abnormally wide QRS complex can indicate a delay or abnormality in conduction through the ventricle. Causes of wide QRS complexes can include bundle branch blocks, Wolff-Parkinson White syndrome, hyperkalemia, medication effects, and ventricular tachycardia, fibrillation or ectopic beats.

Additional Assessments: The T wave & the QT interval The T wave represents ventricular repolarization. It usually deflects upright in all leads except aVR and V1. Assess the T wave for abnormalities in shape or consistency and for inversion in leads where it normally is upright. T wave abnormalities may be seen with myocardial ischemia or infarction, bundle branch blocks, pulmonary embolism, electrolyte imbalances and ventricular hypertrophy, among other conditions.

The QT interval represents the total time for ventricular depolarization and repolarization. Abnormalities in the QT interval can indicate risk for serious ventricular arrhythmias. Prolonged QT intervals can also be caused by medication effects, hypocalcemia, myocarditis and CNS lesions.

ECG Monitoring – 5 Step Analysis3rd Step: Assessment of the P waves

4th Step: Assessment of the PR interval

5th Step: Assessment of the QRS Complex

Normal Sinus RhythmRate: 60-100 beats per minute (BPM)Rhythm: RegularP waves: upright, normal shape, consistent, one before each QRS complexPR interval: 0.12 – 0.20 seconds (normal)QRS: 0.10 seconds or less

Sinus Bradycardia

Show strips from module

Rate less than 60 BPMCan result in decreased cardiac output

Causes : medication effects (calcium channel blockers, digoxin, beta blockers), increased vagal tonesinus node disease, hypothyroidism, hypothermia, ischemia, increased intracranial pressureTreatments: atropine (drug of choice), epinephrine or dopamine, transcutaneous of tranvenous pacing

Sinus Tachycardia Rate usually 100-160 bpm

Causes: increased activity, fever, anxiety/fear, pain, infection, hypoxia, acute MI, hypovolemia,medication effects (epinephrine, atropine), stimulants (caffeine, nicotine, or cocaine), CHFTreatment: Treat the underlying cause.

Sinus Arrhythmia Rate usually 60-100 bpm but may be faster or slowerRhythm is irregular (shortened R-R intervals during inspiration, lengthened during expiration)

There is not usually any treatment required for sinus arrhythmia.. If significant sinus brady-dysrhythmia occurs and patient is symptomatic, treat for sinus bradycardia.

Sinus Rhythms

ECG MonitoringArrhythmia Review

Sinoatrial Block Rate is usually normal but will decrease with pausesRhythm is irregular

Causes: SA node disease, acute MI, medication effects (digoxin, quinidine, procainamide), CAD,myocarditis, CHF, increased vagal tone or stimulation.Treatment: treatment is the same for symptomatic bradycardia, if present.

Sinus Pause/ Arrest Rate is usually normal but will decrease with pausesRhythm is irregular

Causes: SA node disease, acute MI, medication effects (digoxin, quinidine, procainamide), myocarditis, hyperkalemia, increased vagal tone or stimulation.Treatment: treatment is the same for symptomatic bradycardia, if present.

Sinus Rhythms (continued)

ECG MonitoringArrhythmia Review

Atrial RhythmsPremature Atrial Contractions (PACs) Rate is variable, depending on underlying rhythm

Rhythm will be irregular at point of PACsPremature P waves will be different than sinus P waves , but vary depending on site

Causes : hypokalemia, hypomagnesemia, anxiety, stimulants (caffeine, tobacco or alcohol),digitalis toxicity, and myocardial ischemia or injury.Treatment: not usually required if PACs are infrequent; treat underlying cause

Ectopic Atrial RhythmsRate is less than 100 bpmRegular rhythmP waves are different than sinus P waves , but will depending on site; may be inverted

Causes : same as PACs.Treatment: not usually required.

Wandering Atrial Pacemaker Rate is less than 100 bpmIrregular rhythmAt least three different morphologies of P waves (all vary from sinus P waves)

Causes: digitalis toxicity, acute rheumatic fever, asthma, COPD, SA node disease, atrial hypertrophy and acute MI.Treatment: does not usually require treatment.

Multifocal atrial tachycardia Rate is greater than 100 bpmIrregular rhythmAt least three different morphologies of P waves (all vary from sinus P waves)

Causes: COPD, CHF, and hypoxia.Treatment: treat the underlying disorder.

Atrial Flutter Atrial rate is 250-350 bpm; ventricular rate is variable.Saw-toothed flutter waves (no regular P waves)

Causes: stimulants (alcohol, nicotine, etc.), stress, fatigue, electrolyte imbalances, acute MI, ischemic heart disease, valvular disease, pulmonary embolism, digitalis or quinidine toxicity. It can also occur following open-heart surgery.Treatment: may include: cardioversion, calcium-channel blockers, beta-blockers, digoxin, warfarin (to prevent emboli)

Atrial Fibrillation Atrial rate is usually >350-400 bpm; ventricular rate is variableFibrillatory waves (no regular P waves)

Causes: stimulants (alcohol, nicotine, etc.), stress, fatigue, electrolyte imbalances, acute MI, open- heart surgery, ischemic heart disease, valvular disease, and hypertension.

Treatments : cardioversion, calcium-channel blockers, beta-blockers, digoxin, warfarin (to prevent emboli)

Atrioventricular Nodal Reentrant Tachycardia (AVNRT) Rate is 150-250 bpmP waves may be hidden in QRS or may appear a pseudo S or R wave

In AVNRT, reentry is due to the presence of both a fast and slow pathway within the AV node that can allow the electrical impulse to reverse direction and generate another heartbeat.Treatments: Vagal maneuvers are the initial treatment for stable AVNRT.If vagal maneuvers are unsuccessful, adenosine may be administered.

Atrial Rhythms (continued)

ECG MonitoringArrhythmia Review

Premature Junctional Complexes Rate depends on underlying rhythmRegular rhythm with premature beatsP waves may be before, after or hidden in QRS; if visible, inverted in leads II, III and aVF.

Causes: stimulants (caffeine, tobacco, alcohol), electrolyte imbalance, heart disease, ischemia or MI, hypoxia, digitalis toxicity and sinus node dysfunction.Treatments: no treatment is usually necessary; treat the underlying cause.

Junctional Escape Beats & Rhythms Junctional escape rhythm is comprised of three or more junctional escape beats in a row.Rate is 40-60 bpmP waves may be before, after or hidden in QRS;if visible, inverted in leads II, III and aVF. Causes: heart disease, acute MI, hypoxia, sinus node dysfunction, cardiac surgery and with certain medications (digitalis toxicity, beta-blockers, calcium-channel blockers).Treatment: if infrequent, treatment may not be necessary. If patient is symptomatic, may include atropine, pacing, or digibind (if related to digitalis toxicity).

Accelerated Junctional Rhythms & Junctional Tachycardia Rate is 60-100 for accelerated junctional rhythm; 100-150 for junctional tachycardiaP waves may be before, after or hidden in QRS;if visible, inverted in leads II, III and aVF.

Causes: electrolyte imbalances, digitalis toxicity, ischemia, MI and myocarditis.Treatment: depends on severity of symptoms; may include vagal maneuvers, adenosine, digibind (if related to digitalis toxicity), antiarrhythmics, pacing or ablation therapy.

Junctional Arrhythmias

ECG MonitoringArrhythmia Review

Premature Ventricular Complexes (PVCs) *Frequent PVCs (more than 6 per minute) can be life threatening.

Rate depends on underlying rhythmRegular rhythm with premature beatsNo P waves with PVCWide, abnormal QRS ; T wave is usually in opposite direction of QRS complex.

Causes: stimulants (caffeine, nicotine, alcohol), stress, and fatigue, ischemia, MI,CHF, electrolyte imbalance, acid-base imbalance, digitalis toxicity, and medication effects (sympathomimetics, beta-agonists, tricyclic antidepressants).Treatments: based on the cause and the patient’s symptoms.

Idioventricular rhythms (IVR) Idioventricular rhythms are composed of 3 or more continuous ventricular escape beats.Ventricular rate is 20-40 bpm (atrial rate not discernible)No P wavesWide, abnormal QRS ; T wave is usually in opposite direction of QRS complex.

Causes: electrolyte imbalances, digitalis toxicity, myocardial ischemia or injury, and cardiomyopathy.Treatment: increase heart rate, may require transcutaneous pacing, atropine

Accelerated Idioventricular Rhythm (AIVR) Ventricular rate is 40-100 bpm (atrial rate not discernible)No p wavesWide, abnormal QRS complex; T wave is usually in opposite direction of QRS complex.

Causes: digitalis toxicity, MI, myocardial ischemia or injury, and cardiomyopathy.Treatment: if unstable, cardioversion or pacing may be needed.

Ventricular Rhythms

ECG MonitoringArrhythmia Review

Ventricular Tachycardia*Life threatening arrhythmia

Ventricular rate 100-250 bpm (atrial rate not discernible)P waves may or may not be present; not associated with QRS complexWide, abnormal QRS complex

Causes : electrolyte imbalance, acid-base imbalance, myocardial ischemia or infarction, drug toxicity (digitalis, other antiarrhythmics), cardiomyopathy, infection (myocarditis, Chagas disease), CNS stimulants (cocaine, amphetamines)Treatment: If the patient is symptomatic and has palpable pulses, cardioversion is the treatment of choice. If the patient does not have palpable pulses, immediate defibrillation is required.

Torsades de pointes*Life threatening arrhythmia

Ventricular rate 150-250 bpm (atrial rate not discernible)No P wavesWide, abnormal QRS complexChanges in QRS shape, amplitude (height) and width

Causes: conditions associated with prolonged QT interval , including medications (quinidine and procainamide, among others) and electrolyte imbalances (hypokalemia, hypomagnesia, hypocalcemia).

Treatment : address the cause of the prolonged QT interval. Unstable patients should be treated with defibrillation.

Ventricular fibrillation*Life threatening arrhythmia

No discernible rateChaotic, rapid, irregular rhythmNo discernible P waves or QRS complexes

Causes: myocardial ischemia or infarction, electrolyte imbalance, cardiomyopathy, hypoxia, congenital conditions, electrocution, untreated ventricular tachycardia, R-on-T PVCs.Treatment: Unless advanced life support is started immediately, ventricular fibrillation is a fatal rhythm. VF requires defibrillation as soon as possible. Vasopressors (epinephrine, vasopressin) and antiarrhythmics (amiodarone) may also be used – follow current ACLS protocol.

Ventricular Rhythms (continued)

ECG MonitoringArrhythmia Review

First Degree Atrioventricular (AV) Block PR interval >0.20 secondsCauses: acute MI,medication effects (digitalis, calcium channel blockers, beta-blockers, among others), electrolyte imbalances, myocarditis, AV node diseaseTreatments: usually no treatment needed for first-degree AV block.

Second Degree Atrioventricular (AV) Block, Mobitz Type 1 PR interval lengthens after each P wave until QRS is eventually dropped, then cycle starts again

Causes: acute MI,medication effects (digitalis, calcium channel blockers, beta-blockers, among others), electrolyte imbalances, myocarditis, AV node diseaseTreatments: usually no treatment needed.

Second-Degree Atrioventricular (AV) block, Mobitz Type II Impulses intermittently blocked resulting in dropped QRS complexesP waves occur at consistent intervals

Causes: anteroseptal MI, structural heart disease ,cardiac surgery, medication effects , infiltrative conditions , inflammatory conditions , autoimmune conditions , hyperkalemiaTreatment: temporary pacing until a permanent pacemaker can be placed.

Mobitz type II is a more serious condition than type I and can rapidly progress to third-degree heart block.

Third-degree Atrioventricular (AV) block Atrial impulse are not conducted to the ventricles. Secondary pacemaker in the AV node or below pace s the ventricles.No correlation between P waves and QRS complexes.QRS will be narrow if secondary pacemaker is junctional, wide if it is ventricular.

Causes: same as second-degree AV blockTreatment: most patients will require placement of a permanent pacemaker.

ECG MonitoringArrhythmia Review

Atrioventricular Blocks

Pulseless Electrical ActivityPulseless electrical activity (PEA) is not a specific arrhythmia, but occurs when an organized rhythm is seen on the ECG tracing but ventricular contraction does not occur and, therefore, the patient is pulseless.

Show strip from module

Pulseless electrical activity can present as various rhythms on the ECG tracing, including sinus rhythm, bradycardias and tachycardia.

Pacemakers

Pacemakers can pace either the atria or the ventricles (single chamber pacemakers) or both (dual chamber pacemakers). • In atrial pacing, a spike will be seen prior to the P wave.• In ventricular pacing, a spike will be seen before the QRS

complex. • Spikes before the P wave and QRS complex will be present

when the patient has a dual chamber pacemaker.

Pacemaker Problems Notable on the ECG

Failure to pace Absence of pacemaker spikes when the patient’s heart rate is below the pacemaker rate.

Failure to capture Pacemaker spikes will be seen on the ECG but they will not be followed by a P wave (in atrial pacing) or a QRS complex (in ventricular pacing).

Failure to sense The pacemaker spike will be seen in an inappropriate place on the ECG (for example, after or near a QRS complex in ventricular pacing).

Show pacemaker strips from module

ECG MonitoringArrhythmia Review