BASIC ECG INTERPRETATION

Electrophysiology The cardiac cell has 2 primary electrolytes: Sodium (Na+) and Potassium (K+).

Resting cardiac cell (K+) is mostly on the inside, while (Na+) is mostly on the outside of the cell. Sodium has a stronger charge than potassium making the outside of the cell more positive that the inside. Positive and negative charges are balanced in a resting state which equals no electrical charges = polarized state. Cells are able to modify their membrane and pull sodium into the cell while potassium exits the cell. Resulting in the initiation of electrical flow = Sodium Pump.

Polarization – The phase of readiness; the muscle is relaxed and the cardiac cells are ready to receive an electrical impulse

Depolarization – The phase of contractions; the cardiac cells have transmitted an electrical impulse, causing the to contract

Repolarization – The recovery phase; the muscle has contracted and the cells are returning to a ready state.

Conduction System

1. Sinoatrial (SA) Node 2. Intraatrial Pathway 3. Intranodal Pathway 4. Atrioventricular(AV) junction 5. Bundle of His 6. Left Bundle Branch 7. Right Bundle Branch 8. Purkinje Fibers

Inherent Rates

SA Node 60-100 BPM

AV Junction 40-60 BPM

Ventricle 20-40- BPM Nervous System Influence

Sympathetic – Affects the atria and the ventricles

Increases:  Heart Rate  Conduction  Irritability

Parasympathetic- Affects the atria

Decreases:  Heart Rate  Conduction  Irritability

Irritability is when a site speeds up and takes over as the pacemaker.

Measurements

If electricity flows toward the (+) electrode, the pattern will be upright. If electricity flows toward the (-) electrode, the pattern will be downward.

Graph Paper Measurements

One large box = .20 sec One small box = .04 sec One small box vertical = 1 mm

When properly calibrated a 1 Millivolt will produce a defection measuring 10 mm tall.

Waves

P Wave

 Usually the first wave form  Originates in the SA node  Stimulates the Right  Reaches AV node  Downslope of the P wave reflects stimulation of Left Atrium

Normal Characteristics  Smooth and rounded  From beginning of P wave to beginning of QRS complex  Includes P wave and PR segment  Normal duration: 0.12 to 0.20 second  No more than 2.5 mm in height  No more than .11 second in duration  (+) in Leads I,II, aVF and v2-v6

Abnormal Characteristics

Tall, Pointed, wide, notched P wave may reflect COPD, CHF, valvular disease, atrial enlargement

QRS Complex QRS Complex represents ventricular depolarization.

Q Wave Always negative waveform, 1st negative wave after P wave. Depolarization of interventricular septum Normal  Less than .04 sec in duration  Less thatn1/3 the height of R wave Abnormal  More than .04 sec  More than 1/3 height of R wave

R Wave 1st positive wave following P wave

S Wave Negative waveform following R Wave RS – Depolarization of right and left ventricle If a QRS complex is entirely positive it is considered an R wave. If the QRS complex is entirely negative it is considered a QS wave. If there are 2 positive deflections in the same complex the 2nd is called R prime written R1 . If there are 2 negative deflections in the same complex following a R wave it is called S prime, written S1 QRS Duration = .08 - .12 second

Abnormal QRS Complex QRS measuring .10-.12 second can be considered incomplete BBB

T Wave Ventricular Repolarization

Beginning of the is the absolute Refractory time

Normal • Asymmetric • Direction of T wave normally direction as the QRS wave that precedes it. • Usually 5 mm or less in height in the limb lead • Usually 10 mm or less in precordial leads • Usually .5 mm or more in height in leads I and II

Abnormal • Opposite direction of the preceding QRS complex • Negative T wave suggests MI • Tall, pointed – Hyperkalemia • Low amplitude T wave – hypokalemic • Deep and inverted is associated with cerebral disease U Wave The U wave follows the T wave. It suggests repolarization of the purkinje fibers. It is usually round, small and less than 1.5 mm. Easily seen when the heart rate is slow. They are usually tallest in V2 and V3. They appear in the same direction as the T wave that precedes it.

Tall U Wave Causes • Electrolyte imbalance – hypokalemia • Medications: quinidine, procainamide, amiodarone, digitalis • Hyperthyroidism • Central nervous system disease • Long QT syndrome

Negative U Wave • Suggestive of organic Heart disease • Patients with ischemic heart disease

Segments

PR Segment • Represents activation of the AV node, Bundle of His, Bundle Branches and Purkinje Fibers. • Atrial repolarization occurs during this time. • PR Segment may be depressed in the presence of or chronic pulmonary disease. • Anything >0.8 mm is pathological

ST Segment • Represents early part of repolarization of the right and left ventricles. • ST segment depression suggest • ST segment elevation suggest injury • Other causes of ST segment elevation may suggest , ventricular aneurysm • ST segment elevation with concavity is usually benign. • ST segment elevation with coved is called an acute injury pattern. • Digitalis cases a depression (scoop) of the ST segment

J Point The point where the QRS complexes and the ST segment meet is called the Junction (J Point). Look at the point where the end of the QRS complex makes a sudden sharp change in direction

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Intervals

PRI • From beginning of P wave to beginning of QRS complex • Includes P wave and PR segment • Reflects depolarization of the right and the left atria. • Normally shortens as heart rate increases • Normally lengthens as heart rate decreases • Measures 0.12 – 0.20 second

Causes of Abnormal PRI • Patients taking beta-blockers or calcium channel blockers • 1st degree AV block • Hypothyroidism • Digitalis toxicity • Less than 0.12 second, impulse originates in an ectopic pacemaker in the atria close to the AV node or in the AV junction.

QT Interval • Represents total ventricular activity. Depolarization to repolarization. • Measured from beginning of QRS to end of T wave. • A QT interval that is more than half the R-R interval is considered prolonged • QT intervals may be caused by electrolyte disorders and medications • Generally not considered abnormal unless the QT interval corrected for the heart rate exceeds 0.44 second

R-R and P-P Intervals • Used to determine the rate and regularity of a cardiac rhythm. • R-R intervals is used to determine ventricular rhythm regularity • P-P intervals are used to determine atria rhythm regularity.

Analyzing a Rhythm Strip

Assess the Rate Method 1: Six Second Method – Take a 6 second strip and multiply by 10 to find the number of complexes in a minute.

Method 2: Large Boxes – Count the number of large boxes between two consecutive R waves (R-R interval) and divide into 300.

Method 3: Small Boxes – Count the number of small boxes between two consecutive R waves and divide into 1500 Method 4: Sequence Method – Select an R wave that falls on a dark vertical line. Number the next 6 consecutive dark vertical lines as follows: 300, 150, 100, 75, 60, and 50. Note where the R wave falls in relation to the 6 dark vertical lines already marked.

Assess Rhythm/Regularity Ventricular Rhythm – measure the distance between two consecutive R-R intervals.

Atrial Rhythm – Measure the distance between two consecutive P-P intervals.

If the variation between the shortest and longest R-R intervals (P-P intervals) is less than four small boxes (0.16) the rhythm is termed essentially regular. This is usually due to ectopic beats. If the intervals vary by more than 0.16 second, the rhythm is considered to be regularly irregular.

Identify and Examine P Wave • Do all the P waves look the same in size, shape and position? • If no P wave is present the rhythm originated in the AV junction or the ventricles • If the P wave is positive the rhythm probably begins in the SA node. • If the P wave is negative or absent and the QRS is regular, the rhythm probably started in the AV junction

Assess Intervals (Evaluate Conduction) PRI – Normal PR interval is 0.12 – 0.20 second

QRS Duration – Normal is 0.08 – 0.12 second

QT Interval – If the QT interval is less than half the R-R interval it is probable normal.

Evaluate the overall Appearances of the Rhythm ST Segment – Determine the presence of elevation or depression.

T Wave – Are the T waves upright and of normal height? The T wave following an abnormal QRS complex is usually opposite in direction of the QRS. Negative T wave would suggest ischemia. Tall, pointed T waves are commonly seen in hyperkalemia.

Sinus Rhythms

Rhythm that begins in the SA node has the following characteristics:  A positive P wave before each QRS complex  P waves that look alike  A constant PR interval  A regular atrial and ventricular rhythm

An electrical impulse that beings in the SA node may be affected by the following  Medications  Diseases or conditions that cause the heart rate to speed up, slow down or beat irregularly  Diseases or condition that delay or block the impulse from leaving the SA node  Diseases or conditions that prevent an impulse from being generated in the SA node

Characteristics of Sinus Rhythm: Rate 60-100 BPM Rhythm P-P interval regular, R-R interval regular P Wave Positive in lead II, on precedes each QRS complex, P waves look alike PR duration 0.12-0.20 second and constant from beat to beat QRS duration 0.12 second or less unless an intraventricular conduction delay exists

Sinus

Characteristics of : Rate Less than 60 BPM Rhythm P-P interval regular, R-r interval regular P Waves Positive in lead II, one precedes each QRS complex, P waves look alike PR Interval 0.12-0.20 second and constant from beat to beat QRS Duration 0.12 second or less unless an intraventricular conduction delay exists

Causes of Sinus Bradycardia:  Inferior, Posterior MI  Disease of the SA node  Vagal stimulation  Hypoxia  Hypothermia  Increased intracranial pressure  Hypothyroidism  Hypokalemia  Post heart transplant  Obstructive sleep apnea  Medications; calcium channel blockers, digitalis, beta blockers, amiodarone, sotalol

Signs and Symptoms of Hemodynamic Compromise:  AMS  Signs of Shock  Low BP  CHF/ Pulmonary congestion  CP  Cold, clammy skin  SOB  Fall in urine output Sinus

Characteristics of Rate 101-180 BPM Rhythm P-P interval regular, R-R interval regular P Wave Positive in lead II, one precedes each QRS complex, P waves look alike PR Interval 0.12.-0.20 second (may shorten with faster rate) constant from beat to beat QRS Duration 0.12 second or less unless an intraventricular conduction delay exists

Causes of Sinus Tachycardia  Exercise  Hyperthyroidism  Fever  Caffeine-containing beverages  Pain  Nicotine  Fear and anxiety  Medications; epinephrine, atropine,  Hypoxia dopamine, dobutamine  Congestive  Drugs: cocaine, amphetamines,  Acute “ecstasy”, cannabis  Infection

 Sympathetic stimulation  Shock  Dehydration, hypovolemic

 Pulmonary embolism

Sinus Sinus arrhythmia is when the SA node fires irregularly. Sinus arrhythmia can be associated with the phase of respiration. It occurs with changes in intrathoracic pressure. Most commonly seen in patients under the age of 30. Non-respiratory sinus arrhythmia is common after acute inferior wall MI and with increased intracranial pressure. Medications such as digitalis and morphine can also cause sinus .

Sinoatrial Block The pacemaker cells within the SA node initiate an impulse but it is blocked as it exits the SA node.

Characteristics of Rate Usually normal but varies because of the pause Rhythm Irregular due to the pause caused by the SA block P Wave Positive in lead II, P waves look alike PR Interval 0.12-0.20 second and constant from beat to beat QRS Duration 0.12 second or less unless an intraventricular conduction delay exists

Causes of SA Block  Acute MI   Congestive Heart Failure  Carotid Sinus sensitivity  Increased vagal tone

Sinus Arrest Sinus arrest is a disorder of the property of automaticity. The pacemaker cells of the SA node fail to initiate an electrical impulse for one or more beats.

Characteristics of Sinus Arrest Rate Usually normal but varies because of the pause Rhythm Irregular – the pause is of undetermined length and is not the same distance as other P-P intervals. P Waves Positive in lead II, P waves look alike. PR Interval 0.12-0.20 second and constant from beat to beat QRS Duration 0.12 second or less unless an intraventricular conduction delay exists

Causes of Sinus Arrest  Hypoxia  Myocardial ischemia or infarction  Hyperkalemia  Digitalis toxicity  Reactions to medications; beta blocker, calcium channel blockers  Carotid sinus sensitivity  Increased vagal tone  Hemodynamic compromise; weakness, lightheadedness, dizziness, syncope

Atrial Rhythms

Atrial Dysrhythmia: Mechanisms

Altered automaticity occurs in normal pacemaker cells and in myocardial working cells that do not normally function as pacemaker sites

Causes of Altered Automaticity  Ischemia  Drug toxicity  Hypocalcemia  Imbalance of electrolytes across the cardiac cell membranes

Triggered Activity results from abnormal electrical impulses that sometimes occur during repolarization when cells are normally quiet.

Causes of Triggered Activity  Hypoxia  Catecholamine increase  Hypomagnesemia  Myocardial ischemia and injury  Medications that prolong repolarization

Reentry is a condition in which an impulse returns to stimulate tissue that was previously depolarized.

Reentry Requires  A potential conduction circuit or circular conduction pathway  A block within part of the circuit  Delayed conduction within the remainder of the circuit

Common Causes of Reentry  Hyperkalemia  Myocardial ischemia  Some antiarrhythmic medications

Premature Atrial Complexes Premature Atrial Complexes (PACs) Premature Junctional Complexes (PJCs) Premature Ventricular Complexes (PVCs)

Premature Atrial Complexes

PACs occurs when an irritable site with the atria fires before the next SA node impulse is due to fire.

PACs are identified by:  Early P waves  Positive P waves that differ in shape from sinus P waves  Early P waves that may or may not be followed by a QRS complex

Characteristics of PACs Rate Usually within normal range, depends on underlying rhythm Rhythm Regular with premature beats P Waves Premature, positive in lead II, one before each QRS complex, often differ in shape from sinus P waves – may be flattened, notched, pointed biphasic PR Interval May be normal or prolonged depending on the prematurity of the beat QRS Duration Usually 0.12 second or less but may be wide (aberrant) or absent, depending on the prematurity of the beat.

Noncompensatory Verses Compensatory Pause Non compensatory (incomplete) pause often follows a PAC. The SA node resets its rhythm for the next beat. A compensatory (complete) pause often follows premature ventricular complexes (PVCs).

Aberrantly Conducted PACs PACs associated with a wide QRS complex. This indicates that conduction through the ventricles is abnormal

PACs: Patterns  Pairs (coupled): Two PACs in a row  Runs – Three or more PACs in a row; often called paroxysmal or paroxysmal supraventricular tachycardia  Atrial : Every other beat is a PAC  Atrial Trigeminy: Every third beat is a PAC  Atrial Quadrigeminy: Every fourth beat is a PAC

Causes of PACs  Emotional Stress  Digitalis toxicity  CHF  Electrolyte imbalance  Acute coronary syndromes  Hyperthyroidism  Mental and physical fatigue  Stimulants: caffeine, tobacco,  Atrial enlargement cocaine 

Wandering Atrial Pacemaker Multiformed atrial rhythm is the new term for wandering atrial pacemaker. The P wave varies in size, shape and direction.

Characteristics of Wandering Atrial Pacemaker Rate Usually 60-100 BPM Rhythm May be irregular as the pacemaker site shifts from the SA node to ectopic atrial locations and the AV junction P Wave Size, shape and direction may change from beat to beat. Must have at least 3 different looking P waves for diagnosis PR Interval Variable QRS Duration 0.12 second or less unless an intraventricular conduct6ion delay exists

Causes of Wandering Atrial Pacemaker  Underlying heart disease  Digitalis toxicity  Observed in normal healthy people particularly in athletes.

Multifocal Atrial Tachycardia

MAT is when the wandering atrial pacemaker is associated with a ventricular rate greater than 100 BPM. Do not confuse with atrial . Both rhythms are irregular but P waves are clearly visible in MAT.

Causes of MAT  Severe chronic COPD  Hypoxia  Acute coronary syndromes  Digoxin toxicity  Rheumatic heart disease  Theophylline toxicity  Electrolyte imbalances Supraventricular Tachycardia SVT begins above the bifurcation of the bundle of His.

3 types of SVT  Atrial tachycardia – atria fires automatically at a rapid rate.  AV nodal reentrant tachycardia – The impulse spins around the AV nodal area.  AV reentrant tachycardia – the impulse begins above the ventricles but travels via a pathway other than the AV node and bundle of His.

Atrial Tachycardia Result of altered automaticity or triggered activity. It consists of a series of rapid beats from an irritable site in the atria.

Characteristics of Atrial Tachycardia Rate 100-250 BPM Rhythm Regular P Waves One positive P wave precedes each QRA in lead II; P waves differ in shape from sinus P wave. PR Interval May be shorter or longer than normal QRS Duration 0.12 second or less unless an intraventricular conduction delay exists

Causes of Atrial Tachycardia  Stimulant use; caffeine, albuterol, theophylline, cocaine  Infection  Electrolyte imbalance  Acute illness with excessive catecholamine release  Myocardial infarction

AV Nodal Reentrant Tachycardia (AVNRT) Most common type of SVT. It is caused by reentry in the area of the AV node.

Characteristic of AV Nodal Reentrant Tachycardia (AVNRT) Rate 150-250 BPM Rhythm Ventricular rhythm is usually very regular P Waves P waver are often hidden in the QRS complex. PR Interval P waves are not seen before the QRS complex; therefore the PR interval is not measurable QRS Duration 0.12 second or less unless an intraventricular conduction delay exists. Causes  Hypoxia  Caffeine  Stress  Smoking  Overexertion  Sleep deprivation  Anxiety  Medications

AV Reentrant Tachycardia (AVRT) AVRT involves a pathway of impulse conduction outside the AV node and bundle of His.

3 Preexcitation syndromes

 Wolff Parkinson White (WPW) syndrome – accessory pathway is called the Kent bundle. This bundle connects the atria directly to the ventricles, bypassing the normal conduction. o Short PR with delta wave

 Lown Ganong Levine (LGL) syndrome – the accessory pathway is called the James bundle. This bundle connects the atria directly to the lower portion of the AV node, partially bypassing the AV node. o Short PR without delta wave

 Unnamed Preexcitation syndrome – involved Mahaim fibers. These fibers do not bypass the AV node but originate below the AV node and insert into the ventricular wall. o Normal PR with delta wave

Characteristics of Wolff Parkinson White Syndrome Rate Usually 60-100 BPM Rhythm Regular unless associated with P Waves Normal and positive in lead II unless WPW is associated with Atrial Fibrillation PR Interval If P waves are observed, less than 0.12 second QRS Duration Usually greater than 0.12 second. Slurred upstroke of the QRS complex may be seen in on or more leads.

Atrial Flutter Characteristics of Rate Atrial rate 350-450 BPM, typical 300 BPM ventricular rate variable Rhythm Atrial regular, ventricular regular or irregular depending on AV conduction P Wave No identifiable P waves; saw toothed “flutter” waves are present PR Interval Not measureable QRS Duration 0.12 second or less but may be widened if flutter wave are buried in the QRS complex or an intraventricular conduction delay exists

Conditions Associated with Atrial Flutter  Hypoxia   Pulmonary embolism  Hyperthyroidism  Chronic lung disease  Digitalis or quinidine toxicity  Mitral or stenosis  Cardiac surgery pneumonia ischemic heart disease  Pericarditis/Myocarditis  Complications of myocardial infarction

Atrial Fibrillation Characteristics of Atrial Fibrillation Rate Atrial rate usually 400-600 BPM, ventricular rate variable Rhythm Ventricular rhythm usually irregularly irregular P waves No identifiable P waves, fibrillatory waves present PR interval Not measurable QRS duration 0.12 second or less but may be widened if an intraventricular conduction delay exists

Conditions Associated with Atrial Fibrillation  Hypertension  Chronic lung disease  Ischemic heart disease  Diabetes  Advanced age  Stress  Rheumatic heart disease  Excessive caffeine  Cardiomyopathy CHF  Hypoxia  Congenital heart disease  Hypokalemia  Sick sinus syndrome  Hypoglycemia  WPW pericarditis  Hyperthyroidism  Pulmonary embolism  Electrocution

Junctional Rhythms

Rhythms originating from the AV junction are now called Junctional Dysrhythmias.

Premature Junctional Complexes

PJC occurs when an irritable site within the AV junction fires before the next SA node impulse is due to fire

Characteristics of Premature Junction complexes Rate Usually within normal range Rhythm Regular with premature beats P waves May occur before, during or after the QRS, if visible, the P wave is inverted in leads II, II, aVF PR Interval If a P wave occurs before the QRS, the PR interval will usually be less than 0.12, if no P wave occurs before the QRS there will be no PR interval QRS Duration Usually 0.12 second or less unless it is aberrantly conducted

Causes of PJCs  Congestive heart failure  Digitalis toxicity  Acute coronary syndromes  Electrolyte imbalance  Mental and physical fatigue  Rheumatic heart disease  Valvular heart disease  Stimulants: caffeine, tobacco

Junctional Escape Beats/Rhythm

Characteristic of Junctional Escape Beats Rate Usually within normal range Rhythm Regular with LATE beats P waves May occur before, during or after the QRS, If visible, the P wave is inverted in leads II, III, and aVF. PR Interval If a P wave occurs before the QRS, the PR interval will usually be less 0.12 second, if no P wave occurs before the QRS, there will be no PR interval QRS Duration Usually 0.12 second or less unless it is aberrantly conducted

Causes of Junctional Escape Beats  Acute coronary syndromes  Hypoxia  Rheumatic heart disease  Valvular disease  SA node disease  Increased parasympathetic tone  Immediately after cardiac surgery  Effects of medication; digitalis, quinidine, beta blockers, calcium channel blockers

Characteristics of Junctional Escape Rhythm Rate 40-60 BPM Rhythm Very regular P waves May occur before, during or after the QRS, if visible, the P wave is inverted in leads II, III, aVF. PR interval If a P wave occurs before the QRS, the PR interval will be < 0.12 second QRS Duration Usually 0.12 second or less unless it is aberrantly conducted

Accelerated

Characteristics of Accelerated Junction Rhythm Rate 61-100 BPM Rhythm Very regular P waves May occur before, during or after the QRS, if visible the P wave is inverted in leads II, III, aVF. PR interval If a P wave occurs before the QRS, the PR interval will be < 0.12 second QRS Duration Usually 0.12 second or less unless it is aberrantly conducted

Causes of Accelerated Junction Rhythm  Digitalis toxicity, acute myocardial infarction  Cardiac surgery   COPD  Hypokalemia

Junctional Tachycardia

Characteristics of Rate 101-180 BPM Rhythm Very regular P Waves May occur before during, or after the QRS; if visible, the P wave is inverted in leads II, III and aVF. PR interval If a P wave occurs before the QRS, the PR interval will be < 0.12 second QRS Duration Usually 0.12 second or less unless it is aberrantly conducted

Causes of Junctional Tachycardia   CHF  Theophylline  Digitalis toxicity

Junctional Dysrhythmias at a Glance  Junctional Rhythm 40-60 BPM  Accelerated Junctional Rhythm 61-100 BPM  Junctional Tachycardia 101-180 BPM

Ventricular Rhythms

Premature Ventricular Complexes

Types of PVCs Patterns:  Pairs: Two sequential PVCs  Runs: Three or more PVCs in a row  Bigeminal PVCs: Every other Beat is PVC  Trigeminal PVCs: Every third beat is a PVC  Quadrigeminal PVCs: every Fourth Beat is a PVC

Uniform and Multiform PVCs

If the begin from the same anatomic site they are called uniform PVCs. Multiform look different from one another. They are not necessarily multifocal.

R-on -T PVCs

This occurs when the R wave of the PVC falls on the T wave of the preceding beat.

Characteristics of Premature Ventricular Complexes Rate Usually within normal range Rhythm Essentially regular with premature beats P Waves Usually absent PR interval None with the PVC because the ectopic originates in the ventricle QRS Duration Greater than 0.12 sec, wide and bizarre, T wave usually in opposite direction of the QRS complex

Causes of PVCs  Normal variant  CHF  Hypoxia  Increased sympathetic tone  Stress, anxiety  Acute coronary syndromes  Exercise  Stimulants; caffeine, tobacco  Digitalis toxicity  Medications: sympathomimetic,  Acid base imbalance cyclic antidepressants,  Myocardial ischemia phenothiazine’s  Electrolyte imbalance

Ventricular Escape Beats/Rhythms

Characteristics of Ventricular Escape Beats Rate Usually within normal range Rhythm Essentially regulars with late beats, the ventricular escape beat occurs after the next expected sinus beat P Wave Usually absent or with retrograde conduction to the atria, may appear after the QRS PR Interval None with the ventricular escape beat because the originates in the ventricles QRS Duration Greater than 0.12 second, wide and bizarre, T wave frequently in opposite direction of the QRS complex

A ventricular escape or idioventricular rhythm exists when three or more ventricular escape beats occur in a row at a rate of 20-40 BPM.

Characteristics of Idioventricular Rhythm Rate 20-40 BPM Rhythm Essentially regular P wave Usually absent or with retrograde conduction to the atria, may appear after the QRS PR Interval None QRS Duration Greater than 0.12 second, T wave frequently in opposite direction of the QRS complex

Causes of Idioventricular Rhythm  The SA node and the AV junction fail to initiate an electrical impulse  The rate of discharge of the SA node or AV junction becomes less than the intrinsic rate of the ventricles  Impulses generated by a supraventricular pacemaker site are blocked  Myocardial infarction  Digitalis toxicity  Metabolic imbalances

Accelerated Idioventricular Rhythm

Characteristics of Accelerated Idioventricular Rhythm Rate 41-100 BPM Rhythm Essentially regular P Wave Usually absent or with retrograde conduction to the atria, may appear after the QRS PR Interval None QRS Duration Greater than 0.12 second, T wave frequently in opposite direction of the QRS complex

Causes of Accelerated Idioventricular Rhythm  Digitalis toxicity  Cocaine toxicity  Subarachnoid hemorrhage  Acute myocarditis  Hypertensive heart disease 

Ventricular Tachycardia exists when three or more PVCs occur in a row at a rate greater than 100 BPM.

Monomorphic VT

Characteristics of Monomorphic Ventricular Tachycardia Rate 101-250 Rhythm Essentially regular P Wave May be present or absent, if present, they have no set relationship to the QRS complexes appearing between the QRS’s at a rate different from that of the VT PR Interval None QRS Duration Greater than 0.12 second, often difficult to differentiate between the QRS and T wave Polymorphic VT

Characteristic of Polymorphic Ventricular Tachycardia Rate 150-300 BPM Rhythm May be regular or irregular P Wave None PR Interval None QRS Duration Greater than 0.12 second, gradual alteration in amplitude and direction of the QRS complexes.

Causes of Monomorphic or Polymorphic Ventricular Tachycardia  Acute coronary syndromes  Cardiomyopathy  Tricyclic antidepressant overdose  Digitalis toxicity  Valvular heart disease  Cocaine abuse  prolapse  Acid base imbalance  Trauma; myocardial contusion, invasive cardiac procedures  Electrolyte imbalance; hypokalemia, hyperkalemia, Hypomagnesaemia

Ventricular Fibrillation

Characteristics of Rate Cannot be determined because there are no discernible waves or complexes to measure Rhythm Rapid and chaotic with no pattern or regularity P Waves None PR Interval None QRS Duration None

Causes of Ventricular Fibrillation  Increased sympathetic nervous system activity  Vagal stimulation  Electrolyte imbalance  Antiarrhythmics and other medications  Environmental factors  Hypertrophy  Acute coronary syndromes  Heart failure  Arrhythmias

Asystole (Cardiac Standstill)

Characteristics of Rate Ventricular usually not discernible but atrial activity may be seen Rhythm Ventricular not discernible, atrial may be discernible P Waves Usually not discernible PR Interval Not Measurable QRS Duration Absent

Atrioventricular (AV) Blocks

Classifications of AV Block

Classification by Degree Name of Block First degree AV block Incomplete Second- Degree AV Block Type 1 Incomplete Second – Degree AV Block Type 2 Incomplete Third – Degree AV Block Complete

Classification by Site/Location Site Name of Block AV Node First – Degree AV Block Second – Degree AV Block Type 1 Third – Degree AV Block Infranodal (Subnodal) Second – Degree AV Block Type 2 (uncommon) Bundle of His Third – Degree AV Block Bundle Branches Second – Degree AV Block Type 2 (more common) Third – Degree AV Block

The clinical significance of an AV block depends on the following:  The degree (severity of the block  The rate of the escape pacemaker (junctional vs. ventricular)  The patient’s response to that ventricular rate First – Degree AV Block

Characteristics of First – Degree AV Block Rate Usually within normal range Rhythm Regular P Waves Normal in size and shape, one positive P wave before each QRS in leads II, III and aVF PR Interval Prolonged, greater than 0.20 second but constant QRS Duration Usually 0.12 second or less unless an intraventricular conduction delay exists

Causes of First – Degree AV Block  Ischemia or injury to the AV node or junction  Medications; Quinidine, procainamide, beta blockers, calcium channel blockers, digitalis, amiodarone  Rheumatic heart disease  Hyperkalemia  Acute myocardial infarction (often inferior wall MI)  Increased vagal tone

Second-Degree AV Block Second – Degree AV Block Type 1 (Wenckebach, Mobitz Type 1)

Characteristics of Second – Degree AV Block Type 1 Rate Atrial rate is greater than the ventricular rate Rhythm Atrial regular (P’s plot through time), Ventricular irregular P Wave Normal in size and shape; some p waves are not followed by a QRS complex (more P’s than QRS’s) PR Interval Lengthens with each cycle until a P wave appears without a QRS complex, The PRI after the nonconducted beat is shorter than the interval preceding the nonconducted beat. QRS Duration Usually 0.12 second or less but is periodically dropped

Causes of Second – Degree AV Block Type 1  Right coronary artery supplies the AV node in most of the population.  Parasympathetic tone increases, conduction through the AV node is slowed.

Second – Degree AV Block Type 2 (Mobitz Type II)

Characteristics of Second – Degree AV Block Type 2 Rate Atrial rate is greater than the ventricular rate, ventricular rate is often slow Rhythm Atrial regular (Ps plot through time), ventricular irregular

P Waves Normal in size and shape; some P waves are not followed by a QRS complex (more Ps that QRSs) QRS Duration Usually 0.12 second or greater, periodically absent after P wave

Causes of Second – Degree AV Block Type 2  Bundle branches receive their primary blood supply from the left coronary artery. Disease of the left coronary artery or an anterior MI is usually associated with blocks that occur with the bundle branches.  Acute myocarditis  Organic Heart Disease

Second – Degree AV Block Type 2, 2:1 Conduction (2:1 AV Block)

Characteristics of Second Degree AV Block 2:1 Conduction Rate Atrial rate is twice the ventricular rate Rhythm Atrial regular (p’s plot through time), ventricular regular P Waves Normal in size and shape; every other P wave is flowed by a QRS complex (more Ps that QRSs) PR Interval Constant QRS Duration Within normal limits, if the block occurs above the bundle of HIS (probably type 1); wide if the block occurs below the bundle of His (probably type II) absent after every other p wave.

Third – Degree AV Block

Characteristics of Third Degree AV Block Rate Atrial rate is greater than the ventricular rate; Ventricular rate determined by origin of the escape rhythm Rhythm Atria regular (P’s plot through time), ventricular regular, there is no relationship between the atrial and ventricular rhythms P Waves Normal in size and Shape PR interval None: The atria and ventricles beat independently of each other, thus there is no true PR interval QRS Duration Narrow or wide depending on the location of the escape pacemaker and the condition of the intraventricular conduction system; narrow = junctional pacemaker, wide = ventricular pacemaker Cause of Third Degree AV Block  Inferior MI, third degree AV block often resolves on its own within a week.  Anterior MI, third degree AV block may develop suddenly without warning within 12 -24 hours after the onset of acute ischemia

P Wave and AV Blocks AV Block P Wave Conduction First Degree All P waves conducted by delayed Second Degree Some P waves conducted, others blocked Third Degree No P waves conducted

AV Blocks: Summary Second Degree Type 1 Second Degree Type 2 Ventricular Rhythm Irregular Irregular PR Interval Progressively Lengthening Constant QRS Width Usually narrow Usually wide Second Degree 2:1 Third Degree (complete) Block Conduction Ventricular Rhythm Regular Regular PR Interval Constant None – No relationship between P waves and QRS complexes QRS Width May be narrow or wide May be narrow or wide

References:

ECGs Made Easy by Barbara Aehlert, RN BSPA 12 Lead ECG for Acute and Critical Care Providers by Bob Page Introduction to Basic Cardiac Dysrhythmias 3rd Edition Basic Arrhythmias 6th Edition by Gail Walraven 12 Lead ECG The Art of Interpretation