Alfrin Ecg

ECGs MADE EASY NORMAL ECG

ELECTROCARDIOGRAM

The electrocardiogram (ECG) is a graphic recording of the electrical potentials produced by the cardiac tissue. – Electrical impulse formation occurs within the conduction system of the heart. – Excitation of the muscle fibers throughout the myocardium results in cardiac contraction.

The ECG is recorded by applying electrodes to various locations on the body surface and connecting them to a recording apparatus.

ELECTROCARDIOGRAM

Clinical Value of the ECG – – – – – – –

Atrial and ventricular hypertrophy Myocardial ischemia and infarction Pericarditis Systemic diseases that affect the heart Determination of the effect of cardiac drugs Disturbances in electrolyte balance Evaluation of function of cardiac pacemakers

ELECTROCARDIOGRAM

Considerable diagnostic value – Conduction delay of atrial and ventricular electrical impulses – Determination of the origin and behavior of dysrhythmias

ELECTROCARDIOGRAM

Value of ECG in the following clinical conditions – Prediction of sudden cardiac death – Prediction of ischemic pre-conditioning – Prediction of adverse states in AMI, post-MI and silent ischemia cases – Progression/regression of LV mass

RECORDING AND MONITORING AN ECG

Lead Configurations – Bipolar Leads • Two electrodes placed at 2 different sites • Register the difference in potential between these 2 leads

– Unipolar leads • Measure the absolute electrical potential at one site • Requires a reference site • Reference site formed by the limb leads

12 LEAD ECG

Limb Leads RA LA LL RL

Red Yellow Green Black

Right arm Left arm Left leg Right leg

Chest Leads V1

Red

4th ICS RPSB

V2

Yellow

4th ICS LPSB

V3

Green

Midway between V2 and V4

V4

Brown

5th ICS LMCL

ELECTROPHYSIOLOGY OF THE HEART

Four Electrophysiologic Events Involved in the Genesis of the ECG – – – –

Impulse formation Transmission of the impulse Depolarization Repolarization

TRANSMEMBRANE ACTION POTENTIAL

REFRACTORINESS

LAYERS OF THE HEART WALL Epicardium – Coronary arteries are found in this layer

Myocardium – Responsible for contraction of the heart

Endocardium – Lines the inside of the myocardium – Covers the heart valves

CONDUCTION SYSTEM OF THE HEART

SA Node Atrial Muscle AV Node Bundle of His Bundle Branches Purkinje Fibers Ventricular Muscle

MYOCARDIAL CELL TYPES

Kinds of Cardiac Cells

Where Found

Primary Function

Primary Property

Myocardial cells

Myocardium

Contraction and Relaxation

Contractility

Specialized cells of the electrical conduction system

Electrical conduction system

Generation and conduction of electrical impulses

Automaticity Conductivity

TERMINOLOGY Chronotropic Effect – Refers to a change in heart rate – A positive chronotropic effect refers to an increase in heart rate – A negative chronotropic effect refers to a decrease in heart rate

Dromotropic Effect – Refers to a change in the speed of conduction through the AV junction – A positive dromotropic effect results in an increase in AV conduction velocity – A negative dromotropic effect results in a decrease in AV conduction velocity

Inotropic Effect – Refers to a change in myocardial contractility – A postive inotropic effect results in an increase in myocardial contractility – A negative inotropic effect results in a decrease in myocardial

TERMINOLOGY Waveform – Movement away from the baseline in either a positive or negative direction

Segment – A line between wave forms

Interval – A waveform and a segment

Complex – Consists of several waveforms

ECG PAPER

ELECTROGRAM

Upward deflection

Downward deflection

Diphasic deflection

-

+

-

+

-

+

AVL

I

AVR

AVF

THE NORMAL ELECTROCARDIOGRAM

P wave – Generated by activation of the atria

PR segment – Represents the duration of atrioventricular (AV) conduction

QRS complex – Produced by activation of both ventricles

ST-T wave – Reflects ventricular recovery

STANDARD 12 LEAD ECG

The P wave – Atrial activation – Height < 0.2 mV (2 mm) – Duration < 0.12 sec

STANDARD 12 LEAD ECG

P-R Interval – Intraatrial, internodal, His purkinje conduction – Duration 0.12 to 0.20 or 0.22 sec

STANDARD 12 LEAD ECG

The QRS Complex – Ventricular activation – Duration of 100 msec

STANDARD 12 LEAD ECG

The ST-segment – Phase 2 of transmembrane potential – Isoelectric in normal subjects

STANDARD 12 LEAD ECG

The T wave – Upright after the age of 16 – Juvenile T wave

STANDARD 12 LEAD ECG

The U wave – Surface reflection of negative after potential – Repolarization of Purkinje fibers – Ventricular relaxation

STANDARD 12 LEAD ECG

The QT Interval – From beginning of QRS to end of T wave – Reflects the duration of depolarization and repolarization – Bezett: Q-Tc Interval = Q-T/ R-R

ANALYZING A RHYTHM STRIP

Rate Rhythm Axis P wave PR Interval QRS Complex T wave Q-T Interval

ANALYZING A RHYTHM STRIP

What is the rate? – To determine the ventricular rate,measure the distance between 2 consecutive R-waves (R-R interval) – To determine the atrial rate, measure the distance between 2 consecutive P-waves (P-P interval)

What Is The Rate?

Ventricular Rate – Small squares (R-R Interval) / 1500 – Big squares (R-R Interval) / 300

What Is The Rate?

Sinus rhythm

Atrial Fibrillation – QRS complexes in 6-sec strip X 10

ANALYZING A RHYTHM STRIP

Is the rhythm regular or irregular? – To determine if the ventricular rhythm is regular or irregular, measure the distance between 2 consecutive R-R intervals and compare that distance with the other R-r intervals. – For atrial rhythm, measure the distance between 2 consecutive P-P intervals. – Generally, a variation of up to 0.12 seconds (3 small boxes) is acceptable. The slower the heart rate, the more acceptable the variation.

ANALYZING A RHYTHM STRIP

What Is The Axis? Normal – 0 – (+90)

Left axis – 0 – (-90)

AVL

I

Right axis AVR

– (+90) – (+180)

Extreme axis – (-90) – (-180)

AVF

What Is The Axis?

}

10 AVL

I

Lead I

}

AVR

10

AVF

AVF

ANALYZING A RHYTHM STRIP

Is there 1 P wave before each QRS? – Are P waves present and uniform in appearance? – Is there a P wave before each QRS or are there P waves that are not followed by QRS complexes? – Is the atrial activity occurring so rapidly that there are more atrial beats than QRS complexes?

ANALYZING A RHYTHM STRIP

Is the PR interval within normal limits? – If the PR interval is less than 0.12 or more than 0.20 second, conduction followed an abnormal pathway or the impulse was delayed in the area of the AV node. – Is the PR interval of conducted beats constant or does it vary?

ANALYZING A RHYTHM STRIP

Is the QRS narrow or wide? – What is the duration of the QRS complex? • If it is 0.10 second or less (narrow), it is presumed to be supraventricular in origin. • If it is greater than 0.12 second (wide), it is probably ventricular in origin. – Do the QRS’s occur uniformly throughout the strip?

ANALYZING A RHYTHM STRIP

Interpret the rhythm – Specifying the site where the dysrhythmia originated (sinus), the mechanism (bradycardia), and the vetnricular rate. – For example, “sinus bradycardia with a ventricular response (rate) of 38/min.”

ANALYZING RHYTHM STRIP

Localization I, AVL – High lateral

II, III, AVF – Inferior

AVL

I

AVR

AVF

ANALYZING THE RHYTHM STRIP Localization V1,V2 – Septal

V3,V4 – Anterior

V5,V6 – Apicolateral

V1-V3 or V4 – Anteroseptal

V3 or V4-V6 – Anterolateral

V1-V6 – Extensive anterior I,AVL,V5,V6 - Lateral

ANALYZING A RHYTHM STRIP

How is the rhythm clinically significant?

NORMAL SINUS RHYTHM

Rate Rhythm

60-100 beats per minute Atrial regular Ventricular regular P waves Uniform in appearance, upright, normal shape, one preceding each QRS complex PR interval 0.12-0.20 second QRS 0.10 second or less. If greater than 0.10 second in duration, the QRS is termed “wide” since the existence of a bundle branch block or other intraventricular conduction defect cannot be accurately detected in a single-lead.

Sinus Rhythms Normal Sinus Rhythm Rate Rhythm P waves PR interval QRS

60-100 beats per minute Atrial regular Ventricular regular Uniform in appearance, upright, normal shape, one preceding each QRS complex 0.12-0.20 second 0.10 second or less. If greater than 0.10 second in duration, the QRS is termed “wide” since the existence of a bundle branch block or other intraventricular conduction defect cannot be accurately detected in a single-lead.

Sinus Rhythms Sinus Bradycardia Rate Rhythm P waves PR interval QRS

Less than 60 beats per minute Atrial regular Ventricular regular Uniform in appearance, upright, normal shape, one preceding each QRS complex 0.12-0.20 second Usually 0.10 second or less

Sinus Rhythms Sinus Tachycardia Rate Rhythm P waves PR interval QRS

Usually 100-160 beats per minute Atrial regular Ventricular regular Uniform in appearance, upright, normal shape, one preceding each QRS complex 0.12-0.20 second Usually 0.10 second or less

Sinus Rhythms Normal Heart Rates in Children Age Neonate Infant (6 mos) Toddler Preschooler School-aged Adolescent

Awake Heart Rate (per minute) 100-180 100-160 80-110 70-110 65-110 60-90

Sleeping Heart Rate (per minute) 80-160 75-160 60-90 60-90 60-90 50-90

Sinus Rhythms Sinus Dysrhythmia (Arrhythmia) Rate Rhythm P waves PR interval QRS

Usually 100-160 beats per minute but may be faster or slower Irregular (R-R intervals shorten during inspiration and lengthen during expiration) Uniform in appearance, upright, normal shape, one preceding each QRS complex 0.12-0.20 second Usually 0.10 second or less

Sinus Rhythms Sinoatrial (SA) Block Rate Rhythm P waves PR interval QRS

Usually normal but varies because of pause Irregular – the pause is the same as (or an exact multiple of) the distance between two other P-P intervals Uniform in appearance, upright, normal shape, one preceding each QRS complex 0.12-0.20 second Usually 0.10 second or less

Sinus Rhythms Sinus Arrest Rate Rhythm P waves PR interval QRS

Usually normal but varies because of the pause Irregular – the pause is of undetermined length (more than one PQRST complex is omitted) and is not the same distance as other P-P intervals. Uniform in appearance, upright, normal shape, one preceding each QRS complex 0.12-0.20 second Usually 0.10 second or less

Atrial Rhythms Premature Atrial Complexes 1. 2.

Early (premature) P waves Upright P waves that differ in shape from normal sinus P waves in Lead II •

3.

P waves may be biphasic (partly positive, partly negative), flattened, notched or pointed

The early P wave may or may not be followed by a QRS complex

Atrial Rhythms Compensatory vs. Non-compensatory Pause To determine whether or not the pause following a premature complex is compensatory or non-compensatory, measure the distance between three normal beats. Compare that distance between three beats, one of which includes the premature complex. Non-compensatory (incomplete) – if the normal beat following the premature complex occurs before it was expected (i.e., when the distance is not the same) Compensatory (complete) – if the normal beat following the premature complex occurs when expected (i.e., when the distance is the same).

Atrial Rhythms Premature Atrial Complexes (PACs) Rate Rhythm P waves PR interval QRS

Usually normal but depends on underlying rhythm Essentially regular with premature beats Premature Differ from sinus P waves – may be flattened, notched, pointed, biphasic, or lost in the preceding T wave Varies from 0.12-0.20 second when the pacemaker site is near the SA node; 0.12 second when the pacemaker site is nearer the AV junction Usually less than 0.10 second but may be prolonged. The QRS of the PAC is similar to those of the underlying rhythm unless the PAC is abnormally conducted.

Atrial Rhythms Vagal Maneuvers Vagal maneuvers – are methods used to stimulate baroreceptors in the internal carotid arteries and the aortic arch. Stimulation of these receptors results in reflex stimulation of the vagus nerve and release of acetylcholine. Acetylcholine slows conduction in the AV node, resulting in slowing of the heart rate • Coughing • Bearing down • Squatting • Breath-holding • Carotid sinus pressure (massage) • Immersion of the face in ice water • Stimulation of the gag reflex Carotid pressure should be avoided in older patients. Simultaneous, bilateral carotid pressure should never be performed.

Atrial Rhythms The Unstable Patient Signs and Symptoms • Shock • Chest pain • Hypotension • Shortness of breath • Pulmonary congestion • Congestive heart failure • Acute myocardial infarction • Decreased level of consciousness

Atrial Rhythms Supraventricular Tachycardia Rate Rhythm P waves

PR interval

QRS

150-250 beats per minute Regular Atrial P waves may be seen which differ from sinus P waves (may be flattened, notched, pointed, or biphasic). P waves are usually identifiable at the lower end of the rate range but are seldom identifiable at rates above 200. May be lost in the preceding T wave. Usually not measurable because the P wave is difficult to distinguish from the preceding T wave. If P waves are seen, the RR interval will usually measure 0.12-0.20 second. Less than 0.10 second unless an intraventricular conduction defect exists.

Atrial Rhythms ELECTRICAL THERAPY – Synchronized Countershock Description and Purpose Synchronized countershock reduces the potential for delivery of energy during the vulnerable period of the T wave (relative refractory period). A synchronizing circuit allows the delivery of a countershock to be “programmed”. The machine searches for the peak of the QRS complex (R wave deflection) and delivers the shock a few milliseconds after the highest part of the R wave. Indications: • Supraventricular tachycardia • Atrial fibrillation • Atrial flutter • Unstable ventricular tachycardia with pause

Atrial Rhythms Wandering Atrial Pacemaker (Multiformed Atrial Rhythm) Rate Rhythm P waves

PR interval QRS

60-100. If the rate is greater than 100 beats per minute, the rhythm is termed multifocal (or chaotic) atrial tachycardia. Atrial – irregular Ventricular - irregular Size, shape, and direction may change from beat to beat. At least three different P waves are required for a diagnosis of wandering atrial pacemaker Variable Usually less than 0.10 second unless an intraventricular conduction defect exists

Atrial Rhythms Atrial Flutter Rate

Rhythm P waves PR interval QRS

Atrial rate 250-350 beats per minute; ventricular rate variable – determined by AV blockade. The ventricular rate will usually not exceed 180 beats per minute due to the intrinsic conduction rate of the AV junction. Atrial regular Ventricular may be regular or irregular Not identifiable P waves; saw-toothed “flutter waves” Not measurable Usually less than 0.10 second but may be widened if flutter waves are buried in the QRS complex or if an intraventricular conduction defect exists.

Atrial Rhythms Atrial Fribrillation Rate Rhythm P waves PR interval QRS

Atrial rate usually greater than 350-400 beats per minute; ventricular rate variable Ventricular rhythms usually very irregular; a regular ventricular rhythm may occur because of digitalis toxicity. No identifiable P waves; fibrillatory waves present. Erratic wavy baseline. Not measurable Usually less than 0.10 second but may be widened if an intraventricular conduction defect exists.

Atrial Rhythms Wolff-Parkinson-White (WPW) Syndrome Rate Rhythm P waves PR interval QRS

If the underlying rhythm is sinus in origin, the rate is usually 60-100 beats per minute. Regular unless associated with atrial fibrillation Normal and upright unless WPW is associated with atrial fibrillation If P waves are seen, less than 0.12 second Usually greater than 0.12 second. Slurred upstroke of the QRS complex (delta wave) is often seen in one or more leads)

Junctional Rhythms Premature Junctional Complexes Rate Rhythm P waves PR interval

QRS

Usually normal, but depends on the underlying rhythm Essentially regular with premature beats May occur before, during, or after the QRS If visible, the P wave is inverted in leads II, III, AVF If the P wave occurs before the QRS, the PR interval will be usually less than or equal to 0.12 second. If no P wave occurs before the QRS, there will be no PR interval. Usually 0.10 second or less unless an intraventricular conduction defect exists.

Junctional Rhythms Junctional Escape Beat Rate Rhythm P waves PR interval

QRS

Usually normal, but depends on the underlying rhythm Essentially regular with LATE beats May occur before, during, or after the QRS If visible, the P wave is inverted in leads II, III, AVF If the P wave occurs before the QRS, the PR interval will be usually less than or equal to 0.12 second. If no P wave occurs before the QRS, there will be no PR interval. Usually 0.10 second or less unless an intraventricular conduction defect exists.

Junctional Rhythms Junctional Escape Rhythm Rate Rhythm P waves PR interval

QRS

40 to 60 beats per minute Atrial and ventricular rhythm very regular May occur before, during, or after the QRS If visible, the P wave is inverted in leads II, III, AVF If the P wave occurs before the QRS, the PR interval will be usually less than or equal to 0.12 second. If no P wave occurs before the QRS, there will be no PR interval. Usually 0.10 second or less unless an intraventricular conduction defect exists.

Junctional Rhythms Accelerated Junctional Rhythm Rate Rhythm P waves PR interval

QRS

60 to 100 beats per minute Atrial and ventricular rhythm very regular May occur before, during, or after the QRS If visible, the P wave is inverted in leads II, III, AVF If the P wave occurs before the QRS, the PR interval will be usually less than or equal to 0.12 second. If no P wave occurs before the QRS, there will be no PR interval. Usually 0.10 second or less unless an intraventricular conduction defect exists.

Junctional Rhythms The Unstable Patient Signs and Symptoms • Shock • Chest pain • Hypotension • Shortness of breath • Pulmonary congestion • Congestive heart failure • Acute myocardial infarction • Decreased level of consciousness

Junctional Rhythms Junctional Tachycardia Rate Rhythm P waves PR interval

QRS

100 to 180 beats per minute Atrial and ventricular rhythm very regular May occur before, during, or after the QRS If visible, the P wave is inverted in leads II, III, AVF If the P wave occurs before the QRS, the PR interval will be usually less than or equal to 0.12 second. If no P wave occurs before the QRS, there will be no PR interval. Usually 0.10 second or less unless an intraventricular conduction defect exists.

Ventricular Rhythms Premature Ventricular Complexes Rate Rhythm P waves PR interval QRS

Usually normal but depends on the underlying rhythm Essentially regular with premature beats. If the PVC is an interpolated PVC, the rhythm will be regular. There is no P wave associated with the PVC None with the PVCs because the ectopic beat originates in the ventricle Greater than 0.12 second. Wide and bizarre. T wave frequently in opposite direction of the QRS complex.

Ventricular Rhythms Patterns of PVCs 1. 2. 3. 4. 5.

Pairs (couplets) – two sequential PVCs Runs or bursts – three or more sequential PVCs are called vntricular tachycardia (VT) Bigeminal PVCs (ventricular bigeminy) – every other beat is a PVC Trigeminal PVCs (ventricular trigeminy) – every third beat is a PVC Quadrigeminal PVCs (ventricular quadrigeminy) – every fourth beat is a PVC

Ventricular Rhythms Common Causes of PVCs • • • • • • • • • • • • •

Normal variant Anxiety Exercise Hypoxia Digitalis toxicity Acid-base imbalance Myocardial ischemia Electrolyte imbalance (hypokalemia, hypocalcemia, hypercalcemia, hypomagnesemia) Congestive heart failure Increased sympathetic tone Acute myocardial infarction Stimulants (alcohol, caffeine, tobacco) Drugs (sympathomimetics, cyclic antidepressants, phenothiazines)

Ventricular Rhythms Warning Dysrhythmias

• • • •

Six or more PVCs per minute PVCs that occurred in pairs (couplets) or in runs or three or more (ventricular tachycardia) PVCs that fell on the T wave of the preceding beat (R-on T phenomenon) PVCs that differed in shape (multiformed PVCs)

Ventricular Rhythms Ventricular Escape Beat Rate Rhythm P waves PR interval QRS

Atrial and ventricular rate dependent upon the underlying rhythm. Irregular. The ventricular escape beat occurs LATE, after the next expected sinus beat. There is no P wave associated with escape beat. None with the escape beat because the complex originates from the ventricles. Greater than 0.12 second. T wave deflection is opposite that of the QRS complex.

Ventricular Rhythms Idioventricular (Ventricular Escape) Rhythm Rate Rhythm P waves PR interval QRS

Atrial not discernible, ventricular 20-40 beats per minute Atrial not discernible Ventricular essentially regular Absent None Greater than 0.12 second. T wave deflection is in the opposite direction of the QRS.

Ventricular Rhythms Accelerated Idioventricular Rhythm Rate Rhythm P waves PR interval QRS

Atrial not discernible, ventricular 40-100 beats per minute Atrial not discernible Ventricular essentially regular Absent None Greater than 0.12 second. T wave deflection is in the opposite direction of the QRS.

Ventricular Rhythms Ventricular Tachycardia (VT) Rate Rhythm P waves

PR interval QRS

Atrial rate not discernible, ventricular rate 100-250 beats per minute Atrial rhythm not discernible Ventricular rhythm is essentially regular 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. None Greater than 0.12 second. Often difficult to differentiate between the QRS and the T wave.

Ventricular Rhythms VENTRICULAR TACHYCARDIA - CAUSES • • • • • • • • • • • • •

Hypoxia Exercise R-on T PVCs Catecholamines Digitalis toxicity Myocardial ischemia Acid-base imbalance Electrolyte imbalance Ventricular aneurysm Coronary artery disease Rheumatic heart disease Acute myocardial infarction CNS stimulants (cocaine, amphetamines)

Ventricular Rhythms LONG QT INTERVAL - CAUSES Drug induced • Cyclic antidepressants • Phenothiazines • Type 1A antidysrhythmics (quinidine, procainamide, disopyramide) • Organophosphate insecticides Eating disorders (bulimia, anorexia) Electrolyte abnormalities (hypomagnesemia, hypokalemia, hypocalcemia)

Ventricular Rhythms ANTIDYSRHYTHMIC CLASSIFICATIONS Group I

Group II Group III Group IV

Primarily inhibit the fast sodium channel in cardiac tissue, resulting in an increased refractory period 1A - increased conduction velocity and prolong the action potential (Quinidine, Procainamide, Disopyramide) 1B - Either increase or have no effect on conduction velocity (Lidocaine, Phenytoin, Tocainide, Mexiletine) 1C - Decrease conduction velocity (Flecainide, Encainide) Beta-adrenergic blockers (Propranolol) Prolong repolarization (Bretylium, Amiodarone) Block slow calcium channels, resulting in decreased automaticity, and depression of myocardial and smooth muscle contraction (Verapamil, Nifedipine, Diltiazem)

Ventricular Rhythms Torsades de Pointes (TdP) Rate Rhythm P waves PR interval QRS

Atrial rate not discernible, ventricular rate 150-250 beats per minute Atrial not discernible Ventricular may be regular or irregular None None Greater than 0.12 second. Gradual alteration in the amplitude and direction of the QRS

Ventricular Rhythms Ventricular Fibrillation Rate Rhythm P waves PR interval QRS

Cannot be determined since there are no discernible waves or complexes to measure Rapid and chaotic with no pattern or regularity Not discernible Not discernible Not discernible

Ventricular Rhythms Defibrillation (Unsynchronized Countershock) Description and Purpose: The purpose of defibrillation is to produce momentary asystole. The shock attempts to completely depolarize the myocardium and provide an opportunity for the natural pacemaker centers of the heart to resume normal activity. Defibrillation is a random delivery of energy – there is no relation of the discharge of energy to the cardiac cycle. Indications: • Unstable ventricular tachycardia with a pulse • Pulseless ventricular tachycardia • Ventricular fibrillation • Sustained Torsades de Pointes

Ventricular Rhythms Asystole Rate Rhythm P waves PR interval QRS

Ventricular usually indiscernible but may see some atrial activity. Atrial may be discernible. Ventricular indiscernible. Usually not discernible Not measurable Absent

Ventricular Rhythms Causes of Pulseless Electrical Activity (MATCHx4ED) Myocardial infarction (massive acute) Acidosis Tension pneumothorax Cardiac tamponade Hypovolemia (most common cause) Hypoxia Hyperkalemia Hypothermia Embolus (massive pulmonary) Drug overdoses (cyclic antidepressants, calcium channel blockers, beta-blockers, digitalis)

Atrioventricular Blocks Classification of AV Blocks Degree of block

Partial (incomplete) blocks

First-degree AV block Second-degree AV block type I Second-degree AV block type II Second-degree AV block 2:1 conduction Third-degree AV block

Complete block Site of block

First-degree AV block Second-degree AV block type I Third-degree AV block

AV node

Infranodal

Bundle of His Bundle branches

Second-degree AV block type II – (uncommon) Third-degree AV block Second-degree AV block type II – (more common) Third-degree AV block

Atrioventricular Blocks First Degree AV Block Rate Rhythm P waves PR interval QRS

Atrial and ventricular rates the same; dependent upon underlying rhythm. Atrial and ventricular regular Normal in size and shape Only one P wave before each QRS Prolonged (greater than 0.20 second) but constant Usually 0.10 second or less unless an intraventricular conduction exists

Atrioventricular Blocks Second-Degree AV Block, Type I (Wenckebach) Rate Rhythm P waves PR interval

QRS

Atrial rate is greater than the ventricular rate. Both are often within normal limits. Atrial regular (P’s plot through) Ventricular irregular. Normal in size and shape. Some P waves are not followed by a QRS complex (more P’s than QRS’s). Lengthens with each cycle (although lengthening may be very slight), until a P wave appears without a QRS complex. The PRI after the nonconducted beat. Usually 0.10 second or less but is periodically dropped.

Atrioventricular Blocks Second-Degree AV Block, Type II (Mobitz) Rate Rhythm P waves PR interval

QRS

Atrial rate is greater than the ventricular rate. Ventricular rate is often slow. Atrial regular (P’s plot through) Ventricular irregular. Normal in size and shape. Some P waves are not followed by a QRS complex (more P’s than QRS’s). Within normal limits or prolonged but always constant for the conducted beats. There may be some shortening of the PRI that follows a nonconducted P wave. Usually 0.10 second or greater, periodically absent after P waves.

Atrioventricular Blocks Second-Degree AV Block, 2:1 Conduction Rate Rhythm P waves PR interval QRS

Atrial rate is greater than the ventricular rate. Atrial regular (P’s plot through) Ventricular regular. Normal in size and shape; every other P wave is followed by a QRS complex (more P’s than QRS’s) Constant Within normal limits if the block occurs above the bundle of His (probably type I); wide if the block occurs at or below the bundle of His (probably type II); absent after every other P wave.

Atrioventricular Blocks Complete (Third-Degree) AV Block Rate Rhythm P waves PR interval QRS

Atrial rate is greater than the ventricular rate. The ventricular rate is determined by the origin of the escape rhythm. Atrial regular (P’s plot through). Ventricular regular. There is no relationship between the atrial and ventricular rhythm. Normal in size and shape. None – the atria and ventricles beat independently of each other, thus there is no true PR interval. Narrow or broad depending on the location of the escape pacemaker and the condition of the intraventricular conduction system. Narrow = junctional pacemaker; wide = ventricular pacemaker.

Atrioventricular Blocks Classification of AV Blocks

Ventricular Rhythm PR Interval QRS Width

Ventricular Rhythm PR Interval

Second-Degree AV Block Type I

Second-Degree AV Block Type II

Irregular Lengthening Usually narrow

Irregular Constant Usually wide

Second-Degree AV Block, 2:1 Conduction

Complete (Third-Degree) AV Block

Regular Constant

Regular None – no relationship between P waves and QRS complexes May be narrow or wide

QRS Width May be narrow or wide