ECG

EMRG1230

ECG Paper

Made up of big and little boxes. Each big box contains 5 little boxes.

1 little box is 0.04 seconds

Each large box is 0.2 seconds

A full ECG is 10 seconds long

P wave

Formed as impulse is generated in atria. Represents atrial depolarization

Smooth round upright shape immediatly proceding QRS complex
Duration: <110 ms

Amplitude: <2.5 mm tall

What to look for with P wave?

• If there is no P wave

• If it is present but not followed by a QRS complex

• Can give clues on Pacemaker site

• P waves that vary in size and configuration

• Morphology: upright or inverse

PR interval

Time it takes for atria to depolarize and impulse to get to the AV Node

A slight delay normally occurs

Measured from start of P wave until the begining of the QRS complex

Usually 0.12-0.20 seconds

First Degree AV Block

A PR interval that is longer than 0.20 seconds

May indicate injury to AV junction

Wolff-Parkinson-White Syndrome

PR interval shorter than 0.12 seconds is present in these cases

Variable PRI

Variable PRI may indicate either a wandering atrial pacemaker or a second-degree AV nodal block

PR depression may occurr with pericarditis

QRS Complex

Narrow with sharply pointed waves. Has a duration less than 0.12 seconds

Represents depolarization of simultaneously contracting ventricles

Should follow each P wave

Q Wave

First negative deflection after P wave

Can be present or absent

R Wave

First positive deflection after the P wave

if there is no Q wave visible, this will be the first initial wave of the QRS complex

S Wave

First negative deflection after the R wave

J Point

Point where QRS complex ends and ST segment begins

Represents end of ventricular depolarization and the beginning of ventricular repolerization

Note:
Locating the J point may make it easier to identify the ST segment when you are looking for elevation

ST Segment

Lime between the end of the QRS complex and beginning of the T wave

T Wave

Represents ventricular repolerization

Asymmetric and is half the size of the QRS wave

Typically have a slower uppstroke and a faster downstroke

TP Segment

Isoelectric line or baseline

Neither positive nor negative

Flat, straight, horizontal line that begins at the end of the T wave and ends at the start of the next P wave

QT Interval

Represents all the electrical activity of one complete ventricular cycle from ventricular depolarization to ventricular repolerization

Begins with onset of Q and ends at T

If no Q wave, Begins at R wave

Normally lasts 0.36 to 0.44 seconds varying based on HR, Age, Sex

QT Interval lengths

• As the HR decreases, the QT interval shortens

• As the HR increases, the QT interval lengthens

Prolonged QT indicates that the heart is experiencing an extended refractory period

5 Step Method To Reading an ECG Rhythm Strip

You will usually use lead II to perform rhythm interpretation; five-step method

1. Determine if the QRS complex is wide or narrow.

2. Identify the P waves and measure the PRI.

3. Determine the relationship of the P waves with the QRS complex.

4. Determine rhythm regularity.

5. Measure the heart rate.

When Reading RCG Rythm Strip

• Use 120 ms as the cut-off between narrow and wide QRS complexes

• Note whether P waves are upright and within normal parameters or absent.

• Check PRI for evidence of AV nodal delay.

• Is there only one P wave for every QRS complex

Determining HR (6 Sec Method)

Remember that the P wave rate and QRS complex rate may be different

• Simplest and most accurate method when rhythm is irregular or between approximately 50 and 100

• Count the number of QRS complexes in a 6-second strip, and multiply that number by 10 to obtain the rate per minute

Determining HR (Sequence Method)

• Memorize the following sequence: 300, 150, 100, 75, 60, 50, 43, 38, 33.

• Find an R wave on a heavy line and count off “300, 150, 100 . . .” until you reach the next R wave

• If the R-R interval spans fewer than three large boxes, the rate is greater than 100.

• If it covers more than five large boxes, the rate is less than 60.

Systematic Analysis of ECG Strip

• Are QRS complexes present?

• Are there P waves?

• What is the PRI?

• Is the rhythm regular or irregular?

• What is the rate?

Specific Cardiac Dysrhythmias

• AV node blocks or bundle branch blocks

• Ventricular fibrillation

• Bradycardias and tachycardias

• Atrial fibrillation

Normal Sinus Rythms

• Intrinsic rate of 60 to 100 beats/minute

• Regular, with minimal variation between RR intervals

• P wave is present, upright, and precedes each QRS complex (<100ms wide)

• Constant PR Interval

Sinus Bradycardia

• Complexes and morphology the same as NSR, only the rate differs

• Rate of less than 60 beats/minute

• Rhythm is regular.

• Treatment focuses on the patient’s tolerance to the bradycardia

Sinus Tachycardia

• Rate of more than 100 beats/minute

• Rhythm is regular.

• Increases the work of the heart

• Treatment is related to the underlying cause

Sinus Arrhythmia

• Slight variation of a sinus rhythm

• Bainbridge reflex- sudden changes in pressure

• Increases SV and blood pressure

• Normal finding in children and young adults

Sinus Arrest

• SA node fails to initiate an impulse.

• SA node resumes normal functioning.

• Occasional episodes are not significant.

• Treatment based on the overall HR and tolerance

Sick Sinus Syndrome

Encompasses a variety of rhythms. All evidence that the SA node is not functioning normally

Some patients may experience a syncopal or near syncopal episode, dizziness, and palpitations

Sinoatrial Block

Results from either the Pacemaker cells or the transitional cells failing to produce an impulse

After the dropped beat, the cycle continues on time

Characteristics:

• Rate: varies

• Irregular

• P waves present, except when dropped

• P:QRS- 1:1

• QRS width is normal

Atrial Rhythms

Rhythms originating from the atria will have upright P waves that precede each QRS complex but that are not as well rounded as those coming from the SA node.

Wandering Atrial Pacemaker

• Pacemaker moves from the SA node to various areas within the atria.

• Rhythm is slightly irregular.

• Patients with significant lung disease

• Treatment is usually not indicated.

Supraventricular Tachycardia (SVT)

• Typically, P waves are not present, due to the rate they are “buried” in the QRS complex

• May sometimes appear inverted or retrograde

• Regular rhythm

• Narrow QRS (usually less the 120ms)

• Rate typically 140-280 bpm

PSVT- Paroxysmal SVT

• An abrupt onset and offset can be seen

Atrial Flutter

• Atrial rate and ventricular rate will be different, (ventricular will be a fraction of the atrial)

• Atrial commonly 250-350 bpm

• Usually regular, but may be variable

• P waves- “saw tooth” appearance

• QRS width is normal

• P:QRS ratio- variable, most commonly 2:1 but can

go higher

Atrial Fibrillation

• No discernable P waves

• QRS complexes are innervated haphazardly in an irregularly irregular pattern

• Ventricular rate is guided by occasional activation from one of the pacemaker sources

• QRS width is normal

• Rate is variable, ventricular response can be fast or slow

• Fibrillatory waves may mimic P waves- this will lead to misinterpretation

Multifocal Atrial Tachycardia (MAT)

• HR >100, usually between 100-150

• Irregularly irregular

• At least 3 distinct P wave morphologies

• Absence of single dominant arial pacemaker

• Some P waves may be non conducted

Junctional Escape Rhythm

• Junctional rhythm with a rate of 40-60 bpm

• QRS complexes typically narrow (<120ms)

• No relationship between the QRS complex and any preceding atrial activity

• Regular rhythm

• P waves may appear inverted, before, during or after

the QRS

Occurs when the rate of the supraventricular impulses arriving at the AV node or ventricle is less then the intrinsic rate of the ectopic pacemaker

Accelerated Junctional Rhythm

Occurs when the junctional pacemaker that is firing the impulses takes over the normal pacing function of the SA due to damage to/issues with normal conduction (slow SA)

• Rate of 60-100

• Regular

• P wave may be absent, antegrade or retrograde

• QRS width is normal

• P:QRS- if present, 1:1, if absent, none

Junctional Tachycardia

Same etiology as junctional rhythms, however the rate is >100 bpm

• P waves- retrograde

• QRS- narrow

• PR Interval is short

• Regular rhythm

Premature Junctional Complex (PJC’s)

A beat that originates prematurely in the AV node. Travels through the normal conduction system of the ventricles, so the QRS complex it creates is identical to the others. Can occur sporadically or as part of a regular, grouped pattern (bigeminy, trigeminy)

Characteristics:

• Narrow QRS either without a preceding P wave or a retrograde P wave

• Occurs sooner then the next beat is expected

First Degree Heart Block

Characteristics:

• Rate- depends on underlying rhythm

• Regular

• P waves- Normal

• PR Interval- >0.20 seconds

Each impulse is delayed slightly longer. Impulse eventually passes.

Least serious of the heart blocks and is first indication of damage to the AV node

Second Degree Heart Block (Type 1) Wenckebach

Caused by a diseased AV node with a long refractory period. This results in the PR interval lengthening between successive beats until a beat is dropped. At that point, the cycle begins again

Characteristics:

• Regularly irregular

• Dropped beats

• P:QRS- Variable

Second Degree Heart Block Type II

Groups beats with one dropped beet between each group

• PR interval is THE SAME

Caused by a diseased AV node- typically indicative of worsening cardiac issues, specifically complete heart block

Third Degree Heart Block (Complete Block)

All impulses are prevented and ventricles develop their own pacemaker

• Complete absence of AV conduction

• None of the supraventricular impulses are conducted to the ventricles

• Atria and ventricles firing separately

• Typically a bradycardic rate

Idioventricular Rhythm (Wide and slow, It’s Idio)

Occurs when a ventricular focus acts as the primary pacemaker for the heart. QRS complexes are wide and bizarre

Characteristics:

• Rate: 20-40 bpm

• Regular

• P waves- Absent

• P:QRS- N/A

• QRS Width- wide (>120ms/.120 s), bizarre appearance

Accelerated Idioventricular Rhythm (AIVR)

Characteristics:

• Rate of 40-100 bpm

• Regular rhythm

• P waves- Absent

• QRS: Wide (>0.12s), bizarre appearance

Faster version of Idioventricular rhythm

Ventricular Tachycardia (V-Tach)

• Rate exceeding 100 beats/minute; QRS complex will measure greater than 0.12 s

• Regular, with no variation between RR intervals

• P waves are not normally visualized.

• QRS complexes are monomorphic.

• Polymorphic

• Extremely serious

Sustained- duration of > 30 seconds or requiring intervention due to hemodynamic instability

Non Sustained- 3 or more consecutive ventricular complexes terminating spontaneously in <30 seconds

Monomorphic V-Tach

• Regular rhythm

• Originated form a single focus within the ventricles

• Produces uniform QRS complexes

• Classified as stable vs. non stable

Polymorphic V-Tach

A form of Ventricular Tachycardia in which there are multiple ventricular foci and the resultant QRS complexes vary in size and shape.

Most common cause is myocardial ischemia

Torsades De Pointes

Occurs when there is an underlying prolonged QT interval

• A type of polymorphic V-Tach

• Axis of the QRS complex changes from positive to negative in a haphazard fashion

• Means “twisting of points”

• Can convert to NSR or V Fib- treat this vey carefully as it precursor/notifier of death!

Premature Ventricular Complex (PVC)

Caused by the premature firing of the ventricular cell. Ventricular pacer fires before the SA node. This causes the ventricles to be in a refractory state when the normal impulse tries to get through, causing the ventricles do not fire at their normal time

Underlying pacing rhythm/schedule is not altered, so the beat following the PVC will arrive on time

This is a compensatory pause

Multifocal Vs Unifocal

Multifocal- arising from 2 or more ectopic foci. Results in multiple QRS morphologies

Unifocal- arising from a single ectopic foci. Results in each PVC looking identical

Repeating Pattern Types for PVC’s

Couplet- two consecutive PVC’s

Bigeminy- every other beat is a PVC

Trigeminy- every third beat is a PVC

Quadrigeminy- every fourth beat is a PVC

Ventricular Fibrillation (V-Fib)

Rhythm in which the entire heart is no longer contracting. Quivering without organized contraction, cardiac chaos, approx. 500 bpm firing

• Random depolarization of many cells

• Rhythm most commonly seen in cardiac arrests

• Responds well to defibrillation

CPR compressions help make the heart more susceptible to defibrillation

Asystole

“Flatline”

Entire heart is no longer contracting.

Many cells have no energy for contraction.

Generally a confirmation of death

May be treated in certain circumstances