Presented By:Aamir SharifBEMS Final ProfessionalDept. Of EMS The University Of Poonch Rawalakot AJ&K

ELECTROCARDIOGRAPHY

Objectives

• The Basics• Interpretation• Clinical Pearls• Practice Recognition

Introduction

• The electrocardiogram (ECG) is one of the simplest and oldest cardiac investigations available, yet it can provide a wealth of useful information and remains an essential part of the assessment of cardiac patients.

The ECG

“An ECG is simply a representation of the electrical activity of the heart muscle as it changes with time,

usually printed on paper for easier analysis”

Like other muscles, cardiac muscle contracts in response to electrical depolarization of the muscle cells. It is the sum of this electrical activity, when

amplified and recorded for just a few seconds that we know as an ECG.

Cont.....

• The ECG device detects and amplifies the tiny electrical changes on the skin that are caused when the heart muscle depolarizes during each heartbeat. At rest, each heart muscle cell has a negative charge, called the membrane potential, across its cell membrane. Decreasing this negative charge towards zero, via the influx of the positive cations, Na+ and Ca++, is called depolarization, which activates the mechanisms in the cell that cause it to contract.

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THE CONDUCTINGY SYSTEM • During each heartbeat, a healthy

heart will have an orderly progression of a wave of depolarisation that is triggered by the cells in the sinoatrial node, spreads out through the atrium, passes through the atrioventricular node and then spreads all over the ventricles. This is detected as tiny rises and falls in the voltage between two electrodes placed either side of the heart which is displayed as a wavy line either on a screen or on paper. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle.

Lead Placement• By convention, we record the standard

surface ECG using 12 different recording lead ‘directions,’ though rather confusingly only 10 recording electrodes on the skin are required to achieve this.

• Six of these are recorded from the chest overlying the heart – the chest or precordial leads also called V1, V2, V3, V4, V5 and V6.

• Four are recorded from the limbs – the limb leads The limb leads are called leads I, II, III, AVR, AVL and AVF.

• It is essential that each of the 10 recording electrodes is placed in its correct position, otherwise the appearance of the ECG will be changed significantly, preventing correct interpretation.

Normal E.C.G• A typical ECG (Limb Lead II) tracing of the cardiac

cycle (heartbeat) consists of a • P wave• QRS complex• T wave• & U wave(which is normally invisiblein 50 to 75% of ECGs bcozit is hidden by the T wave and upcoming new P wave)

Lets look at how the conduction system related to what we record on the ECG.

• P wave: the sequential activation (depolarization) of the right and left atria .(Atrial Repolarization merge with QRS complex)

• QRS complex: right and left ventricular depolarization (normally the ventricles are activated simultaneously)

• T wave ventricular repolarization• U wave: origin for this wave is not

clear - but probably represents "after depolarization" in the ventricles

Feature Description Duration

RR interval

The interval between an R wave and the next R wave: Normal resting heart rate is between 60 and 100 bpm

0.6 to 1.2s

PR interval

The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. The PR interval reflects the time the electrical impulse takes to travel from the sinus node through the AV node and entering the ventricles. The PR interval is, therefore, a good estimate of AV node function

120 to 200ms

VAT(Ventricular activation time)

It is time required for ventricular depolarization This is from onset of QRS complex to the peak of R wave

0.03 to 0.05 sec for left ventricles

QT interval

The QT interval is measured from the beginning of the QRS complex to the end of the T wave. A prolonged QT interval is a risk factor for ventricular tachyarrhythmias and sudden death.

Up to 0.42 sec in heart rate of 60 bpm

Interpretation • Develop a systematic approach to reading ECGs and use it every

time.The system we will practice is:– Rate– Rhythm (including intervals and blocks)– Axis Deviation– Hypertrophy– Ischemia– P wave– PR Interval– Q wave– QRS complex– ST Segment– T wave

Rate• Before discussing how to calculate

heart Rate we Should have knowledge about ECG paper.

• Paper• ECG paper is traditionally divided

into 1mm squares. Vertically, ten blocks usually correspond to 1 mV, and on the horizontal axis, the paper speed is usually 25mm/s, so one block is 0.04s (or 40ms). Note that we also have "big blocks" which are 5mm on their side

Cont..• EKG paper is a grid where time is

measured along the horizontal axis.

• Each small square is 1 mm in length and represents 0.04 seconds.

• Each larger square is 5 mm in length and represents 0.2 seconds.

• Voltage is measured along the vertical axis.

• 10 mm is equal to 1mV in voltage.

Cont..• Knowing the paper speed, it's easy to work

out heart rate. It's also very convenient to have a quick way of eyeballing the rate, and one method is as follows:

• Remember the sequence: 300, 150, 100, 75, 60, 50

• Identify an R wave that falls on the marker of a `big block'

• Count the number of big blocks to the next R wave.

• If the number of big blocks is 1, the rate is 300, if it's two, then the rate is 150, and so on. Rates in between these numbers are easy to `interpolate'.

Number of big boxes

Rate

1 300

2 150

3 100

4 75

5 60

6 50

Rhythm

• This is checked by the intervals b/w two R peaks or two S waves is equal in all leads, the rhythm is said to regular & if it is not. The rhythm is said to be irregular.

• If rhythm is not, the rhythm is said to be irregular or irregularly irregular.

• If the regularity is after regular intervals the rhythm is regularly irregular,Otherwise irregular irregular.

• Irregular rhythm is called Arrhythmias

Heart rate can be easily calculated from the ECG strip

• When the rhythm is regular, the heart rate is 300 divided by the number of large squares between the QRS complexes. For example, if there are 4 large squares between regular QRS complexes, the heart rate is 75 (300/4=75). OR

• Each second of time is represented by 250 mm (5 large squares) along the horizontal axis. So if the number of large squares between each QRS complex is:

• 5 - the HR is 60 beats per minute. • 3 - the HR is 100 per minute.• 2 - the HR is 150 per minute.• The second method can be used with an irregular

rhythm to estimate the rate. Count the number of R waves in a 6 second strip and multiply by 10.– For example, if there are 7 R waves in a 6

second strip, the heart rate is 70 (7x10=70).

Arrhythmias• These are groups of disorders.In which there is disturbance of cardiac

rhythm.These are classified into following groups• 1. sinus arrhythmia• 2. Atrial arrhythmia• 3.AV junctional (nodal)arrhythmia• 4.Ventricular arrhythmia• 5.Miscellaneous

(a) Accelerated conduction(b) Heart block (c) Conduction defect

Sinus Arrhythmia• Sinus arrhythmia: The normal increase in heart rate that occurs during

inspiration (when you breathe in). This is a natural response and is more accentuated in children than adults.

• The "sinus" refers to the natural pacemaker of the heart which is called the sinoatrial (or sinus) node. It is located in the wall of the right atrium (the right upper chamber of the heart). Normal cardiac impulses start there and are transmitted to the atria and down to the ventricles (the lower chambers of the heart).

• Sinus tachycardia refers to a fast heartbeat (tachycardia) because of rapid firing of the sinoatrial (sinus) node. This occurs in response to exercise, exertion, excitement, pain, fever, excessive thyroid hormone, low blood oxygen (hypoxia), stimulant drugs (such as caffeine), etc.

• The lack of normal sinus rhythm is an arrhythmia, an abnormal heart rhythm

Bradycardia-Tachycardia Syndrome• Also known as Sick sinus syndrome

Atrial Arrhythmia

• Types of Atrial Arrhythmias

• Atrial Ectopic Beats• Supraventricular tachycardia (SVT).• Atrial fibrillation.• Atrial flutter.

Atrial Ectopic Beats• Atrial ectopic beats (AEB) refers to a contraction of the upper heart

chamber which occurs before it would be expected.• Also known as premature atrial beats, premature atrial complex

(PAC), or atrial extrasystole.• As people age, extra beats tend to happen more frequently even in

perfectly healthy individuals. AEB may be triggered bystress, caffeine, smoking, and some medicines,i.e ephedrine or pseudoephedrine .

• AEB may also be the result of an enlarged atria, lung disease, or the result of reduced blood supply to that area of the heart.

Atrial tachycardia orSupraventricular tachycardia (SVT).

• Supraventricular tachycardia (SVT) means that from time to time our heart beats very fast for a reason other than exercise, high fever, or stress.

Types of SVT include:• Atrioventricular nodal reentrant

tachycardia (AVNRT).• Atrioventricular reciprocating

tachycardia (AVRT), including Wolff-Parkinson-White syndrome.

Atrial flutter.• When the heart rate is sufficiently elevated so that the isoelectric

interval between the end of T and beginning of P disappears, the arrhythmia is called atrial flutter.

• The origin is also believed to involve a reentrant atrial pathway. The frequency of these fluctuations is between 220 and 300/min. The AV-node and, thereafter, the ventricles are generally activated by every second or every third atrial impulse

Atrial fibrillation.• Atrial fibrillation (AF or A-fib) is where the signal doesn't originate

only from the SA node, and so the atrium doesn't contract simultaneously, causing an incredibly high heart rate, as well as lack of atrial systole. It is the most common cardiac arrhythmia (irregular heart beat). It may cause no symptoms, but it is often associated with palpitations, fainting, chest pain, or congestive heart failure.

AV Junctional (Nodal) Arrhythmia• In junctional rhythm, the sinoatrial node does not control the heart's rhythm - this

can happen in the case of a block in conduction somewhere along the pathway described above. When this happens, the heart's atrioventricular node takes over as the pacemaker.

• In the case of a junctional rhythm, the atria will actually still contract before the ventricles; however, this does not happen by the normal pathway and instead is due to retrograde conduction (conduction comes from the ventricles or from the AV node into and through the atria).[3]

• Junctional rhythm can be diagnosed by looking at an EKG: it usually presents without a P wave or with an inverted P wave. Retrograde P waves refers to the depolarization from the AV node back towards the SA node

Ventricular Arrhythmia

• Ventricular ectopic beats• Ventricular Tachycardia• Ventricular Fibrillation

Ventricular Ectopic beats• A ventricular ectopic beat (VEB) is an extra heart-beat originating in

the lower chamber of the heart. This beat, also called a premature ventricular contraction (PVC), occurs before the beat triggered by the heart's normal function.

• Ventricular ectopic beats are common and do not indicate a problem in people without heart disease. However, if a person has aortic stenosis, heart failure, or a previous heart attack, VEBs may be followed by ventricular tachycardia and fibrillation, which can lead to suddendeath.

Ventricular Tachycardia

• Ventricular tachycardia (VT) is a fast heart rhythm that occurs in one of the ventricles of your heart. It is like one electrical short circuit that races in a circle. In a VT, the heart beats with each race around the circuit at rates from 150 to 250 bpm.

Ventricular Fibrillation

• VF originates from many different locations in the ventricles, each one trying to signal the heart to beat. In this case, the heart beats much faster than normal, sometimes over 300 beats a minute. The lower chambers quiver instead of contract, and very little, if any, blood is pumped from the heart to the rest of the body. If your heart is in VF, you can become unconscious very quickly.

HEART Block

• AV blocks– First degree block

• PR interval fixed and > 0.2 sec – Second degree block, Mobitz type 1

• PR gradually lengthened, then drop QRS – Second degree block, Mobitz type 2

• PR fixed, but drop QRS randomly– Type 3 block

• PR and QRS dissociated

First-degree AV block

• First-degree AV block, or PR prolongation, is a disease of the electrical conduction system of the heart in which the PR interval is lengthened beyond 0.20 seconds.[1]

• In first-degree AV block, the impulse conducting from atria to ventricles through the AV node is delayed and travels slower than normal.

2nd degree HB

• Type 1 (Mobitz I/Wenckebach) • Type 2 (Mobitz II/Hay)

Type 1 (Mobitz I/Wenckebach)• progressive prolongation of the PR interval on (ECG) • consecutive beats followed by a blocked P wave (i.e., a 'dropped' QRS

complex). After the dropped QRS complex, the PR interval resets and the cycle repeats.

• One of the baseline assumptions when determining if an individual has Mobitz I heart block is that the atrial rhythm has to be regular. If the atrial rhythm is not regular, there could be alternative explanations as to why certain P waves do not conduct to the ventricles

Type 2 (Mobitz II/Hay)• Type 2 Second-degree AV block, also

known as "Mobitz II," is almost always a disease of the distal conduction system (His-Purkinje System).

• Mobitz II heart block is characterized on a surface ECG by intermittently nonconducted P waves not preceded by PR prolongation and not followed by PR shortening. The medical significance of this type of AV block is that it may progress rapidly to complete heart block, in which no escape rhythm may emerge.

Third-degree AV block• Also known as complete heart block, is a medical condition in which the impulse

generated in the SA node in the atrium does not propagate to the ventricles.[1]

• an accessory pacemaker in the lower chambers will typically activate the ventricles. This is known as an escape rhythm. Since this accessory pacemaker also activates independently of the impulse generated at the SA node, two independent rhythms can be noted on the electrocardiogram (ECG).

• The P waves with a regular P to P interval represents the first rhythm.• The QRS complexes with a regular R to R interval represent the second rhythm.

The PR interval will be variable, as the hallmark of complete heart block is no apparent relationship between P waves and QRS complexes

Ischemia

Remaining................– Rate– Rhythm (including intervals and blocks)– Axis Deviation– Hypertrophy– Ischemia– P waves– PR Interval– Q wave– QRS complex– ST Segment– T wave