cardiac physiology and introduction to

Cardiac Physiology and Introduction to ECG

Essentials of Sleep Technology

EKG Review

Objectives

1. To become familiar with cardiac anatomy and physiology, and the cardiac electro‐conduction system.

2. To understand the representation of cardiac activity on an ECG

3. To begin to be able to recognize normal and abnormal cardiac rhythms that may be seen on a polysomnogram, and develop the ability to describe and document ECG rhythms


The Heart

The heart consists of 4 chambers• Right Atrium• Left Atrium• Right Ventricle• Left Ventricle

The left and right chambers are eachseparated by a septum. Valves allow blood flow between chambers.

LV


The Cardiac Cycle

Definition

A cardiac cycle is one complete heartbeat.

It consists of two phases:

• contraction

• relaxation


Blood’s major component:

• Hemoglobin‐ iron containing protein, found in the red blood cells of the blood, facilitates transportation of oxygen

• Hemoglobin transports oxygen from the lungs to the rest of the body.


Blood Vessels

• 2 types:

Arteries: muscular/elastic (pulsate), carry oxygenated blood away from the heart.

Veins: thinner/ not as muscular, carry blood back to the heart


Major Blood Vessels

• Aorta: “Main” blood vessel that comes out of the heart delivering oxygenated blood to the body and heart

• Coronary arteries: smaller blood vessels that supply the heart


Blood Pressure

• Refers to the force exerted by the circulating blood on the walls of the blood vessels.

• Blood moves through:

• arteries, arterioles, capillaries and veins

• Normal blood pressure: 120/80 mmHg


Electrical Conduction of the Heart Initiates contraction

• Sino‐Atrial Node (SA Node) (60‐100 bpm)

• Atrio‐ventricular Node (AV Node) (0.04 sec)

• Bundle of His (40‐60 bpm)

• Purkinje Fibers (15‐40bpm)



Standard PSG leads

Lead I or Lead II are the leads used in a PSG.

Lead I : Records electrical activity between the

right arm and the left arm.

Lead II : Records electrical activity between the

right arm and the left abdomen or left left leg.

The deflection of the waveforms is determined by:

• The location of electrodes on the body.

• The selection of a negative and positive electrode


Components of the EKG

Three basic waveforms make up the EKG

• P Wave

• QRS complex

• T wave



Components of the EKG

Electrical activity during

one cardiac cycle

• Sinus node impulse

• Atrial contraction

• Ventricular contraction

• Ventricular repolarization

Corresponding waveform on EKG

• Precedes P wave, not visible on EKG

• P wave

• QRS complex

• T wave


Normal Sinus Rhythm (NSR)

• Heart Rate ‐ Normal rate is 60‐100 bpm

• Rhythm ‐ Atrial and ventricular rhythms are

regular

• P wave ‐ Identical and proceed each QRS

• QRS complex ‐ narrow, follows each P wave


Sinus Arrhythmia


Sinus Arrhythmia

Normal variation ‐ related to resp. rate.

• Heart Rate ‐ 60‐100 bpm. May slow down to less than 60 and increase to more than 100.

• Rhythm ‐ slightly irregular

• P Wave ‐ identical and precede each QRS.


Sinus Bradycardia

• Heart Rate ‐ less than 40 bpm ages 6‐adult

• Rhythm ‐ regular

• P waves ‐ normal, precede each QRS

• QRS ‐ usually normal, followed by T wave

Intervention ‐ none, unless symptomatic ‐( dizziness or chest pain ) ‐ Notify M.D.


Sinus Tachycardia

• Heart Rate ‐ greater than 90 bpm for adults

• Rhythm ‐ regular

• P waves ‐ usually normal, all followed by QRS,

but may be buried in QRS.

• QRS ‐ normal

Significance: normal response by heart in demand for increase in blood flow.

Intervention/ notification: circumstance /lab protocol


Sinus Tachycardia


Premature Atrial Contractions (PAC)

• Conduction ‐ atrial focus outside SA node

• Rhythm ‐ irregular when the PAC occurs

• P waves ‐ premature and abnormal

• R‐R interval ‐ unequal when PAC is present

Significance ‐ usually benign in patients without heart disease. May be related to caffeine use.

Intervention ‐monitor for frequency, differentiate from PVC.


Premature Atrial Contractions


Atrial Flutter

• Rate ‐ Atrial: rapid (250‐350 bpm),

Ventricular: irregular (60‐100)

• Rhythm ‐ usually regular

• P Wave ‐ saw‐toothed (F waves)

• QRS ‐ normal

Intervention ‐ document, monitor for extremely rapid ventricular rate. Treated with medication or cardioversion


Atrial Flutter


Atrial Fibrillation

Numerous unorganized ectopic atria foci dischargeAtria quivers vs contracting

Irregularly irregular ventricular rhythm • QRS – normal• P waves – not consistent, vary in size, shape, and

timing

Significance ‐ possible reduced cardiac outputIntervention ‐ document and monitor


Atrial Fibrillation


Atrioventricular (AV) Blocks

Definition ‐ A delay in conduction time at the

AV node.1st Degree

• 2nd Degree

• Type 1 (Wenckeback)

• Type 2

• 3rd Degree


Atrioventricular Block, (AV Block)1st degree

Definition ‐ A steady delay in conduction time at the AV node.

• Rate ‐ Atrial and Ventricular : (60‐100)BPM

• Rhythm ‐ Atrial and Ventricular : Regular

• P Waves ‐ identical and precede QRS

• QRS ‐ usually normal

• P‐R Interval ‐ Prolonged, but constant

Significance and Intervention ‐ Usually none


AV Block ‐ 1st degree


AV Block – 1st Degree


AV Block ‐ Second DegreeType 1 or Wenckebach

Definition ‐ Conduction disturbance in AV node

in which each successive impulse is conducted later and later.

Eventually an impulse arrives during the absolute refractory period and cannot be conducted.


2nd Degree AV Block Wenckebach

• Rate ‐ Atrial rate is greater than ventricular.

60‐100 bpm

• Rhythm ‐ Atrial: regular, Ventricular: irreg.

R‐R interval progressively shortens, until a P wave appears without a QRS complex (dropped beat). Cycle then repeats.

• P Waves ‐ Normal

• P‐R Interval ‐ Gradually lengthens until a QRS is dropped

• QRS ‐ Normal, but dropped periodicallyEssentials of Sleep Technology

2nd Degree AV Block ‐Type 1

Significance and Intervention ‐

• No intervention is necessary

• Monitor for possible progression to higher degree of block


2nd Degree AV Block ‐Type 1


2nd Degree AV Block‐ Type II

Definition ‐ A complete block of the conduction system at the AV node level in which dropped beats occur without warning.

• Rate ‐ Atrial: usually normal, Ventricular: may be WNL, but is slower than atrial.

• Rhythm ‐ Atrial: regular, P‐P intervals are constant. Ventricular: regular or irregular.

• P Waves ‐ Normal, but some not followed by a QRS complex.



• QRS Complex : Normal or widened, depending on exact location of the block.

* Note that in Type II block the P‐R and R‐R intervals do not vary preceding a dropped beat.

Significance : More serious than Type I because the frequency and severity is unpredictable.

Intervention : Depends on patient’s symptoms.

Rule out artifact, document and notify M.D.



AV Block, Third‐Degree

Definition ‐ All atrial impulses are blocked at the AV junction, and the atria and ventricles beat independently.

• Rate ‐ Atrial is faster than ventricular. Ventricular rate is 40‐60 bpm.

• Rhythm ‐ Regular P‐P intervals and regular R‐R intervals, but no relationship between the atrial and ventricular rhythm.

• P Waves ‐ Normal


AV Block, Third Degree

• QRS Complex ‐ Depends on where the ventricular beat originates. Complex may be narrow, wide or wide and bizarre.

* Most distinguishing feature is that atria beat independently of the ventricles.

Significance and Intervention ‐ If the ventricular pacemaker fails, cardiac arrest can occur. Document, monitor and notify M.D.


AV Block, Third Degree


Ventricular Arrhythmia


Premature Ventricular Contractions (PVCs)

Definition ‐ An ectopic beat originating in the ventriclesoccurs earlier than expected and

often followed by compensatory pause.

May be uniform(unifocal) or multi‐focal.

• Rhythm ‐ atrial and ventricular: irregular as a result of the PVCs.

• P Waves ‐may be present or absent, often buried

in the PVC

• QRS ‐ early, wide and bizarre


PVCs ‐ cont’d

• Significance ‐ can occur in healthy people

without a cause. Isolated PVCs are of no significance. More serious in presence of heart disease. Two consecutive PVCs are called coupling, three or more are VT.

• Intervention ‐ If isolated, document and monitor for increasing frequency or presence of multi‐focal PVCs


PVC


PVC Samples


PVCs ‐ Dangerous Forms

PVCs which require special attention:

• Couplets ( 2 successive)


Couplet


Couplets




• Bigeminy (every other beat is a PVC)


Bigeminy






• Trigeminy ( every third beat is a PVC)


Trigeminy







• Multifocal PVCs ‐ PVCs without uniform appearance


Multiform/ Multifocal PVCs







• Multifocal PVCs ‐ PVCs without uniform appearance

• Frequent (more than 6 per minute)


Frequent PVCs


PVC Combinations

Trigeminy

Bigeminy


Assessing PVCs

• How often do they occur? (6 or more = tx)

• What is their pattern? Do they appear in clusters? E.g.: couplets, runs, bigeminy, trigeminy.

• Do they look alike? Are they uniform (unifocal) or multiform? ( multi‐focal)


Premature Junctional Beat

• Ectopic focus is close to AV node

• premature

• no P wave or inverted

• QRS is normal


Premature AtrialBeat

Premature JunctionalBeat

Premature VentricularContraction


Premature Junctional Contraction


Ventricular Tachycardia (V‐tach)

Definition ‐More than 3 PVCs occur in succession at a rate of more than 100 bpm

Rhythm ‐ can be regular or irregular

P Waves ‐ usually not visible

QRS ‐ wide and bizarre

Significance ‐ life‐threatening

Intervention ‐ determine patient responsiveness, and symptoms. Initiate Code response

*bursts of V tach less than 100 bpm : document and monitor


Ventricular Tachycardia (V‐tach)


2 Types of Tachycardia

Described by width of the QRS complex

1) Narrow Complex Tachycardia: min. of 3 consecutive beats, > 100 bpm, QRS duration < 120 msec.

2) Wide Complex Tachycardia: min. of 3 consecutive beats, > 100 bpm, QRS duration > 120 msec.


Ventricular Fibrillation(V‐Fib)

Definition ‐ unorganized electrical impulse,

no conduction or ventricular contraction.

• Rhythm ‐ rapid and chaotic.

• P Waves ‐ not discernible

• QRS ‐ not discernible


Intervention ‐ quickly rule‐out artifact, determine patient responsiveness and symptoms. Initiate Code response and CPR if absent pulse


Ventricular Fibrillation(V‐Fib)


Asystole

Definition ‐ A total absence of electrical activity/cardiac pauses greater than 3 sec. (ages 6 – adult)

• Rhythm ‐ absent

• P Waves ‐may be present or absent

• QRS ‐ absent


Intervention ‐ quickly rule‐out artifact, determine patient responsiveness and symptoms. Initiate Code response and CPR if absent pulse


Asystole

OSAS‐Related Brady‐Tachy

Intervention ‐ Document and observe for prolonged sinus pause during bradycardia and associated arrhythmia.

Anticipate ‐ Both apnea and arrhythmia may worsen in REM sleep.


PSG with Brady‐Tachy

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