Rhythm recognition

Anatomy and Physiology

Cardiac muscles


External layer of the heart

Coronary arteries are found in this layer


Middle and thickest layer

Responsible for contraction


Innermost layer of the heart

Lines the myocardium

Covers the heart valves


Tricuspid – separates right atrium and ventricle

Pulmonic– Between right ventricle and pulmonary valve

Mitral – Between left atrium and ventricle

Aortic – Between left ventricle and aorta

Coronary arteries

Right Supplies:

 Right atrium

 Right ventricle

 Inferior and posterior of left ventricle

Left Supplies

 Anterior and lateral left ventricle

 Left atrium

 Part of right ventricle

CNS control

Brain stem (Medulla oblogota) originates two nerves

Sympathetic for stimulation of the rate and contractions. Located mainly in the ventricles

Parasympathetic( vagal nerve) located in the atria for slowing and controlling rate.

 characteristics of the HeartCardiac cells have basically four characteristics

Excitability – the ability to respond to outside stimulus

Automaticity – The ability to produce an electrical impulse without outside stimulus

Conductivity – Receives impulse and ability to pass impulse on to other cells

Contractility – The ability for the cells to shorten causing muscle contractions

Conduction system

Sinoatrial node

Cluster of cells located in the upper posterior portion of the right atrium

Depolarizes faster than other cells in the heart, therefore responsible for pacing the heart

Intrinsic rate of 60 – 100 bpm.

Atrioventricular node (AV node)

Located in the lower portion of the right atrium

Possess no pacemaker cells

Has two functions

To delay impulse to allow atria to contract

Receives electrical impulses and direct them down pathway towards the ventricles.

Bundle of His

Also known as the common bundle

Located in the upper portion of the interventricular septum

Connects the AV node with the bundle branches

Intrinsic rate of 40 – 60 bpm

Bundle of His and the AV node are known as the AV junction

Right and left bundle branches

RBB innervates the right ventricle

LBB divides into two bundles called fascicles

Supplies the left ventricle which is thicker and more muscular

The two fascicles are known as the left anterior and left posterior fascicles

Purkinje fibers

Originate from the bundle branches and branch into smaller webs and invade approximately 1/3 into the myocardium.

This network causes equal contraction throughout the ventricles

Intrinsic rate is 20 - 40 bpm

Wave forms

  Guide to EKG Interpretation

P wave

First wave of the cardiac cycle

Originates in the SA node.

Upright from the isometric line

PR interval

Reflects the contraction or depolarization of the atria

Demonstrates the delay of the impulse at the AV Node.


QRS complex

Ventricle contraction (depolarization)

Q wave is negative, which means it falls under the isometric line

Represents depolarization at the isoventricle septum

R wave is the first positive spike following the Q wave

S wave negative wave following the R

S and R wave represent the depolarization of the ventricles.

T wave

Ventricle Repolarization. Preparing to receive further impulses from the SA node – Bundle of His

Separated into two factors

Absolute refractory: relative safe period

Relative refractory: Unsafe secondary to the ventricles can misfire if another site sends impulse, causing the patient into a cardiac dysrhythmia. 



Sinus rhythms

normal sinus rhythmNormal sinus rhythms - P wave QRS T wave

 Sinus Bradycardia - Rate slower than 60 bpm

Sinus Tachycardia – rate greater than 100 bpm

AV Blocks

1st degree AV Block1st degree AV block – PR interval > .20 seconds


2nd degree AV block type 1 wenckebach -PR interval elongates until total drop of signal and returns to cycle


2nd degree AV block type 2 Classical Pr interval remains constant until several p waves are seen without QRS following


Total AV block 3rd degree no relationship between P wave and QRS.  Intrinsic rates from both regions take over bpm.


Atrial Dysrhythmias

Atrial Fibrillation Impulse generated from other Atrial sites other than the SA node. With Fib usually from multiple sites

No P wave presentation

Atrial Tachycardia

Rate > 100 bpm

No P wave

Decreased cardiac output

Atrial Flutter

Occurs usually in the right atrium

More common in men

Can occur at any age

Signifies underlying disease

Ventricle dysrhythmia’s

Premature Ventricle Contractions(PVC’s)

Can be unifocal or mulitifocal

Usually secondary to hypoxia

Prominent cause for R on T phenomena

Most common of arrhythmia’s

Ventricle Tachycardia

Rate 100 – 250 bpm

If pulse is present will not last long

Single impulse point

  Ventricle Fibrillation

Impulse from multiple sites

Can be course or fine

No organized Repolarization






CNS control

Atrial rhythms

Ventricle rhythms