Basic CardiologyBasic CardiologyTopic Number 1Topic Number 1

Electrocardiogram

❖ ECG versus EKG

❖ = graphical recording of the electrical activity of the heart

Electrical Stimulation of the Heart

❖ SA node

❖ pacemaker

❖ AV junction (bridge)

❖ AV node

❖ bundle of His

❖ Bundle branches

❖ right

❖ left

❖ fasicles (small subdivisions)

❖ Purkinje fibers

Sinoatrial (SA) Node

❖ Right atrium

❖ Inherent rhythm 80-100 bpm)

❖ Usually sets the heart rate (sinus rhythm)

Internodal & Interarterial Pathways

❖ Internodal

❖ Anterior

❖ Middle (Wenckebach branch)

❖ Posterior

❖ Interarterial

❖ Bachmann’s branch and descending branch

❖ 50 msec

Atrioventricular (AV) Node

❖ Located at the base of the right atria near the interventricular septum

❖ Smaller cells, fewer gap junctions, therefore slower

❖ 100 msec

❖ Maximal rate is ~230 per minute; also maximal ventricular rate

AV or Bundle of His

❖ Only cellular connection between atria and ventricles

❖ Together with AV node make up the AV junctional tissue

❖ Intrinsic heart rate of 40-60 bpm

❖ If SA node fails, AV junctional tissue can control heart rate

❖ Slows down the cardiac impluse

Bundle Branches❖ Right and left branches

❖ Two left branches (sometimes three)

❖ Left anterior fascicle or left anterior bundle branch; thinner, carries impulses to septum, left anterior wall, and anterior papillary muscle

❖ Left posterior fascicle or l. post. bundle branch; thicker, carries impulses to posterior, inferior, left ventricular free wall and posterior papillary m. with dual blood supply, less likely to become ischemic,

❖ Both left and right BB travel down towards the apex of the heart where they fan out into Purkinje fibers

Purkinje Fibers

❖ Pass through the ventricular myocardium

❖ Contraction starts at the apex

❖ Fast rate of action potential generation, numerous sodium ion channels and mitochondria and fewer myofibrils

Electrical Stimulation of the Heart

❖ Video

Electrocardiogram

SA node

AV node

Bundle branches Purkinje fibers

Atrial depolarization Ventricle depolarization Ventricle repolarization

Electrocardiogram

Rhythms

❖ Normal conduction

❖ Sinus Rhythm

❖ Abnormal conduction

❖ Junctional rhythm

❖ e.g. escape pacemaker

❖ Ventricular rhythm

Cardiac Conductivity

❖ SA node and atria - fast

❖ AV node - slow

❖ Purkinje fibers - faster

Cardiac Automaticity❖ Automaticity

❖ SA node - primary pacemaker

❖ Other sites e.g. AV junction

❖ Automaticity of pacemakers outside the sinus node can increase

❖ Ectopic (non-sinus) pacemaker

❖ a run of ectopic beats can lead to abnormal tachycardia

Abnormalities

❖ AV heart block = blockage of stimuli through AV junction

❖ Bundle Branch Block = disease of bundle branches

❖ ST segment changes = damage to ventricular muscle

Coronary Arteries

Coronary Arteries❖ There are two coronary arteries, Left

and Right.

❖ The left starts as the 1/2 - 1 cm long Left Main (LM) and divides into the Left Anterior Descending (LAD) and Left Circumflex (LCX).

❖ The Right Coronary Artery (RCA) swings around (and supply) the right ventricle and continues in most cases down the posterior aspect of the heart in the grove where RV meets LV.

❖ The RCA on the posterior part of the heart is often called the Posterior Descending Artery (PDA), in most cases it originate from the RCA but in some cases it comes from LCX.

Coronary Artery Perfusion

Coronary Artery Perfusion

LAD

Supply the anterior septum, the anterior wall, and in most cases apex.It might wrap-around apex and supply the most apical portion of the inferior and lateral wall.In a short axis cut usually supply from 9 o'clock to 1 o'clock.

LCXSupply the lateral wall, usually from 2 o'clock to 4 o'clock in a short axis cut.

RCASupply the posterior lateral segments, the inferior segments, and the posterior septum.Usually from 5 o'clock to 8 o'clock in a short axis cut.

Class Organization1. Resting 12 lead ECG

1. Understanding normal 12 lead ECG and conditions that cause abnormal depolarization and repolarization

2. Recognizing abnormal rhythms and AV conduction disturbances

3. Associating the ECG arrhythmia with its pathology

2. Exercise ECG

1. Recognizing abnormal rhythms and AV conduction disturbances

2. Associating the ECG arrhythmia with its pathology