Basic Cardiology The Heart Pericardium Epicardium Myocardium atrial

Basic Cardiology

The Heart ❖ Pericardium ❖ Epicardium ❖ Myocardium ❖ ❖ atrial muscle ❖ ventricular muscle ❖ conductive tissue Endocardium

The Heart

Myocardium ❖ branch ❖ intercalated disks with gap junctions

Intercalated Disc

Electrical Stimulation of the Heart

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 Interatrial ❖ Anterior Interarterial band or Bachmann’s bundle

Atrioventricular (AV) Junction ❖ AV Node ❖ Located at the base of the right atria near the interventricular septum ❖ Smaller cells, fewer gap junctions, slower ❖ Maximal rate is ~230 per minute; also maximal ventricular rate

AV Junction ❖ ❖ AV Bundle 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 impulse

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

“If you understand the normal physiologic stimulation of the heart, you have the basis for understanding the abnormalities of heart rhythm and conduction the produce distinctive ECG patterns. ” p. 5

Electrocardiogram SA node AV node Atrial depolarization Bundle branches Ventricle depolarization Purkinje fibers Ventricle repola

Electrocardiogram

Rhythms ❖ Normal conduction ❖ ❖ Sinus Rhythm Abnormal conduction ❖ Junctional rhythm ❖ ❖ e. g. escape pacemaker Ventricular rhythm

Cardiac Conductivity ❖ SA node - slow ❖ Internodal pathways - fast ❖ AV node - slow ❖ Purkinje fibers - faster

Cardiac Automaticity ❖ ❖ Automaticity ❖ SA node - primary pacemaker ❖ Other sites e. g. AV junction Certain conditions increase the automaticity of ectopic pacemakers ❖ Ectopic = outside of the sinus node pacemaker (nonsinus)

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 ❖ The Left Main (LM) ❖ Left Anterior Descending (LAD) ❖ Left Circumflex (LCX). ❖ The Right Coronary Artery (RCA) ❖ 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 LAD Supply the anterior septum, the anterior wall, and in most cases apex. 9 o'clock to 1 o'clock. Supply the lateral wall LCX 2 o'clock to 4 o'clock RCA Supply the posterior lateral segments, the inferior segments, and the posterior septum. 5 o'clock to 8 o'clock

Class Organization 1. 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