Chapters 11, 12, 13

Electrocardiogram

Dr. Marko LjubkovićDepartment of Physiology

Normal EKG

EKG – Principle of Detection

AP vs. EKG

EKG Leads

Standard leadsPrecordial (chest) leads

Current Flows during Ventricular Depolarization

Cardiac Current Vectors

Axes of the leads

Average cardiac electrical axis (mean of all instantaneous vectors)

Resultant (instantaneous) vector

Vectorial Analyses

Determination of projected vectors with standard leads

Vectorial Analysis of the Normal EKG

Instantaneous vectors during atrial depolarization (similar to average vector)

Instantaneous vectors during ventricular depolarization

Q wave – left part of the septum depolarizes first

Vectorial Analysis of the Normal EKG

Ventricular repolarization

Vectorial Analysis of the Normal EKG

Average Cardiac Electrical Axis

• Constructed from QRS complexes of standard leads

• Indicates the mean direction of depolarization spreading through the ventricle

• Normally around 59º

• May be pathologically altered (axis deviation)

Ventricular Hypertrophy

Left ventricular hypertrophy Right ventricular hypertrophy

Bundle Branch Block

Blok lijeve grane snopa

• Vector directed to the side of the block

• QRS prolonged

Arrhythmias

Abnormal sinus rythms:

• Tachycadia (fever, sympathetic stimulation)

• Bradycardia (athletes, carotid sinus syndrome)

Atrioventricular Block

Possible causes:

• AV node ischemia

• AV node or bundle compression

• Myocarditis

• Excessive vagal stimulation

First degree block

Second degree block

Complete AV block

Premature Contractions (Extrasystolae)

Atrial extrasystole

AV nodal extrasystole

Ventricular extrasystolae

Paroxysmal Tachycardia

• Supraventricular (atrial and AV nodal) Common in young, healthy individuals

• Ventricular Often caused by ischemia May precede ventricular fibrilation

Ventricular Fibrillation

• Electric shock to the heart (alternating current ~ 60 Hz)

• Pathological cardiac alterations

• Dilatation

• Reduced velocity of conduction

Atrial Fibrillation

• Common in dilated atria

• Lack of P waves• QRS-T complexes preserved• Irregular rhythm