PAS 407 Heart Conduction

P wave

- SA node depolarization

- atrial contraction

PR segment

- delay at AV node

QRS complex

- ventrical depolarization

- atrial repolarization

ST segment

- plateau phase between ventricular depolarization and repolarization

T wave

- ventricle repolarization

first phase of cardiac cycle

Passive/Ventricular filling

- heart is in diastole and at "relaxation"

- 80% of blood freely pools into the ventricles

second phase of cardiac cycle

atrial contraction

- remaining 20% of blood contracted into the ventricles by the atria

third phase of cardiac cycle

isovolumetric ventricular contraction

- pressure slowly begins to rise in the ventricles and they start to contract

- the cuspid valves close causing the first heart sound "lub"

fourth phase of the cardiac cycle

ventricular ejection

- pressure is at its highest in the ventricles and blood is ejected into the major vessels the aorta and pulmonary trunk

final phase of the cardiac cycle

ventricular relaxation

- ventricles relax and the semilunar valves close causing the second heart sound "dub"

abnormalities in the ST segment can suggest a ____________

myocardial infarction (heart attack)

inverted T waves is correlated with..

an area of ischemia

peaking T waves

hyperkalemia, early myocardial infarction

ventrilcular fibrillation (V fib)

- random patterns of depolarization/repolarization across different aspects of the ventricular wall

- blood cannot properly be delivered to the major vessels

- In an EKG, no QRS complex can be seen or a wormy or squiggly appearance

ectopic pacemaker

- areas of excitability that depolarize rapidly other than the SA node

- this can start in the ventricles causing a PVC "premature ventricular contraction"

- EKG, typically no P wave or PR segment