Physiological Science 111B Module 2 Lecture 4

Front 1

Electrocardiogram (EKG) Features

Back 1

P Wave: atrial depolarization
P-R Interval: AV nodal conduction delay
QRS Complex: ventricular depolarization (atrial repolarization simultaneously)
S-T Interval: ventricles are contracting and emptying
T Wave: ventricular repolarization; ventricles are relaxing and filling
T-P Interval: time during which ventricles are relaxing and filling

Front 2

Abnormalities in the EKG are indicative of cardiac dysfunction, such as arrhythmias, ventricular hypertrophy and myocardial infarction.

Back 2

Tachycardia/Bradycardia (Fast/Slow HR): distance b/w 2 consecutive QRS Complexes
Atrial fibrillation: rapid, irregular, uncoordinated depolarizations of the atria with no definite P waves; accordingly, atrial contractions are chaotic and unsynchronized.
Myocardial Perfusion: ventricular repolarization (T Phase) is very sensitive to this
Coronary Artery Disease: ppl with this have abnormalities of the ST segment during myocardial ischemia (inadequate delivery of oxygenated blood to heart tissue)
Preventricular Contractions (PVC):ventricle depolarizes before it should

Front 3

Cardiac Cycle: Diastole

Back 3

RELAXATION AND FILLING
Passive filling of the ventricles occurs by suction as the ventricles relax. This begins when the atrial pressure exceed the ventricular pressure

Front 4

Cardiac Cycle: Atrial Contraction

Back 4

The atria add only ~20% of the volume to the ventricle and the ventricular pressure increases slightly; note that the P Wave (atrial depolarization) precedes atrial contraction.

Front 5

Cardiac Cycle: Isovolumic Ventricular Contraction

Back 5

The cardiac muscle is generating force, but the aortic valve has not opened yet and thus there is no change in ventricular volume. The valve opens once the left ventricular pressure reaches the aortic pressure.

Front 6

Cardiac Cycle: Systole

Back 6

VENTRICULAR CONTRACTION AND EMPTYING
Notice that not all of the blood that is in the chamber is ejected during ventricular contraction. Also notice that the QRS complex appears prior to the beginning of the systolic period.

Front 7

Cardiac Cycle: Isovolumic Ventricular Relaxation

Back 7

The heart is no longer ejecting blood, as the pressure in the aorta is greater than in the left ventricle causing the aortic valve to close.

Front 8

Cardiac Cycle: Other Points

Back 8

-The dichrotic notch is due to the disturbance of the blood rebounding against the closed aortic valve.
-At rest about 1/3 of the cycle is spent in systole and 2/3 in diastole.
-One will also hear 2 major heart sounds that correspond to closing of the valves. The first sound is due to closure of the AV valves and the second is due to the closure of the aortic/pulmonary valves.