THE HEARTBEAT CARDIAC PHYSIOLOGY In a single heartbeat

THE HEARTBEAT

CARDIAC PHYSIOLOGY • In a single heartbeat the entire heart contracts in series, atria the ventricles. • The heartbeat begins with an action potential generated by the pacemaker cells. • This action potential then stimulates the contraction of cardiac muscle cells which contract and force blood in the right direction at the right time in the system.

CARDIAC PHYSIOLOGY • When the right atria fills with blood, the cardiac muscle cells contract, decreasing the internal space of the chamber and forces the blood to move via the tricuspid valve to the right ventricle.

CARDIAC PHYSIOLOGY • The same thing happens to force the blood from the right ventricle to the lungs and again on the left side of the heart going from left atria to left ventricle and then left ventricle to aorta. • The contraction of right and left atria occur simultaneously as does the right and left ventricular contractions.

Cardiac Cycle

Monitoring Electrical Events of the Heartbeat • Echocardiogram: Creates an image of the electrical events of the heartbeat (blood flow too).

Monitoring Electrical Events of the Heartbeat • The electrical events of the heart while beating, can be monitored from the surface of the body using a device called and ECG/EKG (electrocardiogram).

Electrical Events of the Heart • Each time the heart beats, – A wave of depolarization (action potential impulse) Is initiated at the SA node. – It then radiates through the atria, reaches the AV node. – From the Av node it travels down the Bundle of His, into the interventricular septum all the way down to the apex. – It then turns and spreads through the ventricular wall.

Electrical Events of the Heart

Using & Reading an ECG/EKG • The ECG/EKG has leads (a pad that attaches to the surface of the chest). • The leads are arranged on the chest and can detect the action potential impulse of the cardiac tissue of the heart.

Using & Reading an ECG/EKG

Using & Reading and EKG • P-wave: Depolarization of atria, occurs about 100 msec before the atria contract • QRS complex appears as the ventricles depolarize, and the ventricles begin to contract shortly after the peak of the R-wave, this impulse is much stronger than that of the atria because of the muscle mass of the ventricle. • T-wave indicates ventricular repolarization, ( shows the relaxation of the muscle of the ventricle wall. – you don’t see the repolarization of the atria because it is masked by the QRS complex.

Using & Reading an ECG/EKG