CARDIAC CYCLE AND HEART

SOUNDS

CONDUCTION SYSTEM OF THE HEART a. Sinoatrial node (SA node) b. Atrioventricular node (AV node) c. Atrioventricular bundle (AV

bundle) d. Right and left atrioventricular

bundle branches e. Purkinje fibers

SINOATRIAL NODE

Located Junction of Superior Vena Cava Specialized Pacemaker Cells

Intrinsic Rhythm- without stimulation by nerve impulses from brain and spinal cord

Initiates impulses at regular intervals

ATRIOVENTRICULAR NODES From SA node to Contraction of both

Atriums Internodal Bundles- Right Atrium Interartial Bundle- Left Atrium Internodal Bundles to Atrioventricular

node

BUNDLE OF HIS Av Node to Bundle of His (AV Bundle) Left and Right Bundle Branches Branches to Purkinje Fibers Simultaneously Contract Ventricles

HEARTBEAT SA node Intrinsic Rhythmical rate 70-75

beats

What happens when SA node loses ability to initiate impulse?Another Excitable Component takes overAbnormal/ ectopic pacemakers

AV Node or Purkinje Fibers Slower rate than SA Node AV Node- 40-60 beats per min

CONDUCTION OF THE HEART VIDEO Heart Conduction Animation McGraw Hill

ELECTROCARDIOGRAM (ECG) ECG (EKG)

a recording of the electrical activity (changes) during a cardiac cycle

How it worksTwo Electrodes of VoltmeterPassing of Action Potential between two

electrodes

ECG WAVES P Wave – depolarization(+) of the atria

(atrial contraction – systole)SA Node Atria

QRS Complex – depolarization of the ventricles (ventricular contraction, systole)AV Purkinje Fibers

T Wave – Repolarization(-) of the ventricles

CARDIAC CYCLE Cardiac Cycle is all the events

associated with the blood flow through the heart during one complete heartbeatSystole – contraction period of a chamber –

ejection of blood.Diastole – relaxation period of a

chamber – filling of blood

Contraction (Eject) and Relaxation (Filling) ALWAYS follows electrical events seen in an ECG

CARDIAC CYCLE SA Node initiates action potential.

Atrial systole (1) causes Atrial pressure to increase, blood sent to ventricles through AV valve. (P Wave)

Ventricular Systole caused by impulsetraveling down Bundle of His to PurkinjeFibers (QRS Wave)

CARDIAC CYCLE Isovolumetric Ventricular Contraction (2)

AV valves snap close causing the “Lubb” sound at the pressure rises in the ventricles

Ejection (3) of blood into pulmonary circuitpressure in ventricle is greater than in the

arteries so semilunar valves are forced open.As pressure drops the Semilunar Valves snap

close causing “Dubb” sound

CARDIAC CYCLE Isovolumetric Ventricular Relaxation (4)

Diastole begins, all valves closed. Once pressure has dropped low enough, the AV valves open and…..

Passive Ventricular Filling (5) because atrial pressure is higher than ventricle pressure. Toward the end of this period, atrial systole begins.

HEART SOUNDS Closing of the heart valves Described as “Lubb – Dubb”

Basic rhythm is lubb-dubb, pause, lubb-dubb, pause, lubb-dubb, pause.

First sound “Lubb” is the longest and loudest occurring when AV valves close.

Second sound “Dubb” is short, sharp sound occurring when Semilunar valves close.

ABNORMAL SOUNDS – HEART MURMURS Sound is due to turbulence Generally, heart murmurs indicate heart

valve problem “Swishing” sound indicates an

incompetent valve - partially open valve after it should be closed so the blood backflows through the valve

High-pitched or click sound indicates a stenotic valve – the valve should be wide open, but it is not.