Cardiac Cycle
•  1 complete contraction and relaxation of
the heart
•  Diastole - the time during which cardiac muscle relaxes.
•  Systole - the time in which cardiac muscle is contracting.
– Atrial systole
– Atrial diastole
– Ventricle systole
– Ventricle diastole
– Quiescent period
Animation of Cardiac cycle
•  http://
www.getbodysmart.co
m/ap/
circulatorysystem/
heart/
mechanicalevents/
cardiaccycle/
tutorial.html
Electrical conduction in the Heart
  SA node (sinoatrial
node)
  AV node
(atrioventricular node)
  Bundles of His
  Purkinje Fibers
Animation of transmission of
signal
http://www.lifehugger.com/pic/
1801/
Normal_ECG_wave_Animation
•
Sinoatrial node (SA
node) - main pacemaker
of the heart
•  in the right atrium
(near the entry of
the superior vena
cava)
•  Atrioventricular node
(AV node) - found near
the floor of rt. Atrium
•  Note of interest:
•  The AV node
–  delays the transmission of action
potentials slightly,
–  allowing the atria to complete their
contraction before the ventricles begin their
contraction.
Electrocardiogram (ECG)
•  Composite of all action potentials of
myocardial cells
•  detected, amplified and recorded by
electrodes on arms, legs and chest
ECG
•  P wave - atrial systole
–  SA node fires
–  occurs right before atria contract
•  QRS complex - atrial diastole and ventricles
systole
–  atrial diastole (signal obscured)
–  AV node fires, occurs right before ventricles
contract
•  T wave - ventricles diastole
–  ventricular repolarization (get ready to fire again,
refill with blood)
Animation of ECG
http://www.getbodysmart.com/
ap2/circulatorysystem/heart/
electricalevents/ecg/tutorial.html
Normal Electrocardiogram (ECG)
Electrical Activity of Myocardium
1)atria begin to
depolarize
2) atria depolarize
3)ventricles begin to
depolarize at apex;
atria repolarize
4)ventricles depolarize
5) ventricles begin to
repolarize at apex
6) ventricles repolarize
Summary of cycle - animation
http://www.nhlbi.nih.gov/health/
dci/Diseases/hhw/
hhw_electrical.html
Diagnostic Value of ECG
•
1.
2.
3.
4.
Invaluable for diagnosing
abnormalities in:
conduction pathways
MI
heart enlargement
electrolyte and hormone imbalances
ECGs, Normal & Abnormal
No P waves
ECGs, Abnormal
Arrhythmia: conduction failure at AV node
No pumping action occurs
Heart Sounds
•
Auscultation - listening to sounds made
by body
1.  First heart sound (S1),
•
•
louder and longer “lubb”,
occurs with closure of AV valves
2.  Second heart sound (S2),
•
•
softer and sharper “dupp”
occurs with closure of semilunar valves
Unbalanced Ventricular
Output
Unbalanced Ventricular
Output
Cycle of a Heartbeat:
1.  Atrial Systole: - atria contract - blood is forced into the ventricles
•  P wave occurs right before this
2.  Ventricular Systole - ventricles contract •  blood is forced into the pulmonary artery and aorta
3. Atrial Diastole •  Occurs during ventricular systole
•  Atria refill with blood and muscles “relax”
•  2 and 3 occur during the QRS wave
4. Ventricular diastole •  Ventricles fill with blood from atria
•  T wave occurs