1. EKG AUTORHYTHMICITY

2. Figure 21.11 The Cardiac Cycle
Start
Atrial systole begins: Atrial contraction forces a small amount of additional blood into relaxed ventricles.
Atrial systole ends, atrial diastole begins
0 msec
800 msec
100 msec
Atr
ial sy
sto le
Ven
tri
cul ar
dia
sto le
Ven
tri
cul ar sy
sto le
Cardiac cycle
Ventricular systole— first phase: Ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves.
Ventricular diastole—late: All chambers are relaxed. Ventricles fill passively.
Atr
ial
dia
sto le
370 msec
Ventricular systole— second phase: As ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected.
Ventricular diastole—early: As ventricles relax, pressure in ventricles drops; blood flows back against cusps of semilunar valves and forces them closed. Blood flows into the relaxed atria. 2

3. EKG
Electrokardiogram- device to record the action potential of cardiac muscle summation
Cannot detect force of contraction
Cannot detect Blood Pressure
Can detect abnormal heart rates/ rhythems
Can detect abnormal conduction pathways
Can detect hypertrophy and atrophy and relative position of damage
P Wave- Action potential depolarization of atrial myocardium
Causes Atrial contraction
QRS Complex- Ventricular depolarization
Causes onset of ventricular contraction
Also atrial repolarization masked by QRS signal
T Wave- repolarization before ventricular relaxation
U wave – repolarization of the purkinje fibers
PQ/PR Interval- .16 sec- atria contract and relax
QT Interval- .3 sec- ventricles contract and relax
1 Cardiac Cycle- from onset muscle contraction to next

6. Autorhythmicity of Cardiac Muscle
Action potentials in heart without external stimuli
After each action potential the membrane potential returns to its resting membrane potential
Unstable slow ion channels open and cause depolarization
This causes fast channels to open and increase depolarization
When depolarization reaches threshold--action potential happens more often in SA Node because more slow channels
Plateau Phase- Prolonged period of depolarization, separates contractions in the heart
Heart has long action potential so the heart will rest between contractions and not tetanic contractions
Absolute refractory period – CM insensitive to further stimuli

7. Figure 21.11 The Cardiac Cycle
Start
Atrial systole begins: Atrial contraction forces a small amount of additional blood into relaxed ventricles.
Atrial systole ends, atrial diastole begins
0 msec
800 msec
100 msec
Atr
ial sy
sto le
Ven
tri
cul ar
dia
sto le
Ven
tri
cul ar sy
sto le
Cardiac cycle
Ventricular systole— first phase: Ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves.
Ventricular diastole—late: All chambers are relaxed. Ventricles fill passively.
Atr
ial
dia
sto le
370 msec
Ventricular systole— second phase: As ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected.
Ventricular diastole—early: As ventricles relax, pressure in ventricles drops; blood flows back against cusps of semilunar valves and forces them closed. Blood flows into the relaxed atria. 7

8. The Cardiac Cycle ANIMATION The Heart: Cardiac Cycle
ANIMATION The Cardiac Cycle: Part 1
ANIMATION The Cardiac Cycle: Part 2
ANIMATION The Cardiac Cycle: Part 3
ANIMATION The Cardiac Cycle: Part 4
ANIMATION The Cardiac Cycle: Part 5 8