Download Cardiac Cycle (PPT#4)

Cardiac Cycle
► The
two atria contract at the same time,
then they relax while the two ventricles
simultaneously contract.
► The contraction phase of the ventricle
chambers is called systole.
► The relaxation phase is called diastole.
► At a normal heart rate, one cardiac cycle
last for 0.8 seconds!
Cardiac Cycle Continued….
► Cardiac
Cycle = “events of one complete
heart beat”
► Mid-to-late diastole (relaxation) = blood
flows into ventricles
► Ventricular systole (contraction) = blood
pressure builds before ventricles contract
pushing blood out
► Early diastole = atria finish re-filling;
ventricular pressure is low
The Normal Conduction System
What is an Electrocardiogram?
The electrocardiogram (EKG or ECG) is a
graphic display of the electrical events of the
cardiac cycle.
Each event has a
distinctive waveform,
the study of which can
lead to greater insight
into a patient’s cardiac
output.
EKG Waves
Wave Interpretation
►P
Wave = contraction of atria
► PQ Wave = signal arrives at AV node slowing
down a bit to allow ventricles to fill with blood
► Q Wave = signal moves to Bundle of His and
divides into the bundles and Purkinje fibers
► R Wave = contraction of left ventricle
► S Wave = contraction of right ventricle
► T Wave = ventricles relaxing
Rule of 300
►Take
the number of “big boxes” between
neighboring QRS complexes, and divide this
into 300. The result will be approximately
equal to the heart rate
►Although
fast, this method only works for
regular rhythms.
What is the heart rate?
(300 / 6) = 50 bpm
What is the heart rate?
(300 / ~ 4) = ~ 75 bpm
What is the heart rate?
(300 / 1.5) = 200 bpm
10 Second Rule
►As
most EKGs record 10 seconds of
rhythm per page, one can simply count the
number of beats present on the EKG and
multiply by 6 to get the number of beats per
60 seconds.
►This
method works well for irregular
rhythms.
What is the heart rate?
33 x 6 = 198 bpm
Pulse
“Heart Rate”
►Pulse
 Pressure wave of blood
►Monitored
at “pressure
points” in arteries
where pulse is easily
palpated
►Pulse averages 70–76
beats per minute at
rest
Blood Pressure
►Measurements
by health professionals are
made on the pressure in large arteries
 Systolic—pressure at the peak of ventricular
contraction
 Diastolic—pressure when ventricles relax
 Write systolic pressure first and diastolic last
(120/80 mm Hg)
►Pressure
in blood vessels decreases as
distance from the heart increases
Measuring Arterial Blood Pressure
Measuring Arterial Blood Pressure