Cardiac Cycle

1
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!

2
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

3
(No Transcript)
4
The Normal Conduction System
5
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
patients cardiac pathophysiology.
6
EKG Waves
7
(No Transcript)
8
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

9
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 rate
• Although fast, this method only works for regular
  rhythms.

10
What is the heart rate?
www.uptodate.com
(300 / 6) 50 bpm
11
What is the heart rate?
www.uptodate.com
(300 / 4) 75 bpm
12
What is the heart rate?
(300 / 1.5) 200 bpm
13
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.

14
What is the heart rate?
33 x 6 198 bpm