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!
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.
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. (300 / 6) = 50 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 found • Pulse averages 70–80 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