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