Cardiac Cycle The two atria contract at the same time, then they relax while the two ventricles simultaneously contract. The two atria contract at the.

Cardiac CycleCardiac Cycle

►The two atria contract at the same The two atria contract at the same time, then they relax while the two time, then they relax while the two ventricles simultaneously contract.ventricles simultaneously contract.

►The contraction phase of the ventricle The contraction phase of the ventricle chambers is called chambers is called systolesystole..

►The relaxation phase is called The relaxation phase is called diastolediastole..►At a normal heart rate, one cardiac At a normal heart rate, one cardiac

cycle last for cycle last for 0.8 seconds0.8 seconds!!

Cardiac Cycle Continued….Cardiac Cycle Continued….

►Cardiac CycleCardiac Cycle = “events of one = “events of one complete heart beat”complete heart beat”

►Mid-to-late Mid-to-late diastolediastole (relaxation) = (relaxation) = blood flows into ventriclesblood flows into ventricles

►Ventricular Ventricular systolesystole (contraction) = (contraction) = blood pressure builds before ventricles blood pressure builds before ventricles contract pushing blood outcontract pushing blood out

►Early diastole = atria finish re-filling; Early diastole = atria finish re-filling; ventricular pressure is lowventricular pressure is low

The Normal Conduction The Normal Conduction SystemSystem

The electrocardiogram (EKG or ECG) is The electrocardiogram (EKG or ECG) is a graphic display of the electrical a graphic display of the electrical events of the cardiac cycle.events of the cardiac cycle.

What is an What is an Electrocardiogram?Electrocardiogram?

Each event has a Each event has a distinctive waveform, distinctive waveform, the study of which the study of which can lead to greater can lead to greater insight into a insight into a patient’s cardiac patient’s cardiac output.output.

EKG WavesEKG Waves

Wave InterpretationWave Interpretation

►P WaveP Wave = contraction of atria = contraction of atria►PQ WavePQ Wave = signal arrives at AV node = signal arrives at AV node

slowing down a bit to allow ventricles to fill slowing down a bit to allow ventricles to fill with bloodwith blood

►Q WaveQ Wave = signal moves to Bundle of His = signal moves to Bundle of His and divides into the bundles and Purkinje and divides into the bundles and Purkinje fibersfibers

►R WaveR Wave = contraction of left ventricle = contraction of left ventricle►S WaveS Wave = contraction of right ventricle = contraction of right ventricle►T WaveT Wave = ventricles relaxing = ventricles relaxing

Rule of 300Rule of 300

►Take the number of “big boxes” Take the number of “big boxes” between neighboring QRS complexes, between neighboring QRS complexes, and divide this into 300. The result will and divide this into 300. The result will be approximately equal to the heart be approximately equal to the heart raterate

►Although fast, this method only Although fast, this method only works for regular rhythms.works for regular rhythms.

What is the heart rate?What is the heart rate?

(300 / 6) = 50 bpm

What is the heart rate?What is the heart rate?

(300 / ~ 4) = ~ 75 bpm

What is the heart rate?What is the heart rate?

(300 / 1.5) = 200 bpm

10 Second Rule10 Second Rule

►As most EKGs record 10 seconds of As most EKGs record 10 seconds of rhythm per page, one can simply count rhythm per page, one can simply count the number of beats present on the the number of beats present on the EKG and multiply by 6 to get the EKG and multiply by 6 to get the number of beats per 60 seconds.number of beats per 60 seconds.

►This method works well for irregular This method works well for irregular rhythms.rhythms.

What is the heart rate?What is the heart rate?

33 x 6 = 198 bpm

PulsePulse“Heart Rate”“Heart Rate”

►PulsePulse Pressure wave of Pressure wave of

bloodblood

►Monitored at Monitored at “pressure points” in “pressure points” in arteries where pulse arteries where pulse is easily palpatedis easily palpated

►Pulse averages 70–Pulse averages 70–76 beats per minute 76 beats per minute at restat rest

Blood PressureBlood Pressure

►Measurements by health professionals are Measurements by health professionals are made on the pressure in large arteriesmade on the pressure in large arteries Systolic—pressure at the peak of ventricular Systolic—pressure at the peak of ventricular

contraction contraction Diastolic—pressure when ventricles relaxDiastolic—pressure when ventricles relax Write systolic pressure first and diastolic last Write systolic pressure first and diastolic last

(120/80 mm Hg)(120/80 mm Hg)

►Pressure in blood vessels decreases as Pressure in blood vessels decreases as distance from the heart increasesdistance from the heart increases

Measuring Arterial Blood PressureMeasuring Arterial Blood Pressure

Measuring Arterial Blood PressureMeasuring Arterial Blood Pressure