EKG and the Cardiac Cycle Study Guide Flashcards
3 portions of a cardiac action potential
- Depolarization: opens fast Na+ channels, extracellular Na+ enters (rising phase of action potential)
- Voltage change opens ca2+ channels, influx of extracellular ca2+ (plateau)
- repolarization : results from inactivated ca2+ channels; the opening of K+ channels – an efflux of K+ (ca2+ either pumped out of cell or into SR, resting potential is restored)
significance of the plateau phase
Sustained contraction ensures efficient ejection of blood from ventricles, and the longer absolute refractory period avoids tetany
3 waves/deflections on a typical EKG
P wave, QRS complex, T wave
electrical event causes p wave to appear
movement of the depolarization wave from SA to AV node
electrical event causes qrs complex to appear
ventricular depolarization, precedes ventricular contraction
electrical event causes t wave to appear
results from ventricular repolarization
Why is atrial repolarization not seen on a typical EKG?
Its occurs during ventricular depolarization – the resulting wave is obscured by the QRS complex
interval
duration of time that includes 1 segment and 1+ wave
Segment
a region between two waves
What is the possible clinical significance of an elevated or depressed ST segment?
They can indicate cardiac ischemia (reduced blood flow to the heart)
4 electrical events and the 4 correlating mechanical events of each cardiac cycle
Atrial depolarization = DIASTOLE
Ventricular depolarization = SYSTOLE
Atrial repolarization = SYSTOLE
Ventricular repolarization = DIASTOLE
* electrical events always precede mechanical events
Systole
contraction – blood is forced out of the heart’s chambers
Diastole
blood refills the heart’s chambers
4 steps of the cardiac cycle
- Ventricular filling
- Isovolumetric contraction
- Ventricular ejection
- Isovolumetric relaxation
cardiac steps when the ventricles are closed chambers
Isovolumetric contraction and Isovolumetric relaxation
AV and SL valves are open or closed in each step of the cardiac cycle?
Ventricular filling – AV VALVES OPEN, SL VALVES CLOSED
Isovolumetric contraction – AV VALVES CLOSE, SL VALVES CLOSE
Ventricular ejection – AV VALVES CLOSE, SL VALVES OPEN
Isovolumetric relaxation – SL VALVES CLOSE, AV VALVES CLOSE
EDV - end diastolic volume
the maximum volume of blood that the ventricles will contain in the cardiac cycle
ESV
the un-ejected blood remaining in the ventricular chambers
Dicrotic Notch
a brief rise in aortic pressure caused by blood rebounding off the newly closed aortic valve
Which is a higher-pressure circuit: the pulmonary or the systemic?
Systemic circulation = higher pressure
average pressure in the pulmonary trunk
24/10 mmHg
average pressure in the aorta
120/80 mmHg
How does pressure correlate with what you’ve learned about ventricular anatomy and workload?
the left side, with the aorta in the systemic circulation, has a much higher workload bc it is spreading blood to the whole body
What causes the sounds heard during auscultation?
closure of valves
Closure of the _____ Valves is the 1st Sound (“lub”).
av
Closure of the __ Valves is the 2nd Sound (“dup”).
sl
heart murmur
Abnormal heart sound due to turbulent blood flow
How can a heart murmur eventually result in a weakened myocardium
Backflow of blood / turbulent flow of blood due to malfunctioning valves can weaken myocardium, as it will have to work harder (stenotic (narrow) valves cause a clicking sounds from reduced blood flow)
