17-3: EKG and the Cardiac Cycle Flashcards
electrocardiogram
impulses transmitted through the conduction system cause electrical currents that can be detected on the body’s surface with an electrocardiograph
P wave
first small upward curve, indicates atrial depolarization (spread of impulse from SA node through atria)
QRS complex
downward deflection (Q - impulse to apex) followed by large upright triangular wave (R), ending in second downward deflection (S). Indicates ventricular depolariation (spread of impulse through the ventricles)
T wave
dome-shaped upward curve; indicates ventricular repolarization (atrial repolarization wave is hidden by QRS wave)
reading the EKG
changes in timing or pattern of the EKG may reveal a diseased or damaged heart
enlarged P wave
enlarged atria, as in mitral stenosis (a narrow valve causes blood to back up into the atrium, causing it to enlarge)
PQ interval
the time required for the impulse to travel through the atria and AV node to the ventricles
longer PQ interval
may be due to scars or inflammation
enlarged Q wave
may indicate myocardial infarction
enlarged R wave
indicates enlarged ventricles (eg. lung disease)
shorter ST segment
heart is getting low O2
flattened T wave
cardiac ischemia (insufficient blood flow in coronary vessels)
elevated T wave
hyperkalemia (potessium levels are high)
cardiac cycle
sequences of events in one heartbeat (about 0.8 seconds)
systole
contraction
diastole
relaxation
complete diastole
all chambers are relaxed, pressure in the heart is low
In complete diastole, ___ blood flows into __, and __ blood flows into ___.
deoxy; right atrium from SVC, IVC, and coronary sinus; oxy; left atrium from pulmonary veins
What causes the AV valves to open?
increasing blood flow into the atria causes the atrial pressure to rise above ventricular pressure, causing the AV valves to open
period of ventricular filling
with AV valves open, 70-80% of blood flows passively from atria to ventricles
What happens after the period of ventricular filling?
SA node fires, and the impulse spreads over the atria; atrial depolarization - P wave
atrial systole
contraction of the atria
What causes atrial systole?
spread of the impulse from the SA node causes the 2 atria to contract simultaneously, forcing the remaining blood into the ventricles
After atrial systole, the impulse ___.
reaches the AV node, travels down the bundle of His into the ventricular walls, creating the QRS wave (ventricular depolarization)
ventricular systole
contraction of the ventricles
What creates the first heart sound?
as the atria relax, the ventricles begin to contract, causing an abrupt rise in ventricular pressure, causing the AV valves to close
isovolumetric contraction phase
period in ventricular systole with all valves closed
During ventricular systole, the continuing rise in pressure causes ___, and blood ___.
the SL valves to open; is forced out into the large arteries leaving the heart (ventricular ejection)
During ventricular systole, the atria ___.
are relaxed and starting to fill with blood
quiescent period
return to diastole after ventricular systole and ejection
What causes the second heart sound?
After ventricular ejection, the pressure in the ventricles decreases rapidly and blood in the aorta and pulmonary trunk starts to flow back; this causes the SL valves to close and create the second heart sound
isovolumetric relaxation phase
all valves are closed, and all chambers relaxed; the atria have begun filling with blood, and eventually the increased atrial pressure will cause the AV valves to open
The isovolumetric relaxation phase ends in the period ___.
of ventricular filling, when the AV valves open due to increased pressure in the atria
