d) as ventricles relax, the pressure in the ventricular space drops, this causes the AV valves to swing open since
pressure in atria is now greater
--blood rushes into the ventricles, initiating the 1st 1/3rd of ventricle filling (rapid filling)
2) P wave
a) SA node fires, impulse travels throughout the 2 atria as myofibers depolarize
b) as the P wave is halfway complete, the atria begin to contract/undergo systole (why not at the beginning of the
P wave: it has taken a split second for the action potential to travel over the sarcolemma, through T-tubules to
sarcomeres, and for the calcium to move troponin & tropomyosin out of the way)
c) the AV valves are open; semilunar valves are closed
d) after the initial flow, blood continues to flow into the ventricles at a slower rate (diastasis, the 2nd 1/3rd)
--an enlarged P wave may indicate an enlarged atrium (which may result from a narrow AV valve as in mitral
stenosis)
3) P-Q Interval
; measured from the beginning of the P wave to the beginning of Q
a) after a delay at the AV node, the impulse travels through the AV bundle, right & left bundle branches, and
conduction myofibers
b) atria are in systole
c) AV valves are open
d) the last 1/3rd of ventricular filling as 30 ml is pumped to them; ventricles can pump 70% their capacity without
atrial contraction, this is sufficient for survival
11
4) QRS COMPLEX
a) ventricular depolarization as impulse spreads over myofibers; has this odd shape because the 2 ventricles are
different in size and they don't depolarize precisely together; the electrical event of atrial repolarization is hidden
by this complex
b) atria relax after repolarization; ventricles begin systole halfway into the QRS complex
c) AV valves shut
d) ventricular contraction, as contract, blood is pushed against the AV valves, forcing them shut
--resulting blood turbulence results in "lubb" sound
--this is isometric contraction (no shortening of the muscle, just an increase of force), increases
ventricular pressure
--an enlarged Q wave may indicate a myocardial infarction; enlarged R may indicate enlarged ventricles
5) S-T Segment
, measured from the end of S to the beginning of T
a) as ventricular myofibers plateau, the contraction is maintained
b) atria are in diastole; ventricles in systole
c) AV valves shut; semilunar valves open
d) when ventricular pressure surpasses the pressure of the arteries running from them (80 mm Hg for the left
ventricle, 15-20 mmHg for the right), the semilunar valves open
--the amount of blood ejected (usually around 70 ml) is known as the stroke volume
--ventricular ejection, requires .25 seconds
--
as blood is ejected into aorta, its pressure rises from its minimum of 80 mm Hg to its maximum of
about 120 mm Hg
