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10 Cards in this Set

  • Front
  • Back
What is the result of increased sympathetic stimulation?
Increases heart rate, atrial and ventricular contractility, and increases norepinephrine release at the ventricular sympathetic nerve endings.
How does excessive abdominal fat affect axis deviation?
The mechanical pressure of the fat causes a rotation of the heart to the left, resulting in a leftward shift of the mean electrical axis. Pulmonary hypertension causes enlargement of the right heart and thus causes right axis deviation.
What is the relationship between acetylcholine and permeability of cardiac muscle?
Acetylcholine does not increase permeability of cardiac muscle to calcium ions, but will cause hyperpolarization of the SA and AV nodes by increasing permeabilityto K+ ions. This causes a decreased heart rate.
What does paroxysmal mean?
The heart rate becomes rapid in paroxysms that begin suddenly and can last for a few seconds, minutes, hours or longer. It is believed to occur by a re-entrant circus movement feedback pathway, that sets up an area of local repeated self re-excitation.
What is the normal resting membrane potential of the SA node?
-55 millivolts. As sodium leaks into the membrane, an upward drift of the membrane potential occurs until it reaches -40mv. This is the threshold level that initiates the action potential at the SA node.
What is the formula for calculation of ejection fraction?
EF= __________

What causes an inverted P wave that occurs after the QRS complex?
The P wave following a premature contraction in the AV node is inverted b/c the cardiac impulse travels backward into the atria at the same time it travels forward into the ventricles. If it occurs high in the AV junction an inverted P wave occurs before the QRS complex. If it originates in the middle of the AV junction, the P wave is superimposed on the QRS complex and cannot be seen.
The strength and contraction of cardiac muscle depend on the amount of calcium surrounding cardiac myocytes. True/False
True. Cardiac muscle stores much more calcium in its tubular system than skeletal muscle does and it is much more dependent on extracellular calcium than skeletal muscle is. An abundance of calcium is bound by the mucopolysaccharides inside the T tubule.
Why is the heartbeat following a premature atrial contraction weakened.
It is weakened because the diastolic period is very short in this condition. The ventricular filling time is short and the stroke volume decreases. The probability of these contractions increases with toxic irritation of the heart and local ischemic areas.
During Stokes-Adams syndrome, where does the AV block begin?
The AV block begins suddenly, and can persist for a few seconds to several weeks. The new pacemaker of the heart is distal to the point of blockade, but it is usually the AV node or the AV bundle.