Answers to Practice Questions

 March 13 - Dr. Partridge

1.  correct answer is A.  one effect of Beta 1 activation is to increase funny current which increases slope of phase 4.
B is incorrect because vagal stimulation has the opposite effect of sympathetic.
C is incorrect because fast sodium channels do not operate in phase 4.
D is incorrect because increasing K conductance hyperpolarizes membranes.

March 16 - I clicker ECG session

1.  answer is b. -30 degrees.  Since lead II is biphasic the mean electrical axis is perpindicular to that lead = either -30 or +150.  Since aVL is positive, it must be -30 degrees.  this is on the top border of physiological left axis deviation.



March 16 - Dr. Resta

1. Point D is the answer.  Reduced cytosolic calcium would result in reduced contractility (reduced inotropy).  Another cause of shifting from point 1 to point D would be increased afterload.  Pressure volume loops are useful for distinguishing between these two possible causes. 


2. D. an increase in venous return.  An increase in vernous return will increase end diastolic volume, thereby increasing stroke volume (Starling's Law).

administration of a beta 1 blocker - would shift the curve downward (decreased contractility)

administration of a beta 1 agonist - would shift the curve upward (increased contractility)

administration of a calcium channel blocker - would slow conduction time but not change filling in a normal heart

decreased filling time (tachycardia) - would shift point 1 to point A

3. B. Administration of an alpha-1 antagonist drug- would cause venodilation and decreased venous return (nitrate vasodilators would have the same effect)

A. A. Administration of a beta-1 antagonist drug - would shift from point 1 to point D (- ionotropy)

D. Stimulation of the parasympathetic nervous system - would slow heart rate and allow for increased filling

E. Exercise - would increase heart rate but also venous return

C. Bradycardia at rest - would increase filling time = increased volume