Lecture 8 Flashcards
What is the SA node composed of and what does it connect to?
Composed of special cardiac muscle fibers; connects directly to atrial fibers
What is the resting membrane potential of SA node fibers and what is threshold?
Resting: -55 to -60 mV
Threshold: -40 mV
What is the ventricular fiber resting potential?
-85 to -90 mV
What do you call action potentials that originate anywhere other than the SA node?
Ectopic focus or pacemaker
What part of the heart is parasympathetic innervation distributed to and what neurotransmitter does it use?
SA and AV nodes; acetylcholine
What part of the heart is sympathetic innervation distributed to and what neurotransmitter does it use?
All parts of the heart, but mainly the ventricles; norepinephrine
What does the P wave in an EKG represent?
Atrial depolarization
What does the QRS wave in an EKG represent?
Ventricular depolarization and it hides atrial depolarization
What does the T wave in an EKG represent?
Ventricular repolarization
What does the P-Q interval represent?
Time from SA node firing to ventricles firing (usually .16s)
What does the Q-T interval represent?
Time from ventricular depolarization to repolarization (usually .35s)
Connections of limb lead 1 and what direction does it measure?
Negative terminal on right arm
Positive terminal on left arm
Looks at the heart from right to left
Connections of limb lead 2 and what direction does it measure?
Negative terminal on right arm
Positive terminal on left leg
Looks at the heart from upper right to lower left
Connections of limb lead 3 and what direction does it measure?
Negative terminal on left arm
Positive terminal on left leg
Looks at the heart from upper left to lower left
Definition of a vector
Arrow that points in the direction of the electrical potential generated by the current flow with the arrowhead in the positive direction; length of the arrow is proportional to the voltage of the potential
What is the angle (direction) of lead 1?
0 degrees
What is the angle (direction) of lead 2?
60 degrees
What is the angle (direction) of lead 3?
120 degrees
What is the mean electrical axis of the heart and in what direction does it measure?
59 degrees; direction of the electrical potential from negative to positive is from the base of the ventricles toward the apex
What is another name for the atrial T-wave?
Atrial depolarization; hidden by the QRS wave of ventricles
What can cause deviations from the mean electrical axis of the heart?
Change in position of heart in the chest
Hypertrophy of one ventricle
Bundle branch block
Fluid in pericardium
What is a high voltage EKG and what is the most common cause?
Occurs when the sum of voltages of all the QRS complexes of the 3 standard leads is greater than 4 mV; most common cause is hypertrophy of the ventricle
What causes a decrease in voltage of the heart?
Cardiac myopathies and conditions surrounding the heart
What causes QRS waves to be longer than normal (bizarre complexes)?
Hypertrophy or dilation of the left or right ventricle as a result of destruction of cardiac muscle and replacement by scar tissue or multiple small blocks in the conduction impulses at many points in the purkinje system
What abnormalities cause current of injury?
Mechanical trauma, infectious processes, and ischemia (most common)
What effect does current of injury have on a QRS complex?
Abnormal negative current flows from infarcted area and spreads toward the rest of the ventricles
What is the J point on an EKG?
Reference point for analyzing current of injury; occurs at the very end of the QRS wave and is the point at which all parts of the ventricle, including the injured areas, have become depolarized
