CV - electrocardiogram Flashcards
the ___________ node is the typical cardiac pacemaker.
SA
the SA node is the typical cardiac pacemaker because it has the ___________ spontaneous rate.
fastest
the AV node has a slower spontaneous rate and delays conduction at the junction between the ___________ and ___________.
atria
ventricles
purkinje cells conduct faster than ___________ cells.
contractile myocytes
parking cells allow extremely rapid conduction from the AV node to the ventricles through the ___________ and their extensions into the myocardium.
left and right bundles
what does the P wave of an ECG represent?
depolarization of the atria
what does the QRS of an ECG represent?
depolarization in the ventricles
what does the T wave of an ECG represent?
repolarization of the ventricles
is repolarization of the atria appreciated on an ECG?
no, repolarization of the atria is not seen because it normally occurs at the same time as ventricular depolarization and is buried in the much larger QRS signal from the ventricles
if the QRS is positive, the T wave should be ___________.
positive
if the QRS is negative, the T wave should be ___________.
negative
discordance between the QRS and T waves in any lead is pathological, reflecting abnormalities such as ___________ or ___________.
ischemia
ventricular hypertrophy
the endocardium depolarizes ___________ the epicardium.
before
epicardial cells repolarize ___________ endocardial cells.
before
epicardial cells repolarize before endocardial cells because they have shorter ___________.
action potential duration
the first signal on the ECG is the ___________.
P wave
the P wave is generated by ___________ of first the right and then the left atrium.
depolarization
describe the Q of the QRS wave on an ECG.
an initial negative deflection during ventricular depolarization
describe the R of the QRS wave on an ECG.
the upward deflection
describe the S of the QRS wave on an ECG.
a terminal negative deflection
if the activation wave is toward the sensing electrode, a ___________ deflection will be recorded.
positive (upward)
the greater the muscle mass the ___________ the voltage recorded.
greater
the pattern of the deflection varies with the ___________ of the recording electrodes.
position
the SA node is located high in the ___________ and the depolarization wave sweeps ___________ and ___________.
right atrium
downward
leftward
a lead with a positive electrode near the right arm normally has a predominantly ___________ QRS.
negative
a lead with a positive electrode near the left leg has a ___________ QRS.
positive
the upper portion of the septum is depolarized from ___________ to ___________.
left to right
what are the sites at which conduction can be delayed or blocked with clinical consequences? (6)
sinoatrial (SA) node atrioventricular (AV) node right bundle branch left bundle branch posterior fascicular branch anterior fascicular branch
SA node abnormalities commonly cause ___________, resulting in ___________ or ___________.
“sick sinus syndrome”
slow sinus rates
takeover by other pacemakers which may be either faster or slower
3 types of AV block
first degree: conduction is delayed but all P waves conduct to the ventricles
second degree: some P waves conduct but others do not
third degree: none of the P waves conduct and a ventricular pacemaker takes over
how does a right bundle branch block appear on ECG?
QRS widening with delayed conduction to the right ventricle
how does a left bundle branch block appear on ECG?
QRS widening with delayed conduction to the left ventricle
how does a fascicle block appear on ECG?
shifts in direction of depolarization but no QRS widening
what is the normal sequence of activation of the ventricles?
1 upper portion of the septum is depolarized from left to right
2 there is then depolarization downward int he septum to the apex
3 depolarization is from endocardium to epicardium
4 depolarization moves upward from the apex in the free walls of both ventricles
5 finally there is depolarization of the base of the ventricles
what are the common mechanisms leading to arrhythmia?
reentry
ectopic foci
triggered activity
describe abnormal reentry
abnormal reentry pathways can be present in the atria, ventricles or the junctional tissues, and occurs when there is a unidirectional block and slowed conduction through the reentry pathway
reentry is the most common mechanism of serious tachycardias
describe ectopic foci
ectopic foci occur when a focus of myocardium outside the conduction system acquires automaticity; if the rate of depolarization exceeds that of the SA node, an abnormal rhythm occurs
ectopic foci result in isolated “ectopic beats” or sustained tachyarrhythmias
describe triggered activity
abnormal “afterpolarizations” may be triggered by the preceding action potential; delayed afterpolarizations appearing after an action potential is complete can trigger arrhythmias, and afterpolarizations when action potentials have only partially depolarized triggers a tachyarrhythmia
arrhythmias due to this mechanism are usually associated with a delay in repolarization seen in the ECG as a “long QT interval”
what induces the depolarization in phase 0 of the slow cardiac action potential?
calcium current
why do contractile myocytes display a more rapid depolarization during phase 0 of the fast cardiac action potential?
sodium current
why do purkinje cells conduct faster than contractile myocytes?
they have more fast Na+ channels
what phase of the action potential does the initial R spike on an ECG correspond to?
phase 0
what phase of the action potential does the ST segment on an ECG correspond to?
phase 2
what phase of the action potential does the T wave on an ECG correspond to?
phase 3
what phase of the action potential does the plateau following the T wave on an ECG correspond to?
phase 4
