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114 Cards in this Set
- Front
- Back
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What is 'autorhythmicity'?
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The ability of the heart to maintain its rhythmic pulsation without external factors
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'The ability of the heart to maintain its rhythmic pulsation without external factors' defines...
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Autorhythmicity
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Only some cells of the myocardium can show spontaneous electrical activity given suitable conditions (i.e. only some have the potential to be pacemaker cells) T/F
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F. All of the cells in the myocardium have the ability to become pacemaker cells. However, normally only the cells of the SA node show such activity
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Where is the SA node located?
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Wall of the right atrium, near the junction with the superior vena cava
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In the absence of any extrinsic nervous input, the SA node cells will drive the heart at a rate of around 100 bpm and will spontaneously generate an action potential every...
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600ms or so
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What is the name for the structure which is the only bridge of conducting tissue between the atria and the ventricles?
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The AV node
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'Consists of a narrow bundle of small-diameter fibres which have relatively few gap junctions linking them to their neighbours' describes...
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The AV node (NB This makes conduction through the AV node slow and so excitation to the ventricles is delayed for around 0.1s at this point - this ensures that atria have time to contract before the ventricular muscle is excited)
0936150111 |
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Is the bundle of His in the septum of the heart, or around the ventricular walls?
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Centre of the heart
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What is the endocardium?
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The innermost layer of tissue that lines the chambers of the heart
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'The innermost layer of tissue that lines the chambers of the heart' is termed...
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The endocardium
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What is faster, conduction through the Purkinje fibre network, or through the myocardium itself?
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The Purkinje fibre network is much faster
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Why is conduction of the heart unidirectional?
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The myocyte membrane goes through a refractory period immediately after its action potential, and so cannot have another action potential until after a certain time
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'An inadequate blood supply to an organ or part of the body, esp. the heart muscles' defines...
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Ischemia
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What is ischemia?
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An inadequate blood supply to an organ or part of the body, esp. the heart muscles (myocardial ischemia)
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What is a cardiac arrhythmia, and what is it also known as?
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A term for any of a large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart
AKA cardiac dysrhythmia |
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'A term for any of a large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart' defines...
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Cardiac arrhythmia/dysrhythmia
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Give some of the most common arrhythmias
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Atrial fibrillation
Extra contractions of the ventricles (ventricular extrasystoles/ectopic beats) Progressive stages of heart block (in which excitation from the atria to the ventricles is impaired) |
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The ECG can be used to determined the 'electrical axis' of the heart as a whole. What does this refer to?
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The general direction of the heart's depolarization wavefront (or mean electrical vector) in the frontal plane
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'The general direction of the heart's depolarization wavefront (or mean electrical vector) in the frontal plane' refers to...
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The heart's 'electrical axis'
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How is the ECG recorded?
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By placing electrodes at different points on the body surface and measuring voltage differences between these points with the aid of an electronic amplifier
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What are the two types of ECG leads?
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Bipolar and unipolar leads
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These leads record the voltage between electrodes placed on the wrists and left ankle (right ankle acts as earth)
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Bipolar leads
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What is the function of bipolar leads?
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They record the voltage between electrodes placed on the wrists and left ankle (right ankle acts as earth)
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These leads record the voltage between a single electrode placed on the body surface an an electrode that is maintained at zero potential.
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Unipolar leads
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What is the function of unipolar leads?
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They are leads that record the voltage between a single electrode placed on the body surface an an electrode that is maintained at zero potential.
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What are the bipolar limb leads known as?
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Limb lead I, II and III
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What kind of excitation does lead I record?
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Excitation that is moving along the axis between the right and left sides of the heart
(+ve = left arm, -ve = right arm) |
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What kind of excitation does lead II record?
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Excitation moving from the right upper portion of the heart to the tip of the ventricles
*Gives rise to the most prominent R wave* (+ve = left leg, -ve = right arm) |
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What kind of excitation does lead III record?
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Excitation spreading along an axis between the left atrium and the tip of the ventricles
(+ve = left leg, -ve = left arm) |
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(random question for another lecture) What is a glycoside?
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Molecules in which a sugar is bound to a non-carbohydrate moiety, usually a small organic molecule
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(random question for another lecture) Molecules in which a sugar is bound to a non-carbohydrate moiety, usually a small organic molecule
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A glycoside
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What are the two types of unipolar leads used in electrocardiography?
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Augmented limb leads and chest (precordial) leads
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What are the three main deflections in each cardiac cycle shown in a normal ECG?
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P wave, QRS complex and T wave and
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What does the P wave of the ECG correspond to?
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Electrical currents generated as the *atria depolarize prior to contraction*
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What does the QRS complex of the ECG correspond to?
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Depolarization of the ventricles
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What does the T wave of the ECG correspond to?
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Repolarization of the ventricles
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Why does atrial repolarization not appear on the ECG?
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It happens at the same time as ventricular depolarization and is masked by the QRS complex
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The cardiac cycle is initiated by depolarization of the SA node, but why isn't this seen on the ECG trace?
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The mass of tissue involved is very small.
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What is the 'isoelectric line' of the ECG?
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The part of the record in which there are *no measurable deflections*.
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Why is the T wave so broad?
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Some ventricular fibres begin to repolarize earlier than others
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Occasionally the T wave is followed by a low-amplitude wave known as the U wave. What is the origin of this?
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Unclear! Thought to represent repolarization of the papillary muscles or Purkinje fibers.
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Changes in heart rate are known as ____________ effects.
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Chronotropic effects
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What are 'chronotropic effects' wrt the heart?
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Chronotropic effects are those which bring about a change to the heart rate
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The parasympathetic supply to the heart is via the _____ nerves which, when activated speed up/slow the heart. This is known as...
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Vagus nerves
Slow the heart Negative chronotropy |
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What must the resting heart rate be below in order to classify it as bradycardia?
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60 bpm
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A heart rate at rest that is below 60 bpm is called...
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bradycardia
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Stimulation of the ___________ nerves increases increase the heart rate. This is known as a...
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Sympathetic nerves
Positive chronotropy |
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What does the resting heart rate need to be, in beats per minute, in order to classify it as tachycardia?
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Above 100 bpm
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A resting heart rate above 100 bpm is known as...
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Tachycardia
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The resting heart is dominated by the sympathetic innervation T/F
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F, it is dominated by the parasympathetic innervation
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Vagal nerve fibres synapse with postganglionic parasympathetic neurons outside/within the heart
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Within the heart. The short postganglionic fibres synapse mainly on the cells of the SA and AV nodes.
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How do parasympathetic nerve fibres slow the heart rate down?
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The short postganglionic fibres synapse with the cells of the SA and AV nodes which release ACh from their terminals, this increases the permeability of the nodal cells to potassium. This decreases the slope of the pacemaker potential AND hyperpolarizes the membrane potential.
These changes increase the time take for the pacemaker potential to reach the threshold, so the interval between successive APs is longer and the heart rate falls. Vagal stimulation also reduces the rate of conduction of the cardiac impulse from the atria to the ventricles by decreasing the excitability of AV bundle fibres |
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What is the heart rate of a normal, healthy adult at rest?
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70 bpm
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What is the bpm of a denervated heart? What does this say about the vagus nerve?
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100 times per minute (this is the intrinsic rate of discharge of the myocytes of the SA node.
As normal is 70 bpm, this shows that the vagus nerves exert a tonic inhibitory action on the SA node to slow the intrinsic heart rate |
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If one substance is said to 'antagonise' another, what does it mean?
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A substance that interferes with or inhibits the physiological action of another
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'A substance that interferes with or inhibits the physiological action of another'
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An antagonist
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The sympathetic preganglionic nerves that supply the heart originate in spinal segments...
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T1 - T6 (mainly T1-T3)
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Where do the sympathetic nerves that supply the heart synapse?
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In the ganglia of the thoracic sympathetic chain. They then project to the heart via long postganglionic fibres
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When one talks about the 'varicosities' of a nerve, what does that mean?
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It refers to a 'swelling' in the nerve
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The swellings (varicosities) of the postganglionic fibres of the sympathetic nerves secrete norepinephrine T/F
NB effect of stimulating these sympathetic nerves is to increase the heart rate |
T - norepinephrine (NE) or noradrenaline (NA/NAd) act to increase heart rate
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How is norepinephrine believed to increase heart rate?
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Thought to increase the permeability of the pacemaker cell membrane to sodium and calcium ions. Therefore, the SA node can reach threshold more quickly and the interval between successive APs is reduced.
Conduction time through the AV node is ALSO reduced by sympathetic stimulation |
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What is the normal number of leads used for an ECG?
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12 (3 limb leads [I, II and III] 3 augmented limb leads [aVL, aVR and aVF] and 6 chest leads [V(1)-V(6)])
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What are the names for the three different types of ECG leads?
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Limb (3)
Augmented (3) Chest (6) =12 |
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The three limb leads and three augmented limb leads each provide information about the activity of the heart viewed from a specific point on the transverse/vertical plane
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Vertical (frontal)
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The six chest leads provide information about the activity of the heart from a specific point in the transverse/verticle plane
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Transverse
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What does the amplitude of the ECG signal represent?
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The mass of cardiac muscle involved
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What does the polarity of the ECG signal in any lead at a given time reflect?
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The average direction of current flow with respect to that lead
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The ECG can be used to find the site of any abnormal pacemaker activity T/F
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T
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What is 'sinus rhythm'?
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A term used in medicine to describe the normal beating of the heart
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What is 'sinus bradycardia'?
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Can be a normal heart rhythm of less than 60 bpm. However, may be clinically significant as sinus bradycardia can be present in fainting attacks, hypothermia and hypothyroidism
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How can you calculate heart rate using the R-R interval?
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bpm = 60/R-R interval
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What is the QT(c) interval?
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The QT interval corrected for heart rate
QT interval/sqrt(R-R interval) |
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What is special about the PR interval wrt children adolescence
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The PR interval is shorter than the normal 0.12-0.21 s (easy to remember!)
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The P wave is normally smooth and rounded, and entirely positive or entirely negative in all leads except...
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V1
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What are 'escape rhythms'?
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Rhythms where the fundamental rhythm of the heart is taken over by a part of the heart other than the SA node, because the SA node's activity is much slower than normal.
They are named after the position: Atrial origin = atrial rhythms AV node origin = junctional rhythms Ventricular origin = ventricular rhythm |
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What is a junctional rhythm?
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A type of escape rhythm originating in, or near to, the AV node
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In some people, particularly the elderly, the SA node fails to excite the atria in a regular manner, resulting in a slow resting heart rate that does not increase appropriately with exercise. This is called...
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Sick sinus syndrome (many causes)
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How can one often treat arrhythmias caused by failure of the SA node to excite the heart?
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By implantation of an artificial pacemaker
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Each ECG lead detects the average current flowing towards or away from it at any instant in time T/F
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T
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'Refers to the direction of the largest electrical dipole recorded from the frontal plane'
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The electrical axis
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How can you assess the electrical axis?
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Compare the amplitude of the R wave in the three libm leads
Or calculate the resultant vector of the activity recorded by lead I and lead aVF (these two leads record the electrical activity in the horizontal and vertical planes respectively |
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What can determination of the cardiac axis be useful for? Wrt diagnosis
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Can diagnose:
Right ventricular hypertrophy Conduction defects Pulmonary embolus |
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If one has a large right atria (left atrial hypertrophy), what difference would be seen on the ECG? Why?
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Large, peaked P wave. This arises because the right atrium depolarizes before the left atrium
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If one has a large left atrial enlargement (left atrial hypertrophy), usually caused by a mitral stenosis, what is the effect of the P wave?
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The P wave is bbroadened and may have a double peak (a 'bifid' P wave)
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What is 'stenosis'?
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The abnormal narrowing of a passage in the body
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'The abnormal narrowing of a passage in the body' defines...
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Stenosis
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What is heart block?
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A defects in the conduction of the electrical activity of the heart
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'A defect in the conduction of the electrical activity of the heart' is known as...
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Heart block
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Impairment with the conduction from the atria to the ventricles is known as what kind of block? How is it classified?
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Atrio-ventricular block.
Classified according to severity as first, second or third degree heart block |
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Impairment of conduction through the bundle of His is known as what kind of block? Is it only through the main bundle?
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Known as 'bundle block'
May affect the main bundle or any of its branches (branch bundle block) |
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What is characteristic of first degree heart block?
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An abnormally long PR interval (PR>0.2s)
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'An abnormally long PR interval (PR>0.2s)' is indicative of what kind of heart block?
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First degree heart block
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'There is an intermittent failure of excitation to pass to the ventricles' describes what kind of heart block?
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Second degree heart block
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What are the three types of second degree heart block?
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Mobitz type I (AKA Wenckebach phenomenon/Wenckebach block), Mobitz type II and 2:1 or 3:1 block
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What is the visual change to an ECG with 2:1 or 3:1 block?
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Every second or third P wave elicits are QRS complex
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'Every second or third P wave elicits are QRS complex' is what kind of block?
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2:1 or 3:1 block
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In this type of heart block the wave of excitation originating in the SA node fails to excite the ventricles
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Third degree heart block
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Does the bundle of His originate before, or after the AV node?
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Before, the AV node is an enlargement of the bundle of His
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In some situations, the excitation reaches the AV node and passes through the bundle of His only to be delayed or fail to pass from one or other branch to the ventricular muscle. This is known as...
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Bundle branch block
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What is bundle branch block? What is a feature of it?
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When the excitation reaches the AV node and passes through the bundle of His only to be delayed or fail to pass from one or other branch to the ventricular muscle.
Broadened QRS complex as wave spreads more slowly |
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'A bundle of structures, such as nerve or muscle fibers or conducting vessels in plants' defines...
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A fascicle (fah-sick-ul)
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What is a fascicle (fah-sick-ul)?
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'A bundle of structures, such as nerve or muscle fibers or conducting vessels in plants'
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Arrhythmias originating in the atria or nodal region are often called...
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Supraventricular rhythms (?also atrial rhythms)
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Supraventricular rhythms (?and also atrial rhythms)
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Arrhythmias originating in the atria or nodal region are often called...
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What is 'extrasystole'?
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When the atria or ventricles contract earlier than expected/out of rhythm. This is an *ectopic beat*.
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Term for when the atria or ventricles contract earlier than expected/out of rhythm. This is an *ectopic beat*.
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Extrasystole
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Retrograde (backward) excitation is normally prevented by the long refractory period of the cardiac cells. In some circumstances this regulation breaks down and premature excitation can occur via __-_____ circuits
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re-entry circuits
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What is the name for a syndrome which is an example of a re-entry circuit?
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Wolf-Parkinson-White syndrome
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What is Wolf-Parkinson-White syndrome?
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An example of a re-entry circuit. Affected individuals have an accessory pathway connecting atrium and ventricle, usually on the left side of the heart. This is known as the bundle of Kent.
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In Wolf-Parkinson-White syndrome, affected individuals have an accessory pathway connecting atrium and ventricle, usually on the left side of the heart. This is known as the bundle of ____.
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Bundle of Kent (NB unlike AV node, excitation is NOT delayed here, hence consequence of the ventricles being excited too early)
1021160111 |
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What is the term for low plasma potassium levels?
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Hypokalemia
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When one part of the heart is deprived of oxygen and that part dies (necrosis) what is the term given for the dead part?
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The 'cardiac infarct'
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In hyperkalemia, the T wave is accentuated/flattened
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Accentuated
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In hypercalcemia, the QT interval is shortened/lengthened
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Shrtened
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