2/5 Britton Electrical and Mechanical Events of the Heart Flashcards
1
Q
The prevalence of CV disease in adults over 20 years of age is:
A
48%
2
Q
The function of the heart is essentially:
A
A pump for blood flow through the circulatory system
3
Q
Human heart must beat ______ for one’s entire life
A
Regularly and continuously
4
Q
Myocardium
A
Cardiac muscle tissue
5
Q
Myocardium is composed of what types of cardiac muscle?
A
- Atrial
- Ventricular
- Conductive muscle fibers
6
Q
Together, muscle cell types produce the:
A
Organized contraction of the heart
7
Q
_____ generate contractile force
A
Atrial and ventricular myocytes
8
Q
Atrial and ventricular myocytes are also known as:
A
- Contractile cells
- Working myocardium
9
Q
Atrial and ventricular myocytes contract _____ as skeletal muscle, except:
A
The same way; the duration of the contraction is much longer
10
Q
Conductive muscle fibers are _____ that allow for:
A
specialized muscle fibers; generation of AP’s; rapid conduction of AP’s
11
Q
_____ contract only feebly because it contains few contractile cells
A
Conductive muscle fibers
12
Q
Cardiac muscle cells are ____ coupled via:
A
Electricaly; gap junctions
13
Q
Gap junctions form a _____ synapse
A
Electrical
14
Q
Gap junctions are positioned at regions called:
A
Intercalated discs
15
Q
Intercalated discs are unique to:
A
Cardiac muscle
16
Q
Gap junctions allow for:
A
flow of electrical current and AP propagation between adjacent cells
17
Q
_____ are vital for the coordinated electrical activity of cardiac muscle cells
A
Gap junctions
18
Q
The electrical activity of the heart originates:
A
Within the heart itself
19
Q
The heart has its own:
A
Auto-rhythmicity
20
Q
True or false: the heart requires neural input to generate action potentials
A
False - does not require
21
Q
Auto-rhythmicity is due to ____ cells
A
Pacemaker cells
22
Q
Pacemaker cells are ____
A
Modified cardiomyocytes
23
Q
Where are pacemaker cells located?
A
- SA node
- AV node
24
Q
____ is also called the sinus node
A
SA node
25
Cardiac muscle cells either:
- exhibit automatic rhythmical electrical discharge of APs
- conduct APs through the heart
26
Cardiac muscles have an _____ difference across the cell membrane, termed _____
Electrical potential; resting membrane potential
27
In a ventricular cell, resting membrane potential is:
-90 mV
28
RMP of cardiac cell is close to:
Ek (equilibrium potential for K+)
29
Resting membrane potential is determined by:
- the concentration of ions across the cell membrane
- relative permeability of the cell membrane to these ions (if selective ions are open or closed)
- membrane pumps that transport ions across the cell membrane and maintain ionic gradients
30
Ion pumps and exchangers on the cardiac cell membrane maintain ____ for Na+, K+, Ca2+
ionic gradients
31
Ion pumps associated with cardiac cell electrophysiology
- Na+/K+ ATPase (3:2)
- PMCA (plasma membrane Ca2+ ATPase)
- NCX (Na+/Ca2+ exchanger, 3:1)
32
During each cardiac cycle, what happens?
Na+, K+, Ca2+ ions move back and forth across the cardiomyocyte cell membrane (thereby changing Vm)
33
Cardiac APs occur when:
Membrane potential **depolarizes and then repolarizes** back to its resting state (similar to neuronal APs)
34
APs occur in ____ cardiac cell types, but the appearance ____ depending on the cell type
All; varies
35
What are the two types of cardiac APs?
- Myocardium (non-pacemaker AP)
- SA node (pacemaker AP)
36
Non-pacemaker AP is triggered by:
Depolarizing current from adjacent muscle cells
37
Pacemaker cells are capable of:
Spontaneous AP generation
38
An AP is a recording of:
Cell's membrane potential versus time
39
What are the 5 phases of myocardium action potentials?
0. Depolarization
1. Brief repolarization
2. Plateau
3. Rapid repolarization
4. RMP
40
What is the duration of a myocardium action potential?
200-400 msec (roughly how long the contraction lasts)
41
Cardiac AP is largely dominated by the movement of:
Na+, Ca2+, K+ ions
42
# Myocardium action potentials
Phase 0
- Upstroke/rapid depolarization
- **Na+ channels open**
- Membrane potential shifts into positive voltage range
43
# Myocardium action potentials
Phase 1
- early repolarization
- K+ channels open
- sets the potential for phase 2
44
# Myocardium action potentials
Phase 2
- Ca2+ channels open
- K+ channels are still open
- long phase marks the entry of Ca2+ into the cell
45
# Myocardium action potentials
Phase 3
- rapid repolarization
- Additional K+ channels open
- Membrane potential returning to its resting value
46
# Myocardium action potentials
Phase 4
Stable at -90 mV in myocardium
47
How do ion channels make the cardiac cell membrane permeable to ions?
- selective for particular ions
- open and closed states
- exhibit gating properties (voltage/ligand gated)
48
The phases of the AP are the result of:
Ion movement down their electrochemical gradients (established by active pumps and exchangers)
49
The cardiac AP reflects the ____ behavior of numerous individual ____ and their ____
Integrated; ion channels; ionic currents
50
____ always precedes muscle contraction
AP
51
Long AP duration allows:
- cardiac muscle to contract for this same long period
- heart chambers to fully contract and eject blood
52
Features of APs in cardiac myocytes
- Cardiac AP has a long duration
- Cardiac AP has a plateau
- have refractory periods
53
____ are largely responsible for the plateau portion
Voltage-gated Ca2+ channels
54
Voltage gated K+ channels in cardiac myocyte membranes are ____ to open
Slower than usual (delayed repolarization of membrane potential)
55
Interval of time during which cardiac cells are unexcitable to the initiation of a new AP
Refractory period
56
Cardiac cells are refractory during AP phases ____, termed the ____
0, 1, 2, part of 3; effective refractory period (ERP)
57
ERP of ventricular AP is ___ msec
200 (approximately the duration of the AP)
58
ERP occurs due to:
Na+ channels remain inactivated following channel closing during phase 1
59
____ is a protective mechanism in the heart, prevents multiple APs from occurring
ERP
60
Relative refractory period
Interval of time during which a 2nd AP can be initiated with a greater stimulus than before
61
What are afterdepolarizations?
Depolarizations of muscle cells during the AP
62
When do afterdepolarizations occur?
Can occur in the **relative refractory period** if amplitude of depolarization is large enough to reach threshold
63
Afterdepolarizations must be preceded by at least ____, thus the term _____ is used
One AP; Triggered activity
64
True or false: afterdepolarizations occur spontaneously
False - they are triggered by prior activation of the heart (previous AP)
65
Early afterdepolarizations may occur spontaneously in patients with ______
Congenital long QT syndrome (LQTS) due to defective K+ channels
66
Early afterdepolarizations (EAD's) occur during what phase?
Phase 3
67
Early afterdepolarizations (EAD's) are usually caused by:
- hypokalemia
- K+ channel blockade
- drugs
68
Delayed afterdepolarizations are facilitated by ____
Intracellular Ca2+ overload
69
Delayed afterdepolarizations are usually caused by:
- Ischemia
- Catecholamines (NE, Epi)
- Drugs (digitalis)
70
Delayed afterdepolarizations occur during what phase?
Phase 4
71
Pacemaker potentials are generated in the ____ and are different from _____
SA node and AV node; working myocardium APs
72
The resting membrane potential is _____ in the SA node
Less negative (-50 to -65 mV)
73
In the SA node, the resting membrane potential is unstable and exhibits a ____
slow diastolic depolarization
74
The slope of the upstroke in a pacemaker potential during phase _____ is ____ steep
Phase 0 depolarization; less (slower rate of depolarization)
75
What are the phases of a pacemaker action potential?
4, 0, 3
76
What happens during phase 4 of a SA node potential?
- Diastolic depolarization
- Slow Na+ influx (HCN channels)
77
Diastolic depolarization during phase 4 of SA node potential is also known as:
- Funny current
- Pacemaker potential
78
What happens during phase 0 of a SA node potential?
- Rapid depolarization
- Ca2+ channels that open when Vm reaches threshold and depolarization occurs (-40 mV)
79
# SA node pacemaker potentials
2 types of Ca2+ channels
- T-type (open transiently)
- L-type (long lasting)
80
What happens during phase 3 of a SA node potential?
Repolarization via K+ channels
81
The leaking of _____ during the resting phase is called the pacemaker potential
Na+
82
Why is the pacemaker potential called the funny current (lf)?
It displays unusual properties
83
The funny current is a ____ current with a 3-fold higher selectivity for ____ than for ____
Mixed Na+-K+; Na+; K+
84
The funny current conducts an ____ current that generates the _____ in pacemaker cells
Inward; slow membrane depolarization
85
True or false: the funny current is activated by membrane depolarization
False: it is activated by hyperpolarization rather than depolarization
86
The funny current has dual modulation by:
Voltage and cAMP
87
What channels are responsible for the pacemaker current?
HCN ion channel
| Hyperpolarization-activated Cyclic Nucleotide gated channels
88
HCN channels are preferentially present in:
SA node and AV node
89
HCN channels are more permeable to:
Na+ ions (over K+ ions)
90
HCN channels are gated by both:
Voltage and cyclic nucleotides (cAMP)
91
Key to automaticity in SA node potentials
**Slow depolarizing baseline drift** of the membrane potential
92
How is the automaticity of SA node cells explained?
SA nodal cells start leaking Na+ into the cell as soon as they return to their resting state
93
The rate of APs initiated in the SA node is determined by:
How fast Na+ moves inward through HCN channels
94
If more HCN channels open, ____ moves inward faster, reaching the threshold for _____ faster and ____ the time/duration between APs
Na+; the activation of voltage-gated Ca2+ channels; shortens
95
The heart is innervated by the ___. The network of nerves supplying the heart is the ____
ANS; cardiac plexus
96
In the SA and AV node, what nerve terminals end on the SA node and AV node to modulate heart rate?
- Sympathetic adrenergic
- Parasympathetic cholinergic
97
In ventricular muscle, _____ fibers innervate to modulate heart contractility
Sympathetic adrenergic
98
In addition to sympathetic nerve innervation, what else can modulate heart contractility?
Catecholamines circulating in the blood following sympathetic stimulation of adrenal glands
99
The sympathetic and parasympathetic branches have ____ effects on heart rate by modulating the opening and closing of ____
Opposite; HCN channels
100
Describe the mechanism of sympathetic ANS modulation of the SA node
101
Describe the mechanism of parasympathetic ANS modulation of the SA node
102
ANS neurotransmitters change the rate of diastolic depolarization in the SA node via:
Lf (HCN channels)
103
Sympathetic innervation at the SA node leads to _____ depolarization rate via the funny current
Faster (steeper slope)
104
Parasympathetic innervation at the SA node leads to _____ depolarization rate via the funny current
Slower (less steep slope)
105
What are the components of the cardiac conduction system?
- SA node
- AV node
- AV bundle
- Right and left bundle branches
- Purkinje fibers
| these are all **specialized muscle cells**
106
The normal rhythmical electrical impulse (AP) is generated in the ____. Then the AP travels to the ____ through ____ cells and to the right and left ventricle through the _____ and _____. This stimulates _____
SA node; right and left atria; myocardial cells; AV node and His-Purkinje fibers; myocardial cells to contract
107
Trace the conduction system of the heart
108
The _____ of the cardiac AP varies in different regions of the heart
Conduction velocity
109
AP conduction in the AV node is ______ more than ____ msec before appearing in the AV bundle, which allows for:
delayed; 100; time for the atria to contract and empty blood into the ventricles before ventricular contraction begins
110
What is another name for the SA node?
Sinus node
111
What is another name for the AV bundle
Bundle of His
112
____ node has the slowest conduction
AV (0.05 m/sec)
113
____ have the fastest conduction velocity
Purkinje fibers (4 m/sec)
114
Using surface electrodes, the spread of electrical current within the heart can be recorded with:
ECG
115
Recording ECG employs what technique?
Einthoven's triangle
116
What is Einthoven's triangle?
Imaginary triangle that surrounds the heart at right arm, left arm, left leg
117
Pairs of electrodes are called:
Leads
118
Lead I
RA (-) to LA (+)
119
Lead II
RA (-) to LL (+)
120
Lead III
LA (-) to LL (+)
121
The _____ is more common for viewing the electrical activity of the heart
12 lead ECG
122
In addition to the 3 standard limb leads, there are:
- 3 augmented limb leads (Lead aVR, aVL, aVF)
- 6 precordial (V1-V6) chest leads
123
The ECG shows the pattern of depolarization/repolarization that is produced by APs generated by:
A population of cardiac muscle cells
124
The ECG is measurable because the electrical activity of cardiac cells is _____ during the cardiac cycle
Synchronized
125
True or false: the ECG provides information about electrical and mechanical activity of the heart
False - only electrical (spread of excitation)
126
Mechanical activity of the heart is portrayed in:
Echocardiogram
127
What are the normal ECG waveforms?
P, Q, R, S, T
128
The complete PQRST makes up a:
Depolarization-repolarization cycle
129
P wave represents:
Atrial depolarization
130
QRS complex portrays ____ and hides _____
Ventricular depolarization; atrial repolarization
131
T wave represents:
Ventricular repolarization
132
What information does the ECG provide?
- Heart rate
- Site of pacemaker origination
- Rate of AV node conduction
- Pathway of ventricular activation
133
What is the RR interval?
Time between heart beats
134
What is the PR interval?
Time taken for impulse to spread over atrium, AV node, Bundle of His
135
____ determines whether impulse conduction is normal
PR interval
136
____ reflects the slow impulse conduction through the AV node
PR segment
137
The PR ____ is an isoelectric point with no change in electrical activity
Segment
138
What is the QT interval?
The time taken for depolarization and repolarization of the ventricles
139
_____ reflects the time from ventricular depolarization ends until ventricular repolarization begins
ST segment
140
_____ corresponds to the plateau phase 2 of the AP and is an isoelectric point
ST segment
141
What 3 criteria are needed to qualify as normal sinus rhythm?
- AP must originate in SA node
- SA node impulses occur regularly at a rate of 60-100 impulses/min
- Electrical activation of the myocardium must occur in the correct sequence and with correct timing and delays
142
By examining the ____ for a couple of cycles, you can determine whether the rate and rhythm is steady or irregular
R-R interval
143
_____ are disorders of AP generation or impulse conduction
Arrhythmias
144
- In a normal scenario, ___ is the primary pacemaker and controls rate of AP regulation.
- In a pathological scenario, ____ can take over AP generation, causing ____ electrical activity and cardiac contraction. Foci can include:
- SA node
- Foci other than the SA node; disorganized; AV node, His-Purkinje fibers, atria
145
Arrhythmias can be caused by:
- Ischemia
- Structural changes in the conduction system
- Mutations on ion channels
146
Bradycardia
Slow heart rate; fewer than 60 beats/min
147
Tachycardia
Fast heart rate; more than 100 beats/min
148
What would make the heart beat faster or slower?
Input from the ANS
149
1st, 2nd, and 3rd degree atrioventricular blocks are examples of:
Bradyarrhythmias
150
What is a 1st degree AV block?
PR interval is extended
151
What is a 2nd degree AV block?
Not every QRS complex is followed by a P wave
152
What is a 3rd degree AV block?
P waves and QRS complex appear independently but regularly from each other
153
Atrial fibrillation
A quivering or irregular heart beat
154
Atrial fibrillation can lead to:
Blood clots, stroke, heart failure, other heart-related complications
155
Myocardial infarction shows a characteristic alteration in the ____, termed a ______
ST segment; STEMI (ST Elevation in MI)
156
- Ca2+ entering the cardiac cell during phase ____ of the AP triggers the release of Ca2+ from the SR
- Ca2+ binds to ____, inhibiting the TnI allowing myosin to bind to actin
- Ca2+ is returned to the ___
- At the end of phase 2 of the AP, uncoupling (relaxation) begins to occur when ____
2; TnC; SR; concentration of Ca2+ falls
157
AP always precedes:
Contraction
158
Contraction is the force generated by interaction of:
Actin and myosin
159
Contraction requires the _____ of intracellular Ca2+
Transient elevation
160
Calcium is elevated by:
- increasing Ca2+ influx via Ca2+ channels
- Increasing release of Ca2+ by the SR
- Sensitizing TnC to Ca2+
161
Cardiac contractility can be modulated by:
SNS and catecholamines
162
___ released by sympathetic nerves that innervate cardiac muscle
NE
163
____ in blood following SNS stimulation of the adrenals
NE and E
164
# Cardiac Muscle Contractility
E and NE bind to ____ receptors. This increases ____ and ____ which phosphorylate multiple proteins that modulate ____. This results in ____ and ____
- Beta 1 adrenergic
- cAMP and protein kinases
- Ca2+ uptake and release
- elevated Ca2+ levels and increases heart contractility
