APEX Monitoring III: CARDIAC RHYTHMS Flashcards
Which pathway depolarizes the LA?
Bachman bundle
What are 3 internodal tracts that travel from the SA node to the AV node
Bachmann bundle
Wenckebach tract
Thorel tract
Kent’s bundle is a
Pathologic accessory pathway that is responsible for Wolf Parkinson-White syndrome.
Cardiac Conduction system contains:
SA node Internodal tracts AV node Bundle of HIS Bundle Branches Purkinje fibers
3 internodal tracts
Anterior Internodal tract
MIddle Internodal tract
Posterior internodal tract
The anterior internodal tract is the
Bachmann bundle
The middle internodal tract
Wenckeback tract
The posterior internodal tract
Thorel tract
Conduction velocity quantified
how fast an electrochemical impulse propagates along a neural pathway.
Conduction velocities of the cardiac conduction pathway : SA and AV nodes
0.02 - 0.1 m/sec (slow conduction )
Conduction velocities of the cardiac conduction pathway : HIS bundle, bundle branches and purkinje fibers
1-4 m/sec (fast conduction)
Conduction velocities of the cardiac conduction pathway : MYOCARDIAL MUSCLE CELLS
0.3 - 1 m/sec (intermediate)
Conduction velocity is a funciton of
Resting membrane potential
Amplitude of the action potentila
Rate or change in membrane potential during phase O
Conduction velocity is affected by
ANS tone Hyperkalemia induced closure of fast Na+ channesl Ischemia Acidosis Antiarrhythmic drugs
There is a band of connective tissue that electrically isolates the atria from the
ventricles.
What is the only electrical pathway between the cardiac chambers?
AV node
AV node is the
Gatekeeper of electrical transmission between the atria and the ventricles.
Accessory Pathway : James Fiber
Connect Atrium to AV node
Accessory Pathway : Atria HIsian Fiber
Connect Atrium to HIs bundle
Accessory Pathway : Kent’s Bundle
Connect Atrium to Ventricle
Accessory Pathway : Mahaim Bundle
AV node to ventricle
What are the 5 phases of the ventricular action potential
0 , 1, 2, 3, 4
Phase O is
Rapid depolarization (QRS)
Phase 1 is the
Initial repolarization (QRS)
Phase 2 is the
plateau phase (QT interval)
Phase 3 is the
Final repolarization (T Wave)
Phase 4 is the
Resting phase (T -> QRS)
Depolarization Na+ movement
In
Initial repolarization ion movement
Cl- –> in
K+ –> out
Plateau movement ion movement
Ca2+ in
K-> Out
Final repolarization ion movement
K + out
Resting phase ion movement
Na+ Out
What is the ABSOLUTE REFRACTORY period?
No stimulus (no matter how strong) can depolarize the myocyte.
What is the RELATIVE REFRACTORY period?
Larger than normal stimulus required to depolarize the myocyte.
EKG event: P Wave : Electrical event in ATRIA and ventricle
Atria: depolarization begins
Ventricles; NONE
EKG event: PR INTERVAL: Electrical event in ATRIA and ventricle
Atria: Depolarization complete
Ventricles: NONE
EKG event:QRS : Electrical event in ATRIA and ventricles
ATRIA: Repolarization
Ventricles: Depolarization begins
EKG event: ST segment : Electrical event in ATRIA and ventricle
ATRIA:NONE
VENTRICLES: DEPOLARIZATION complete
EKG event: T Wave : Electrical event in ATRIA and ventricles
ATRIA: NONE
VENTRICLES: Repolarization begins
EKG event: after T Wave : Electrical event in ATRIA and ventricl
Atria: NONE
REPOLARIZATION complete
EKG signs of Pericarditis
PR interval depression
EKG signs of HYPOKALEMIA
U wave
EKG signs of Intracranial hemorrhage
Peaked T wave
EKG signs of WPW syndrome
Delta wave
Duration of P wave in sec____
0.08-0.12
Amplitude of P wave in mm
< 2.5
Prolonged with 1st degree HB
P wave
PR intervanl normal
0.12 -0.20 sec
Q wave when to consider MI
Amplitude is greater than 1/3 R wave
Duration is greater than 0.04 seconds
Depth is greater than 1 mm
Normal QRS is
<0.10
Normal QRS amplitude progressively
increase from V1-V6, normal R wave progression.
If QRS complex if increased consider
LVH
BBB
Ectopic beat
WPW
QTc interval normal value in men
< 0.45
QTc interval normal value in women
< 0.47
ST segment when to consider MI
ST elevation or depression greater than 1 mm
ST elevation also caused by (other than the obvious MI)
Hyperkalemia
Endocarditis
T wave amplitude should be in precordial leads
Less than 10mm
T wave amplitude should be in limb leads
Less than 6 mm
Usually T wave points in the
Same direction as QRS
When T wave point in opposite direction of QRS
if repolarization is prolonged by MI, BBB
Peaked T waves are caused by
MI
LVH
Intracranial bleed
U wave if greater than
1.5mm, consider HYPOKALEMIA
Where is the J point ?
The point where the QRS complex and the ST segment begins.
By measuring the J point, relative to the PR segment we can
quantify the amount of ST elevation and depression
High potassium on T, QT, QRS
Early to late signs
Narrow peaked T Short QT Wide QRS Low P amplitude Wide PR Nodal BLOCK Sine wave fusion of QRS and T --> VF or asystole.
Too low potassium on QT
Long QT interval
Hypercalcemia on QT
Short QT
Hypocalcemia on QT
Long QT
Very low mag on QT
Long QT
The waveform on the EKG is a measure of the
Mean electrical vector
2 vectors to understand
Vector of depolarization
Vector of repolarization
Each lead consist of
One negative electrode
One positive electrode
Vector of depolarization
QRS complex
Direction the heart
Depolarizes from 1, base =>apex and 2. Endocardium–> Epicardium
Polarity the myocytes go from
internally (-) to internally (+) THIS PRODUCES A POSITIVE ELECTRICAL CURRENT
When does a positive deflection occur?
when the vector of depolarization TOWARDS the positive electrode.
When does a negative deflection occur?
when the vector of depolarization AWAY from the positive electrode.
When does a BIPHASIC deflection occurs?
when the vector of depolarization PERPENDICULAR to the positive electrode.
Vector of REPOLARIZATION
T wave
Direction the heart repolarizes form
- apex –> Base and 2. Epicardium –> Endocardium
Think of repolarization as the
Opposite of depolarization
Polarity the myocytes from internally (+) to internally (-) this produces a
Negative electrical current
A positive deflection occurs when the wave travels
AWAY from the positive electrode
The vector of repolarization travels in the
Opposite direction as the vector of depolarization
The vector of repolarization produces a
negative current
12 leads are
12 cameras
How many bipolar leads
3
How many limb leads
3
How many precordial leads
6
What are the bipolar leads
I, II, III
What are the limb leads
aVR
aVL
aVF
What are the precordial leads
V1 V2 V3 V4 V5 V6
Septum leads are
V1, V2
Anterior leads are
V3, V4
Lateral leads are
I, aVL, V5, V6
Inferior leads are
II, III, aVF
The mean electrical vector tends to point to
Towards areas of hypertrophy (more tissue to depolarize)
Away from areas of Myocardial infarction (The vector must travel around these areas)
The mean electrical vector normal value is between
-30 degrees and +90 degrees
Axis represents the
direction of the mean electrical vector in the frontal area.
Examine those 2 leads to determine axis
I and aVF
Normal axis: I and AVF
Both positive
Left axis deviation
Lead I positive
Lead avF negative
Right axis deviation
Lead I negative
Lead avF positive
Extreme Right axis deviation
Lead I and avF negative
Leads reaching toward each other then we have (l pointing down and avF pointing up)
Right axis deviation
Leads Leaving each other (L pointing up and avF pointing down_ then we have
LEFT AXIS deviation
Left axis is more
more negative than -30 degrees
Right axis is more
More positive than 90 degrees.
Axis deviation with COPD
Right
Axis deviation with chronic HTN
Left
Axis deviation with Acute bronchospasm
Right
Axis deviation with Cor pulmonale
Right
Axis deviation with Pulmonary HTN
Right
Axis devation with PE
right
Axis deviation with LBBB
Left
Axis deviation with Aortic stenosis
Left
Axis deviation with aortic insuffieciency
Left
Axis deviation with mitral regurgitation
Left
Adenosine is an
Endogenous nucleoside slows the conduction through the AV node.
ACtion of adenosine
Stimulate the cardiac adenosine-1 receptor , adenosine activates K currents, which hyperpolarizes the cell membrane and reduces action potential.
2 things Adenosine good for
SVT
WPW
Adenosine effective in treating Afib?
No
Adenosine effective in treating Aflutter?
No
Adenosine effective in treating Torsdades de pointes
No
Lidocaine class
IB
Amiodarone Class
III
Beta Blocker antiarrythmic class
Class II
CCB antiarrythmic class
Class IV.
Class I drugs inhibit
fast sodium channels
Class II drugs decrease the
rate of depolarization
Class III drugs inhibit
Posstaium ion channels
Class IV drugs inhibit
Slow calcium channels.
Sinus arrhythmia occurs when the
SA note pacing rate with respiration. its usually benign
What is the Bainbridge reflex?
When an increased in venous return stretches the RA and SA node causing the HR to increase. It should make sense that it would cause sinus arrythmia.
Inhalation effect on on intrathoracic pressure?
Decrease intrathoracic pressure –> Increase VR and increase HR.
Exhalation effect on on intrathoracic pressure?
Increase intrathoracic pressure –> Decrease VR and decrease HR.
SInus bradycardia defined as
HR < 60
What is the most common source of bradycardia?
Increased vagal tone.
What is the first line of Tx for bradycardia?
Atropine.
What can cause paradoxical bradycardia with atropine? Mediated by?
Underdosing it < 0.5mg IV. Presynaptic muscarinic receptors.
Severely symptomatic patients with bradycardia should receive
Immediate transcutaneous pacing.
Beta Blocker or CCB overdose treatment.
GLUCAGON
How does glucagon work ?
Stimulating glucagon on the myocardium. INCREASING cAMP leading to increase HR, contractility, and AV conduction.
What is the initial dose of glucagon?
50-70mcg/kg q3-5 min, can be FOLLOWED By infusion at 2-10 mg/hr
What causes tachycardia?
Increase intrinsic firing rate of the SA node or sympathetic stimulation.
Some etiologies of tachycardia
Hypovolemia, hypoxemia, infection. MH, Thyrotoxicosis
What is the effect of tachycardia on oxygen balance?
Increase myocardial oxygen demand WHILE decreasing oxygen supply.
Tachycardia can precipitate what ?
MI and CHF in patients with POOR CARDIAC RESERVE>
Tachycardia and patients with CAD
Precipitate MI and/or infarction