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
Best initial treatment of tachycardia
Treating the underlying cause
Best 2nd treatment of tachycardia
rate control with Bblockers or CCBs.
AFib is an
irregular rhythm with the absence of a P wave
With Afib, Chaotic electrical activity in the
Atrium is conducted to the ventricle at a varied and irregular
Afib and effect on CO
LOSS OF ATRIAL kick
Afib and perioperative mortality
Increase risk
Main problem with afib is
Risk of atrial thrombus formation (risk of stroke)
Afib with RVR
reduces diastolic filing time and is ASSOCIATED WITH severe reduction in CO
Afib with RVR associated with severe reduction of CO as manifested by
syncope
chest pain
SOB
2 Treatments of Afib with RVR
Beta blockers, CCB, Digoxin
AND anticoagulation
Acute onset of Afib treated with
Cardioversion (start at 100Joules)
AFIB onset and its implications
If onset is older than 48 hours (or if onset is undertermined) a TEE must be performed to rule out atrial thrombus.
Arrhythmia that is an indication to cancel surgery
new onset afib; aflutter
What is the most COMMON POSTOP tachydysrhythmia? when does it usually occurs and who is at risk?
Atrial fibrillation ; 2-4 days’’ older patients post CT surgery.
Aflutter compared to afib is
Organized supraventricular rhythm
Aflutter is recognizable with what kind of pattern.
Saw tooth pattern
In aflutter what is the atrial rate
250-350
During a flutter , each atrial depolarization produces an
Atrial contraction , but not all atrial depolarizations are conducted past the AV node.
Usually defined with AFLUTTER
Defined ration of atrial to ventricular contractions.
In atrial flutter, what prevents all impulses from being transmitted to the ventricles?
Effective refractory period.
If atrial flutter onset is older than 48 hours or unknown?
TEE must be performed to r/o atrial thrombus.
Risk with RVR
can lead to hemodynamic instability
Treatment of aflutter
Rate control or cardioversion
Hemodynamically unstable atrial flutter should be treated with cardioversion start at
50 Joules
PVC originated from Foci b
Below the AV node, such as the QRS complex is wide
PVCs that arise from a single location are
unifocal (the morphology is the same on the EKG)
PVCs that arise from multiple location are
Multifocal (different QRS morphologies on the EKG)
Electrolytes disturbances associated with PVCs
Hypomagnesemia
Hypokalemia
Heart issues associated with PVCs
MI or infarction
SNS stimulation (acidosis, Hypercabia, hypoxia)
Valvular disease
Cardiomyopathy
Associated with PVCs other factors
Caffeine
Cocaine
Alcohol
A PVC that lands on the
2nd half of the T wave meaning during the relative refractory period can precipitate the R on T phenomenon
PVCS should be treated when?
Frequent > 6 /min polymorphic or occurs in runs of 3 or more
Treatment of PVCs
reverse underlying cause
Repositioning central line that may be irritating the RA
Medication treatment of PVCs
Treated with LIDOCAINE 1-1.5 mg/kg. if not resolved follow by infusion 1-4 mg/min
What is BRUGADA Syndrome?
Sodium ion channelpathy in the heart.
What can BRUGADA syndrome cause?
Sudden nocturnal death due to Vtach or fibrillation
Brugada most common in males from
SOUTHEAST asia
BRUGADA syndrome Diagnosis EKG findings include a
RBBB and ST segment elevation in V1-V3
Pt with BRUGADA syndrome may require
ICD or pad placement during surgery.
First degree HB : THE PRI is
> 0.20 second
Affected regions in first degree
AV node or HIS bundle
Etiology of HB
Age related degenrative changes, CAD, digoxin and amiodarone.
Treatment of HB
Monitor (usually asymptomatic)
Longer, longer, longer, drop then you have a
Wenckebach (2nd degree type I HB)
PR interval In 2nd degree HB type I
The PR interval becomes progressively long with each cycle, but the last P wave does not conduct to the ventricles, then the cycle repeats.
Why does the PR gets longer with a 2nd degree HB type I
Each successive depolarization increases the duration of the refractory period in the AV node. The last P in the cycle dropped, because it arrives at the AV node while it’s in the ABSOLUTE refractory period. This beat is not conducted but the pause that follows provides enough time for the AV node to reset. Then the cycle repeats.
Affected region in 2nd degree HB type I
AV node.
Etiology in 2nd degree HB type I
structural conduction defect, MI, BBlockers, CCBs, digoxin, sympatholytics agents.
Treatment of 2nd degree HB type I
Asymptomatic: just monitor
Symptomatic: then GIVE ATROPINE
2nd degree HB Block (Mobitz type II) if some Ps dont get through then you have a
Mobitz II
2nd degree HB Block (Mobitz type II) Some Ps conduct to the ventricles, while
Others don’t (there is usually a set ratio 2:1 or 3:1. After the dropped QRS the next P arrives right on time.
Affected region on 2nd degree HB Block Mobitz type II.
HIs bundle or bundle branche
Etiology in 2nd degree HB Block Mobitz type II
structural conduction defect or infarction .
Treatment of 2nd degree HB Block Mobitz type II
Often symptomatic
Pacemaker
atropine often not effective.
Key point of 2nd degree HB Block Mobitz type II
HIGH RISK OF PROGRESSING TO COMPLETE HB>
If Ps and Qs dont agree then you have
3rd degree.
AV dissociation with atria and ventricles have their onw rates
Third degree HB
With 3rd degree HB block in the AV node has a
narrow QRS (rate 45-55bpm)
With 3rd degree HB block Below the AV node has a
wide QRS (rate 30-40)
Etiology of 3rd degree HB
Fibrotic degeneration of the atrial conduction system. Lenegre’s disease.
Treatment of 3rd degree HB
PM
ISOPROTERENOL (chemical PM)
3rd Degree HB symptoms
Often symptomatic: syncope, dyspnea, weakness, vertigo.
Key points about 3rd degree HB symptoms
Can lead to CHF due to decreased HR and CO
Stokes-Adams attack is associated with
3rd degree HB
What is STOKES-ADAMs ATTaCK?
Decreased CO –> Decrease cerebral perfusion –> Syncope
How are antiarrhythmic drugs are classified according to their ability to
Block specific ion channels and currents of the cardiac action potential
Mechanism of action of CLASS IA
Moderate depression of phase O
Prolongs phase 3 repolarization (K+ channel block –> Prolonged QT )
Class I anti-arhythmic action on what 2 phases
Phase 0 and Phase 3
Mechanism of action of CLASS IB
Weak depression of phase O
Shortened phase 3
Examples of Class IA
Quinidine
Procainamide
Disopyramide
Examples of Class IB
Lidocaine, Phenytoin
Mechanism of action of CLASS IC
STRONG depression of phase O
Little effect on phase 3 repolarization
Examples of Class IC
Flecainide, Propafenone
Class 2 are the
Beta Blockers
Mechanism of action of Beta Blockers
Slows phase 4 depolarization in SA node
Class III are the
K+ Channels
Mechanism of action of K+ Channel Blockers (Class III)
Prolongs Phase 3 repolarization (prolonged QT)
Increase ERP
Class IV are the
Ca2+ Channel blockers
Mechanism of action of Ca2+ CCB
Decrease conduction through the AV node
How is adenosine metabolized
Plasma
Half time of adenosine
5 seconds
Adenosine useful for
SVT
WPW with a narrow QRS
Adenosine and reactive airway
Bronchospasm in asthmatic patients.
How to dose adenosine? Peripheral IV
First dose: 6mg
Second dose : 12 mg if required
How to dose adenosine? Central line
First dose: 3 mg
Second dose: 6mg
WPW is associated with : what kind of re-entry
Atrial -ventricular reentry
When does WPW occurs?
When an accessory pathway joins the atrium to the ventricle: called Kent’s Bundle
Most common cause of tachyarrythmias are
Reentry pathways
Explain the impulse conduction through the normal pathway?
SA node –> AV node –> HIS bundle –> Bundle branches—> purkinje fibers
Can impulse move backwards?
No because all the tissues behind the impulse remain in the absolute refractory period
What is the ratio of SA node depolarization and cardiac contraction?
1:1
Single pathway conduction system: how does it occur?
As the cardiac impulse propagates, it may encounter an area that can create an electrical circuit. It will travel along both pathways. Left and right at the same speed. Meet in the middle and cancel each other out.NO opportunity for reentry.
What is reentry?
single cardiac impulse can move backwards and excite the same part of the myocardium over andover.
Ratio of SA node discharge and cardiac contraction can exceed 1:1 ratio, there is a risk that
an impuse that circles around the reentry pathway will precipitate a reentry tachyarrhythmia.
How to break a circuit for reentry? 2 ways
Slowing down conduction velocity through the circuit
Increasing the refractory period of the cells at the location of the unidirectional block
3 possible causes of reentry?
Conduction occurs over a long distance
Conduction velocity is too slow
Refractory period is shorter.
Example of conduction over a long distance
Left atrial dilation due to mitral stenosis
Example of conduction velocity is too slow
Ischemia
Hyperkalemia
Refractory period is shorter example
Epinephrine
Electric shock from alternating current.
Patient with WPW develops afib during surgery , 2 medications to give
Procainamide
Amiodarone
What is the most common pre-excitation syndrome?
WPW
Defining feature of WPW
Consists of an accessory conduction pathway that bypasses the AV node (Kent’s bundle)
The accessory pathway forms a direct line of communication between the atrium and the ventricel
Kent’s bundle
During the normal conduction pathway, the cardiac impulse is delayed where?
At the AV node, meaning the AV node has a long refractory period.
What happens during the accessory pathway?
There is not delay , impulse move quickly from the atrium to the ventricle. There is no gatekeeper function .
How is WPW Diagnosed?
routine EKG , or hx of tachydysrhythmias.
Characteristicts of WPW on EKG
**Delta wave
**Short PR < 0.12 second
***wide QRS complex
possible t wave inversion
Why is there a delta wave?
Because of ventricular preexcitation.
WPW syndrome is classified in
Type A and type B.
WPW type A
right bundle branch block with right ventricular hypertrophy
WPW Type B
resembles left bundle branch block with left ventricle hypertrophy.
Most common tachydysrhythmia associated with WPW?
AV nodal reentry tachycardia
AV nodal reentry tachycardia classified as
Orthodromic or antidromic
Orthodromic vs antidromic: more common
Orthodromic (`90% cases) Antidromic (10% of cases)
Reentry conduction pathway with orthodromic
Atrium –> AV node –> Ventricle–> Accessory pathway —> Atrium
Reentry conduction pathway with antidromic
Atrium –> Accessory pathway —> Ventricle–> AV node –> ATrium
QRS morphology with orthodromic
Narrow
QRS morphology with antidromic
Wide
QRS in orthodromic: what happens with ventricular depolarization?
Normal via the HIS- Purkinje system
QRS in antidromic: what happens with ventricular depolarization?
Ventricular depolarization is slower since HIS system is bypassed.
Goal of Treatment of orthodromic
Block conduction at the AV node pathway (Increase the AV node refractory period)
Block conduction at the AV node pathway for orthodromic treatment include
Vagal maneuvers Amiodarone Adenosine BBlockers Veraparmil Cardioversion
Goal of Treatment of antidromic:
Block conduction at the accessory pathway (Increase accessory pathway refractory period)
Block conduction at the accessory pathway with those treatment for antidromic
Procainamide
Amiodarone
Cardioversion .
Do not do this with antidromic pathway?
Do not give agents that increase the refractory period of the AV node, because doing so will favor conduction through the accessory pathway.
Orthodromic vs antidromic which one is more dangerous?
Antidromic
Why is antidromic more dangerous?
Because the gatekeeper function of the AV node is bypassed and the HR can increase well beyond the heart’s pumping ability (dramatically reduces filling time)
If you give an AV nodal blocking drug to a patient with antidromic AVNRT what will happen?
You will force the conduction along the accessory pathway. This can induce Vfib. THEREFORE avoid drugs that BLOCK CONDUCTION through the AV node.
Drugs to AVOID with antidromic AVNRT include
Adenosine Digoxin CCBs (Diltiazem and verapamil) BBlockers Lidocaine.
Safe opitions for both orthodromic and ANTIDROMIC AVNRT?
Amiodarone
Cardioversion
Afib and WPW : Because there is no delay in the accessory pathway,
A rapid atrial rate can be conducted to the ventricles in a 1:1 ration .
During atrial fibrillaiton , the atria can depolarize up to
300x per minutes.
Combination of AF and WPW can precipitate 3 thins
CHF
Vfib
Death .
Why is Procainamide the tx of choice for WPW?
It increases the REFRACTORY PERIOD in the accessory pathway.
IF the patient is hemodynamically unstable,best option is
Cardioversion
What is the definitive treatment for accessory pathway?
Radiofrequency ablation
Risk with radiofrequency ablation of pathways involving the Left atrium?
Imposes a risk of thermal injury to the left atrium and the esophagus.
What is required when there is ablation of a pathway involving the left atrium?
Esophageal temperature is required.
If the temperature rises during periods of ablation, YOU MUST INFORM THE CARDIOLOGIST IMMEDIATELY.
Increases the likelihood of torsades de pointes in the patient with Long QT syndrome 3 things
Furosemide
Hyperventilation
Methadone
Patients with long QT syndrome at risk for
Torsades de pointes.
Patients with long QT syndrome should not receive
Methadone
The only narcotic known to increase the QT interval
Methadone
Furosemide and QT interval
Can cause hypokalemia and hypomagnesemia which can further prolong the QT interval
Hyperventilation and QT
Hyperventilation shifts K+into cells, decreases serum K and prolong the QT interval
Twisting of the spikes
Torsades de pointes.
Underlying cause of torsade de pintes?
Delay in ventricular repolarization (phase 3 of the action potential). se
Torsades de pointes is ______But can deteriorate to
Self limiting; ventricular fibrillation.
Torsades de pointes QT
Torsades associated with long QT
Causes of torsade de pointes mnemonic
Phenothiazines Other meds Intracranial bleed No known cause Type I antiarrythmics Electrolytes disturbance Syndromes
Antiemetic drugs causes Long QT
Haloperinol
Droperinol
Ondansetron
Antiarrhythmic causing prolonged QT
Amiodarone (especially with hypokalemia)
Quinidine
Genetic syndromes associated with Prolonged QT
Romano-ward syndrome
Timothy syndrome
QT interval and HR
Inversely related with HR.
Prolonged QT parameter in men
> 0.45 seconds
Prolonged QT parameter in women
> 0.47 seconds
Other text consider QT _______ prolong
> 40 seconds
PVC or poorly timed pacer discharge during the
relative refractory periods (during the second half of the T wave) can cause torsades pointes. (R on T phenomenon)
Prevention and treatment: Patients with Long QT syndrome may require
Beta blocker prophylaxis and /or ICD placement
Avoid SNS stimulation
Acute treatment for torsades de pointes include
Reversing the UNDERLYING cause and/or shorten the QT interval.
Acute treatment of torsades de pointes with meds
Magnesium sulfate
Cardiac pacing to increase th HR will reduce the action potential duration and the QT interval.
Pacemaker Position I is
Chamber PACED
Pacemaker positionII is
Chamber SENSED
Pacemaker position III is
Response to sensed event
Pacemaker position IV is
Programmability
PM mnemonic for position
PaSeR
When is a pacemaker required?
Heart unable to produce a normal rate and rhythm.
3 major indications for pacemaker
Long QT syndrome
Dilated cardiomyopathy
Hypertrophic obstructive cardiomyopathy
Major indications for pacemaker nodal issue
Symptomatic diseases of impulse formation (SA node disease or AV node disease
What does a pacemaker consistst of
Pulse generator and pacing leads that deliver electrical current to the heart.
Epicardial leads function
stimulate the surface of the heart.
Transvenous lead function
stimulated the cardiac chambers (RA and or RV)
Position I can be one of 4
O=none
A=Atrium
V= Ventricle
D= Dual
Position II can be one of 4
O=none
A=Atrium
V= Ventricle
D= Dual
Position III can be one of 4
T= Sensed activity tells the pacemaker to fire
I = Sensed activity tells the pacemaker NOT to fire
D-= if native activity is sensed , then pacing is inhibited
If native activity is not sense, then the pacemaker fire.
Position III can be one of 4
None
triggered
Inhibited
Dual(D+T)
Position IV can be one of 2
O= none R= rate modulation
None or rate modulcaiton indicates the
programmability of the pacemaker. ability to adjust HR in response to physiologic need. Sensors can measure respiration, acid base status,vibration,etc.
Position V indicates that
The PM can pace multiples sites.
This mode improves AV synchrony
DDD
This of this as a bckup mode: only fires when the native heart rate fails belowa predetermined rate
Single-Chamber demand pacing
This of this as a bckup mode: only fires when the native heart rate fails belowa predetermined rate
Single-Chamber demand pacing : AAI, VVI
This mode makes sure that the atrium contracts first followed by the ventricle
Dual-chamber AV sequential Demand Pacing (DDD)
There is no sense or inhibition with this mode
Asynchronous pacing
There is no sense or inhibition with this mode
Asynchronous pacing AOO, VOO, DOO
IF the atrium is paced, what happens to the electrical signal>
Travels through the AV node and the QRS maintain its normal , narrow appearance.
IF the ventricle is paced, what happens to the electrical signal>
is delivered beyond the AV node and the QRS takes on a WIDE APPEARANCE>
The pacemaker can fail to capture because of
hypocarbia (which can cause HYPOKALEMIA) made the myocardium more resistant to depolarizaiton.
Types of scapel that decreases the chance of EMI
Ultrasonic Harmonic Scapel.
Electrocautery that reduces the risk of EMI
Changing from coagulation to cutting
Hypothermia and HR
Bradycardia
MAGNET role : placing a magnet over the device does what?
Converts the PACEMAKER to an asynchronous mode.
The best answer for magnet is to
consult with the manufacture to determine how a magnet affects the pacemaker.
Magnet over an ICD
Suspends the ICD and prevents shock delivery
PM and ICD magnet
Suspeds the ICD and prevents shock delivery
Has no effect on the PM function (PM will be subject to EMI)
How to minimize the risk of PM failure
- Pulse generator failure
- Lead failure
- Failure to capture.
Risk of EMI is the greatest with the use of
Electrocautery and radiofrequency ablation.
Monopolar vs bipolar cautery?
Monopolar causes more EMI than bipolar
If surgeon insists of monopolar cautery
Insist on short bursts (0.5 seconds)
The risk of EMI is highest when
the electrocautery tip is used within a 15 cm radius of the pulse generator
Conditions that may cause PM to fire but there may be a failure to capture?
Hyper and hypokalemia
Hypocapnia
Hypothermia
MI
MRI contraindicated
PM or ICD
Lithotripsy and PM
LIthotripsy is not contraindicated, beam should be directed away from the pulse generator.
ECT and PM
ECT not contraindicated.
Not a reason to avoid this med with PM
Succinylcholine
The single most important informationto know preoperatively when the pacemaker fails?
Preoperatively find out what the patient’s underlying rhythm is .
Consider isoproterenol, Epinephrine and/or atropine.
K+ and conditions that can affect PM
Hyper and hypokalemia
4 others conditions that can affect PM
Hypocapnia (Intracellular K shift) Hypothermia MI Fibrotic tissue buildup around the pacing leads Antiarrhythmic medications.
Hyper/hypocalcemia with QT
Hyper makes it shorter , hypo makes it longer.
When QT at risk for torsades
When longer than >0.5 seconds
What is the lead that is always positive
LEFT LEG
What is the lead that is always negative
RIGHT ARM
Left AXIS Deviation is
Right AXIS deviation is
> 90 degrees
What is the MOST COMMON CAUSE of ACUTE MI
Sinus tachycardia (because it simultaneously increases myocardial oxygen demands while decreasing O2 supply.
3 meds for a flutter
Amiodarone
Diltiazem
Verapamil
PVCs causes by
Digoxin toxicity
Hypokalemia
Best drug for the treatment of symptomatic PVCs
Lidocaine.
Safest to administer to a patient with prolonged QT syndrome?
Metoprolol
Genetic disorder linked to MH
King DENBOROUGH
2 potential causes of 1st degree HB
Amiodarone
Advanced age
Reference point for measuring changes in the ST segment is
PR segment
Adenosine best in the treatment of
SVT
Allows you to quantify the amount of ST elevation and depression
J point
Causes the greatest risk of EMI
Coagulation setting of a MONOPOLAR CAUTERY.