Transcript Arrhythmias - Llusurgery .org

Arrhythmias
Valerie Seabaugh MD
Jerry L Pettis Memorial VA Hospital
Today’s discussion
Normal ECG components
 Normal wave conduction physiology
 Bradycardia
 Tachycardia
 Pacemakers and Automatic internal
cardiac defibrillators (AICD)

Normal ECG

By convention, electrical pulses
conducted toward the ECG lead are
positive those conducted away are
negative
The P wave




Represents atrial
depolarization
Duration is measure of
time required for
depolarization to
spread through the
atria to the AV node
Is usually upright in I,
II, and aVF
Negative in aVR
variable in III, aVL
The PR interval


Represents time
required for a
supraventricular
impulse to depolarize
the atria, traverse the
AV node, and enter the
ventricle
Normal is 0.12 to 0.20
seconds, greater than
0.20 is considered first
degree AV block
The QRS complex





Represents ventricular
depolarization
Q wave – first negative
deflection
R wave – first positive
deflection after a P wave
S wave – negative
deflection following an R
wave
Normal is between 0.06
and 0.10 sec
The ST segment




The isoelectric segment
following depolarization and
preceding ventricular
repolarization
From the end repolarization
of the QRS to the beginning
of the T wave
In contrast to PR and QRS
intervals, the ST segment
length can be variable
Elevation or depression of
the ST segment by 0.1 mV
from the baseline is
abnormal
The T wave
Represents ventricular repolarization
 T wave vector normally “tracks” with
the QRS vector. If QRS is
predominantly negative an inverted T
wave is not necessarily abnormal

The QT interval
From the beginning of the QRS
complex to the end of the T wave
 Represents electrical systole
 Is usually <0.425 seconds duration
when corrected for heart rate (QTc =
corrected QT interval)

Membrane potential in the
ventricle, atria, and Purkinje
system



Phase 0 – Na+
enters the cell
Phase 1 – initial
repolarization by
K+ moving out of
the cell
Phase 2 – plateau
of action potential
caused by Ca++
moving into cell

Stoelting p 69
Membrane potential in the
ventricle, atria, and Purkinje
system



Phase 3 – Ca++
conductance
decreases but K+
conductance
increases with K+
moving out of cell
Phase 4 – K+ moving
out returns cell to
resting potential
This differs in the SA
node where influx of
Ca++ starts action
potential
Effect of electrolyte disturbance
on cardiac rhythm
Effect of electrolyte disturbance
on cardiac rhythm
Hypocalcemia – prolonged QT
interval, ST segment, V Tach,
Torsades
 Hypercalcemia – shortened QT
interval
 Hypomagnesemia – widened QRS,
cardiac irritability

Bradycardia – Disturbances of
cardiac impulse conduction


First degree AV heart block
Second degree







Mobitz I
Mobitz II
Unifasicular block
R bundle branch block
L bundle branch block
Third degree (trifascicular ) heart block
Defined as HR less than 60
First degree AV block



Think of ischemia if it is a
new onset for the pt.
Can also be caused from
digitalis, aortic
regurgitation, increased
vagal tone
Usually asymptomatic
2nd degree AV block

Mobitz I (Wenckeback) progressive
prolongtion of PR until a beat is
entirely blocked
2nd degree AV block
Mobitz II

Sudden interruption of the conduction
of an impulse without prior
prolongation of the PR
2nd degree AV block
Mobitz II
More serious than Mobitz I because it
is more likely to progress to complete
heart block
 More likely to require pacemaker
 “Missing a beat without warning is
TWICE as scary”

Right bundle branch block



Conduction block over the
R bundle branch which is
present in 1% of hospital
patients
May be seen in pts with
pulm dz, ASD, or increased
R ventricular pressures
Often clinically insignificant
Right bundle branch block


QRS complex
exceeds 0.1
second
Broad rSR complex
in V1 an V3
L bundle branch block


Often associated with
ischemic heart disease,
LVH/chronic HTN, or valve
disease
Difficult to diagnose MI in the
presence of LBBB
L bundle branch block

QRS complex more
than 0.12 seconds
with wide notched
R waves in all
leads
Unifascicular block


3 fascicles of the His-Perkinje system
 Right fascicle, Left anterior fascicle, Left posterior fascicle
A block of one of the L fascicles can occur
 One of the L fascicles plus RBBB can lead to complete heart
block
Complete heart block

Complete absence of conduction of impulse
from atria to ventricle




If block is proximal to AV node HR will be 4555 BPM
If block is distal to AV node (infranodal) HR
will be 30-40 BPM with a wide QRS
(ventricular in origin)
Can be caused by fibrotic degeneration,
ischemia, cardiomyopathy, ankylosing
spondylitis, iatrogenic (cardiac surgery),
drugs, hyperkalemia
TX is pacing
Bradycardia

1001 Differential dxs for bradycardia
including:

Hypovolemia, hypoxia, acidosis,
hypoglycemia, hypothermia, hyperkalemia,
overdose, tension pneumo, increased ICP,
pesticide exposure, noxious surgical
stimulation (ocular pressure, scrotal/ovarian
traction, abd insufflation, laryngoscopy), PE,
MI, carotid sinus stimulation, narcotics,
succinylcholine, sleep apnea, normal
physiology of well-trained athlete,
hypothyroidism . . . etc
Tachycardia
(Heart rate greater than 100)

Three key questions:
IS THE PATIENT STABLE?
 Is the QRS narrow or wide?
 Is the rhythm regular or irregular?

Tachycardia

Narrow complex


Regular rhythm is
probably a
reentrant
tachycardia
Irregular rhythm is
probably A fib or A
flutter

Wide complex


Regular rhythm
could be SVT with
aberrant
waveform or VT
Irregular rhythm
could be A fib with
aberrant
waveform,
polymorphic V
tach, torsades
Narrow versus wide complex
tachycardia

Narrow complex more likely from an
atrial origin


Aka SVT (supraventricular
tachycardia)
Wide complex more likely from a
ventricular origin

VT more serious since the concern is
that the rhythm may degrade to V Fib
Narrow complex tachycardia
Sinus tachycardia


Most common cause of tachycardia
Rhythm originates from AV node in
response to stress







Hypovolemia
Pain
Fever
Exercise
Substance withdrawl
Agitation (in the ICU) . . . etc
Treatment is to identify and treat the
stressor (if necessary)
Narrow complex tachycardia
Supraventricular tachycardia

SVT can be loosely defined in 3 types

Atrial tachycardia-AV node passively
conducts impulse from atria to ventricles
• A fib, A flutter, atrial tachycardia


Atrioventricular nodal reentrant tachycardiareentrant focus is adjacent to AV node and
AV node propogates reentrant impulse
AV reentrant tachycardia-accessory pathway
bypasses the AV node
• WPW
Narrow complex tachycardia
Supraventricular tachycardia

Atrial tachycardia

Ectopic atrial focus (outside the atrial
node) becomes irritable and can
override atrial rhythm
• See P waves of different morphology
Narrow complex tachycardia

Atrial fibrillation with RVR
Atrial depolarization rate is 400 –
600/minute
 AV node acts as gatekeeper and only
conducts 100-180 of these
depolarizations each minute


Atrial Flutter

Atrial depolarization rate is 250450/minute
Narrow complex tachycardia
A fib/A flutter

A Fib

A flutter
Narrow complex tachycardia
A fib/A flutter

Treatment

If patient is unstable tx is always
cardioversion
• 50 J for A flutter, 100-200 for a fib
progressing to 200, 300, 360

For stable patients control rate with B
blockers, diltiazem, consider
amiodorone for new onset
Narrow complex tachycardia
AVNRT & AVRT



Reentry tachycardia
requires two pathways over
which impulses are
conducted at different
velocities
Can originate adjacent to
the AV node
Pathway may completely
bypass AV node (giving
rise to WPW)
Narrow complex tachycardia
AVNRT & AVRT

If the supraventricular tachycardia is
due to AV node reentry then it should
be terminated by anything that
transiently blocks the AV node
Carotid massage
 Valsalva
 Adenosine


Definitive tx is ablation of the
accessory pathway
Narrow complex tachycardia
AVNRT & AVRT

Accessory pathway which bypasses
AV node poses risk for sudden
cardiac death due to tachyarrhythmias

WPW syndrome on ECG has delta
wave or slurred deflection of
beginning of QRS, QRS greater than
0.12 sec
Pacemakers and AICDs
Chamber
paced
Chamber
sensed
Response of
generator
Prgrammable
functions of
the generator
V = ventricle
V = ventricle
T = triggered
P=
programmable
rate
A = atrium
A = atrium
I = inhibited
M= multi
programmable
D = dual
(atrium and
ventricle
D = dual
D = dual
C=
communicating
O = none
O = none
O = fixed
(asynchrynous) (asynchrynous) function
ICD (implantable/internal
cardiac defibrillator)

For patients with a high risk or
personal history of ventricular
fibrillation

Device delivers a defibrillating shock if
V tach or V fib is sensed
Things to consider in
pacemaker/ICD patients
Central venous line placement can
displace recently placed transvenous
electrodes
 Grounding pad needs to be placed far
away from device
 If cautery is used near device, current
should be as low as possible and
delivered in short bursts

Things to consider in
pacemaker/ICD patients


Should defibrillation be necessary in
pacemaker patient, paddles should not be
placed directly over the pulse generator and
patient may have lower stimulation
threshold
For ICDs it is usually prudent to disable the
device since sensing of electrocautery may
trigger shock

External defibrillator should be readily
available and device should be turned on
immediately post op
THINGS TO REMEMBER

Your response to a patients dysrhythmia is
dependent on whether the patient is stable
or unstable


Bradycardia of 45 in an Olympic athlete is
acceptable for a BP of 120/80 but not for
60/40
A heart rate of 130 is NORMAL in an infant
but could cause an MI for a 78 year old
hypertensive, diabetic, smoker

You are walking down the hall of the
surgical floor when a nurse
recognizes that you are on the
surgical team and stops you regarding
Mr. Brown. He is a 28 y/o that had an
appendectomy at midnight last night.
His heart rate was 120 when the CNA
took his vitals 5 minutes ago. What is
your next step?

You go to see Mr. Brown. He does not
appear to be in pain, but does look
pale and anxious. You pick up his
wrist and count a thready pulse of
135.
His vitals are RR 28, BP 85/65, Temp
100.9
 He states he has no heart problems or
history of syncope. He runs 2 miles a
day. His father died of an MI at 54.

On further exam you notice Mr.
Brown’s abdomen seems more tender
than you would expect.
 The lab calls with a panic value of
Hgb of 5.2 for Mr. Brown

You receive a stat page to the ward
because Mr. Jones has been found to
be lethargic this morning. He is only
mumbling incomprensibly when you
ask him questions or shake his
shoulder.
 Mr. Jones is a 78 year old that had a
total knee replacement yesterday.

Vital signs are SpO2 85%, HR 45, RR
6, BP 82/40
 Mr. Jones is lying in bed with his
mouth hanging open. His eyes are
rolled back. He is making course,
snoring sounds with his respirations.
His dressing looks clean and dry. He
has NS for IVF running at 120/hour
and a morphine PCA.

After oxygen mask is placed his
saturation improves to 95%
 0.5 mg of atropine improves his heart
rate to 85
 His mental status improves somewhat
but he is still extremely somnalent

On further exam Mr. Jones is noted to
have a PCA basal dose of 4 mg/hour
of morphine.
 After administering naloxone, Mr.
Jones becomes responsive,
conversant and begins asking for a
breakfast tray
