chap 10 Flashcards
when complete heart block occurs at level of AV node the most rapid automatic activity arises from where and at what rate ?
the heart rate produced by the cells below the AV node usually relatively fast - often about 50 per min
= escape rhythm
is pacing required in complete heart block ?
qrs complex may be narrow - in the setting of narrow complex CHB often may not require pacing - because HR not low and little chance of going into asystole
causes of CHB ?
degenerative tissue fibrosis
anteroseptal myocardial infarction
cardiomyopathies
calcific valve disease
automatic activity arising below the bundle of his due to CHB is likely to have what qrs ?
distal purkinjee - qrs complexes are broad
pacing for CHB below bundle of hiss?
the escape rhythm is unreliable
and may fail - leading to syncope - stokes adams attack
or
fail completely causing ventricular standstill
= broad complex CHB requires pacing
if long ventricular pauses = make this urgent (>3sec)
what in the egg strip can give an indication for successful pacing ?
presence of p waves
in whom is pacing rarely successful
and most successful
asystole
during ventricular a-systole , there is still p waves due to ventricular stand still = pacing more likely to achieve cardiac output than in most cases of complete systole
what is capture ?
is pacing stimulus induce immediate qrs complex
what are the different modes of pacing ?
NON INVASIVE:
percutaneous - fist pacing
transcutaneous -does not provide reliable ventricular stimulation (discomfort for conscious patient)
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INVASIVE
temporary transvenous pacing
permanent pacing - implanted pacemaker
when is percussion fist pacing used ?
succesful in ventricular standstill accompanied by continuing p waves
used instead CPR - produce adequate CO
what inhibit the transcutaneous pacemaker ?
spontaneous QRS complex
movement artefact on ECG - if artefact still appears to be inhibiting pacemaker - switch pacemaker to fixed rate pacing
appropriate pacing rate for transcutaneous pacing in adults ?
60-90 per min
but some circumstance with av block of ventricular rate of 50 - slower pacing to 40-30
further adjustments in transcutaneous pacing ?
if pacing device has adjustable energy output
start at lowest first , gradually increase until each pacing spike is closely followed by qrs complex indicating electrical capture
always check if the qrs complex is followed by a t wave and palpable pulse (fails to create pulse = PEA)
if highest current setting reached and electrical capture not occurred - adjust the pads / electrode positions
continued failure to capture - hyperkalaemia ? non viable myocardium ?
when transcutaneous pacing provides adequate CO - senior input to switch to trans venous
most transcutaneous pacing , paces the heart in what mode ?
in demand mode
what are the disadvantages of transcutaneous pacing ?
conscious patient can experience a lot of discomfort
consider IV analgesia and sedation
NO DANGER FOR PEOPLE TO CONTACT PATIENT when patient being paced transcutaneous
reasons why trans venous pacing failures
high threshold - need to place one f the electrodes on the apex of the right ventricle where it is least likley to be displaced
pacing threshold is taken by gradually reducing voltage
aim to achieve threshold <1 V at time of lead insertion
higher voltage means the elecytrode is not touching the myoicardium
usual to pace the heart with 3-4V well above the initial pacing threshold - transeint rise in pacing threshold over days is expected
check threshold daily so the voltage given is over the threshold i8f not loss of capture may occur - seen on ecg as pacing spike without qrs complex
sudden increase in pacing threshold , as you will see in the ECG as a loss of capture is due to displacemnt of electrode - ake sure to increase the voltage above the threshold , and obtain chest x ray to see where the electrode is
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Connection failure
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Lead displacement
Lead is usually positioned in the base of of the right ventricle - there should be enough slack in the lead to allow for changes in patient posture and deep inspiration.
when lead displaced in the right ventricle can lead to vf and Vt
can patient with tranvenous pacing go into cardiac tamponade
very rarely yes
with no pacing there can be ?
ventricular standstill = short lived cause - syncope
long standing - cardiac arrest
is there is a patient with with an implanted SC pacemaker or ICD and requires electric carduoversion what do you do ?
place defib pads - 8cm fro the device
devices are usually implanted below the clavicle - and these devices have no problem with the use of standard defib
what happens when a pacemaker ICD is places below the right clavicle instead of left or just below the axilla?
use AP position for defib
below right clavicle devices are usually leadless
problems with implanted permanent pacemakers
lead displacement may occur as an early complication , BUT RARELY OCCURS 4-6 WEEKS AFTER
MISDIAGNOSE AN ARRYTHMIA MISINTERPRET OTHER ELECTRICAL SIGNALS and deliver inappropriate hocks
what s the difference between simple pacemaker and ICD ?
simple ICD can deliver shock when it detects fast VT or VF
many devices programmed to also deliver critically timed pacing stimuli to prevent these sort of arrhythmia
when’d o we resort to defib in ICD ?
when VT accelerates and degenerates into VF
indication for icd ?
HIGH RISK OF VF
MAY IMPROOVE SURVIVAL IN PATIENT WITH MASSIVE MYOCRADIAL INFRACTION
how to temporarily disable ICD?
holding ring magnet overlying the device usually above the pectoral
cardiac arrest with ICD
DO CPR
= reports of transient myalgia and parathesia from the shock of ICD to the person doing CPR
if this decreases the quality of CPR - consider deactivating the ICD
if shockable rhythm present and not terminated by ICD = defib = BE CAREFUL WITH THE PADS
f person dies with active ICD ?
arrange for deactivation of ICD
must be removed before cremation
When using transcutaneous pacing:
electrical capture typically occurs with a current of?
50-100 mA
