10. Cardiac pacing Flashcards
intrinsic rate produced by
1) SA node
2) AV junctional region
3) distal His-Purkinje fibres
1) 60-70
2) 40-50
3) 0-30
T/F: in CHB the QRS complex will always been wide
false - when CHB occurs at the level of the AV node, the cells immediately below the block become the new pacemaker and normally beat about 50/min - narrow QRS as its rapidly conducted to the ventricles through an intact bundle of His
when automatic activity occurs lower in the distal purkinje fibres, this leads to slow and unreliable rhythm - this escape rhythm may fail transiently leading to syncope called ___ ___ attack
stokes adams attack
T/F: broad complex CHB requires cardiac pacing
true - urgently if there’s long ventricular pauses (>3s)
T/F: pacing is rarely successful in asystole
true - do not routinely attempt pacing in the absence of p waves
if a pacing stimulus induces an immediate QRS complex this is referred to as ‘_____’
capture
pacing may be classified as
1) non-invasive e.g. …
2) invasive e.g. …
1) percussion (‘fist’ pacing), transcutaneous
2) temporary transvenous pacing, permanent pacing
how to perform percussion pacing? (do if bradycardia so profound it causes clinical cardiac arrest)
with the side of a closed fist deliver repeat firm thumps to the praecordium, just lateral to the lower left sternal edge - raise the hand about 20cm above the chest before each thump
check for pulse and QRS complexes on the ECG
if no pulse start CPR
major disadvantage of transcutaneous pacing?
causes discomfort in a conscious patient
ideal placement of pads for pacing?
ideally the conventional right pectoral and left apical positions
if not possible use AP positions
(if using a pacing device that is not capable of defibrillation, use AP position for pacing pads so defib pads can still be applied)
T/F: if there is significant movement artefact, change the pacing device from demand mode to fixed-rate pacing
true
an appropriate pacing rate is normally what for adults?
60-90/ min
(slower in CHB)
when doing transcutaneous pacing, continue to increase the energy until what is achieved
until each pacing spike is followed immediately by a QRS complex, indicating electrical capture
(ensure the QRS is followed by a T wave so you know its not artefact)
what to do if the highest current setting is reaching in transcutaneous pacing and electrical capture has not occurred?
try changing electrode positions
continued failure to achieve electrical capture may indicate non-viable myocardium or other conditions e.g. severe hyperkalaemia
good electrical capture that fails to generate a pulse constitutes what rhythm?
PEA
T/F: there is no hazard from transcutaneous pacing to people who are in contact with the patient
true
although there’s no benefit to giving pacing during CPR so best to turn off
what are the three ways in which temporary transvenous pacing systems can fail?
1) high threshold (usually paced at 3-4V stimulus, well above the initial pacing threshold which is aimed at <1V
2) connection failure
3) lead displacement
when a temporary pacing lead is inserted, the usual aim is to position the tip where in the heart?
in the apex of the right ventricle - where it’s least likely to be displaced
what to do if there is a sudden increase in the threshold of a tranvenous pacer
get a CXR to check the lead placement - as this may be caused by displacement and need repositioning
recheck pacing threshold if theres a loss of capture
what is the pacing ‘threshold’ of a tranvenous pacemaker
the minimum voltage required to stimulate the ventricle
most tranvenous pacing leads are UNIPOLAR/ BIPOLAR
bipolar
what possible cause should be considered if a patient with a recently implanted pacing lead suffers a PEA arrest?
cardiac tamponade caused by perforation of the right ventricular wall
T/F: when displacement of a pacing lead or perforation of the ventricle occurs, the ECG will still show a pacing spike
true - but there is likely to be intermittent or complete loss of capture of the pacing stimulus
if a pt with an implanted s/c pacemaker or ICD has a cardiac arrest or requires cardioversion, place the defib pads >____cm fro m the device
8
what is the primary function of an ICD?
to terminate a life-threatening tachyarrhythmia
how can an ICD be disabled temporarily if it misfires causing discomfort to the patient?
place a ring magnet over it
T/F: an ICD must be deactivate prior to its removal from the body/ an autopsy
True
