Cardiothoracic Flashcards
What are the types of pacing?
Transvenous
- Method; electrode into ventricle
- Clinical: semiemergent
- Access: CVC+PAC
- Benefits: reliable
- Limitations: CVC complications
Epicardial
- Method; pacing attached to epicardium
- Clinical: post CTS surg
- Access: atrial wires (right epigastrium) ventricular wires (left epigastrium)
- Benefits: small, easy to remove
- Limitations: infection, less reliable, dislodge, bleeding when removed
Transthoracic
- Method; pacing needle or cath through chest
- Clinical: last resort
- Access: subxyphoid or left parasternal
- Benefits: life saving
- Limitations: myocardial/coronary artery laceration, abdominal organ injury, tamponade
Transcutaneous
- Method; pacing via pads
- Clinical: emergency as a bridge
- Access: external only
- Benefits: life saving
- Limitations: large amounts of current, painful, skeletal muscle stimulation
What are the components of
a bipolar temporary pacing
1) Generator
2) Bridging cable
3) Bipolar epicardial wires
- negative pole - cathode - must be in direct contact with myocardium. Delivers stimulus
two wires sutured into the muscle, insulated stainless steel.
Wire knot in the skin to prevent dislodgement
What is a unipolar pacing system?
Only a cathode to depolarise with current passing through the body.
Can be made into unipolar for troubleshooting - only for ventricular pacing.
What is the indication for a temporary pacemaker post op?
1) Bradycardia
- cardioplegia, hypothermia, anesthetics, swelling of myocardium, surgical trauma to conduction system, intra-op ischaemic
2) Reduced cardiac output
- CO=SVxHR - can support the underlying rhythm.
3) anticipation of complete heart block
- post valvular surgery they are at high risk.
What pacing options are available post operatively?
Ideal settings are AAI and DDD to maintain atrial contribution
In post valvular surgery high risk of heart block
- VVI (ventricular backup)
What problems can occur in to sensing pacemakers post operatively?
Failure to sense - Pacing induced arrhythmias
- R on T phenomena with ventricular pacing and can precipitate VT/VF
Oversensing - failure to pace. Could be patient related (muscle potentials, shivering/seizures, mobile phones/diathermy)
What is a sensitivity threshold?
minimum size electrical event that can be detected by the pacemaker
- lower the number the more sensitive
for a check we set the sensitivity to be even more sensitive (by halving then minus one).
Usual settings
- 0mV to 0.5mV (min 0.5) atria
- 0mV to 2.0 mV (min 2.0) for ventricles
What is Capture?
the ability of the current delivered to affect depolarisation
- Electrical capture - on the ECG every pacing spike = rhythm
Mechanical - both electrical and cardiac output. HR correlating with the art line.
What is the Output threshold?
minimum amount of current required to initiate depolarisation
- output to be more after a check (doubling and adding one)
usually 4mA or higher
Report if atrial output threshold >10mA
Ventricular output threshold >5mA
Summarise output/sensitivity threshold checks
Set sensitivity - half minus 1 (0.5mV atria, ventricle 2.0mV)
Set output as double plus 1
Appropriate mode
Appropriate rate
Pacing codes and what they stand for?
Chamber Paced Letter 1
Chamber Sensed Letter 2
Sensing Response Letter 3
A= atrium V = ventricle O = none
Response
T = triggered
I = inhibited (sensing response)
D = dual (atrium and ventricle inhibited)
What is synchronous mode?
ability to recognise the intrinsic heart rate and not pace over the top
What are the types of pacing modes?
AAI
- pacing atrium, sensing atrium and inhibiting pacing if sensing occurs.
- Benefits: ideal for normal conducting heart, if PR prolongation use dual chamber mode
- Limitations: not suitable if AV conduction not intact (i.e. CHB), not recommended for AF or flutter
VVI
- pacing ventricle, sensing ventricle, inhibiting in response to event outside refractory period
- Benefits: good in impaired AV conduction - good in bradycardia or atrial arrhythmia
Limitations: loss of syncrohony
DDD
- pacing to atrial ventricles (dual), sensing both, and inhibit/initiate in both
- benefits: maintains AV synchrony
- limitations: upper rate limit is adjustable.
What is asynchronous mode?
at a set rate irrespective of patients underlying rhythm
AOO/VOO/DOO
VOO/DOO - in asystole or severe bradycardia
- can cause AF, flutter, Vf/VT
How do you test a pacemaker?
1) stable patient
2) determine underlying rhythm
- reduce rate until 50bpm reached
3) determine sensitivity thresholds (only if stable)
- reduce to 10bpm and reduce output to 0.1mA (no capture)
- increase the number of sensitivity setting until failure to sense (light stops flashing)
4) determine the output capture threshold
- increase the pacing rate to 10bpm above thyrhm
What is a strategic way to trouble shoot pacemaker problems?
Equipment
- pacing wires/cables/box
- old blood? clean wires. Change polarity consider skin lead insertion
Patient
- resus? pacing failure cause?
- treat reason for arrest
- tamponade? myocardial ischaemia? electrolytes? acidosis?
Why are post cardiac patients likely to bleed?
on the bypass circuit there is citrate and pump blood has heparin. Typically protamine is used to reverse the coagulopathy however sometimes there is reduced ionised calcium due to heparin
What are some complications from cardiac surgery?
Cannulation issues
- multiple sites = risk of atheroma, arterial dissection, bleeding, air emobolism
Foreign surface
- inflammation, coagulation, fibrinolysis, microemboli
- temperature changes (hypothermia)
Increased clotting/bleeding
Myocardial stunning
Post-pump pulmonary dysfunction (atelectasis to ARDS)
CNS effects (cerebral dysfunction)
Renal effects - pulsatile flow on CPB - global renal blood flow reduced
Tendency for increase need for fluid/fluid overload
Immune suppression
- suppression of B and T lymphoctes for 1-3days
Stress response
- increased catecholeamines - wound healing reduction, euthyroid sick syndrome, hyperglycemia
What are some things to take note of in handover?
anaesthetics
- pulmonary pressure on PA (esp with MV replacement)
- pre/post op TOE findings
- difficult airway? induction difficulty? on bypass any issues?
cardiopulmonary bypass
- bypass time
- cross clamp time
- issues coming off bypass
- issues with cannulation
Surgical
- who the surgeon is
- indications for surgery
- whether emerg or elective
- complications
- what parameters would they like to be informed for?
What are the routine care aims for a post cardiac surgery patient?
MAP 65-70 cardiac index >2.2 central venous saturation >50% Hb >70 (aim >80 if high vasoactive req) Mag >1 Ionised Ca >1.0
When you call the CTS team post surgery in ICU?
- significant bleeding (req >2units)
- if Drain output 400mls in 1hr, 200mls/hr for 2hrs or 100mls/hr for 4 hrs
- inotrope commencement with unexpected increase
- significant arrhythmias - VT or sustained VT
Major deterioration in condition
- neurologic injury
- ischaemic limb
- ARF or RRT req
- referral to specialty (e.g. gastro)
What are the interventions for someone who has bleeding post CTS?
- FFP if INR >1.5
- cryoprecipitate 10units if fibrinogen <1.5
- platelets if platelets <50
- desmopressin 0.3mg/kg if uraemia or post CPB
- prothrombinex 25-50units.kg if warfarin and INR raised
- protamine 25-50mg if recent heparin and APTT raised
DO NOT USE PROTAMINE IF ON ECMO
Preventative measures
ph>7.2
temp >35
ionised calcium >1.1
CALS for post cardiothoracic patients - why the need?
- External CPR ineffective in tamponade
- external CPR ineffective if extreme hypovolemia is present
- external CPR ineffective in tension pneumothorax
- early re-sternostomy is the optimum strategy
There are three pathways in CALS, briefly explain the 3 and the management
VF/VT
- 3x shocks charge to 200
- amiodarone
- CPR
- re-sternotomy
asystole
- emergency button on pacing box, set to maximum
- CPR
PEA arrest
- pause pacing to see underlying VF
- CPR if not VF
- prepare re-sternotomy
