Cardioversion Flashcards
(19 cards)
Name 5 indications for cardioversion
Termination of hemodynamically unstable tachyarrhythmias
- Supraventricular tachycardia (Afib, Aflutter, atrial tachycardia)
- Ventricular tachycardia (monomorphic)
- all available antiarrhythmic drugs have failed
- termination of lone AFib
- development of tachyarrhythmia amenable to cardioversion under GA
What rhythms cannot be treated with cardioversion? What should those rhythms be treated with instead?
- VFib
- very irregular, rapid polymorphic VT
–> defibrillation
What is the pathophysiological principle of cardioversion?
shock is deliverd to a critical mass of myocardium –> myocytes experience a coordinated change in voltage (=deplolarization) followed by a refractory state –> SN can reegain control
What % of the shock delivered transthoracically reaches the myocardium?
4%
Across what % of the ventricular myocardium must the vector of the shock travel in face of VT in order for the cardioversion to be successful?
70%
What influences the success of shock termination?
- amount of energy delivered
- path of current relative to the position of the heart
- transthoracic impedance
Name 5 factors that determine thoracic impedance?
- size and confirmation of the chest
- water and fat content
- pulmonary volume size
- size and position of the paddles
- force applied to the paddles
What is cardioverter-defibrillator?
A device that delivers a preselected amount of electrical current to the heart.
Name the 3 types of cardioverter-defibrillators?
- external
- transesophageal
- transvenous
What are the components of a cardioveter-defibrillator?
- battery
- transformer (converts alertnating current into direct current)
- capacitor (stores electrical charges during charging time + releases them)
- internal electrolic components (adjusts energy, duration of shock and waveform)
–> Most cardioverter-defibrillators are multifunction devices used for monitoring, cardioversion and ecternal pacing.
What electrophysiological mechanism of tachyarrhythmias is cardioversion most effective in?
reentry > enhanced automaticity
What makes it more likely that a patient stays in sinus rhythm after cardioversion?
No structural heart diease present
How do you prepar for cardioversion (monitoring, drugs, patient preparation)?
- Drugs: antiarrhythmics to treat tachyarrhythmias (procainamide, lidocaine, amiodarone) + bradyarrhythmias (atropin)
- Oxygen support
- continuous ECG monitoring
- check electrolytes (incl. magnesium)
- check systolic function + for effusions (echo)
- prepare airway management
- prepare for GA: propofol/etomidate
- dorsal recumbency
- clip chest bilaterally between 3rd + 6th ICS
- apply cardioversion adhesive patches (for VT –> over ventricles ; for SVTs over atria - higher up at chest)
What can happen after induction of GA?
- resolution of tachyarrhythmias (driven by SNS)
- rapid drop in BP due to loss of vasomotor tone secondary to anaesthetics
- decompensation of rhythm into VFib
What is important when setting up the cardioverter-defibrillator?
Select synchronous mode, so that the shock is timed to be deliverd at the peak of the R wave = absolute refractory period
–> must often be repeated for every single shock as device defaults back into asynchroneous mode after delivery of shock
What can happen if a shock is delivered around the peak of the T-wave?
= vulnarable period
shock reaches ventricles during their repolarization, which is characterized by tissue heterogeneity –> induction of VFib possible
What is the starting energy required for cardioversion?
2J/kg
What should be done aftrer successful cardioversion?
Administer antiarrhythmics to prevent recurrence of arrhythmia
Name X complications of cardioversion
- induction of VFib (if deliverd around T-wave)
- risks of GA
- skin burns
- thromboembolic events
