Implantable cardiac devices Flashcards
Briefly discuss pacemakers
All pacemakers have three basic componenets
1) the pulse generate - houses the power source
2) the eclectronic circuitry
3) the lead system
Nearly all are lithium powered pulse generators which normally function for 4-10 years
Permanent pacemakers have endocardial elads that are positioned in contact with the endocardium of the right ventricule and in the case of dual chamber device the right atrium
Leads may be either bipolar or unipolar.
A bipolar endocardial lead has both the negative and positive electroges separated by approximatly 1cm within the heart. A unipolar lead has the -ve electroge in contact with the endocardial surface and the positive pole is the metallic casing of the pulse generate
Discuss class 1 indications for PPM
1) 3rd degree and advanced 2nd degree block at any anatomic level assocaited with any of the following
- Symptomatic bradycardia or ventricular dysrhythmias presumed to be a result of a AV block
- symptomatic brady secondary to drugs required for dysrhythmia management
2) symptomatic brady resulting from 2nd degree av block regarldess of type or site
3) asymptomatic persistent 3rd degree with awake ventricualr rate over 40BPM with LV dysfucntion or if the block is below the AV node
4) chronic bigasicular or trifascicular block with intermittent 3rd degree
Discuss class 1 indications for ICD
1) cardiac arrest resulting from VF or VT not aused by transient or reversible event
2) spont sustanied VT
3) Syncope or undertermined origin with clinically relevant HD significant sustained VT or VF induced at EP study when drug therapy is ineffective or not tolerated
4) non ssutained VT with CAD, prior MI, LV dysfucntion and inducible VF or VT
Discuss letter system
Letter 1 - chamber paced a- atrium V- ventricle D- dual 0-none
Letter 2- chamber sensed A- atrium V-ventricle D- dual 0-none
Letter 3 - sensing response
T- triggered - upon detecting a spont depol or other signal a triggered mode will deliver an electical stimulus
i- inhibited - after sensing a spont depol withholds its pacing stimulus
D- dual
0-none
Letter 4 - programmability P- simple M- multiprogrammanble r- rate adaptive C-comminciating 0-n nnone
Discuss complications of implantation
1) infection
- Presence of foreign body complciates the management and few cases of bacteremia that develop after implantation can be managed with Abs alone.
- In most cases re-implantation and replacement of the lead system is necessary
Thrombophlebitis
- THe incidence of venous obstruction asscoiated with PPM range from 30-50% with approxiamtly 1/3 of patients have complete venous occlusion
- Thrombosis of varying degree can involve the axillary subclavian and inominate veins or the SVC
- Usually asymptomatic due to significant collateralisation
- Although rare SVC syndrome can develop from thrombosis asscoaited with PPM
- Usually respond to systemic anticoagulation but treatment of these clots is controversial as they rarely ever cause PE
Discuss pacemaker syndrome
Pace-maker syndrome
- after PPM a patient may develop new complaints or report a worsening of the symtpoms that promoted evaluation and PPM in the first place
- Approx 20%of patients report syptoms suggsting pacemaker syndrome after insertion
- Syncope, near syncope, orthostatic dizziness, fatigue, exercise intolerance weakness, pain and abnormal pulsatations
- These are caused by a loss of AV syncrony and by the presence of ventriculoatrial conduction
- Most commonly seen in VVI pacing but also described in DDI
- With VVI the ventricle is electrically stimulated jand depolarized resulting in ventricular systole. If the sinus node function is intact the atrai can be depolarised causing the atria to contract against a closed mitral and tricuspid valve. This contraction leads to an increase in jugular and pulmonary venous pressure
- Atrial distention can reult in reflex vasodepressor effectes medaited by the CNS
- If the atiral kick is important to late diastolic ventricular filling basal and orthostatic hypotension may occur
Discuss pacemaker malfunction (failure to capture)
Range from the compelte absence of pacemaker spikes to spikes not followed by a stimulus induced complex.
Complete absence of spikes
- battery depletion
- fracture of the pacemaker laed
- disconnection of the lead from the pulse generator
Failure to capture (can be complete or intermittent)
- most commonly a lead probem
1) lead displacement is the most common cause - CXR may demonstrate the tip of the pacing catheter diplaced from the RV apex
2) Lead fracture produces an insulation break resluting in failure to capture as a result of current leak.
3) Exit block (failure of an adequate stimulus to depol the paced chamber) - most commonly doe to changes in the endocardium in contact with the apcing system
- causes include ischaemia or infarction
- electrolyte disturbance
Discuss pacemaker malfunction (Inappropriate sensing)
Undersensing
- failure to sense may be complete or incomplete
- May result from a change in the sensing parametes selected at teh time of inseriton - this is most commonly encountered after an acute RV infarct or during progressive fibrosis that accompanies many cardiomyopathy
- Lead fracture, displacement and poor contact may also lead to undersensing
- Undersensing is typically recognised on the ECG as the appearance of pacemaker spikes occuring earlier than the programmed rate
Oversensing
- May sense electrical activity taht is not cardiac in origin
Discuss pacemaker malfunction (Inappropriate pacemaker rate )
A pacing rate below the programmed rate is typically foundin pulse generater depletion and does not occur abruptly with lithiuym iodine batteries.
An extreme increase in pacing rate the so called runaway pacemaker is rarly if ever encountered with current pacemaker technology and circuitry
- an endless loop tachycardia may develop during dual chamber pacing when ventriculoatrial conduction occurs and the resulting retograde atrial depol resutls in a stimulated or paced ventricular depol.
- If A flutter developds during dual cahmber pacing flutter waves may be sensed and tracked resulting in rapid paced ventriculr rate.
- In both instances the ventricular rate does not exceed its set upper limit
Discuss the ECG in paced rythym
THe normal function of a single chamber VVI pacemaker is the most easily recoqnized
- after a progrmamed interval is supassed during which intrinsic ventricualr activity did not occur a pacer spike or stimulus artifact appears
- A wide QRS complex appears after the spike
- depol beings in the right ventricular apex and the spread of excitation does not follow the normal depolarisation pathways
- LBBB is the normal pattern - if RBBB consider lead displacement
- IN VVI if atrial depol occurs it is independent of the ventircle (AV dissocaition)
Discuss ACS with a pacemaker
Place leads a safe distance from the pulse generator >10cm than as normal
Immediate return of pacing (capture) may not occur after defib due to global myocardial ischaemia and icnreased pacing threshold and is not an indication of pacemaker malfunction
-Temp transcutaneous pacing may be needed
Discuss IADC
Indications as above
Compatable with dual lead pacemaker
Complications and malfunction almost identical to PPM
ICD discharge during CPR poses no risk to providers although the rescuer may feel a weak shock
Discuss breifly biventricuar pacing
Also known as cardiac resynchronization is therapy for patients with left sided heart failure and ventricular desynchrony
LBBB causes an altered sequence of depolarization of the LV such that the interventricualr septum contract before the LV free wall leading to inefficeint mechanical pumping
Biventricualr pacing resynchronizes the ventricles by simulatneously pacing the left and right eliminating the delay in the LV free wall and improving systolic funciton.
Discuss cardiac assist deviceses
Three types of implanated heart assist devices now exist. These include left ventricular assist device, biventricualr assist device and the total artificial heart.
The most common LVAD produces non pulsative flow therefore patients are essentially pulseless making traditional HD vital sign interpreatiton impossible
Some have backup hand pump methods
