Mod11 Defibrillation Flashcards
SA node
located in RA; has the highest rate of spontaneous depolarization therefore is considered the native pacemaker
AV node
small subendocardial structure composed of atrial conduction fibers; within interatrial septum; receives ANS innovation
3 functions of AV node
provides a delay btw atrial and ventricular contraction; regulates number of impulses that reach ventricles and acts as pacemaker when SA node fails
Purkinje fibers
forms Bundle of His that comes from AV node; bifurates within muscular septum and divides into R and L bundle branches; the branches terminate in the Purkinje fibers; very little ANS innovation
Pacemaker
responsible for initiating and self-propagating wave of depolarization; myocardium has ability to exhibit excitability when stimulated; BUT excitability is NOT directly related to strength of stimulus
Excitability at cellular level
maintained by electrical transmembrane potential where chemical gradient are imperative in generation of potential
Rate of depolarization of myocardium depends on
presence of ischemia/infarct, electrolyte imbalances, some drugs
Artificial pacemaker
device used to temporarily external, temporarily transvenous or permanently (in vitro/implantable) to treat arrhythmias; does this by supplying heart with pulse of energy
Artificial pacemakers are composed of:
one+ pacing leads (thin wires advanced into heart), pulse generator (supplies the power)
Pacing leads composed of;
electrode, conductor, insulation, and connector pin
Active fixation
1/2 methods to hold lead in place; leads have barb or screw that is fixed or retractable and embeds into myocardium
Passive fixation
1/2 methods to hold lead in place; leads have fins at tip that get entangled into trabeculation of ventricle; tip leads are corticosteroid eluding to try and reduce high pacing thresholds shortly after implantation due to the hyperacute injury to the myocardium
Pulse generator includes:
power source (battery), output circuit, and header with connector (to connect leads to generator)
New technology are advanced:
have rate adaptive sensors, have telemetry, and microprocessors that allow storage of diagnostic info
External Telemetry
allows generator to receive info from programmer and to send info back via radiofrequency waves (each manufacturing company uses their own wave freq)
Info retrieved through telemetry:
battery status, lead impedance, current, pulse amplitude, pulse duration and occurrence of arrhythmia
Stimulation threshold
minimum amount of energy a device is required to deliver to produce depolarization of myocardium; DEPENDENT ON pulse duration and pulse amplitude
Sensing
endocardial electrode is responsible for sensing any native heart rhythm; if HR is below/above programmed rate; the PM will be activated
Unipolar leads
has one conductor and one electrode; lead tip that functions as cathode and the pulse generator functions as anode; have larger diameter lead wire and don’t offer as many functions as bipolar
Bipolar leads
2 conductors and 2 electrodes; uses lead tip as cathode but lead ring functions as anode; can be run in unipolar mode; advantage include reduction in intracardiac stimulation and more specific sensing
Single Chamber PM lead configuration
may have lead in just the RIGHT atrium or just the RIGHT ventricle (Depends on conduction disturbance)
Dual chamber PM lead configuration
may have pacing electrodes (leads) in RIGHT atrium AND RIGHT ventricle (allows control over AV delay during exercise (rate response)
Biventricular PM lead placement
leads placed in RIGHT atrium and RIGHT AND LEFT ventricle; used to treat HF
Pacemaker nomenclature
five letter code to describe the basic function of a pacing device; developed by north american society of pacing and electrophysiology AND the british pacing and electrophysiology group)
First position (for coding system)
describes chamber(s) wehre stimulation occurs (CHAMBERS PACED)
second position (for coding system)
describes chamber(s) where sensing occurs (CHAMBERS SENSED)
Third Position (For coding system)
describes response to a sensed event (RESPONSE TO SENSING)
Fourth Position (for coding system)
indicates programmability and rate modulation (PROGRAMMABILITY AND RATE MODULATION)
Fifth Position (for coding system)
describes anti-tachycardia treatment functions
VVIR (common pacemaker)
this device would PACE in the ventricle, SENSE in the ventricle, INHIBIT response to sensed event and be rate modulated
Permanent Pacing
pulse generator is implanted subcutaneously or submuscularly in upper right/left pectoral region; replaced every 8-9 years; leads are inserted permanently via cephalic or subclavian vein
Sites of Lead implantation
endocardial (most common) or epicardial
Procedure of implanting permanent PM (endocardial)
loca anesthetic; small incision just below right/left clavicle; lead wires advanced into heart through subclavian or cephalic vein; small pocket created in upper chest to house generator; test leads for electrical patency, connect them to generator, insert into pocket and stitch
Implanting Permanent PM (epicardial)
small incision at base of sternum to access epicardium; attach leads to epicardium; and implant generator in small abdominal pocket (**more commonly used with children)
Broad Indication for permanent pacing implantation
Bradycardia due to Sinus AV node dysfunction: SA node dysfunction, acquired AV block, chronic bifascicular block, AV block with assoc MI, hypersensitive carotid sinus syndrome and neurocardiogenic syncope
Specific conditions leading to permanent PM implantation
cardiac transplant, neuromuscular disease, sleep apnea syndrome, cardiac sarcoidosis
Prevention and Termination of Arrhythmia by pacing:
cardiac resynchronization therapy, obstructive hypertrophic cardiomyopathy (HCM)
Temporary Pacemakers
can be transvenous or by external patch
Transvenous temporary PM
via jugular, subclavian or femoral vein; standard approach for temporary pacing; pacing catheter is placed into RIGHT VENTRICLE
External Patch (transthoracic) temporary PM
pacing is suitable ONLY for emergency standby or brief pacing (ie. AED)
Temporary Pacing Procedure
position temporary pacing catheter at apex of RV; tie catheter to skin, place sterile dressing over catheter site; pacing lead wires are connceted to external generator by connecting cable; *** often used after open heart surgery when heart block occurs but is expectd to be temporary
Procedure for External Pacemakers
set of pads stuck firmly to patients chest; pads connected to external generator controlling amount of energy delivered and rate of pacing
Reason to have Temporary PM
transient inadequate rhythm, clinical situation with high risk of transient inadequate rhythm, situations in which a permanent PM is required but not readily available
Transient
inadequate rhythm is temporary and will go away; an adequate rhythm will be restored
Inadequate rhythm
indicates temporary pacing; usually bradycardia
Biventricular Pacing (resynchronization therapy (CRT))
treatment for CHF patients; placement of lead in right and left ventricle and sometimes the right atrium; synchronized pacing of R and LV can improve mechanics and hemodynamics of failing heart that has uncoordinated contractions
Long term therapy with CRT (cardiac resynchro therapy) results:
improved clinical symptoms, increased exercise capacity, improve quality of life, cessation/reversal of chronic chamber remodeling
Implantable cardioverter defibrillator (ICDs)
implantable device that continously monitors cardiac rhythm and delivers defibrillating shock in the event of ventricular arrhythmias; used to prevent premature arrhythmic death
Primary prevention for ICDs
determine risk of future ventricular arrhythmic episode (Detailed history, physical exam, assessment of cardiac function complete with ejection fraction)
Secondary prevention for ICDs
refers to cardiac arrest due to VF or VT that is NOT caused by transient or reversible cause
Diseases where ICD would be used:
CAD (MI with decreased systolic function and non-sustained VT), HCM, Long QT syndrome, Brugada syndrome, VF, arrhythmogenic RV dysplasia
Reasons not to use ICD therapy (contraindications)
uncontrollable arrhythmias by traditional therapeutic methods, arrhythmias due to transient or reversible disorders, significant psychiatric illness, terminal illness, syncope of undetermined cause without inducible arrhythmia
