Transcript Pacing Generator

Emergency Cardiac Pacing
• Emergency cardiac pacing may be instituted either
prophylactically or therapeutically.
• Prophylactic indications include patients with a high
risk for AV block.
• Therapeutic indications include symptomatic
bradyarrhythmias and overdrive pacing.
• Transcutaneous and transvenous are the two
techniques most commonly used in the ED.
• Because it can be instituted quickly and
noninvasively, transcutaneous pacing is the technique
of choice in the ED when time is of the essence.
• Transvenous pacing should be reserved for patients
who require prolonged pacing or have a very high
(>30%) risk for heart block.
EMERGENCY TRANSVENOUS CARDIAC PACING
• The technique can be performed in less than 20
minutes in 72% of patients and in less than 5
minutes in 30%.
• Transcutaneous cardiac pacing (TCP) has become
the mainstay of emergency cardiac pacing and is
often used pending placement of a transvenous
catheter or to determine whether potentially
terminal bradyasystolic rhythms will respond to
pacing.
Bradycardias
 Sinus Node Dysfunction:
• may be manifested as sinus arrest,sick sinus syndrome
or sinus bradycardia
• is a common indication for elective permanent pacing,
it is seldom cause for emergency pacemaker insertion.
• 17% percent of patients with AMI will experience
sinus bradycardia (occurs more frequently with inferior
> anterior infarction)
Bradycardias
 Asystolic Arrest:
• Transvenous pacing in an asystolic or bradyasystolic
patient has little value and is not recommended
• Cardiac pacing may be used as a “last-ditch” effort in
bradyasystolic patients but is rarely successful and is
not considered standard practice.
• Given the continued emphasis on the importance of
maximizing chest compressions during CPR,
interrupting CPR to institute emergency pacing is not
recommended
Bradycardias
 AV Block:
• In symptomatic patients without myocardial infarction (MI)
and in asymptomatic patients with a ventricular rate lower
than 40 beats/min, pacemaker therapy is indicated.
• AV block occurring during anterior infarction is believed to
result from diffuse ischemia in the septum and infranodal
conduction tissue.
• Because these patients tend to progress to high-degree
block without warning, a pacemaker is often placed
prophylactically
Bundle Branch Block and Ischemia
• Bundle branch block occurring in AMI is associated with
a higher mortality rate and a greater incidence of third
degree heart block than is uncomplicated infarction.
• Because of the increased risk, consider pacing for the
following conduction blocks:
 New-onset LBBB
 RBBB with left axis deviation or other bifascicular block
 Alternating bundle-branch block
Tachycardias
• Hemodynamically compromising tachycardias are usually treated
by medical means or electrical cardioversion
• Supraventricular dysrhythmias,with the exception of AF, respond
well to atrial pacing.
• By “overdrive” pacing the atria at rates 10 to 20 beats/min faster
than the underlying rhythm, the atria become entrained, and when
the rate is slowed, the rhythm frequently returns to normal sinus.
• Overdrive pacing is especially useful for arrhythmias with recurrent
prolonged QT intervals such as those seen with quinidine toxicity or
torsades de pointes
• Transvenous pacing is also useful in patients with digitalis-induced
dysrhythmias, in whom direct current cardioversion may be
dangerous
Cardiac Pacing for Drug-Induced Dysrhythmias
• Tachycardic rhythms from amphetamines, cocaine,
anticholinergics, cyclic antidepressants,theophylline, and
other drugs do not benefit from cardiac pacing
• Severe bradycardia and heart block often accompany
overdose of digitalis preparations, β-adrenergic blockers,
and CCB
• Cardiac pacing is not generally effective for serious toxininduced bradycardias
Contraindications
• The presence of a prosthetic tricuspid valve is generally
considered to be an absolute contraindication to
transvenous cardiac pacing
• Severe hypothermia will occasionally result in ventricular
fibrillation when pacing is attempted
• Rapid and careful rewarming is often recommended first,
followed by pacing if the patient’s condition does not
improve.
Pacing Generator
• An amperage control allows the operator to vary the amount of
electrical current delivered to the myocardium
• increase the output improves the likelihood of capture
• By increasing the sensitivity, one can convert the unit from a fixed-rate
(asynchronous mode) to a demand (synchronous mode) pacemaker
• Decreasing the setting increases the sensitivity and improves the
likelihood of sensing myocardial depolarization
• In the fixed-rate mode ,the unit does not sense any intrinsic electrical
activity
• In the full-demand mode, however, the pacemaker senses the
underlying ventricular depolarizations, and the unit does not fire as
long as the patient’s ventricular rate is equal to or faster than the set
rate of the pacing generator
Pacing Generator
Pacing Catheters and Electrodes
ECG Machine
Introducer Sheath
• The introducer set is used to enhance passage of the
pacing catheter through the skin, subcutaneous tissue, and
vessel wall.
• The size of the pacing catheter refers to its outside
diameter, whereas the size of the introducer refers to its
inside diameter. Thus, a 5-Fr pacing catheter will fit
through a 5-Fr introducer.
Site Selection
• The four venous channels that provide easy access to the
right ventricle are the brachial, subclavian, femoral, and
internal jugular veins
• The right internal jugular and left subclavian veins have the
straightest anatomic pathway to the RV and are generally
preferred for temporary transvenous pacing
• For subclavian,the infraclavicular approach is most
commonly reported for all temporary transvenous
pacemaker insertions
• This route is preferred because of its easy accessibility,
close proximity to the heart, and ease in catheter
maintenance and stability
Site Selection
Site Selection
Final Assessment
• Assess pacemaker function again, and take a chest film to
ensure proper positioning. Ideal positioning of the pacing
catheter is at the apex of the right ventricle
• A 12-lead ECG tracing should be obtained after placement
of the transvenous pacemaker. If the catheter is within the
right ventricle, a left bundle branch pattern with left axis
deviation should be evident in paced beats
• If an RBBB pattern is noted, coronary sinus placement or
left ventricular pacing secondary to septal penetration
should be suspected.
Final Assessment
Complications
• Therapy for catheter-induced ectopy during insertion
involves repositioning the catheter in the ventricle. This
usually stops the ectopy
• if after repeated attempts it is found that the catheter cannot
be passed without ectopy,myocardial suppressant therapy
may be used to desensitize the myocardium.
• Simply pulling the catheter back and repositioning it in the
right ventricle can usually treat uncomplicated perforation
Complications
Complications
TRANSCUTANEOUS CARDIAC PACING
• May be preferable to transvenous pacing in patients who
have received thrombolytic agents or other anticoagulants
• Although small pediatric electrodes for TCP have been
developed, experience with pediatric TCP has been
limited
• Though generally unsuccessful, TCP may be attempted
for the treatment of asystolic cardiac arrest. In this setting
the technique is efficacious only if used early after the
onset of arrest (usually within 10 minutes).
Pad Placement
• Take care to avoid placing the electrodes over an implanted
pacemaker or defibrillator.
• Remove any transdermal drug delivery patches if they are in
the way.
• Remove excessive hair if time permits
• Place the anterior electrode (cathode or negative electrode) as
close as possible to the point of maximal impulse on the left
anterior chest wall
• Place the second electrode directly posterior to the anterior
electrode
Pad Placement
• There is little risk for electrical injury to health care
providers during TCP.
• The power delivered during each impulse is less than
1/1000 of that delivered during defibrillation
• Inadvertent contact with the active pacing surface results
in only a mild shock.
Pacing Bradycardiac Rhythms
• Slowly increase the output from minimal settings until
capture is achieved
• Generally, a heart rate of 60 to 70 beats/min will maintain
adequate blood pressure
• Assess electrical capture by monitoring the ECG tracing
• Assess mechanical capture by palpating the pulse
• Because of muscular contractions triggered by the pacer,
carotid pulses may be difficult to assess, so palpating the
femoral pulse may be easier
Pacing Bradycardiac Rhythms
• Failure to capture with TCP may be related to electrode
placement or patient size. Patients with barrel-shaped
chests and large amounts of intrathoracic air conduct
electricity poorly and may prove refractory to capture
• Patients who are conscious or who regain consciousness
during TCP will experience discomfort because of muscle
contraction.
• Analgesia with incremental doses of an opioid agent,
sedation with a benzodiazepine compound, or both, will
make this discomfort tolerable until transvenous pacing
can be instituted
Complications
• The major potential complication of TCP is failure to
recognize the presence of underlying treatable ventricular
fibrillation. This complication is primarily due to the size
of the pacing artifact on the ECG screen
• A rare complication of TCP is induction of ventricular
Fibrillation. longer impulse durations used in modern
devices seem to decrease the chance of inducing
ventricular fibrillation