Nerve Stimulator Testing/Therapy

• Nerve stimulators can cause pacemaker oversensing withresultant pacemaker inhibition and cardiac arrest.

• For the patient with an lCD, inappropriate detection ofneuromuscular stimulators, TENS, and chiropracticelectrical muscle stimulation as VT or VF has beenreported.

• Electrical path for nerve stimulator current should not• Electrical path for nerve stimulator current should notcross the generator system or the chest.

Succinylcholine or Etomidate

• In one case, muscle fasciculations might have causedventricular oversensing with resultant pacemakerinhibition.

• Myopotential oversensing (in the absence ofsuccinylcholine) has been observed to interfere withpacemaker function or cause inappropriate ICD therapy.

Emergency Defibrillation or Cardioversion

• Positioning the paddles as far as possible from the pulsegenerator

• Positioning the paddles perpendicular to the major axis ofthe CIED pulse generator (anterior-posterior location).

• Appropriate energy levels and other standard ACLSrecommendations should be employed as needed.

• If an ICD has been deactivated with a magnet that is stillin place, simply remove the magnet and allowing the ICDto defibrillate the patient.

• For some devices (e.G. Boston scientific devices)reapplication of a magnet may be necessary to restoreICD function.

IV. Postoperative Management

1. Cardiac rate and rhythm should be monitoredcontinuously throughout the immediate postoperativeperiod.

2. Back-up pacing capability and cardioversion-defibrillationequipment should be immediately available at all times.

3. For an ICD, all antitachyarrhythmic therapies should berestored.

4. Consultation with a cardiologist or pacemaker-ICDservice may be necessary.

5. The ASA Advisory recommends that all patients with anICD should have their devices restored and interrogatedprior to discharge from the recovery room.

Postoperative considerations in a patient with animplanted cardioverter defibrillator

The End

Threshold margin test (TMT)

• In this test, one or more of the pacemaker pulses isreduced in amplitude, pulse width, or both, in an attemptto gauge the safety margin for pacing voltage.

• Loss of capture on these TMT pulses indicates aninadequate safety margin for pacing.S d i d th t i l i• Some devices reduce the ventricular pacing energy over16 cycles to demonstrate the pacing threshold.

• As a result, many pacing cycles can take place atinsufficient energy for ventricular capture, which canproduce periods of asystole while the magnet is applied.

• Pacing pulse width should be at least three and usuallyfour times the threshold for capture.

Threshold margin test (TMT)

GLOSSARY

� Atrioventricular Delay� The time that a dual-chamber system waits after detecting (or

initiating) an atrial event before pacing the ventricle.� Some generators shorten this time as the heart rate increases

(termed “rate-adaptive AV delay” or “dynamic AV delay”).

GLOSSARY

• Hysteresis - If present, the amount by which the patient'sintrinsic rate must fall below the programmed rate before thegenerator begins pacing.– Some pacers periodically decrease the pacing rate in order to search for

resumption of intrinsic activity (called "Search Hysteresis"). Thesefunctions, when present, can mimic pacemaker malfunction.

• Lower Rate Limit (LRL, also Automatic Rate orProgrammed Rate) - The lowest sustained regular rate atProgrammed Rate) The lowest sustained regular rate atwhich the generator will pace. Typically, the device beginspacing when the patient's intrinsic rate falls below this value.Hysteresis settings can permit an intrinsic heart rate lowerthan the LRL.

GLOSSARY

• Upper Sensor Rate (USR, also called Upper Activity Rate[UAR]) - The maximum rate to which a rate modulatedpacemaker can drive the heart.– USR in a dual chamber mode is not affected by UTR, since, when USR

becomes active, the pacemaker is pacing the atrium.• Upper Tracking Rate (UTR, also called Upper Rate Limitpp g ( , pp

[URL]) - Pacemakers programmed to VDD or DDD modecause the ventricles to track atrial activity. Should a patientdevelop an atrial tachyarrhythmia, such as a supraventriculartachycardia, atrial fibrillation, or atrial flutter, the generator actsto limit ventricular pacing.

NON-CARDIACIMPLANTABLE ELECTRICALDEVICES (IEDs):

Deep Brain Stimulator (DBS)

• Parkinson’s disease,tremors, tics, anddystonias, psychiatricillness (major depression,obsessive-compulsivedisorder), chronic pain,and refractory epilepsyand refractory epilepsy.

• The most common targetsfor stimulation include thethalamus, the globuspalladium, and thesubthalamic nuclei.

Vagal nerve stimulator (VNS)

• For the management ofmedically refractoryepilepsy.

• Mechanism of actioninvolves the stimulation ofafferent vagal nerve fibersthat modulate cerebralthat modulate cerebralneuronal excitability

Sacral nerve stimulator or bladderstimulator

• Urinary incontinence,interstitial cystitis, pelvic pain,and fecal incontinence.

• consists of a lead wirecontaining four platinumelectrodes. The wire isinserted surgically into theinserted surgically into thesacral foramen at S3 on oneside adjacent to the sacralnerve. The generator itself isimplanted subcutaneously inthe hip area.

Phrenic nerve stimulator ordiaphragmatic pacemaker

• Respiratory failure due to highcervical cord injury (C1–C2) orrespiratory center dysfunction(central alveolar hypoventilation).

• Usually performed laparoscopically.• Four electrodes are implanted in

h h ieach phrenic nerve.• A receiver implanted in the

subcutaneous tissue is connected tothe electrodes by platinum leads.

• An external portable battery-operated transmitter generates radiowaves, which are converted to anelectrical stimulus by the receiver.

Spinal cord stimulator (SCS)

• failed back surgerysyndrome (FBSS),complex regional painsyndromes (CRPS),peripheral vasculardisease, and refractoryanginaangina.

• The site of electrodeplacement depends onthe site of pain. Ingeneral, the electrode isplaced at the T9-L1 levelfor lower limb pain, C6 toT2 for angina, and C4 toT1 for upper limb pain.

Gastric pacemaker (GES)

• for the treatment ofgastroparesis refractory toMedical therapy.

• Two bipolar leads are implantedlaparoscopically into the musclewall of the stomach and thenjoined with a subcutaneousjoined with a subcutaneouselectrical stimulator, which isusually placed in the upperabdomen.

Bone stimulator

• to enhance bone growth.• for non-union or delayed unions.• Failed arthrodesis and spinal

fusion have since been addedas indications

Laryngeal nerve stimulator

• To prevent aspiration by causingdynamic laryngotracheal closure.

• In stroke-related dysphagia• The device consists of bipolar

electrodes implanted surgically into arecurrent laryngeal nerve and a

i ti l t i l t dreceiver–stimulator implantedsubcutaneously.

• Activation of the stimulator is performedthrough an external transmitter.

• When swallowing is initiated, thestimulator is activated causing glotticclosure, thus preventing aspiration.

Perioperative management

• Preoperative period– Type and location of non-cardiac IED– Date of implantation and last check– Anesthetic complications during insertion– Current status of IED in terms of symptoms

control– Programability of the device (turning off)– Severity of symptoms when the device is

turned off– Current medications

Perioperative management

• Intraoperative period– To reduce the possibility of creating static electricity

• The temperature in the operating room should be between 20 and24C

• the humidity should be between 50% and 60%.– Device interactions

• electrocautery, external or implanted cardiac pacemakers, external orimplanted defibrillators, PNSs, and magnetic resonance imaging(MRI).

• Diathermy is contraindicated in patients with deep brain, bladder,gastric, phrenic nerve, and SCSs.

• Electrocautery can cause temporary suppression of neurostimulatoroutput and/or reprograming of the device.

• Emergency external defibrillation• Peripheral nerve stimulation• Neuroaxial anesthesia• Magnetic resonance imaging

Device-specific considerations in VNS• The common respiratory side effects of chronic vagal stimulation:

– dyspnea on exertion– altered breathing patterns (gasping)– snoring during sleep– decreased airflow– heightened respiratory effort during sleep

• one-third of patients with refractory epilepsy may have baseline obstructive sleep apnea(OSA).

• A combination of respiratory side effects of chronic vagal nerve stimulation, residualth ti ff t d it t OSA i th i k f t ti i tanesthetic effects, and concomitant OSA may increase the risk of postoperative respiratory

compromise.• Chronic vagal stimulation can cause laryngopharyngeal dysfunction and risk of aspiration of

gastric contents.• In addition, abnormal motion of the vocal cords resulting from vagal stimulation can cause

partial airway obstruction during general anesthesia in patients with a laryngeal maskairway.

• Trauma to vocal cords has been reported in patients managed with an endotracheal tube,as the VNS intermittently adducts the vocal fold against the rigid endotracheal tube.

• Another major effect of chronic vagal stimulation includes changes in heart rate variabilitydue to changes in the sympatho-vagal balance in the heart.

• No study has reported clinically relevant arrhythmias or cardiac side effects related tochronic VNS.

Artificial heart

Chest port

Mechanical heart valve

• Lateral view of thechest shows a Hemextilting bileafletmechanical mitral valveprosthesis. Mediansternotomy wires andsurgical clips are alsosurgical clips are alsoevident.

Mechanical heart valve

• Lateral view of thechest shows a Starr-Edwards caged ballmechanical mitralvalve prosthesis.