Pacemakers and Pacemakers and Defibrillators: Anaesthetic Defibrillators: Anaesthetic

ImplicationsImplications

Wahid Altaf.

Kerry General Hospital.

Introduction.

A pacemaker system is a device capable of generating artificial pacing impulses and delivering them to the heart.

It consists of a pulse generator,lead and appropriate electrodes.

In the past few years electronic pacemaker systems have become extremely important in saving and sustaining the lives of cardiac patients whose normal pacing function of the heart have been impaired.

Pacemakers: its past historyConception of idea

Chloroform was popular in the late 1860s, but when it was used, occasional respiratory and cardiac arrest occurred, as an occasional complication of chloroform anesthesia

To restart the heart, Green in the United Kingdom [1872] applied the output of a 300V battery using hand-held electrodes applied to the base of the neck and the lower left chest.

Interestingly, the electrode applied to the lower left chest stimulated the ventricles. The other electrode applied to the base of the neck delivered current to the phrenic nerve and twitched the diaphragm, causing a brisk inspiratory motion.

Invention process

In 1882, Ziemssen in Germany applied cardiac pacing to a 42-year-old woman who had a large defect in the anterior left chest wall following resection of an enchondroma.

The heart was only covered by skin, on which Ziemssen placed electrodes.

Using induction-coil shocks, he paced the heart with a stimulus frequency higher than that of the normal heart rate

An external pacemaker was designed and built by the Canadian electrical engineer John Hopps in 1950.

Lillehei et al. [1957] reported the use of right ventricular catheter

electrodes with an external pacemaker to pace 66 patients. The pacemaker was built by Earl Bakken, a biomedical engineer, the founder of Medtronic Inc. in 1949, which soon became the pioneer pacemaker company.

Earl's first wearable, battery-powered, transistorized cardiac pacemaker

Invention process (cont.)

From Earl E. Bakken's Book "One Man's

Full life"

"Back at the garage, I dug out a back issue of Popular Electronics magazine in which I recalled seeing a circuit for an electronic, transistorized metronome. The circuit transmitted clicks through a loudspeaker; the rate of the clicks could be adjusted to fit the music. I simply modified that circuit and placed it, without the loudspeaker, in a four-inch-square, inch-and-thick metal box with terminals and switches on the outside - and that, as they say, was that. "

Clinical prototyping

Dr. Rune Elmqvist (1958) designed the world's first implantable pacemaker. It included a pulse generator delivering about two volts with an impulse period of two milliseconds. The original transistors showed large leakage currents and were found not suitable.

Problems of the early pacemakers: breakage of electrode wires, short battery life, the need for surgery for pacemaker and lead implantation

Chardack [1960] described a durable electrode wire made from the alloy that is used in the escapement spring of watches. It was sutured to the epicardium, and a thoracotomy was required.

Pacemaker today!

1980 Large Devices: abdominal site

First human implants Thoracotomy, multiple incisions Primary implanter= cardiac surgeon General anesthesia Long hospital stays Complications from major surgery Perioperative mortality up to 9% Nonprogrammable therapy High-energy shock only Device longevity 1.5 years Fewer than 1,000 implants/year

Pacemaker today-Small devices pectoral site.

First-line therapy for VT/VF patients Treatment of atrial arrhythmias Cardiac resynchronization therapy for HF Transvenous, single incision Local anesthesia; conscious sedation Short hospital stays and few complications Perioperative mortality < 1% Programmable therapy options Single- or dual-chamber therapy Battery longevity up to 9 years More than 100,000 implants/year

Indications of permanent pacemakerimplantation.

1) Acquired AV block: A) Third degree AV block B) Second degree AV block 2) After Myocardial infarction: 3) Bifascicular or Trifascicular block: 4) Sinus node dysfunction: Sinus node dysfunction with symptoms as a result of long term drug therapy Symptomatic chronotropic incompetence 5) Hypertensive carotid sinus and neurocardiac syndromes: Recurrent syncope associated with carotid sinus stimulation Asystole of >3s duration in absence of any medication

Generic codes for pacemaker

I II III IV VPacing Sensing Response Programmability TachycardiaO-None O- None O-None O-None O- NoneA-Atrium A-Atrium I-Inhibited C-Communicating P-PacingV-Ventricle V-Ventricle T-Triggered P-simple S-Shocks programmable D-Dual D-Dual D-dual M-multi D-Dual (A+V) (A+V) (I+T) programmable (P+S) S-Simple S-Simple R-Rate (A or V) (A or V) modulation

Generic codes for Defibrillators

NASPE / BPEG Defibrillator (NBD) code

I II III IV Shock chamber Antitachycardia Tachycardia detection Antibradycardia pacing

pacing chamber chamber

O = None O = None E = Electrogram O = None

A = Atrium A = Atrium H = Hemodynamic A = Atrium

V = Ventricle V = Ventricle V = Ventricle

D = Dual (A+V) D = Dual (A+V) D = Dual (A+V)

Important terms regarding pacemakers.

Pulse Generator Leads Electrode Unipolar Pacing Bipolar Leads Endocardial Pacing Epicardial Pacing Pacing Threshold R Wave Sensitivity Hystersesis Runaway Pacemaker

Types of Pacing Modes

Asynchronous: (AOO, VOO, and DOO) Single Chamber Atrial Pacing (AAI, AAT) sinus arrest

and sinus bradycardia Single Chamber Ventricular Pacing (VVI, VVT) complete

heart block with chronic atrial flutter, atrial fibrillation and long ventricular pauses.

Dual Chamber AV Sequential Pacing (DDD, DVI, DDI, and VDD) AV block, carotid sinus syncope, and sinus node disease.

Programmable Pacemaker Rate responsive pacemaker.

Factors Important from AnaesthesiaPoint of View

Physiological Potassium Myocardial Infarction Antiarrhythmic Drug Therapy Acid Base Status Hypoxia Anaesthetic Drugs

Preoperative Evaluation

Evaluation of the patient. Routine Investigations esp. UnE/ECG/CXR. Pacemaker Evaluation i.e. type of pacemaker

(fixed rate or demand rate),time since implanted, pacemaker rate at the time of implantation, and half-life of the pacemaker battery. Effect of the Magnet Application on Pacemaker Function.

Intraoperative Management

Based on the patient’s underlying disease and the type of surgery.

Continuous ECG monitoring. Both electrical and mechanical evidence of the heart

function should be monitored by manual palpation of the pulse, pulse oximetry, precordial stethoscope and arterial line.

Careful during insertion of the guide wire or central venous catheter.

Anaesthetic technique

Narcotic and inhalational techniques can be used successfully. Skeletal myopotentials, electroconvulsive therapy,

succinylcholine fasciculation, myoclonic movements, or direct muscle stimulation can inappropriately inhibit or trigger stimulation, depending on the programmed pacing modes.

Etomidate and ketamine should be avoided as these cause myoclonic movements.

Pacemaker function should be verified, before and after initiating mechanical ventilation.

If rate responsive mode it should be deactivated before surgery.

Electromagnetic Interference

Direct sources of EMI: Nuclear magnetic resonance imaging, surgical electrocautery or dental pulp vitality tester.

Indirect sources of EMI include radar, orthopedic saw, telemetric devices, mechanical ventilators, lithotriptors, cellular telephones, and whole body vibrations.

Fatal arrhythmias and deaths have been reported with the use of electrocautery leading to failure of pacemaker. Between 1984-1997, the US-FDA was notified of 456 adverse events with pulse generators, 255 from electrocautery and significant number of device failures.

Measures to decrease the possibility of adverse effects due to electrocautery

Bipolar cautery unipolar cautery (grounding plate should be placed

close to the operative site and as far away as possible from the site of pacemaker)

Electrocautery should not be used within 15cm of pacemaker.

Programme to asynchronous mode. Provision of alternative temporary pacing. Drugs (isoproterenol and atropine). Careful with Defibrillation if required.

Careful monitoring of pulse, pulse oximetry and arterial pressure is necessary during electrocautery, as ECG monitoring can also be affected by interference.

The device should always be rechecked after operation.

Specific Perioperative Considerations

Transuretheral Resection of Prostate (TURP) and Uterine Hysteroscopy.

Electroconvulsive Therapy Radiation Nerve Stimulator Testing or Transcutaneous

Electronic Nerve Stimulator Unit (TENS) Lithotripsy Magnetic Resonance Imaging (MRI)

Postoperative care

Full telemetric check . Re-programming back to the original setting. Anti-tachycardia therapies of implantable

defibrillators should obviously be re-programmed to their original settings.

Examples: Any Guess!

Ventricular sensed, ventricular paced

Consistent with VVI

Atrial sensed, ventricular paced

Consistent with DDD or VDD

Atrial paced

Consistent with AAI or DDD

Failure to Pace

Any questions?