The Electrical Management of Cardiac Rhythm Disorders

Tachycardia

History of ICDs

The Genesis of ICDs

● The idea of the ICD came to Dr. Michel Mirowski when his friend died of SCD

● Concept: could a defibrillator be implanted in the body?

● Technological challenges○ Could an implantable device

deliver sufficient energy?

○ Could leads be developed to carry that much energy?

○ How would the device detect arrhythmias?

○ How could defibrillation become “automated”?

Dr. Michel Mirowski● Dr. Harry Heller died of SCD in 1966● His friend, Dr. Michel Mirowski, knew that he might have

lived had he received defibrillation immediately● Technological and even ethical hurdles

○ Was it ethical to even test such a device on humans?● By 1969, Dr. Mirowski was working on the first

experimental models of what would later become the ICD● But it would be almost 20 years before the device was

commercially available!

Time Line

● Sinai Hospital of Baltimore recruited Dr. Mirowski and offered him opportunity to work on ICD idea

● At Sinai, Mirowski teamed up with Martin Mower in the research lab

● In 1969, experimental model● First transvenous defibrillation

(1969)● Canine implants (1970s)● First human implant: 1980

(Johns Hopkins, Baltimore)

Technological Challenges● Capacitor technology allowed small battery to store and

deliver large amount of energy● Transvenous defibrillation leads could carry defibrillation

energy to the inside of the heart● Circuitry could sense cardiac rhythms and interpret

potentially dangerous ventricular tachyarrhythmias● Device could be downsized enough to implant in the body

Early Devices

● 1980-1985 clinical trial of first ICDs

● 1985 FDA approved first ICD for human use

● Those first devices were 10 times the size of modern ICDs!

● Their large size mandated an abdominal implant

● Thoracotomy required to implant leads

Road to ICDs

ICD Evolution● Cardioversion (lower-energy shocks) and “tiered therapy”● Programmability (1988)

○ First ICDs were custom-built since cutoff rates were set at the factory!

● Biphasic waveforms● Multiple zones (VT/VF)● Transvenous ICD leads● Radically downsized generators (pectoral implants)● Full-featured integrated pacemakers

Defibrillation Leads

Single-Coil Defib Leads

● Pacing requires one or more electrodes on the lead to pace sense

● Shocking requires one or more “coils” on the lead to defibrillate● A single-coil lead has one coil on the lead and forms the

electrical circuit by using the ICD can as the other pole to complete the circuit

Modern Defibrillation Leads● Integrated bipolar and true bipolar leads

○ Refers to sensing cardiac signals○ Integrated bipolar uses distal shocking coil to sense

cardiac signals○ True bipolar has dedicated distal sensing electrode

● Single-coil and dual-coil designs● Very thin, comparable to some pacing leads!● Choice of lead fixation mechanisms

○ Active fixation (helix, corkscrew)○ Passive fixation (fins, tines)

● Steroid elution option

Progress: The Implant Procedure

THEN● Open-chest● Took several hours● General anesthesia● Several days hospital stay● Large device● Abdominal implant● No or very limited

programmability

NOW● Minimally invasive implant● Can take < 1 hour● Conscious sedation● May be done outpatient● Devices ~ size of

pacemaker● Pectoral implant● Extensive

programmability

Progress: Device Functionality

THEN● Very few programmable

options● Short service life● Only one therapy (defib)● No pacing capability (if pacing

was needed, a second device might be required)

● Could only be monitored in-clinic

NOW● Lots of programmability,

including advanced features● Four to six years service life● Tiered therapy, even ATP● Full pacing capability including

some dual-chamber rate-responsive pacing with advanced features

● Remote patient monitoring

Device Acceptance● The first ICDs were considered a device of last resort

○ Patients had to be drug-refractory and survived at least two episodes of SCD

● Early concepts pitted drugs against devices as if they were mutually exclusive

● Devices became acceptable as first-line therapy for certain types of secondary-prevention patients

● Today, we know devices can provide additive benefits to drug therapy and that combination therapy (drugs plus devices) is ideal for most patients

● Recent studies have shown the mortality benefits of primary prevention therapy

The Future of ICDs

● Smaller, flatter devices (improved capacitor technology)

● Longer-lived devices (improved battery technology)

● CRT (addition of a third lead)● Remote patient monitoring● Wireless patient monitoring● Special algorithms● Expanded memory● More automatic features● Built-in monitors