Comparison of Failure Rates for External and Implantable Cardioverter-Defibrillators

By Sam Annor(EE5811-Biomedical Instrumentation-Fall

2007).

Overview•Background•Defibrillation process•Defibrillator types•AED usage-pictorial•AED usage-video•Algorithm- how VF is detected•What does it mean algorithm mean?•Results and analysis -failure•ICD usage•ICD failure analysis•Safety/risk analysis•Conclusion•Acknowledgement to Collaborators•References

BackgroundIt is estimated that Cardiovascular diseases account for the majority of death in the US with a total toll of about 11 million people per annum

1Estes III, Mark. “Automatic External Defibrillators in the Public Domain – Am I Ready to Use One?” Circulation 112 (2005): e349–e351.

Two most common heart failures•Ventricular Fibrillation(VF) 

• When a ventricular arrhythmia (irregular heartbeat) becomes very fast and irregular, it's called ventricular fibrillation

• Ventricular Tachycardia(VT)• is a tachycardia, or fast heart rhythm that

originates in one of the ventricles of the heart.

Defribillation• The process used to curtail Ventricular Fibrillation(VF) and Ventricular Tachycardia(VT)•Unless treatment is given in 5 to 10 minutes, ventricular fibrillation

causes death.•Devices Used in the process- Defibrillators

•Two Types-

• Automatic External Defibrillators(AEDs) -in vitro•  • Implantable Cardioverter-Defibrillators(ICDs) – in vivo

Defibrillatorshave electronic  analyzer circuitry  that monitors the cardiac rhythm and alerts when  a defibrillation shock  is needed.

AED in use

Video of AED use

Algorithm The algorithm for recognizing VF and committing to shock delivery is as follows: (1) The AED will begin to charge if it

detects at least two "positive intervals" within a 9.6 sec period. A positive interval is defined as six or more deflections that are at least 0. 150 mV (1.5 mm trough-to-peak) in amplitude with a maximum slope of 3.2 mV/sec (termed VF counts) occurring in a 2.4 sec period (rate at least 150/min).

(2)  The AED will discharge if it detects a third positive interval within 7.2 sec of the start of capacitor charging. Thus it takes a minimum of 4.8sec (2 x 2.4) to begin charging; it requires a minimum of 7.2 sec (3 x 2.4) to commit to a shock after being presented with VF.

Algorithm-recognition patterns

So what if your VF / VT pattern is out of range?Smaller cardiac mass in Children will cause their VF to differ from Adult.

Children have faster supra VT than adult

Results

AnalysisAED failed to properly diagnose VT hence with an average sensitivity of 56%

However for VF the sensitivity was 96% on the average

Whe ICD is used instead of AED Used when ventricular fibrillation and tachycardia are frequent and continuous defibrillation are needed.

Example ICD failure•A 36-year-old man with an ATLAS+ DR V- 243 (St. Jude Medical, Inc., St. Paul, MN, USA) dual chamber implantable cardioverter defibrillator (ICD) received a shock while cycling, but was otherwise asymptomatic

•Medtronic leads are designed for use with an ICD as part of a cardiac system. Leads are intended for delivering therapies and/or sensing in the atrium and/or ventricle of the heart

How safe is safe enough?•Doesn’t everyone know how to be safe?• Several attempts are done to ensure safety like FDA regulation, various compliance- annual trainings, increased litigation, etc. •The fact remains safety education is hard to sell, hard to pay attention to and hard to remember.•Why?

• -reluctance to learn• -resistance to change

Conclusion•Federally, FDA is charge with the mandate of ensuring the medical devices are SAFE. However the FDA relies on the manufacturers to provide with data on malfunction of the device.

• If your are the manufacturer- Will you always report the needed data?

Acknowledgement•Tom O’Dea Ph. D., P. E. C.C.E –Healthcare Engineering•Prof. Jim Holte

References1. Estes III, Mark. “Automatic External Defibrillators in the Public Domain – Am I Ready

to Use One?” Circulation 112 (2005): e349–e351.

2. “Defibrillation.” Wikipedia. 1 Dec. 2007 <http://en.wikipedia.org/wiki/Defibrillator>.

3. KR Stults, DD Brown and RE Kerber. “Efficacy of an automated external defibrillator in the management of out-of-hospital cardiac arrest: validation of the diagnostic algorithm and initial clinical experience in a rural environment” Circulation 73 (1986): 701-709.

4. Frank Cecchin, Dawn B. Jorgenson, Charles I. Berul, James C. Perry, A. Andrew Zimmerman, Brian W. Duncan, Flavian M. Lupinetti, David Snyder, Thomas D. Lyster, Geoffrey L. Rosenthal, Brett Cross and Dianne L. Atkins “Is Arrhythmia Detection by Automatic External Defibrillator Accurate for Children? : Sensitivity and Specificity of an Automatic External Defibrillator Algorithm in 696 Pediatric Arrhythmias” Circulation 103 (2001): 2483-2488.

Questions?

If not…..Based on my presentation why was VT showing lower Sensitivity readings compared to VF in children under 13 years old?