Electrical Therapies Automated External Defibrillators Defibrillation Cardioversion Pacing

Early Defibrillation (1) the most frequent initial rhythm in witnessed SCA is VF, (2) the treatment for VF is electrical defibrillation, (3) the probability of successful defibrillation diminishes rapidly over time (4) VF tends to deteriorate to asystole within a few minutes.

Electrical Therapies Sudden Cardiac Arrest The survival rate from CPR alone is 0-2% CPR will buy you time, it will not stop a VF

New Recommendations to Integrate CPR and AED Use Two critical questions Whether CPR should be provided before defibrillation is attempted ? The number of shocks to be delivered in a sequence before the rescuer resumes CPR?

Shock First Versus CPR First Witnessed: an out-of-hospital arrest and an AED is immediately available on-site, the rescuer should use the AED as soon as possible Not witnessed : EMS personnel, they may give about 5 cycles of CPR before checking the ECG rhythm and attempting defibrillation (Class IIb)

Shock First Versus CPR First HCP witnessed cardiac arrest in hospitals and with AEDs on-site should provide immediate CPR and should use the AED/defibrillator as soon as it is available EMS call-to-arrival intervals were 4 to 5 minutes or longer, victims who received 1 to 3 minutes of CPR before defibrillation

1-Shock Protocol Versus 3-Shock Sequence In 2 studies of out-of-hospital and in-hospital CPR by HCP, chest compressions were performed only 51% to 76% of total CPR time 3-shock sequence performed by AEDs resulted in delays of up to 37 seconds the first-shock efficacy of >90% reported by current biphasic defibrillators

1-Shock AED Rescuers using monophasic AEDs should give an initial shock of 360 J; if VF persists after the first shock, second and subsequent shocks of 360 J should be given But it is not a mandate to recall monophasic AEDs for reprogramming

Defibrillation Defibrillation (shock success) is typically defined as termination of VF for at least 5 seconds following the shock. VF frequently recurs after successful shocks, but this recurrence should not be equated with shock failure.

Defibrillator Monophasic Damped Sinusoidal Wave (MDS) Monophasic truncated Exponential Wave (MTE) Biphasic Truncated Exponential (BTE) Rectilinear Biphasic (RBW)

Damped Sine Wave Unchanged for 30 Years Requires high energy and current. Not highly effective for patients with high transthoracic impedance. The Monophasic Damped Sine (MDS) wave had been, almost exclusively, used for external defibrillation since the 1960s. Its performance is greatly limited in patients with high transthoracic impedances. Escalating energy, aimed at raising the delivered current, is its only means for dealing with high patient impedance. Using energies ranging to 360 joules, monophasic defibrillators can deliver current levels that approach 60 amps. There is a growing body of evidence that shows high energy/current defibrillation produces post-shock myocardial dysfunction.

Biphasic Truncated Exponential The First Generation: Adapted from low impedance ICD applications. Impedance causes waveform to change shape. Many people consider this to be a first generation biphasic technology. It is known as a Biphasic Truncated Exponential (BTE) waveform. The energy is delivered in two phases. The first phase, seen as the positive waveform deflection, is indicative of current flow in one direction. The second, negative phase, indicates current flow in the reverse direction. Offering the promise of smaller size and extended battery life, the BTE waveforms were originally optimized for the low-impedance ICD application. Differing implementations of the BTE waveform have been adapted for external defibrillation by Physio-Control, Agilent Technologies, and others.

Rectilinear Biphasic Waveform Designed Specifically for External Use: Constant Current eliminates high peaks Fixed Duration stabilizes waveform in face of varying impedance levels. The Rectilinear Biphasic waveform (RBW) represents the latest advance in biphasic technologies. In contrast to the BTE waveform, the RBW was developed specifically for external defibrillation. It sought to improve upon earlier biphasics by eliminating high peak currents, and delivering stability in the face of the high and varied impedance levels typically seen with transthoracic defibrillation. The RBW differs from the BTE waveform in two ways. Most notable is a constant current first phase of the RBW that reduces potentially harmful peak currents. Second is the stability of its shape in response to impedance. Both ZOLL Medical and GE Medical (formerly Marquette Electronics) Systems employ the Rectilinear Biphasic waveform.

Effect of Patient Impedance on Biphasic Waveforms Low Impedance High Impedance -20 10 20 30 40 50 4 8 12 -10 First Generation Biphasic Biphasic waveforms most notably differ in their response to patient impedance. This slide shows the differing response of the BTE and RBW technologies. Upon examination one notes that the shape of the BTE waveform changes radically as higher patient impedance levels are encountered. Current levels fall and duration is increased in order to deliver the selected energy. Conversely, delivered current is consistent for the RBW. Recall, we noted earlier that clinical performance is tied to waveform shape. Variability in waveform duration and shape effects the defibrillation threshold, and ultimately, the clinical effectiveness. Rectilinear Biphasic

Biphasic Defibrillation with biphasic waveforms of relatively low energy ( 200 J) is safe and has equivalent or higher efficacy for termination of VF than monophasic waveform shocks of equivalent or higher energy (Class IIa). None of the available evidence has shown superiority of either nonescalating or escalating energy biphasic waveform defibrillation for termination of VF

Biphasic Current research confirms that it is reasonable to use selected energies of 150 J to 200 J with a biphasic truncated exponential waveform or 120 J with a rectilinear biphasic waveform for the initial shock For second and subsequent biphasic shocks, use the same or higher energy (Class IIa).

AED Survival rate of 41% to 74% from out-of-hospital witnessed VF SCA when immediate bystander CPR is provided and defibrillation occurs within about 3 to 5 minutes of collapse Reviewers found no studies that documented the effectiveness of home AED deployment, so there is no recommendation for or against personal or home deployment of AEDs (Class Indeterminate).

AED Implantable medical device Transdermal medication patch Lying in water Hairy chest

AED in Children Biphasic shocks appear to be at least as effective as monophasic shocks and less harmful Dose: 2 J/kg for the first attempt and 4 J/kg for subsequent attempts (Class Indeterminate). If CPR to a child in cardiac arrest and does not have an AED with a pediatric attenuator system, the rescuer should use a standard AED Not used for infants<1y/o

In-Hospital Use of AEDs AEDs should be considered for the hospital setting as a way to facilitate early defibrillation (a goal of 3 minutes from collapse)

Biphasic defibrillator Manufacturers should display the device-specific effective waveform dose range on the face of the device, and providers should use that dose range when attempting defibrillation with that device

Biphasic defibrillator BTE: 150 J to 200 J for initial shock RBW: 120 J for initial shock For second and subsequent shocks, use the same or higher energy (Class IIa). If unaware dose range, 200 J for the first shock and an equal or higher dose for the second and subsequent shocks

Synchronized Cardioversion shock delivery that is timed (synchronized) with the QRS complex avoid shock delivery during the relative refractory portion of the cardiac cycle, when a shock could produce VF If impossible to synchronize a shock (eg, the patient’s rhythm is irregular), use high-energy unsynchronized shocks.

Synchronized Cardioversion Recommended : SVT due to reentry, Af, and atrial flutter Not recommended: (automatic focus)MAT. Atrial Tach, Sinus Tachycardia

Synchronized Cardioversion Af : 100 J to 200 J (Monophasic) AF and other SVT: 50J to 100 J (Monophasic) Cardioversion with biphasic waveforms is now available: 100J to 120J(Biphasic) Monomorphic VT: 100 J, 200 J, 300 J, 360 J). Unstable polymorphic (irregular) VT with or without pulses is treated as VF using unsynchronized high-energy shocks (ie, defibrillation doses).

Pacing Not recommended: asystolic cardiac arrest Considered: symptomatic bradycardia Immediate pacing is indicated if the patient is severely symptomatic, especially when the block is at or below the His Purkinje level If the patient does not respond to transcutaneous pacing Transvenous