Search our site 
Advanced Search
Home | News | Exam dates | Contact us | About us | Testimonials |

You are in Home >> Resources >> Physics and equipment >> Monitoring & Physical principles

Biphasic waveforms

Created: 28/10/2005


Comparing the Transthoracic Biphasic Waveforms

Now that we have highlighted the key elements of effective biphasic waveform design, we turn to a brief overview of other external biphasic waveform technologies on the market. The SMART Biphasic waveform was introduced in 1996 with substantial patent protections. There are also patent restrictions on various other technologies. Consequently, the biphasic technologies are all different as are the associated energy protocols.

Because of these design differences, the energy protocol for each manufacturer’s defibrillator should be individualized. The need for product-specific energy protocols is confirmed by ECRI, a non-profit organization whose mandate it is to objectively evaluate biomedical equipment: "…a waveform designed for low-energy defibrillation may result in an overdose if applied at high energies, while another waveform designed for high-energy may not defibrillate at lower energies." 31

Most importantly, compared to the Philips SMART Biphasic waveform, other manufacturers have relatively few published, peer-reviewed studies to demonstrate the performance of their waveforms. Some manufacturers have no data at all, and others rely heavily upon small sample abstract and animal data to demonstrate waveform performance. Collectively, the amount and breadth of published SMART Biphasic clinical research exceeds that of all other
manufacturers’ waveforms.

The Low-Energy Rectilinear Biphasic Waveform Alternative

The Rectilinear Biphasic Waveform (ZOLL Medical Corporation) shares with SMART Biphasic a low-energy, low-capacitance design, but there are significant differences. Most importantly, the Rectilinear waveform offers only limited peer-reviewed evidence to support its performance. As of this writing, we are aware of no published, peer-reviewed data reflecting performance with the challenging long down-time patient population most difficult to treat effectively.

The Rectilinear waveform does little to adjust current in response to the problem of shunt current pathways within the chest. The waveform utilizes what company literature describes as a "constant current" approach in the first phase of the waveform. In contrast to SMART Biphasic, which modifies peak current, waveform shape and duration based on patient impedance, the Rectilinear approach is to hold the overall waveform duration and ratio between the two phases constant regardless of patient impedance (see Figure 9).

The published adult energy protocol for the Rectilinear Biphasic waveform device starts at 120J and escalates to 200J. As noted earlier, escalating energy was employed historically to increase peak current with inherently inefficient monophasic waveforms, but is not necessary with biphasic when the first shock is adequatley dosed, as in the case with SMART Biphasic.

For any selected energy setting, the actual delivered Rectilinear waveform energy varies widely across the range of patient impedance. Further, the Rectilinear Biphasic waveform loses the constant current profile, essentially becoming a BTE waveform very similar to SMART Biphasic (Figure 10), when patient impedance values exceed 100 ohms and 200J of energy is selected. 32

In summary, the Rectilinear waveform, marketed as a "constant current" waveform, does little to adjust current in response to current shunting in the patient’s chest. The manufacturer abandons the hallmark "constant current" approach for some high impedance patients and, perhaps most importantly, has only limited published data on which to measure its waveform’s performance, none of which reflects performance with the ischemic SCA patient.

Figure 9. SMART Biphasic vs. Rectilinear Biphasic

Figure 10. "Constant" Current Not Always Constant

The High-Energy Biphasic Waveform Alternatives

There are several escalating high-energy biphasic waveforms currently on the market. It is beyond the scope of this paper to describe in detail each of the designs. Instead, we offer a high level summary of technology issues to consider with highenergy waveforms as a class.

The specific methods of impedance compensation vary with the manufacturer. Figure 11 illustrates the SMART Biphasic waveform compared to one of the common high-energy biphasic waveforms on the market. It is evident that the two waveforms modify peak current, waveform shape and duration similarly in response to patient impedance. The big difference is that the high-energy waveforms require high energy to deliver adequate current to the patient because of their large capacitors, while the Philips low-energy BTE waveform delivers adequate current on the first shock without the need to escalate.

Figure 11. SMART Biphasic vs. High-Energy Biphasic

Most importantly, as of this writing there is only one published, peer-reviewed study reflecting waveform performance of one high-energy biphasic waveform with the ischemic, long downtime SCA patient population. This study compared the highenergy ADAPTIV biphasic waveform (Metronic Physio-Control) with a conventional monophasic damped sine (MDS) waveform.33 While first shock efficacy for the biphasic waveform was high, there was an atypical trend towards better MDS waveform performance compared to the ADAPTIV biphasic waveform for all other outcome variables.

Compare these results to a similar study7 in which the SMART Biphasic waveform was associated with improved return to spontaneous circulation, improved survival to hospital admission and discharge, and superior neurological outcome for survivors compared to monophasic treatment.

There is no peer-reviewed research in humans to compare the performance of one biphasic waveform to another. A swine study by Walker, et al. is often cited as evidence of high-energy superiority with moderate to high impedance patients. However, the study utilized a disputed animal model 34,35 that is inconsistent with the way in which impedance actually occurs in either animal or human populations.

The Walker, et al. study also yields results inconsistent with numerous peer-reviewed studies demonstrating superior efficacy of the low-energy SMART Biphasic waveform defibrillator to high-energy therapies across a diverse human population, including patients with high impedance.

In summary, high-energy biphasic waveforms offer little or no published, peer-reviewed data in comparison to that published for the Philips SMART Biphasic waveform, and only one study reflecting performance with the long down-time SCA patient population.

As pointed out, high biphasic energy has been associated with increased cardiac dysfunction.15

Finally, the AHA has issued no science-based recommendations regarding biphasic defibrillation > 200 Joules.


1. Kerber RE et al. Automatic external defibrillators for public access defibrillation: recommendations for specifying and reporting arrhythmia analysis algorithm performance, incorporating new waveforms, and enhancing safety: a statement for health professions from the AHA Task Force on Automatic External Defibrillation, Subcommittee on AED Safety and Efficacy. Circulation 1997; 95: 1677-82.
2. Cummins RO et al. Low-energy biphasic waveform defibrillation: evidence-based review applied to emergency cardiovascular care guidelines: a statement for healthcare professionals from the American Heart Association Committee on Emergency Cardiovascular Care and the Subcommittees on Basic Life Support, Advanced Cardiac Life Support, and Pediatric Resuscitation. Circulation 1998; 97: 1654-67.
3. Cummins RO et al. Guidelines 2000 for cardiopulmonary resuscitation and emergency cardiovascular care. Supplement to Circulation 2000;102(8):I-5,I-63,I-91.
4. White RD et al. Body weight does not affect defibrillation, resuscitation or survival in patients with out-of-hospital cardiac arrest treated with a non-escalating biphasic waveform defibrillator. Crit Care Med 2005; 64: 63-9.
5. White RD et al. Transthoracic impedance does not affect defibrillation, resuscitation, or survival in patients with out-of-hospital cardiac arrest treated with a non-escalating biphasic waveform defibrillator. Resuscitation 2005; 64: 63-9.
6. Capucci A et al. Tripling survival from sudden cardiac arrest via early defibrillation without traditional education in cardiopulmonary resuscitation. Circulation 2002; 106: 1065-70.
7. Schneider T et al. Multicenter, randomized, controlled trial of 150-J biphasic shocks compared with 200-360-J monophasic shocks in the resuscitation of out-of-hospital cardiac arrest victims. Circulation 2000; 102: 1780-7.
8. Page RL et al. Use of automated external defibrillators by a U.S. airline. N Engl J Med 2000; 343: 1210-16.
9. Bardy GH et al. Multicenter comparison of truncated biphasic shock and standard damped sine wave monophasic shocks for transthoracic ventricular defibrillation. Circulation 1996; 94: 2507-14.
10. Xie J et al. High-energy defibrillation increases the severity of postresuscitation myocardial function. Circulation 1997; 96: 683-8.
11. Weaver WD et al. Ventricular defibrillation - a comparative trial using 175J and 320J shocks. N Engl J Med 1982; 307: 1101-6.
12. Reddy RK et al. Biphasic transthoracic defibrillation causes fewer ECG ST-segment changes after shock. Ann Emerg Med 1997; 30: 127-34.
13. Tokano J et al. Effects of ventricular shock strength on cardiac hemodynamics. J Cardiovasc Electrophysiol 1998; 9: 791-7.
14. Tang W et al. The effects of biphasic and conventional monophasic defibrillation on postresuscitation myocardial function. J Am Coll Cardiol 1999; 34: 815-22.
15. Tang W et al. The effects of biphasic waveform design on post-resuscitation myocardial function. J Am Coll Cardiol 2004; 43: 1228-35.
16. Tovar OH et al. Immediate termination of fibrillation at 50% probability of overall success correlates with defibrillation dose-response curve width. J Cardiovasc Electrophysiol 2004; 15: 1207-11.
17. White RD et al. Patient outcomes following defibrillation with a low energy biphasic truncated exponential waveform in out-of-hospital cardiac arrest. Resuscitation 2001; 49: 9-14.
18. White RD. Early out-of-hospital experience with an impedance-compensating low-energy biphasic waveform automatic external defibrillator. J Interv Card Electrophysiol 1997; 1: 203-8.
19. Lerman BB et al. Relation between transcardiac and transthoracic current during defibrillation in humans. Circ Res 1990; 67: 1420-6.
20. Gliner BE et al. Treatment of out-of-hospital cardiac arrest with a low-energy impedance-compensating biphasic waveform automatic external defibrillation. Biomed Instrum Technol 1998; 32: 631-44.
21. White RD et al. Refibrillation, resuscitation and survival in out-of-hospital sudden cardiac arrest victims treated with biphasic automated external defibrillators. Resuscitation 2002; 55: 17-23.
22. Gliner BE et al. Transthoracic defibrillation of swine with monophasic and biphasic waveforms. Circulation 1995; 92: 1634-43.
23. Tang W et al. A comparison of biphasic and monophasic waveform defibrillation after prolonged ventricular fibrillation. Chest 2001; 120: 948-54.
24. Tang W et al. Fixed energy biphasic waveform defibrillation in a pediatric model of cardiac arrest and resuscitation. Crit Care Med 2002; 30: 2736-41.
25. Bardy GH et al. Truncated biphasic pulses for transthoracic defibrillation. Circulation 1995; 91: 1768-74.
26. Gliner BE, White RD. Electrocardiographic evaluation of defibrillation shocks delivered to out-of-hospital sudden cardiac arrest patients. Resuscitation 1999; 41: 133-44.
27. Poole JE et al. Low-energy impedance-compensating biphasic waveforms terminate ventricular fibrillation at high rates in victims of out-of-hospital cardiac arrest. J Cardiovasc Electrophysiol 1997; 8: 1373-85.
28. Caffrey SL et al. Public use of automated external defibrillators. N Engl J Med 2002; 347: 1242-7.
29. Gurnett CA, Atkins DL. Successful use of a biphasic waveform automated external defibrillator in a high-risk child. Am J Cardiol 2000; 86: 1051-3.
30. Martens PR et al. Optimal response to cardiac arrest study: defibrillation waveform effects. Resuscitation 2001; 49: 233-43.
31. Anon. External biphasic defibrillators. Should you catch the wave? Health Devices 2001; 30: 219-21, 223-5.
32. Achleitner U et al. Waveform analysis of biphasic external defibrillators. Resuscitation 2001; 50: 61-70.
33. van Alem AP et al. A prospective, randomized and blinded comparison of first shock success of monophasic and biphasic waveforms in out-of-hospital cardiac arrest. Resuscitation 2003; 58: 17-24.
34. Jones JL et al. Predictions from misleading pig model are potentially harmful to humans. Resuscitation 2003; 59: 365-7.
35. Snyder DE et al. External series resistors accurately model waveform time course, but not cardiac dose in animal models of defibrillation. Resuscitation
2003; 56: 238 [abstract].
SiteSection: Article
  Posting rules

     To view or add comments you must be a registered user and login  

Login Status  

You are not currently logged in.
UK/Ireland Registration
Overseas Registration

  Forgot your password?

All rights reserved © 2016. Designed by AnaesthesiaUK.

{Site map} {Site disclaimer} {Privacy Policy} {Terms and conditions}

 Like us on Facebook