Prospective randomized comparison of anodal monophasic shocks versus biphasic cathodal shocks on defibrillation energy requirements

Prospective randomized comparison of anodal monophasic shocks versus biphasic cathodal shocks on defibrillation energy requirements

S. Adam Strickberger, MD, Emile Daoud, MD, Rajiva Goyal, MD, Kwok K. Chan, MD,

Frank Bogun, MD, Mark Castellani, MD, Mark Harvey, MD, Laura E. Horwood, RN,

Mark Niebauer, MD, K. Ching Man, DO, and Fred Morady, MD Ann Arbor, Mich.

Biphasic shocks are believed to be superior to monophasic shocks. Monophasic anodal shocks, as opposed to cathodal shocks, are associated with improved defibrillation energy requirements (DERs). However, it is unclear how the DER of anodal monophasic shocks compare with conventional biphasic shocks. Therefore the purpose of this study was to prospectively compare the DER of an anodal monophasic shock with that of a cathodal biphasic shock. A transvenous defibrillation lead with distal and proximal shocking electrodes was used. The subjects of this study were 20 consecutive patients with a mean age of 64.2 ± 10.5 years (±SD) and a mean left ventricular ejection fraction of 0.36 ± 0.18. Six had had cardiac arrest. The DER, defined as the lowest energy that converted ventricular fibrillation to sinus rhythm, was determined twice with a step-down protocol (25 J, 20 J, 15 J, 10 J, 5 J, 3 J, 1 J). If the DER was ->25 J, then a subcutaneous patch was deemed necessary for system implantation. In random order the DER was determined with a monophasic anodal shock (distal electrode positive) and then with a cathodal (first phase, distal electrode negative) biphasic shock. The mean DER with anodal monophasic shocks was 15.1 ±8.5 J compared with 13.6 ± 8.1 J with cathodal biphasic shocks (p = 0.4). A DER >-25 J was present in three patients with the monophasic waveform and in three patients with the biphasic waveform (p = NS). In conclusion, the DER and frequency of subcutaneous patch use with an anodal monophasic waveform is comparable to that obtained with a cathodal biphasic waveform. (AM HEART J 1995;131:961-5.)

Implantation of an automatic defibrillator with a nonthoracotomy lead system (NTL) depends on achieving an adequate defibrillation energy require-

From the Division of Cardiology, Department of Internal Medicine, Uni- versity of Michigan Medical Center.

Supported in part by a research grant from Cardiac Pacemakers, Inc., St. Paul, MN

Received for publication July 28, 1995; accepted Sept. 8, 1995.

Reprint requests: S. Adam Strickberger, MD, University of Michigan Med- ical Center, 1500 East Medical Center Dr., B1-F245, Ann Arbor, M148109- 0022.

Copyright © 1996 by Mosby-Year Book, Inc." 0002-8703/96/$5.00 + 0 4/1/70083

ment (DER). Several factors including subcutaneous patch location, 1 the number and location of transvenous electrodes, 2 the type of lead system, 3, 4 and polarity of monophasic shocks 5 have been demonstrated to influence the DER with NTL systems. The polarity of the first phase of a biphasic shock is not believed to influence the DER. 6 In general, the DER with a biphasic shock is believed to be less than that with monophasic shocks, 7-13 although only a single study 13 has addressed this issue with an NTL system. That study, 14 however, did not use anodal monophasic shocks, which appear to reduce the DER. 5 Therefore it is unclear how the defibrillation efficacy of biphasic shocks compares with tha t of monophasic anodal shocks. The purpose of this study was to compare, with a randomized prospective study design, the DER obtained with an anodal monophasic shock with that obtained with a conventional biphasic shock.

METHODS Patient characteristics (Table I). The mean age of the 20

patients included in the study was 64.2 _+ 10.5 years (-+SD). Fourteen of the patients had coronary artery disease, three patients had either idiopathic cardiomyopathy or other types of structural heart disease, and three patients had no structural heart disease. The mean left ventricular ejection fraction was 0.36 ± 0.18. Cardiac arrest was the presenting symptom in six patients, and 14 patients had syncope or ventricular tachycardia. All patients underwent baseline electrophysiologic testing and failed electropharmacologic testing with a mean of 0.5 _+ 0.7 antiarrhythmic drugs before a device was implanted.

Lead specifications and placement. All patients came to the operating room in a postabsorptive state. All antiarrhythmic medications were stopped at least five half-lives before devices were implanted with the exception of five patients in whom amiodarone therapy had been ineffective (Table I). Amiodarone was discontinued i to 5 days before the patients were taken to the operating room. General

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Table I. Pa t i en t character is t ics and defibri l lat ion da ta

DER

Patient Age Heart Antiarrhythmic AMonoW CaBiW no. (yt9 Sex disease L VEF drug (J) (J)

1 63 M CAD 25 Amiodarone 25 25 2 74 M CAD 20 Amiodarone 5 15 3 65 M CAD 45 Amiodarone 30 25 4 77 M CAD 63 None 3 2 5 41 M None 60 None 20 20 6 41 M None 65 None 20 20 7 68 M CAD 20 Amiodarone 10 10 8 74 M CAD 45 None 10 10 9 63 M CAD 40 None 10 20

10 62 M CAD 15 None 20 20 11 72 M IDCM 30 None 20 10 12 77 M IDCM 15 None 30 20 13 51 M None 60 None 5 10 14 67 M CAD 65 None 3 1 15 52 M CAD 20 Amiodarone 20 15 16 65 M CAD 28 None 20 3 17 69 M CAD 20 None 15 25 18 67 M CAD 30 None 15 5 19 67 M IDCM 18 None 15 10 20 69 F CAD 30 None 5 5 Mean ± SD 64.2 ± 10.5 0.36 ± 0.18 "15 ± 8.5 13.6 ± 8.1

AMonoW, Anodal monophasic waveform; CaBiW, cathodal biphasic waveform; CAD, coronary artery disease; IDCM, idiopathic dilated cardiomyopathy; LVEF, left ventricular ejection fraction. *p = 0.4 (anodal monophasic waveform vs cathodal biphasic waveform).

anes thes ia was induced, and then the t ransvenous defibril- la t ion lead was positioned.

The lead used in this s tudy (Model 0074, Cardiac Pace- makers , Inc. [CPI], St. Paul , Minn.) is a tined, passive fix- a t ion lead 100 cm in length, and i t varies along i ts length from 9.5F to 12F in diameter . This lead has two shocking electrodes. The dis ta l shocking electrode is 379 m m 2 and is 1.2 cm proximal to the end of the lead. The proximal shocking electrode is 617 1Tim 2 and is 12.7 cm from the end of the lead. The tip of the lead was posit ioned with the a id of fluoroscopy in the r ight ventr icular apex via the subcla- v ian vein. This posit ioned the dis ta l shocking c0i] in the r ight ventricle and the proximal shocking coil in the r ight a t r ium.

Waveform characteristics, The DER was determined with a monophasic waveform and a biphasic waveform in random order (Fig. 1). The DER was de te rmined with an anodal monophasic waveform (Fig. 1). For the monophasic waveform, the distal electrode functioned as the anode or the positive electrode (anodal monophasic shock). The monophasic waveform used in this s tudy was t runca ted with a fLxed t i l t (65%) and therefore had a var iable pulse width (Fig. 1). For the range of physiologic impedances encountered, the pulse width was 12 to 14 msec. The t ra i l ing edge voltage of this waveform is equal to 65% of the leading edge voltage. This is the s t andard CPI monophasic waveform, except t ha t the "reversed" polar i ty is used. 5

The dis ta l electrode functioned as the cathode or negative electrode for the ini t ia l phase of the biphasic waveform

(Fig. 1). This waveform had a fixed pulse width tha t was p rogrammed according to the measured impedance of a 1 J tes t shock delivered dur ing sinus rhy thm such tha t approximately a 65% ti l t of each phase was achieved. For the range of shock impedances physiologically encountered, a pulse width of 12 to 14 msec was required to achieve a 65% tilt. The dura t ion of each phase was 50% of the total duration. The leading edge voltage of the second phase was 50% of the t ra i l ing edge voltage of the first phase (Fig. 1). The distal shocking coil functioned as the cathode or negative electrode. The selected biphasic waveform character is t ics and selected are recommended by Ventr i tex (Sunnyvale, Calif.).

Determination of defibrillation threshold. All patients provided informed consent under a protocol approved by the H u m a n Research Commit tee of the Univers i ty of Michigan. Before the research protocol was conducted, im- p lan t DER cri ter ia for the defibri l lat ion sys tem were met. Implan t cr i ter ia required three successful conversions of vent r icular fibril lation to sinus rhy thm with a 25 J shock, two successful conversions at 20 J, or a successful conver- sion at 20 J and 15 J. I f a subcutaneous patch was required to meet implan t criteria, the successful shocks, as noted previously, were required with the lead and patch configuration. An adequate defibri l lat ion safety marg in was defined as a t leas t 10 J less than the max imum output of the implan ted defibrillator. After the implan t DER cri ter ia were met, the s tudy protocol was performed. The DERs were de t e rmined with a cathodal biphasic waveform and

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an anodal monophasic waveform in random order (Fig. 1). Ventricular fibrillation was induced with 1 to 3 seconds

of alternating current. An external defibrillator was used to deliver the monophasic shock ~CPI, Model 2806) and the biphasic shock (Ventritex, HVSO2) 10 seconds after an alternating current was initiated. The external defibrillators measured the impedance of each shock.

A standardized step-down protocol was used to determine the DER. Shocks were delivered in the following or- tier until ventricular fibrillation failed to convert to sinus rhythm: 25 J, 20 J, 15 J, 10 J, 5 J, 3 J, and finally 1 J. The DER was defined as the lowest energy successful in converting ventricular fibrillation to sinus rhythm. If the DER was greater than or equal to 25 J, then the DER was considered to be 30 J, and a subcutaneous patch was deemed necessary for system implantation. At least 5 minutes were allowed to elapse between each induction of ventricular fibrillation.

Statistics. Values are expressed as mean _+ 1 SD. DER and impedance measurements were compared by a paired t test. A comparison of the frequency of subcutaneous patch electrode use was performed with a McNemar test. Prob- ability values <0.05 were considered statistically significant.

RESULTS

The resul ts in individual pa t ien ts are p resen ted in Table I. The m e a n DER for anodal monophasic shocks was 15.1 _+ 8.5 J compared wi th 13.6 _+ 8.1 J for cathodal biphasic shocks (p = 0.4). The DER was the same wi th each waveform in seven pat ients , a mean of 8.8 _+ 2.5 J less wi th the anodal monophasic waveform in four pat ients , and a m e a n of 7.2 _+ 5.0 J less wi th the biphasic waveform in nine pat ients . The m e a n impedance was 45 _+ 6 ohms wi th the anodal monophas ic waveform and 41 _+ 7 ohms with the cathodal biphasic waveform (p < 0.01). A DER of ->25 J was obta ined in th ree pat ients wi th the monophasic waveform and in th ree pa t ien ts wi th the biphasic waveform (p = NS). Two of these th ree pa- t ients requi red a subcutaneous pa tch electrode wi th each waveform. Regardless of waveform, all devices were able to be implan ted wi th an adequate de fibril- la t ion safety marg in when a subcutaneous pa tch was added to the t r ansvenous lead.

All pa t ien ts in this s tudy u n d e r w e n t implan ta t ion wi th the defibrillator, which was prescribed before surgery. Most commonly, the implan ted device had a monophas ic waveform (n = 18; CPI Model 1600, 1705), and two pa t ien ts received a device wi th a pro- g rammable waveform (Ventr i tex Model V-100, V-110).

No significant differences were found in the m e a n age, m e a n left ven t r icu la r ejection fraction, use of amiodarone, or type of s t ruc tura l hea r t disease among pa t ien ts in whom the anodal monophasic

v3 L J-vw 1)2

Fig. 1. DER was determined in all patients with both waveforms. Each patient was randomized to have DER determined initially with either anodal monophasic waveform (left) or cathodal biphasic waveform (right). Monopha- sic waveform (left) used distal electrode as anode or positive electrode. Trailing edge voltage (V2) equals 65% of leading edge voltage (V1). Distal electrode functions as cathode for biphasic waveform (right). Duration of monophasic and biphasic shock ranged from 12 to 14 msec. Duration of each phase of biphasic waveform is 50% of total duration. Duration ofbiphasic shock is selected according to impedance of I J test shock into sinus rhythm such that 65% tilt is achieved. Note that for both waveforms V2 equals 65% of V1. For biphasic waveform V3 equals 50% of V2, and V4 equals 65% of V3. See text for complete descrip- tion of each waveform. D1 is duration of first phase, D2 is duration of second phase, and V1 and V2, and V~, and V4 are leading edge and trailing edge voltages of first phase and second phase, respectively.

waveform DER was higher, lower, or the same as wi th the biphasic waveform.

DISCUSSION Main findings. These da ta demons t ra te t h a t the

DER and the f requency of subcutaneous pa tch elec- t rode use associated wi th the anodal monophasic waveform are not significantly different t h a n those observed with the cathodal biphasic waveform. F u r t h e r m o r e these da ta suggest t ha t approxi- ma te ly 85% of defibrillators, w h e th e r used wi th the anodal monophasic waveform or the cathodal biphasic waveform eva lua ted in this report , can be successfully implan ted with t h e t r ansvenous lead alone and t h a t the r ema inde r can be safely implan ted wi th the addit ion of a subcutaneous pa tch to the lead system.

Comparison to previous studies. Previous clinical repor ts have demons t ra t ed a 20% to 30% reduct ion of the DER with an anodal monophasic waveform as opposed to a cathodal monophasic waveform with an epicardial lead sys tem 15, 16 and wi th a t r ansvenous lead system. 5 In contrast , wi th a biphasic waveform the polar i ty of the first phase of the shock does not appear to affect the DER in h u m a n beings undergo- ing defibri l lator implan ta t ion wi th a t r ansvenous lead system. 6 However , the waveform studied in t ha t

May 1996 964 Strickberger et al. American Heart Journal

report 6 was different from the one studied in this study.

Many clinical 11-14 and in vivo 7-1° reports demon- strate the superiority of biphasic shocks over monophasic shocks. Most of the clinical studies have compared these waveforms with epicardial lead systems. n'13 Two recent clinical studies 14, 17 have compared biphasic and monophasic waveforms with an NTL system. These studies differ from this one in several important ways. Block et a1.14 demonstrated improved DERs with a different biphasic waveform but with the same lead system as in this study. In addition, the cathodal monophasic polarity that was used in the previous study, 14 appears to be inferior to the anodal polarity. 5 The results of the second clinical study suggest improved defibrillation efficacy when the same biphasic waveform and lead system used in this study are compared with cathodal monophasic shocks. 17 However, this study was performed retrospectively, the DER data were not obtained in a paired fashion from the same patients, and cathodal but not anodal monophasic shocks were used. In addition, the authors suggested a learning curve for device implantation may have been a significant limitation of the study. These differences in methods could account for the discrepancy between the results of Block et al., 14 and Natale et al., 17 with those contained herein.

An in vivo study has also compared the waveforms used in this report and has demonstrated the biphasic waveform to be more efficacious.IS That study is is different from this study because it was conducted in dogs with structurally and electrically normal hearts and with a significantly different lead system. Hence the results may not apply to the clinical setting in which patients with potentially lifeithreatening ar- rhythmias who often have structurally abnormal hearts are treated with implantable defibrillators.

The frequency of subcutaneous patch use in this study, 15% with anodal monophasic shocks and 15% with biphasic shocks, was similar to subcutaneous patch electrode requirements in previous reports with these waveforms with the studied NTL system.5, 17 Finally, previous studies have demonstrated that not all biphasic waveforms are associated with improved DERs compared with monophasic waveforms.17, 19-21

Limitations. The DER represents a statistical phe- nomenon instead of an absolute number. The value is a function of the technique used to determine it. 22 The technique used in this study probably estimates the energy that will successfully convert ventricular fibrillation to sinus rhythm with approximately 70% s u c c e s s . 23 Therefore a limitation of this study, as

with other clinical DER studies, is that a DER curve was not constructed, and only a single point on the curve was determined. However, the number of shocks required to construct a DER curve in human beings is not clinically feasible.

A second limitation is that the results may not be applicable to other biphasic waveforms or to the studied biphasic waveform with the opposite polarity, although polarity is not believed to affect the DER of biphasic waveforms. 6 Furthermore the biphasic waveform and configuration used in this study is the configuration recommended by the manufacturer, although the defibrillator from this company has many waveform options. These data may also not be generalizable to these same waveforms when used with a different defibrillation lead system.

Clinical implications. These results suggest that biphasic waveforms are not always more efficacious than all monophasic waveforms. Optimization of a waveform to achieve the lowest possible DER and improved clinical efficacy requires prospective evaluation of various waveform and lead system options. 24

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Documents

Prospective randomized comparison of anodal monophasic shocks versus biphasic cathodal shocks on defibrillation energy requirements