Utility of a High Output Implantable Cardioverter Defibrillator

DOI: 10.19102/icrm.2012.030308

¹GHIATH MIKDADI, MD, FACC, ²DOUGLAS MENDOZA, MD, FACC, ¹DONNA FOSTER, PA-C and ³JENNIFER MARTIN, BS, MBA

¹Heart Clinic of Hammond, Hammond, LA
²Ochsner Heart and Vascular Clinic, Hammond, LA
³St. Jude Medical, St. Paul, MN

Download PDF

Follow Us >> Tweet

ABSTRACT. A 30-year-old female with non-ischemic cardiomyopathy was admitted to the Emergency Department after multiple shocks from her implantable cardioverter-defibrillator (ICD) (Fortify, model 2231-40Q) for ventricular arrhythmias, later determined to be caused by an electrolyte imbalance. The high output capability of the ICD to deliver a 40-J shock was able to convert the patient’s rhythm back to sinus after three failed shocks at 36 J, albeit, her initial defibrillation threshold at implant was 20 J.

KEYWORDS. implantable cardioverter defibrillator, ventricular tachycardia, ventricular fibrillation, antitachycardia pacing.

The authors report no conflicts of interest for the published content.
Manuscript received January 10, 2012, final version accepted January 24, 2012.
Address correspondence to: Ghiath Mikdadi, MD, Heart Clinic of Hammond, 16033 Doctors Blvd. Hammond, LA. E-mail: gmikdadi@gmail.com

Case report

A 30-year-old woman with non-ischemic cardiomyopathy, New York heart Association class II heart failure and an ejection fraction of 30% was implanted with a dual-chamber implantable cardioverter-defibrillator (ICD) (Fortify, model 2231-40Q, St. Jude Medical, Inc., St. Paul, MN) for primary prevention 1 month previously, and arrived in the Emergency Department after multiple shocks from her ICD. The patient’s ICD had discharged three times earlier that morning.

The first episode began as ventricular tachycardia (VT), degrading to ventricular fibrillation (VF) after 4 s. The device detected the arrhythmia and began to deliver antitachycardia pacing (ATP) while charging. The ATP was ineffective, and a 36-J (845 V) high-voltage shock was delivered, returning the patient back to sinus rhythm. The second episode occurred 30 min later and again began as VT, quickly degrading into VF. The device delivered a 36-J high-voltage shock, terminating the VF. The final episode occurred an hour later, and once again it began as VT and degraded into VF (Figure 1). The device delivered a high-voltage shock of 36 J; however, this shock did not terminate the arrhythmia. The device subsequently delivered a second shock at 36 J; however, this shock was also unsuccessful. The device charged for a third time and delivered 40 J (890 V), and this high voltage shock was successful in terminating the VF and restoring sinus rhythm.

After further inquiry into the patient’s functional status, laboratory investigations yielded decreased levels of potassium and magnesium as a result of non-compliance with her medication regimen. There were no required programming changes in the device, as the device was already programmed to deliver maximum output, functioning appropriately in this instance of VF. The utilization of ATP was clinically irrelevant in this case, as the rate of the presenting arrhythmia would not have responded. The patient has not had additional shocks since the episodes reported above. The patient’s status is currently reported as stable.

Discussion

During implantation of this device, VF was induced and a first shock of 20 J was delivered, returning the patient to sinus rhythm. This was derived by delivering one confirmatory shock at 20 J below the maximum delivered output of the device, to confirm sufficient energy would be delivered during this type of arrhythmia after implant. With a maximum delivered output of 40 J, this patient had a 20-J safety margin after the device was programmed, and the patient was sent home the following day. In May 2010, St. Jude Medical introduced a line of high output ICDs (Fortify, model 2231-40Q) capable of delivering up to 40 J (890 V). Previous St. Jude Medical ICDs and other market-released ICDs are only capable of delivering up to 36 J (845 V) or similar outputs below 40 J, and in this particular case the increased energy output of this new device to deliver 890 V (40 J) was instrumental in rescuing the patient.

This particular case demonstrates the utility of a higher output device in a subset of patients whose arrhythmias do not respond to a lower defibrillation output for various causes. Historical practice indicates that a 10 J safety margin after defibrillation threshold (DFT) testing is appropriate and acceptable;¹ however, this case demonstrates that an output with only a 10 J safety margin (delivered output of 30 J) would not have been enough energy to defibrillate this patient in this clinical situation.

This case study further makes evident that DFT testing during implant does not necessarily predict the response of clinical arrhythmias to the same defibrillation energy. There is published evidence that certain pharmacological agents cause shifts in DFTs, influencing the effectiveness of the defibrillator, including class Ia, Ib, Ic, and III agents.² There are also many additional factors that can impact a patient’s DFT, including fluctuating serum electrolyte values, changes in myocardial substrate from disease progression, and the maturation of the lead system, leading to shifts in electrodes and consequently defibrillation shocking vectors.³ Not only are electrolyte imbalances a common occurrence in heart failure patients,⁴ but changes in medication regimen and other factors may contribute to a higher acute DFT for many patients that are implanted with an ICD.

References

1. Marchlinski FE, Flores B, Miller JM, Gottlieb CD, Hargrove WC 3rd. Relation of the intraoperative defibrillation threshold to successful postoperative defibrillation with an automatic implantable cardioverter defibrillator. Am J Cardiol 1988; 62:393–398. [CrossRef] [PubMed]
2. Qi X, Dorian P. Antiarrhythmic drugs and ventricular defibrillation energy requirements. Chin Med J (Engl) 1999; 112:1147–1152. [PubMed]
3. Uyguanco ER, Berger A, Budzikowski AS, Gunsburg M, Kassotis J. Management of high defibrillation threshold [Review]. Expert Rev Cardiovasc Ther 2008; 6: 1237–1248. [CrossRef] [PubMed]
4. Dunn SP, Bleske B, Dorsch M, Macaulay T, Van Tassell B, Vardeny O. Nutrition in heart failure: impact of drug therapies and management strategies [Review]. Nutr Clin Pract 2009; 24:60–75. [CrossRef] [PubMed]