Cardiac Rhythm Management
Articles Articles 2012 August

Letter from the Editor in Chief: Managing Patients with High Defibrillation Thresholds

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John Day, MD, FHRS, FACC
The Journal of Innovations in Cardiac Rhythm Management
Director of Heart Rhythm Services
Intermountain Medical Center
Salt Lake City, UT


John Day, Editor-in-Chief

Dear Readers,

Within the Innovative Techniques section of this issue you will find a contribution by Rahaby and Niazi discussing very practical techniques to manage a very difficult clinical situation. The authors share their experiences of high defibrillation thresholds (DFTs), and an inability to defibrillate the patient through an implantable cardioverter-defibrillator (ICD).

In this article, Rahaby and Niazi offer many practical, step-by-step suggestions to manage the high DFT patient at the time of ICD implantation. Certainly, there are several things to initially evaluate, such as making sure all connections are correct and ruling out potential metabolic causes, each of which may contribute to the elevated DFT. When these issues are not the case, simply switching the shock polarity, changing the location of the right ventricular shocking lead, modifying the pulse width or tilting if available, or even disconnecting the superior vena cava coil can easily modify the shock vector and lead to a satisfactory DFT in most patients. Sometimes just discontinuing amiodarone, or starting the patient on sotalol or dofetilide, can lower the DFT.

The challenge really becomes what to do when all of the above measures fail to get the job done. Fortunately, this is a very rare situation, and for some reason this always seems to have occurred late on a Friday afternoon throughout my career. In this situation, outside of an epicardial procedure, there really are only two options available. One may decide to either implant the subcutaneous array or an azygos shocking lead. Of these two options, I have become progressively more impressed with the ease and efficacy of the azygos shocking lead. In fact, we were presented with this type of case just last month at our center.

The patient was a 350-pound 32-year-old Polynesian man with a chronic non-ischemic dilated cardiomyopathy with a wide QRS complex and a left ventricular ejection fraction of 20%. He was not on any antiarrhythmic agents. A biventricular ICD was placed without complication. However, at the end of the case, during shock testing, ventricular fibrillation could not be terminated at any energy level by the device (41-J device), and he had to be rescued by an external defibrillation, which only worked after multiple external shocks had been delivered.

Unfortunately, in this case, as the internal shocks did not work and multiple external shocks finally resuscitated the patient, the patient's clinical status worsened and he became very tenuous hemodynamically. Thus, the only measure that could be tried during the initial implantation was to reverse the polarity, which also failed to defibrillate and also led to multiple external shocks before sinus rhythm could again be achieved. Fearing that further shock testing in this debilitated state could lead to cardiogenic shock, the decision was made to let the patient recover and bring him back to the electrophysiology lab another day.

After much consideration, the patient was brought back to the lab 1 month later for further DFT testing. At the time of his second procedure, a 7-F single-coil Durata (St Jude Medical, Sylmar, CA) lead was inserted into the patient's azygos vein, and the coil of the Durata azygos lead was inserted into the proximal coil of the ICD (Figure 1). The Durata lead was chosen given its smaller diameter, thus allowing easier maneuverability through the tight bend to get the lead inside the azygos vein. With this configuration in place, the patient now had a satisfactory DFT.



The case I have reviewed and the case presented within the Innovative Techniques section of this issue both serve to highlight the potentially beneficial role of an azygos shocking lead in the rare cases where patients may have an extremely high defibrillation threshold at the time of ICD implantation. The technique is not difficult to learn and the standard available tools may be used to facilitate placement of this lead.

In the most recent 10 years of attending the annual Scientific Sessions of the Heart Rhythm Society, I have noted a number of debates making an argument that ICD shock testing is not necessary following device implantation. Although current generation ICDs have improved dramatically, I suspect that, for most cases, shock testing is probably not necessary. However, it is the rare case, similar to the two presented within this issue, which has an unusual shock vector and the standard settings will not defibrillate the patient. In the case at our center, it would have been a tragedy if our young patient had died suddenly because device testing was never conducted ahead of time. Although ICD shock testing is certainly a rather crude old-school approach, until we better understand these patients with unusual defibrillation shock vectors it is probably best if we test the device in the lab to ensure it can adequately defibrillate the patient.