In this issue of Cardiology Review, Dr. Stephen Vlay (page 21) discusses a wide range of issues related to device therapy for cardiac arrhythmias, including evaluation and treatment aspects. The first device he reviews is the implantable loop recorder. This unit clearly helps clinicians who have evaluated patients with recurrent but previously undocumented symptoms, such as palpitations, tachycardia, or syncope. The loop recorder allows clinicians to use a long-term, automated device to document bradycardia or tachycardia in patients who have sporadic but seriously symptomatic episodes. Implantation and interrogation are simple, offering clinicians a major step forward in evaluating these difficult clinical problems.
The second device Dr. Vlay reviews is the pacemaker. Since being introduced in the early 1960s, the dramatic improvements in the reliability of these devices have been superseded by their markedly enhanced pacing and recording capacities. Many data are available to assess the type, frequency, and duration of the arrhythmia. Telemetry data allow clinicians to differentiate between atrial fibrillation, supraventricular tachycardia, ventricular tachycardia, and other arrhythmias. Interrogation of simple modes, such as mode switching, allows episodes of silent atrial fibrillation to be detected. Pacemakers help clinicians assess changes in therapy, such as anticoagulation, primary antifibrillation therapy, and others.
The third section of Dr. Vlay’s review deals with implantable cardioverter defibrillators (ICDs). Since being introduced by Mirowski and Mower in 1973, there has been a
dramatic increase in the use of these
devices.1 The indications for their use have expanded as these devices have become more complex. Significant controversy exists, however, with regard to the indications for their implantation. Questions still exist as to which patients will benefit from prophylactic (primary prevention implantation) versus therapeutic (secondary prevention implantation) use. Data from the secondary prevention trials (AVID, CIDS, and CASH [trial acronyms are defined on the next page]) have been reviewed in detail, but the criteria for identifying the ideal candidate for ICD implantation has not been resolved.2-4
Even more controversy exists as to ICD use in primary prevention. A detailed analysis of trials such as the CABG Patch trial, MUSTT, MADIT, and MADIT II have undergone extensive scrutiny.5-8 Guidelines from both the United States and Europe have been published and should be reviewed by all clinicians who implant these devices.9,10
The use of ICD therapy is further complicated by evaluation of the patient population. The use of prophylactic ICD implantation in those with nonischemic cardiomyopathy has been the subject of intense scru-tiny. Studies reviewing such trials
as GESICA, CHF-STAT, and now AMIOVIRT have been done.11-13 These studies generally present a negative review with regard to the use of prophylactic ICD implantation in patients with nonischemic cardiomyopathy.
Other controversies exist, including the need for a “shock box” with limited capabilities. The advantages of a more complex device, such as dual-chamber ICDs versus single-chamber ICDs, have not fully been evaluated. The latter controversy has been addressed in the DAVID study.14
Another important area reviewed by Dr. Vlay concerns resynchronization therapy—a novel approach to the treatment of congestive heart failure. This form of pacing has gained rapid acceptance among cardiologists. Again, however, significant controversy exists with regard to what parameters should be used as indicators for using this device, from the simplistic use of QRS
duration (with left bundle branch block) to the use of tissue Doppler studies and tagged magnetic res-onance imaging. Several clinical trials (COMPANION, MIRACLE ICD, Contak CD, and CARE HF) have focused on the evolution of this therapy.14-17 One interesting observation from the DAVID study has substantial implications for the entire pop-ulation of pacemaker patients; it
questions whether right ventricular pacing itself promotes desynchronization, thereby causing ventricular function to worsen.
Future of device therapy
Unique applications may be developed for pacing, including therapy for sleep apnea.18 Ultimately the development of a truly biologic pacemaker may be on the horizon.