Perhaps one of the most important developments in modern cardiovascular medicine was the development of the implantable cardioverter–defibrillator (ICD) in the early 1980s. This development has revolutionized the management of patients who have experienced or are at risk for lethal cardiac arrhythmias. These remarkable devices fulfilled a long-held dream of being able to effectively recognize and terminate life-threatening ventricular arrhythmias using a small surgically implanted device.
The overwhelming majority of recipients of the first ICDs were survivors of sudden cardiac death. With the advent of ICDs, there was a significant reduction in the rates of death secondary to ventricular tachycardia (VT) or ventricular fibrillation (VF). The use of ICDs effectively transformed sudden death into a chronic illness. Since then, indications for the implantation of ICDs have broadened to include primary prophylaxis for patients deemed to be at a high risk for sudden cardiac death due to hereditary and congenital conditions such as long QT syndrome, Brugada syndrome, and arrhythmogenic right ventricular dysplasia. With the publication of landmark studies such as the Multicenter Automatic Defibrillator Implantation Trial (MADIT)-I and -II and the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT), over the last few years guidelines from expert panels have also recommended ICD implantation for patients with low ejection fractions secondary to ischemic and non-ischemic cardiomyopathies. The huge expansion in the number of potential candidates requiring ICD implantation has given rise to an increasing interest in the practical ramifications of this therapy—one of the most important being the ability to continue an active lifestyle, which may involve the ability to safely drive a motor vehicle.
While drug treatment of arrhythmias (at least in theory) prevented or reduced episodes of VT and VF leading to sudden cardiac death, the ICD could terminate an episode only once it had already occurred. Loss of consciousness (or even a lapse in orientation) while driving could potentially have devastating consequences. Thus, it was generally felt that driving by patients who had an ICD should be restricted so as to avoid possible injury to either themselves or others. Patients with ICDs were required to wait at least six months before being allowed to drive as it was felt that the risk of recurrence of VT or VF gradually diminished over time to an acceptable level at six months. Over the years, in addition to the expansion in indications for implantation there have been advances in ICD technology, as well as the publication of long-term observational studies that have allowed us to risk-stratify various patient cohorts. The dependence on motor vehicles for day-to-day activities has also increased dramatically. These advances in technology and lifestyle changes have forced both patients and physicians to re-address the issue of driving restrictions.
By today’s standards, the original devices were simplistic: they usually required up to 15 seconds to detect, charge, and shock a potentially lethal arrhythmia. In addition, the early ICDs lacked the ability to provide back-up pacing. Given these limitations, it was not unusual for a patient to have a near-syncopal or syncopal episode when experiencing an ICD discharge. Since their original development over 20 years ago, ICD technology has evolved significantly. Devices are now placed transvenously without the need for extensive surgical procedures, are programmable, and incorporate features such as biphasic waveforms, back-up and anti-tachycardiac pacing, enhanced arrhythmia recognition, and much faster charge times. These developments have made placement comparatively easy and have markedly improved their effectiveness and efficiency in detecting and terminating tachyarrhythmias. These enhancements have facilitated the expansion of the use of ICDs from sudden death survivors to prophylactic placement in individuals who are at a high risk for sudden death.
This rapid expansion of ICD use has led to renewed interest in the issue of driving by patients who have received an ICD. Expert panels that were convened to address the issue initially suggested that a patient who had received an ICD after surviving an episode of sudden death (or a patient who had received an ICD shock for an episode of VT or fibrillation) should not drive for a period of at least six months after implantation.1 The basis for this recommendation was the observation that the likelihood of experiencing another event could be represented by a descending exponential curve, with the highest risk for a recurrence being the period immediately following an event. Following a period of three months, the curve significantly flattens, and at six months it is completely flat.
However, the years following the development of these guidelines saw the rise of ICDs used for prophylactic purposes, where the risk for experiencing a shock was far lower than that of the previous ICD population. A second set of guidelines was then issued concerning these patients, which recommended that driving needed to be restricted only for a period of time sufficient to allow the implantation wound to heal (commonly felt to be around one week).2
The principal problem with all of these recommendations was that they were significantly hampered by the relative dearth of good data available for assessing the actual risk for experiencing an ICD shock while operating a motor vehicle. Driving is considered to be one of the more stressful activities a person encounters in day-to-day life. The associated increase in catecholamine levels noted to occur while driving would intuitively seem to predispose patients to a higher risk for ventricular tachyarrhythmias. However, the actual incidence of and causal relationship between driving and ICD shocks have never been fully studied.
In the Antiarrhythmics Versus Implantable Defibrillators3 (AVID) study, approximately 8% of patients reported having experienced ICD shocks while driving. Although this was an interesting observation, it did not prove a causal relationship between the two. Another major problem was that many patients simply ignored their doctor’s advice regarding driving, as being unable to drive often represented a significant hardship. Indeed, in much of the US today, the inability to drive places significant limitations on an individual’s potential for either employment or education, and renders them for the most part ‘functionally disabled.’ Finally, the risk for sudden cardiac death in the patient population receiving an ICD for primary prophylaxis—although higher than the general population—is far lower than for sudden cardiac death survivors. Thus, restrictions in driving after implantation of prophylactic ICDs in such patients appeared to be unduly excessive.
The situation has improved following the publication of the Triggers of Ventricular Arrhythmia (TOVA)4 study in 2007. This was a prospective multicenter cohort study that evaluated both the driving habits and frequency of ICD discharges in a group of 1,188 patients with ICDs implanted in both sudden cardiac death survivors and for primary prophylaxis in high-risk groups in accordance with the 1998 American College of Cardiology (ACC)/American Heart Association (AHA) guidelines for ICD implantation. The study was designed to compare the risk for ICD shocks during and up to 60 minutes after an episode of driving with the risk for ICD shocks during other activities. Of the patients included in the study, approximately 80% said they drove a car at least once per week, and 75% of patients with recent implants reported that they drove at least once daily, despite recommendations at that time to avoid driving for the first six months after device implantation. Patients who had received an ICD for primary prophylaxis were more likely to continue driving after implantation than those who received devices after an episode of sudden cardiac death.
During an average follow-up period of 562 days, patients reported experiencing a total of 414 ICD shocks, of which 324 (74.6%) were for VT and/or VF. This corresponded to a person suffering a shock within one hour of driving, occurring at a frequency of approximately one episode per 25,116 person-hours of driving. Interestingly, almost 10% of these patients received three to four shocks, and about 6% received more than four shocks.
Due to the lack of information on exposure to driving, not all episodes of ICD shocks could be included in the final analyses. Of the 44 shocks confirmed to have occurred during and within 60 minutes of driving, seven episodes occurred during driving, 30 occurred in the first 30 minutes after driving, and seven episodes occurred in the following 30 minutes after driving. Of particular note was the fact that of the seven patients in the group who experienced an ICD shock while driving, none reported having experienced light-headedness or syncope, and only one of these episodes resulted in a motor vehicle accident. The study concluded that there was a significant increase in the risk for ICD shocks in the first 30 minutes after driving a motor vehicle, but the increase in risk during driving and in the period after the first 30 minutes was not significant.
In the TOVA study, although the majority of ICD discharges occurred after driving rather than during it, the reasons for this were not apparent. However, there was speculation that either exposure to particulate matter while driving or autonomic nervous system changes that occurred in the aftermath of driving may have played a role. There were some important limitations to the study. Principal among these was that it was an observational study that was not intended to demonstrate causality. Also, the data concerning driving were limited to non-anonymous self-reporting by patients. Other studies have shown that patients are far less apt to report episodes when they suspect that the information may be used to restrict their ability to operate a motor vehicle. This would suggest that under-reporting may have occurred to some extent. Another potentially compounding factor is that patients in the TOVA study who have resumed driving may have been significantly healthier than the average patient who undergoes ICD placement.
Where do we go from here? Given the sum total of information currently available, it would appear prudent to continue to follow the most recent set of AHA guidelines in addition to any and all federal, state, and local requirements concerning the operation of a motor vehicle when an individual has an ICD.2 Continued studies will be necessary to help better define the exact risks that patients with an ICD pose to themselves and others, and to evolve guidelines that are just and adequate for all concerned.