**5.2 Bridge to cardiac transplantation/left ventricular assist device**

Heart transplantation or the use of a left ventricular assist device is the only potentially long-term therapeutic option for some patients, but during the waiting period, patients are at high risk for dangerous arrhythmias and may have other comorbid conditions as well. In a study of 121 patients prescribed with the WCD while waiting to receive a donor heart (mean 127 days), 7 patients (5.8%) were shocked appropriately, and all survived [23]. Two inappropriate therapy deliveries occurred deemed to be caused by rapid ventricular response to atrial fibrillation. In this study, two patients died of asystole during the waiting period; asystole is not treated by the WCD because it lacks a pacing capability [23].

#### **5.3 Low ejection fraction in reimbursement-mandated waiting period**

In the USA and other parts of the world, patients with an ejection fraction ≤35% may be required by reimbursement authorities and guidelines to wait out a specific period of time before an ICD may be implanted; these time periods range from 30 to 90 days. This includes patients with cardiomyopathy.

#### **5.4 NYHA Class IV heart failure**

This group of patients meets the requirements for Class IV heart failure but is not otherwise indicated or qualified to receive an ICD. Some of these patients may be waiting for cardiac transplantation, while others may be contraindicated for ICD implant for other reasons (frailty, comorbidities, patient refusal, and so on). The Study of Wearable Cardioverter Defibrillator in Advanced Heart-Failure Patients (SWIFT) was a prospective study of 75 advanced heart failure patients at 2 centers. All patients had low ejection fraction (21.5 10.4% at baseline), were prescribed a WCD, and were followed up for 3 months. In the SWIFT study, 66% of patients had nonischemic cardiomyopathy. Over the course of the study, eight arrhythmic events occurred in five patients, including three episodes of nonsustained VT and one episode of polymorphic VT; all episodes were appropriately treated. No patient in the study received inappropriate therapy delivery. At the end of the study, 28% of patients went on to permanent device implantation, and the cumulative mortality rate at 3 years in this population was 21% for patients with nonischemic cardiomyopathy compared to 21% for those with ischemic cardiomyopathy [19].

both, assuming linear mortality rates in the first 3 months, based on DINAMIT study data) [54]. This imposes a "waiting period" on myocardial infarction patients before a device may be implanted and during which time they may be especially vulnerable to SCD. For many patients and clinicians, this creates a tension between abiding by evidence-based guidelines and meeting reimbursement requirements yet still providing reasonable means to rescue post-AMI patients from SCD [6]. The WCD has been proposed as an interim device for this population during this waiting period before a permanent ICD may be implanted. Further complicating this picture is the fact that some myocardial infarction patients will recover left ventricular function in the weeks following their heart attack to the point that they do not require an ICD at all. Thus, it may be argued that for these patients, the use of the WCD may be to provide possible rescue during recovery from the myocardial

It has been observed that myocardial infarction patients prescribed a WCD and shocked appropriately and successfully to convert a ventricular tachyarrhythmia nevertheless have high mortality rates. While this remains to be elucidated, it suggests that either ventricular tachyarrhythmias in the immediate aftermath of a heart attack are indicative of poor outcomes or the arrhythmia and/or the rescue shock has a destabilizing effect on the patient [55]. The Valsartan in acute myocardial infarction trial (VALIANT) evaluated 14,609 myocardial infarction patients with low ejection fraction for SCD. VALIANT reported myocardial infarction patients with an ejection fraction ≤30% had a mortality of 2.3% per month in the first 30 days after the myocardial infarction (and that 83% of all patients who died of sudden unexpected death died within the first 30 days of hospital discharge). Every decrease of 5% in the ejection fraction was associated with a 21% increase in

The Vest Prevention of Early Sudden Death (VEST) trial found that in myocardial infarction patients with low ejection fractions (≤35%), the WCD did not significantly reduce arrhythmia-associated deaths compared to the control group who did not have a WCD [15]. The rates of arrhythmic death were 1.6% in the WCD and 2.4% in the control group (relative risk 0.67, 95% confidence interval, 0.37–1.21, p = 0.18) [15]. It must be noted in this connection that arrhythmic death can be challenging to adjudicate when the patient dies without a witness. However, even comparing all-cause mortality data did not provide a significant benefit for WCD

Compared to one SCD death per 1000 patient-years in the general population, hemodialysis patients face a 50-fold greater risk of arrhythmic death at 43 deaths per 1000 patient-years [57, 58]. Patients on hemodialysis present clinical challenges in that they are often comorbid and frequently geriatric, may be frail, and are prone to infections. End-stage renal disease and hemodialysis expose these patients to a very considerable risk of arrhythmic death, but many hemodialysis patients are not appropriate candidates for ICD therapy. Compared to historical data, the WCD has

Takotsubo cardiomyopathy, sometimes called "broken-heart syndrome," is a form of cardiomyopathy where the myocardium weakens and remodels. This

been associated with improved survival in renal failure patients [24].

infarction and to avoid unnecessary ICD implantation [6].

*The Wearable Cardioverter-Defibrillator DOI: http://dx.doi.org/10.5772/intechopen.90663*

SCD risk in the first 30 days after myocardial infarction [56].

patients over those who did not have a WCD [15].

**5.7 Renal failure**

**5.8 Other conditions**

**77**

*5.8.1 Takotsubo cardiomyopathy*

## **5.5 Ischemic and nonischemic cardiomyopathy**

Patients with ischemic cardiomyopathy may be indicated for a primary prevention ICD if they have an ejection fraction ≤35% and NYHA functional Class II or III or if they have an ejection fraction ≤30% with NYHA Class I [53]. Nonischemic cardiomyopathy covers a range of conditions that may include inflammatory, toxic, metabolic, genetic, or autoimmunological processes, and arrhythmic activity, including SCD, may be one of the first symptoms of nonischemic cardiomyopathy [5, 13]. Such patients typically fall into the reimbursement-mandated waiting period before a primary prevention ICD can be implanted, and many patients with recent-onset cardiomyopathy recover left ventricular ejection fraction and even experience reverse remodeling to the point that ICD implantation is unwarranted [5]. In cardiomyopathy patients, it is not clear if and how long patients should wait before ICD implantation is either deemed reasonable or unnecessary [5]. Ischemic cardiomyopathy patients may have higher rates of events than nonischemic cardiomyopathy patients [42]. Pharmacological therapy for cardiomyopathy may also improve the ejection fraction, and the WCD may be helpful as medical therapy is optimized [53].

In a retrospective single-center study of patients from June 2004 to May 2015, focus was placed on patients with newly diagnosed cardiomyopathy (254 nonischemic and 271 ischemic) [41]. Patients wore the WCD for a median of 61 days (interquartile range 25–102 days) and for a median of 22 h/day (17–23 h). The study produced 56.7 patient-years of data for nonischemic cardiomyopathy patients, during which no patients got appropriate shocks, but 1.2% (n = 3) were shocked inappropriately. There were 46.7 patient-years of data for ischemic cardiomyopathy, where 2.2% (n = 6) were shocked appropriately and two inappropriately (0.7%) [41].

#### **5.6 Acute myocardial infarction**

The role of defibrillation has been controversial in acute myocardial infarction (AMI) patients since the defibrillator in acute myocardial infarction trial (DINAMIT) reported that early ICD implantation failed to confer a mortality benefit in this arrhythmia-rich population [54]. Current guidelines recommend that following myocardial infarction, patients with compromised left ventricular function do not receive an ICD for a 3-month to 40-day waiting period, whether or not they have been revascularized [53]. In the weeks immediately following a myocardial infarction, patients are vulnerable to a number of potentially lethal conditions, many unrelated to ventricular tachyarrhythmias, so that the mortality rate for myocardial infarction patients with or without an ICD is roughly the same (7.2% for

#### *The Wearable Cardioverter-Defibrillator DOI: http://dx.doi.org/10.5772/intechopen.90663*

be waiting for cardiac transplantation, while others may be contraindicated for ICD implant for other reasons (frailty, comorbidities, patient refusal, and so on). The Study of Wearable Cardioverter Defibrillator in Advanced Heart-Failure Patients (SWIFT) was a prospective study of 75 advanced heart failure patients at 2 centers. All patients had low ejection fraction (21.5 10.4% at baseline), were prescribed a WCD, and were followed up for 3 months. In the SWIFT study, 66% of patients had nonischemic cardiomyopathy. Over the course of the study, eight arrhythmic events occurred in five patients, including three episodes of nonsustained VT and one episode of polymorphic VT; all episodes were appropriately treated. No patient in the study received inappropriate therapy delivery. At the end of the study, 28% of patients went on to permanent device implantation, and the cumulative mortality rate at 3 years in this population was 21% for patients with nonischemic cardio-

myopathy compared to 21% for those with ischemic cardiomyopathy [19].

Patients with ischemic cardiomyopathy may be indicated for a primary prevention ICD if they have an ejection fraction ≤35% and NYHA functional Class II or III or if they have an ejection fraction ≤30% with NYHA Class I [53]. Nonischemic cardiomyopathy covers a range of conditions that may include inflammatory, toxic, metabolic, genetic, or autoimmunological processes, and arrhythmic activity, including SCD, may be one of the first symptoms of nonischemic cardiomyopathy [5, 13]. Such patients typically fall into the reimbursement-mandated waiting period before a primary prevention ICD can be implanted, and many patients with recent-onset cardiomyopathy recover left ventricular ejection fraction and even experience reverse remodeling to the point that ICD implantation is unwarranted [5]. In cardiomyopathy patients, it is not clear if and how long patients should wait before ICD implantation is either deemed reasonable or unnecessary [5]. Ischemic cardiomyopathy patients may have higher rates of events than nonischemic cardiomyopathy patients [42]. Pharmacological therapy for cardiomyopathy may also improve the ejection fraction, and the WCD may be helpful as medical therapy is

In a retrospective single-center study of patients from June 2004 to May 2015,

nonischemic and 271 ischemic) [41]. Patients wore the WCD for a median of 61 days (interquartile range 25–102 days) and for a median of 22 h/day (17–23 h). The study produced 56.7 patient-years of data for nonischemic cardiomyopathy patients, during which no patients got appropriate shocks, but 1.2% (n = 3) were shocked inappropriately. There were 46.7 patient-years of data for ischemic cardiomyopathy, where 2.2% (n = 6) were shocked appropriately and two inappropriately (0.7%) [41].

The role of defibrillation has been controversial in acute myocardial infarction

(DINAMIT) reported that early ICD implantation failed to confer a mortality benefit in this arrhythmia-rich population [54]. Current guidelines recommend that following myocardial infarction, patients with compromised left ventricular function do not receive an ICD for a 3-month to 40-day waiting period, whether or not they have been revascularized [53]. In the weeks immediately following a myocardial infarction, patients are vulnerable to a number of potentially lethal conditions, many unrelated to ventricular tachyarrhythmias, so that the mortality rate for myocardial infarction patients with or without an ICD is roughly the same (7.2% for

focus was placed on patients with newly diagnosed cardiomyopathy (254

(AMI) patients since the defibrillator in acute myocardial infarction trial

**5.5 Ischemic and nonischemic cardiomyopathy**

optimized [53].

*Sudden Cardiac Death*

**76**

**5.6 Acute myocardial infarction**

both, assuming linear mortality rates in the first 3 months, based on DINAMIT study data) [54]. This imposes a "waiting period" on myocardial infarction patients before a device may be implanted and during which time they may be especially vulnerable to SCD. For many patients and clinicians, this creates a tension between abiding by evidence-based guidelines and meeting reimbursement requirements yet still providing reasonable means to rescue post-AMI patients from SCD [6]. The WCD has been proposed as an interim device for this population during this waiting period before a permanent ICD may be implanted. Further complicating this picture is the fact that some myocardial infarction patients will recover left ventricular function in the weeks following their heart attack to the point that they do not require an ICD at all. Thus, it may be argued that for these patients, the use of the WCD may be to provide possible rescue during recovery from the myocardial infarction and to avoid unnecessary ICD implantation [6].

It has been observed that myocardial infarction patients prescribed a WCD and shocked appropriately and successfully to convert a ventricular tachyarrhythmia nevertheless have high mortality rates. While this remains to be elucidated, it suggests that either ventricular tachyarrhythmias in the immediate aftermath of a heart attack are indicative of poor outcomes or the arrhythmia and/or the rescue shock has a destabilizing effect on the patient [55]. The Valsartan in acute myocardial infarction trial (VALIANT) evaluated 14,609 myocardial infarction patients with low ejection fraction for SCD. VALIANT reported myocardial infarction patients with an ejection fraction ≤30% had a mortality of 2.3% per month in the first 30 days after the myocardial infarction (and that 83% of all patients who died of sudden unexpected death died within the first 30 days of hospital discharge). Every decrease of 5% in the ejection fraction was associated with a 21% increase in SCD risk in the first 30 days after myocardial infarction [56].

The Vest Prevention of Early Sudden Death (VEST) trial found that in myocardial infarction patients with low ejection fractions (≤35%), the WCD did not significantly reduce arrhythmia-associated deaths compared to the control group who did not have a WCD [15]. The rates of arrhythmic death were 1.6% in the WCD and 2.4% in the control group (relative risk 0.67, 95% confidence interval, 0.37–1.21, p = 0.18) [15]. It must be noted in this connection that arrhythmic death can be challenging to adjudicate when the patient dies without a witness. However, even comparing all-cause mortality data did not provide a significant benefit for WCD patients over those who did not have a WCD [15].

#### **5.7 Renal failure**

Compared to one SCD death per 1000 patient-years in the general population, hemodialysis patients face a 50-fold greater risk of arrhythmic death at 43 deaths per 1000 patient-years [57, 58]. Patients on hemodialysis present clinical challenges in that they are often comorbid and frequently geriatric, may be frail, and are prone to infections. End-stage renal disease and hemodialysis expose these patients to a very considerable risk of arrhythmic death, but many hemodialysis patients are not appropriate candidates for ICD therapy. Compared to historical data, the WCD has been associated with improved survival in renal failure patients [24].

#### **5.8 Other conditions**

#### *5.8.1 Takotsubo cardiomyopathy*

Takotsubo cardiomyopathy, sometimes called "broken-heart syndrome," is a form of cardiomyopathy where the myocardium weakens and remodels. This

condition is potentially reversible, but while patients experience the cardiomyopathy, they are at risk for potentially life-threatening ventricular tachyarrhythmias, and some develop concomitant QT interval prolongation, further increasing their risk for arrhythmia [5]. In a study based on all data from the USA involving WCD wear from 2007 through 2012, a total of 102 takotsubo patients were identified by the ICD-9 code 429.83. This population was overwhelmingly female (89%) with an initial ejection fraction of 27 6% who wore the WCD for a mean duration of 44 31 days with a mean follow-up of 440 374 days. During the WCD wear time, 2% of patients (n = 2) received an appropriate shock, 1% (n = 1) received two inappropriate shocks, and 2% (n = 2) suffered bradyarrhythmias that required pacing. Two patients in the study died (one asystole and one from an arrhythmia while not wearing the WCD) [59].

**6.1 Pediatric patients**

*The Wearable Cardioverter-Defibrillator DOI: http://dx.doi.org/10.5772/intechopen.90663*

**6.2 Cancer patients**

other reasons [65].

**79**

**6.3 Geriatric patients**

Guidance is available to schools and teachers for children prescribed the WCD. In particular, it is important that educators realize that unlike the automatic external defibrillator systems available in many schools, the WCD will detect arrhythmias and treat them without any bystander intervention [62, 63]. Children seem to adjust well to the WCD. In a study of 231 pediatric WCD patients between the ages of 8 and 17 years monitored a median of 39 days with daily wear time around 21 h/day,

a step-counter accelerometer device reported that activity levels for these

children increased significantly over baseline in the first 3 weeks after getting the WCD (p < 0.001) [64]. This suggests that the WCD does not inhibit or curtail the children's activities and may help them achieve recommended levels of daily exercise.

Some patients with cancer may be at elevated risk for dangerous arrhythmias because of chemotherapy-induced cardiomyopathy or long QT syndrome caused by drugs but may be contraindicated for device implant because of their malignancy or

The prevalence of cardiovascular disease is high in the geriatric population, but there may be reluctance to consider an older patient for WCD therapy, in particular because it may be uncomfortable or feel restricting to them. In a large study of 1732 patients with ischemic and nonischemic cardiomyopathy, patients were grouped by age into younger (<65 years) and older groups (≥65 years). The older group (n = 722) wore the WCD more hours per day (median 22.8 vs. 22.3, p < 0.001) and

had higher rates of events (31.95 vs. 9.82, p = 0.027). Younger patients with

in approximately 0.4–3.0% of patients [6, 18, 33, 43]. See **Table 1**.

The WCD delivers rescue shock therapy only and has no pacing capability. Asystole, a recognized risk factor for dangerous ventricular tachyarrhythmias, may occur in patients with compromised cardiovascular function, such as low ejection fraction. While an ICD can detect and offer pacing support during an asystole

both age groups tolerated WCD therapy well [34].

**7. Appropriate and inappropriate therapy**

nonischemic cardiomyopathy had a higher rate of atrial arrhythmias (150.1 vs. 74.9, p = 0.055), and more following WCD therapy, a greater number of older than younger patients got a permanent ICD (41.8% vs. 36.5%, p = 0.034). Patients in

The WCD has been shown to deliver appropriate high-energy therapy to convert dangerous ventricular tachyarrhythmias. In a postmarket registry of 3569 WCD patients (mean duration wear was 52.6 69.9 days), first shock success occurred in 99% of cases (79/80) for all episodes of conscious VT/VF and in 100% of cases (n = 76) of unconscious VT/VF [33]. Because the WCD is an external device, it is far more exposed to sources of electromagnetic interference (noise) than implanted devices, which may result in oversensing, inappropriate arrhythmia detection, and inappropriate therapy delivery. Patients are signaled about 30 s prior to therapy delivery and may abort the shock by pressing two buttons [39, 40]. For this reason, the rate of inappropriate therapy delivery with the WCD is relatively low, occurring

#### *5.8.2 Peripartum cardiomyopathy*

Peripartum cardiomyopathy results in left ventricular dysfunction that can predispose the patient to SCD. About half of these patients will recover significantly or entirely over the course of about 6 months even without intervention; however, some will not, and all are at high risk for arrhythmias during the course of the condition [5]. In a study of 12 consecutive women with peripartum cardiomyopathy observed at a single center (of whom seven wore the WCD), four episodes of VF occurred in three of the patients wearing the WCD, all of which were successfully terminated. One patient experienced numerous alarms for inappropriate shocks but was able to abort them so that no inappropriate shocks occurred. No deaths occurred. During therapy for heart failure, over the course of the 12-month followup, ejection fractions improved significantly from 24.0 11.8% at baseline to 46.6 7.6%. Patients with a lower ejection fraction at baseline improved more than those with a higher ejection fraction at baseline [60].

#### *5.8.3 Long QT syndrome*

Long QT syndrome (LQTS) is a heritable and potentially fatal cardiac channelopathy that exposes patients to the risk of SCD. LQTS patients are typically treated with beta blockade, left cardiac sympathetic denervation, and, in some cases, a permanent ICD. It is unclear what, if any, role the WCD might play for treating LQTS. A retrospective review of 1027 LQTS patients who were prescribed a WCD as a bridge to possible ICD implantation or other treatments found no inappropriate shocks that were administered by the WCD and only 1 patient received an appropriate shock to terminate VF [61]. Since LQTS is a lifelong condition, the WCD is not an optimal permanent solution in this population, but it may be helpful as newly diagnosed patients consider their therapeutic options or for LQTS patients on medical therapy who are entering high-risk periods of life, such as having to take a medication that might prolong their QT interval further or in postpartum women [61].

#### **6. Special populations**

The WCD is available in different sizes and has an elasticized waistband and adjustable straps, making it suitable for use in a variety of patients, including children. The role of the WCD in certain special populations is being addressed, but there is limited evidence about these groups.
