Patients younger than age 40 years with unexplained SCD, unexplained near drowning, or recurrent exertional syncope, who do not have ischemic or other structural heart disease, should be evaluated for inherited arrhythmia syndromes. Additionally, unexplained premature death (age <35 years) or sudden death in a first-degree family member (age <40 years) should raise suspicion for an inherited arrhythmia syndrome and prompt referral to a cardiovascular specialist, with genetic counseling and genetic testing as indicated by clinical findings. The diagnosis of inherited arrhythmia syndromes can be complicated because of variable penetrance and expressivity of these disorders. Characteristic findings and treatments for these syndromes are reviewed in Table 20.
Catecholaminergic polymorphic VT is a rare disorder characterized by intracellular calcium overload, polymorphic ventricular arrhythmias, and cardiac arrest. The arrhythmias are usually triggered by high-adrenergic states, including strong emotion and exercise. These arrhythmias can also be provoked with epinephrine infusion. β-Blocker therapy and ICD placement are treatments. Patients with catecholaminergic polymorphic VT should avoid exercise.
Early repolarization syndrome should be strongly suspected in patients with unexplained VF arrest, particularly when provoked during exercise. Early repolarization (J-point elevation) is a common and usually benign ECG finding; however, the presence of inferior and lateral early repolarization of more than 1 mm in a patient with VF and/or cardiac arrest should be considered early repolarization syndrome. ICD implantation is indicated in patients with VF or cardiac arrest.
Hypertrophic cardiomyopathy or arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) can often present as SCD in young persons. Hypertrophic cardiomyopathy and arrhythmic risk stratification are discussed in Myocardial Disease. Most patients with ARVC/D present between puberty and young adulthood; however, it can also occur in older age. Patients with ARVC/D usually present with frequent ventricular ectopy and/or monomorphic VT, although severe cases can present with heart failure. The diagnosis is established by ECG abnormalities, family history, the presence of arrhythmias, and structural abnormalities of the right ventricle. Cardiac magnetic resonance imaging can demonstrate enlargement (segments of poorly contracting heart muscle), focal aneurysms, and wall motion abnormalities in the right ventricle (hypokinesis). ARVC/D is usually progressive, and patients with ARVC/D should abstain from vigorous exercise. Patients with ARVC/D and cardiac arrest or risk factors (nonsustained VT, inducible VT) should be offered ICD implantation. β-Blockers are first-line therapy for ventricular arrhythmia, although antiarrhythmic therapy with sotalol or amiodarone or catheter ablation is often required for recurrent VT.
SCD is defined as an instantaneous fatal event or collapse within 1 hour of symptom onset in an apparently healthy person. In patients in whom death was unwitnessed, SCD is considered to have occurred if the patient was known to be alive and well within the past 24 hours. VT and VF are the most common causes of SCD.
In the United States, more than 350,000 episodes of SCD occur each year. The annual risk for SCD is 1:1000 in the general population. The highest incidence occurs in patients with pre-existing structural heart disease, although left ventricular function is normal in most patients experiencing SCD. Risk factors include heart failure, diminished left ventricular function, previous myocardial infarction, unexplained syncope, left ventricular hypertrophy, nonsustained ventricular arrhythmia, chronic kidney disease, and sleep apnea. It is important to distinguish between myocardial infarction and SCD when a family history of cardiac disease is obtained.
Cardiac arrest necessitates immediate cardiopulmonary resuscitation (CPR) and advanced cardiac life support. Basic life support guidelines emphasize the importance of immediate, rapid, and sustained chest compressions in caring for individuals with cardiac arrest. Following activation of the emergency medical system and request for an automated external defibrillator, the patient's pulse should be checked immediately. Chest compressions should be initiated if no definite pulse is detected within 10 seconds. High-quality CPR (30 compressions and 2 breaths per cycle if no advanced airway is present) includes adequate depression of the lower sternum at a rate of at least 100 compressions per minute with adequate time for chest recoil. Interruptions in chest compressions should be minimized. Once an airway has been secured, breaths should be delivered at a rate of 1 breath per 6 seconds (10/min) to avoid breath stacking and increased thoracic pressure, which impedes cardiac output. Defibrillation should occur as soon as possible in patients with a shockable rhythm because time to defibrillation is an important determinant of the likelihood of survival to hospital discharge.
According to the 2020 American Heart Association advanced life support guidelines, the presence or absence of a shockable rhythm guides management after CPR has been initiated. In patients with asystole or pulseless electrical activity, CPR is continued with reassessment of rhythm status for a shockable rhythm every 2 minutes. Epinephrine should be administered intravenously to increase coronary perfusion. Vasopressin provides no advantages over epinephrine. Likewise, atropine should not be used for the treatment of asystole or pulseless electrical activity arrest. Any reversible causes (such as tamponade) should be identified and treated.
Patients with VT/VF should be shocked, followed by immediate resumption of CPR and reassessment of the rhythm in 2 minutes. Epinephrine should be administered after the second shock and every 3 to 5 minutes thereafter. Amiodarone should be given as a bolus if VT/VF continues despite three shocks and epinephrine administration. A second dose of amiodarone can be given if VT/VF persists.
Patients with suspected opioid overdose should receive naloxone, but emergency response systems should be requested immediately and should not be dependent on an observed response to the naloxone.
ICDs have demonstrated efficacy in the primary and secondary prevention of SCD. Patients with sustained ventricular arrhythmias (>30 seconds) or cardiac arrest without a reversible cause have a class I recommendation for secondary prevention ICD placement. Patients with heart failure who meet specific criteria should undergo ICD placement for primary prevention (see Heart Failure). Patients with heart failure and interventricular conduction defects (predominantly left bundle branch block) often benefit from cardiac resynchronization therapy or cardiac resynchronization therapy in combination with a defibrillator.
Patients with ICDs need to avoid strenuous upper extremity exercises, including weight lifting, because of concern for lead stress and subsequent fracture. Inappropriate detection of VT/VF and shocks can result from electromagnetic interference; therefore, patients need to avoid devices that pose risks, such as arc welding equipment and high-voltage machinery. Patients with ICDs who are undergoing invasive procedures or surgery should be evaluated by their electrophysiologist for device reprogramming recommendations.
In the past, ICDs were implanted almost exclusively by using a transvenous approach. New techniques allow for implantation of defibrillators in the lateral chest at the midaxillary line adjacent to the heart with tunneling of the lead under the skin next to the sternum. Subcutaneous defibrillators have several advantages, including reduced risk for device infection.
Device infections have many different forms, ranging from pocket infections to endocarditis. Most infections are due to Staphylococcus epidermidis and Staphylococcus aureus. Symptoms of cardiac device infection include fever, chills, malaise, lassitude, and failure to thrive, particularly in the elderly.
Physical examination of the pocket may reveal erythema, swelling, drainage, or wound dehiscence. In patients suspected of having device infection, several blood cultures, an erythrocyte sedimentation rate, and a C-reactive protein level should be obtained. A transesophageal echocardiogram should be obtained to evaluate for intracardiac or lead vegetations. Aspirating the device pocket is never indicated because this can damage the leads or introduce infection in a sterile or uninfected pocket. PET-CT can also identify infection of the device pocket or leads if other testing is inconclusive.
Treatment of cardiac device infection includes complete extraction of all hardware, debridement of the pocket, sustained antibiotic therapy, and reimplantation at a new location after infection has been eradicated.