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Circulation. 2018;138:e272–e391. DOI: 10.1161/CIR.0000000000000549 September 25, 2018 e281 CLINICAL STATEMENTS AND GUIDELINES

ers, and some antiarrhythmic medications may relieve symptoms of palpitations.S2.2.2-18 PVCs that occur during an exercise test are associated with a higher risk of death.S2.2.2-19 In 1 study, PVCs that occur during recovery are a stronger predictor of death than PVCs occurring only during exercise.S2.2.2-20 However, PVCs are common in trained athletes who have palpitations, in whom there does not appear to be increased risk of death based on studies of small numbers of athletes, at least in those without other cardiovascular abnormalities.S2.2.2-21,S2.2.2-22 Complex PVCs may not represent a benign finding in endurance athletes. An electrophysiological study may be needed to assess patients’ arrhythmogenic risk.S2.2.2-22 Very frequent PVCs, >10 000 to 20 000 a day, can be associated with depressed LV function in some patients that is reversible with control of the PVCs, and has been referred to as PVC-induced cardiomyopathy.S2.2.2-23,S2.2.2-24 (See also Section 8.5. PVC-Induced Cardiomyopathy.) Very rarely, idiopathic PVCs from the outflow tract may trigger malignant VA in patients without structural heart disease.S2.2.2-25,S2.2.2-26

2.1.2 VT and VF During ACS

Approximately half of patients with out-of-hospital cardiac arrest with the first rhythm identified as VF and who survive to hospital admission have evidence of acute MI (AMI).S2.2.2-27 Of all out-of-hospital cardiac arrests, >50% will have significant coronary artery lesions on acute coronary angiography.S2.2.2-27 Of patients hospitalized with AMI, 5% to 10% have VF or sustained VT prior to hospital presentation, and another 5% will have VF or sustained VT after hospital arrival, most within 48 hours of admission. A study of patients with non–ST-elevation ACS who underwent cardiac catheterization within 48 hours found VT/VF in 7.6% of patients, with 60% of those events within 48 hours of admission.S2.2.2-28 Accelerated idioventricular rhythm is a common arrhythmia in patients with acute MI, including patients with ST-segment elevation MI undergoing primary percutaneous coronary intervention (PCI). Accelerated idioventricular rhythm is more closely related to the extent of infarction than to reperfusion itself.S2.2.2-29 Sustained VA that occurs in the setting of an ACS is more often polymorphic VT or VF than monomorphic VT. Risk factors for VT/VF include prior history of hypertension, prior MI, ST-segment changes at presentation, and chronic obstructive pulmonary disease.S2.2.2-30 A nationwide Danish study found that 11.6% of patients with ST-segment elevation MI who underwent PCI had VF prior to the PCI, and that VF was associated with alcohol consumption, preinfarction angina, anterior infarct location, and complete coronary occlusion at the time of coronary angiography.S2.2.2-31 In a select group of patients undergoing primary PCI in a clinical trial, 5.7% developed sustained VT or VF, with two thirds of these events occurring prior to the end of the catheterization, and 90% within 48 hours from the procedure. VT or VF after primary PCI was associated with lower blood pressure, higher heart rate, poor coronary flow at the end of the procedure, and incomplete resolution of ST elevation.S2.2.2-32 Importantly, and in contrast to some earlier studies, VT or VF at any time was associated with a substantially higher risk of death within 90 days. Late VT or VF (after 48 hours of hospital presentation) was associated with a higher risk of death than early VT or VF (within 48 hours of hospital presentation).S2.2.2-33

2.1.3. Sustained VT and VF Not Associated With ACS Patients with structural heart disease are at an increased risk for sustained VT and VF. Sustained VT that is not associated with an ACS is often monomorphic as it is usually due to scar-related reentry, but it may degenerate to VF.S2.2.2-34 The risk and predictors of VT in patients with structural heart disease depend on the type, severity, and duration of structural heart disease, increasing with the severity of ventricular dysfunction and the presence of symptomatic HF. Monomorphic VT occurring in the absence of structural heart disease is commonly referred to as idiopathic VT and is often due to an automatic focus in a characteristic location, giving rise to typical electrocardiographic appearances. Polymorphic VT and VF occurring in the absence of structural heart disease are rare and may be due to a cardiac channelopathy,S2.2.2-35,S2.2.2-36 medication-induced long QT syndrome,S2.2.2-36 or they may be idiopathic.S2.2.2-37,S2.2.2-38

2.2 Sudden Cardiac Death

2.2.1 Incidence of SCD

SCA and its most common consequence, SCD, constitute major public health problems, accounting for approximately 50% of all cardiovascular deaths,S2.2.2-1,S2.2.2-39 with at least 25% being first symptomatic cardiac events.S2.2.2-1,S2.2.2-40,S2.2.2-41 In addition, analyses of the magnitude of SCD are limited, in part because of the broad range of estimates of the risk based on different epidemiological methods.S2.2.2-42 During the past 20 to 30 years, SCD accounted for approximately 230 000 to 350 000 deaths per year in the United States, with a range of  <170 000 to >450 000, depending on epidemiological methods, data sources, and inclusion criteria.S2.2.2-41,S2.2.2-43 The lowest of these extremes came from national extrapolation of data from specific local programs, while the highest rates included noncardiac causes of sudden death such as pulmonary embolism or intracranial bleeding. The mid-range numbers were largely based

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