presentation of AIVR can vary, but given the relatively slow rate and transient nature patients are frequently asymptomatic, although some patients may notice palpitations or lightheadedness, and there may be some associated hypotension if the rate results in a drop in cardiac output. (See 'Accelerated idioventricular rhythm' above.) VT is considered sustained if it lasts more than 30 seconds or is associated with hemodynamic collapse requiring prompt therapy. The clinical presentation may include palpitations, worsening ischemic symptoms due to the elevated heart rate, and hemodynamic compromise or collapse. Patients with faster tachycardias and worse LV systolic function are less likely to tolerate the arrhythmia. (See 'Monomorphic ventricular tachycardia' above.) Polymorphic VT (in the absence of QT prolongation of a sinus complex) is much less common in the setting of an acute MI, but when polymorphic VT occurs early after an acute MI, usually within the first 12 hours after the onset of symptoms, it is typically associated with symptoms or signs of recurrent myocardial ischemia. Patients with polymorphic VT and symptoms typically present with one or more of the following: sudden cardiac arrest, syncope/presyncope, "seizure-like" activity, or palpitations. Importantly, polymorphic VT that persists for more than 10 to 15 seconds often degenerates into VF. (See 'Polymorphic VT' above.) VF is the most frequent mechanism of SCD. It is a rapid, disorganized ventricular arrhythmia, resulting in no uniform ventricular contraction, no cardiac output, and no recordable blood pressure. As such, patients invariably present with sudden collapse (syncope and/or sudden cardiac arrest). (See 'Ventricular fibrillation' above.) 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Long-term recording of cardiac arrhythmias with an implantable cardiac monitor in patients with reduced ejection fraction after acute myocardial infarction: the Cardiac Arrhythmias and Risk Stratification After Acute Myocardial Infarction (CARISMA) study. Circulation 2010; 122:1258. Topic 1060 Version 38.0 https://www.uptodate.com/contents/ventricular-arrhythmias-during-acute-myocardial-infarction-incidence-mechanisms-and-clinical-features/print 16/22 7/5/23, 11:18 AM Ventricular arrhythmias during acute myocardial infarction: Incidence, mechanisms, and clinical features - UpToDate GRAPHICS ECG 12-lead accelerated idioventricular rhythm 12-lead ECG showing idioventricular rhythm with AV dissociation and wide QRS complexes occurring at a rate faster than the sinus rate but slower than 100 bpm (hence not meeting the criteria for ventricular tachycardia). ECG: electrocardiogram. Graphic 118943 Version 2.0 https://www.uptodate.com/contents/ventricular-arrhythmias-during-acute-myocardial-infarction-incidence-mechanisms-and-clinical-features/print 17/22 7/5/23, 11:18 AM Ventricular arrhythmias during acute myocardial infarction: Incidence, mechanisms, and clinical features - UpToDate 12-lead ECG sustained monomorphic VT The electrocardiogram (ECG) hallmark for the diagnosis of sustained monomorphic ventricular tachycardia (S is a wide complex tachycardia with the obvious presence of atrioventricular (AV) dissociation. AV dissociation suggested by the presence of fusion complexes (which reflect a supraventricular impulse coming from above AV node fusing with an impulse generated in the ventricle) or captured complexes (which reflect an impulse coming from above the AV node that depolarizes the ventricles when they are no longer refractory but befor next ventricle-generated complex). Beats 12, 17, and 22 on this ECG likely represent capture beats. Graphic 111254 Version 1.0 https://www.uptodate.com/contents/ventricular-arrhythmias-during-acute-myocardial-infarction-incidence-mechanisms-and-clinical-features/print 18/22 7/5/23, 11:18 AM Ventricular arrhythmias during acute myocardial infarction: Incidence, mechanisms, and clinical features - UpToDate Single lead electrocardiogram (ECG) showing polymorphic ventricular tachycardia (VT) This is an atypical, rapid, and bizarre form of ventricular tachycardia that is characterized by a continuously changing axis of polymorphic QRS morphologies. Graphic 53891 Version 5.0 https://www.uptodate.com/contents/ventricular-arrhythmias-during-acute-myocardial-infarction-incidence-mechanisms-and-clinical-features/print 19/22 7/5/23, 11:18 AM Ventricular arrhythmias during acute myocardial infarction: Incidence, mechanisms, and clinical features - UpToDate ECG 12-lead ventricular fibrillation 12-lead ECG showing course ventricular fibrillation. ECG: electrocardiogram. Graphic 118944 Version 1.0 https://www.uptodate.com/contents/ventricular-arrhythmias-during-acute-myocardial-infarction-incidence-mechanisms-and-clinical-features/print 20/22 7/5/23, 11:18 AM Ventricular arrhythmias during acute myocardial infarction: Incidence, mechanisms, and clinical features - UpToDate Killip classification of acute myocardial infarction Class I No evidence of heart failure Class II Findings consistent with mild to moderate heart failure (eg, S3 gallop, lung rales less than one-half way up the posterior lung fields, or jugular venous distension) Class III Overt pulmonary edema Class IV Cardiogenic shock Graphic 65592 Version 7.0 https://www.uptodate.com/contents/ventricular-arrhythmias-during-acute-myocardial-infarction-incidence-mechanisms-and-clinical-features/print 21/22 7/5/23, 11:18 AM Ventricular arrhythmias during acute myocardial infarction: Incidence, mechanisms, and clinical features - UpToDate Contributor Disclosures Philip J Podrid, MD, FACC No relevant financial relationship(s) with ineligible companies to disclose. James Hoekstra, MD No relevant financial relationship(s) with ineligible companies to disclose. Nisha Parikh, MD, MPH No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/ventricular-arrhythmias-during-acute-myocardial-infarction-incidence-mechanisms-and-clinical-features/print 22/22