Ventricular Fibrillation

Introduction
Background

Ventricular fibrillation (VF) is the most commonly identified arrhythmia in cardiac arrest patients. This arrhythmia is a severe derangement of the heartbeat that usually ends in death within minutes unless corrective measures are promptly taken. The number of survivors after out-of-hospital cardiac arrest has increased with expansion of community-based emergency rescue systems, widespread use of automatic external defibrillators (AEDs), and increasing numbers of lay persons trained in bystander cardiopulmonary resuscitation (CPR).
Pathophysiology

VF occurs in a variety of clinical situations but is most often associated with coronary artery disease (CAD) and as a terminal event. VF may be due to acute myocardial infarction or ischemia, or it may occur in the setting of chronic infarct scar. Intracellular calcium accumulation, the action of free radicals, metabolic alterations, and autonomic modulation are some important influences on the development of VF during ischemia. Thrombolytic agents reduce the incidence of ventricular arrhythmias and inducible ventricular tachycardia (VT) after myocardial infarction (MI).

Cardiovascular events, including sudden cardiac death (SCD) from VF (but not asystole), most frequently occur in the morning and may be related to increased platelet aggregability. (Aspirin reduces the frequency of this form of mortality.) A spike in the number of SCDs appears to occur during the winter months.
VF can occur during any of the following conditions or situations:
Antiarrhythmic drug administration
Hypoxia
Ischemia
Atrial fibrillation
Very rapid ventricular rates in the preexcitation syndrome
Electrical shock administered during cardioversion
Electrical shock caused by accidental contact with improperly grounded equipment
Competitive ventricular pacing to terminate VT
Most prehospitalized patients with cardiac arrest (65-85%) have VF identified as the initial rhythm by emergency rescue personnel. Approximately 20-30% of patients from all documented sudden death events have bradyarrhythmia or asystole at the time of initial contact, indicating a terminal event from massive myocyte necrosis, pump failure, or VF progression to asystole. Only 7-10% have sustained VT as the initial rhythm on contact, and VT is associated with the best overall prognosis.
When documentation is available, it often shows that rapid VT precedes VF. In patients with ischemic heart disease, the most common form of VT is monomorphic, which arises from a reentrant focus.
In patients who survive an MI, it has been demonstrated that those with frequent premature ventricular contractions (PVCs), particularly complex forms such as multiform PVCs, short coupling intervals (R-on-T phenomenon), or VT (salvos of 3 or more ectopic beats), are at increased risk of sudden death. Even though many patients have anatomic and functional cardiac substrates that predispose them to develop ventricular arrhythmias, only a small percentage develop VF. The interplay among the regional ischemia, left ventricular (LV) dysfunction, and transient inciting events (eg, worsened ischemia, acidosis, hypoxemia, wall tension, drugs, metabolic disturbances) has been proposed to be the precipitator of VF.

Frequency
United States

SCD accounts for approximately 300,000 deaths per year in the United States, of which 75-80% are due to VF. More deaths are attributable to VF than to lung cancer, breast cancer, or AIDS. This represents an incidence of 0.08-0.16% per year in the adult population. VF is commonly the first expression of CAD and is responsible for approximately 50% of deaths from CAD, often within the first hour after the onset of an acute MI or coronary syndrome.

In several population-based studies, the incidence of out-of-hospital cardiac arrest has been noted as declining in the past 2 decades, but the proportion of sudden CAD deaths in the United States due to VF has not changed. A high incidence of VF occurs among certain population subgroups (eg, patients with congestive heart failure [CHF] with ejection fraction <30%, patients in the convalescent phase after MI, patients who survived cardiac arrest); unfortunately, only a small percentage of total VF events occur in these patients.

The time dependence of risk for VF has been noted in several studies, with an increased number of events in the first 6-24 months after surviving a major cardiovascular event. Recurrence of VF in survivors of cardiac arrest can be up to 30% in the first year.

International

The frequency of VF in industrialized Western nations is similar to that in the United States. The incidence of VF in other countries varies as a reflection of CAD prevalence in those populations. The trend toward increasing frequency of VF events in developing nations is thought to reflect a change in dietary and lifestyle habits.
Mortality/Morbidity

A witness is not present in up to 40% of the approximately 225,000 deaths attributed to VF in the United States each year. For most people who experience VF, survival depends on the presence of individuals who are competent in performing basic life support, rapid availability or arrival of personnel and apparatus for defibrillation and advanced life support, and transfer to a hospital.

Even under ideal circumstances, only an estimated 20% of patients who have out-of-hospital cardiac arrest survive to hospital discharge. In a study of out-of-hospital cardiac arrest survival in New York City, only 1.4% of patients survived to hospital discharge.1 Other studies in suburban and rural areas have indicated survival rates up to 35%.2 Placement of AEDs throughout communities and training people to use them has the potential to markedly improve outcomes from SCD.
Upon presentation to an emergency department (ED), the most important determinants of survival include (1) an unsupported systolic blood pressure (SBP) greater than 90 mm Hg, (2) a time from loss of consciousness to return of spontaneous circulation (ROSC) of less than 25 minutes, and (3) some degree of neurological responsiveness.
A major adverse outcome from a VF event is anoxic encephalopathy, which occurs in 30-80% of patients.
Race

Most data are inconclusive regarding racial differences and the incidence of VF. Some studies suggest that a greater proportion of coronary deaths were sudden in blacks compared with whites. In a report by Gillum on SCD from 1980-1985, the percentage of CAD deaths occurring out of the hospital and in EDs was found to be higher in blacks than in whites.3
Sex

Men have a higher incidence of VF than women (3:1). This ratio generally reflects the higher incidence of CAD in men. Recent evidence suggests that a major sex difference may exist in the mechanism of MI. Basic and observational data point to the fact that men tend to have coronary plaque rupture, whereas women tend to have plaque erosion. Whether this biologic difference accounts for the male predominance of VF is unclear.
Age

The incidence of VF parallels the incidence of CAD, with the peak of VF occurring in people aged 45-75 years. The incidence of VF increases with age in men and women of all races because the prevalence of CAD increases with age. However, the proportion of sudden deaths from CAD decreases with age. In the Framingham Heart Study, the proportion of sudden CAD deaths was 62% in men aged 45-54 years, but this percentage fell to 58% in men aged 55-64 years and to 42% in men aged 65-74 years.4 According to Kuller, 31% of deaths are sudden in people aged 20-29 years.5
Clinical
History

Obtaining a thorough history from the patient, family members, or other witnesses is necessary to obtain insight into the events surrounding the episode of VF. Patients at risk for VF may have prodromes of chest pain, fatigue, palpitations, and other nonspecific complaints. Up to 45% of persons who have VF have been noted to visit their physician in the 4 weeks before death, although up to 75% of these patients' complaints were not related to the cardiovascular system. A history of LV impairment (LV ejection fraction [LVEF] <30-35%) is the single greatest risk factor for sudden death from VF. Risk factors that relate to CAD and to subsequent MI and ischemic cardiomyopathy are also important and include a family history of premature CAD, smoking, dyslipidemia, hypertension, diabetes, obesity, and sedentary lifestyle. Specific considerations include the following:

Coronary artery disease
Previous cardiac arrest
Syncope
Prior MI, especially within 6 months
LVEF less than 30-35%
History of frequent ventricular ectopy (>10 PVCs/h or nonsustained VT)
Drop in SBP or ventricular ectopy upon stress testing, particularly when associated with acute myocardial ischemia
Dilated cardiomyopathy (DCM) from any cause (but most commonly due to ischemic or idiopathic etiology)
Previous cardiac arrest
Syncope or near-syncope
LVEF less than 30-35%
Use of inotropic medications, particularly in patients with decompensated CHF or acute myocardial ischemia
Hypertrophic cardiomyopathy (HCM), obstructive or nonobstructive
Previous cardiac arrest
Syncope or near-syncope
Family history of SCD
Symptoms of decompensated heart failure
Drop in SBP or ventricular ectopy upon stress testing
Palpitations
Usually asymptomatic
Valvular heart disease
Severe uncorrected aortic or mitral stenosis
Severe mitral or aortic regurgitation
Valve replacement within 6 months
Syncope
History of frequent ventricular ectopy
Myocarditis
LVEF less than 30-35%
Symptoms of decompensated heart failure
Previous cardiac arrest
Syncope or near-syncope
Congenital heart disease
Functional causes
Autonomic nervous system
Metabolic toxic electrolyte imbalance
Long QT syndrome
Family history of long QT syndrome and SCD
Medications that prolong the QT interval (acquired long QT syndrome)
Wolff-Parkinson-White (WPW) syndrome (with atrial fibrillation or atrial flutter with extremely rapid ventricular rates): With extremely rapid conduction over an accessory pathway, degeneration to VF can occur.
Brugada syndrome, arrhythmogenic right ventricular (RV) cardiomyopathy/dysplasia, others

Physical
Risk stratification and prognosis determination is absolutely crucial in the ED evaluation and treatment of patients with VF. Initial evaluation studies show that patients who survive to ED presentation can be stratified by a cardiac arrest score, which has excellent diagnostic value. The cardiac arrest score, developed by Thompson and McCullough, can be used for patients with witnessed out-of-hospital cardiac arrest and is defined by the following criteria:6

Clinical characteristic points
ED SBP greater than 90 mm Hg = 1 point
ED SBP less than 90 mm Hg = 0 points
Time to ROSC less than 25 minutes = 1 point
Time to ROSC more than 25 minutes = 0 points
Neurologically responsive = 1 point
Comatose = 0 point
Maximum score = 3 points
Patients with a score of 3 points can be expected to have an 89% chance of neurologic recovery and an 82% chance of survival to discharge.


Figure A shows neurologic outcome stratified by initial cardiac arrest score. Neurologic recovery is defined as discharged home and ability to care for self. Figure B shows overall survival stratified by initial cardiac arrest score.
Work from McCullough and colleagues indicates that even in the setting of ST elevation and early invasive management with primary angioplasty and intraaortic balloon pump insertion, patients with low cardiac scores are unlikely to survive.7
Severe anoxic encephalopathy in patients with scores of 0, 1, or 2 suggests the use of conservative management with empiric supportive and medical therapy. Given the very poor actuarial survival rates for these patients, invasive management with catheterization and electrophysiology studies (EPS) is rarely justified.
Causes
Ischemic heart disease: Cardiac arrest attributable to ventricular arrhythmias may be due to chronic scar or to acute MI/ischemia. A chronic infarct scar can serve as the focus for reentrant ventricular tachyarrhythmias. This can occur shortly after the infarct or years later. Many studies support the relationship of symptomatic and asymptomatic ischemia as markers of myocardium at risk for arrhythmias. Patients resuscitated from out-of-hospital cardiac arrest have an increased recurrence of cardiac arrest and express an increased incidence of silent ST-segment depression. Experiments inducing myocardial ischemia in animal models have a strong relationship with the development of VF.
In postmortem studies of people who have died from VF, extensive atherosclerosis is the most common pathologic finding.
In survivors of cardiac arrest, coronary heart disease with vessels showing greater than 75% stenosis is observed in 40-86% of patients, depending on the age and sex of the population studied. Autopsy studies show similar results; in one study of 169 hearts, approximately 61% of patients died of VF, and more than 75% stenosis in 3 or 4 vessels and similar severe lesions were present in at least 2 vessels in another 15% of cases. No single coronary artery lesion is associated with an increased risk for VF.
Despite these findings, only approximately 20% of VF-related autopsies have shown evidence of a recent MI. A greater proportion of autopsies (40-70%) show evidence of a healed MI. Many of these hearts also reveal evidence of plaque fissuring, hemorrhage, and thrombosis.
The Coronary Artery Surgery Study (CASS) showed that improving or restoring blood flow to an ischemic myocardium decreased the risk of VF, especially in patients with 3-vessel disease and heart failure, compared with medical treatment over a 5-year period.8 This finding suggests that transient acute ischemia is one of the major triggering events for sudden arrhythmic death.
The efficacy of beta-blocking agents, such as propranolol, in decreasing sudden death mortality rates, especially when administered to patients who had MI with VF, VT, and high-frequency PVCs, is thought to be partially caused by the ability of beta-blockers to decrease ischemia. Beta-blockers also increase the VF threshold in ischemic animals and decrease the rate of ventricular ectopy in patients who had MI.
Reperfusion of ischemic myocardium with thrombolysis or direct angioplasty can induce transient electrical instability by several different mechanisms. Coronary artery spasm is a condition that exposes the myocardium to both ischemia and reperfusion insults. The exact mechanism of coronary artery spasm is not known.
Roles of the autonomic nervous system, especially the alpha-adrenergic activity, vagal activity, vessel susceptibility, and humoral factors, particularly associated with platelet activation and aggregation, are being investigated as possible mechanisms of coronary vasospasm.
Nonatherosclerotic coronary artery abnormalities, including congenital lesions, coronary artery embolism, coronary arteritis, and mechanical abnormalities of the coronary artery, are associated with an increased incidence of sudden death.
Nonischemic cardiomyopathies: Patients with nonischemic cardiomyopathies are the second largest group of patients who experience VF. Nonischemic myopathies, for the purposes of this article, can be divided into dilated and hypertrophic categories.
Dilated cardiomyopathy
Nonischemic DCM is becoming increasingly more common, with an incidence of approximately 7.5 cases per 100,000 persons each year. Of cases of VF, 10% are estimated to be attributable to DCM. The prognosis is very poor for these patients, with a 1-year mortality rate of 10-50%, depending on the New York Heart Association functional class; approximately 30-50% of these deaths are caused by VF.
The causes of DCM are uncertain, but viral, autoimmune, genetic, and environmental (alcohol) origins are implicated. The predominant mechanism of death appears to be ventricular tachyarrhythmia, although bradyarrhythmia and electromechanical dissociation have also been observed, especially in patients with advanced LV dysfunction. Extensive fibrosis of the subendocardium, leading to dilated ventricles and subsequent generation of reentrant tachyarrhythmias, is a proposed mechanism for VF.
Multiple factors contribute to increased risk for VF in this population. The most important hemodynamic predictor is an increase in end-diastolic pressure and subsequent wall tension. Other important factors are increased sympathetic tone, neurohumoral activation, and electrolyte abnormalities.
Many drugs used in the treatment of heart failure, such as antiarrhythmics, inotropic agents, and diuretics, have proarrhythmic properties, which may provoke arrhythmias in some patients.
Unlike ischemic cardiomyopathy, increased asymptomatic ventricular ectopy and nonsustained VT are not predictive of VF in DCM. Approximately 80% of persons with DCM have these findings on Holter monitoring, hence the lessened value of this diagnostic tool. Given the possibility of sustained VT being the underlying cause, aggressively pursue a history of syncope.
Hypertrophic cardiomyopathy
HCM is usually an autosomal dominant, incompletely penetrant genetic disorder resulting from a mutation in one of the many (>45) genes encoding proteins of the cardiac muscle sarcomere. Among the described genetic abnormalities, mutations occur in the genes coding for the beta-myosin heavy chains, cardiac troponin T, and myosin-binding protein C. The incidence of VF in this population is 2-4% per year in adults and 4-6% per year in children and adolescents. HCM is the most common cause of VF in people younger than 30 years.
The vast majority of young people who die of HCM are previously asymptomatic. Most experience VT/VF while at rest or with mild exertional activity; however, in a significant portion of these patients, the VF event occurs after vigorous exertion. HCM is the single greatest cause of VF in athletes and is therefore the major entity for which to screen during the physical examination of an athlete.
The mechanism of VF in HCM is not entirely understood. The postexertional drop in blood pressure and shunting of blood to extracardiac tissues is postulated to worsen the outflow tract gradient and may therefore induce cardiac ischemia and malignant arrhythmias. This downward cycle does not revert spontaneously, and it responds poorly to resuscitative efforts.
Arrhythmogenic RV cardiomyopathy/dysplasia
Arrhythmogenic RV cardiomyopathy/dysplasia is characterized by replacement of the RV wall with fibrofatty tissue. Involvement of the interventricular septum and left ventricle is associated with poorer outcomes.
Genetic defects in chromosomes 1 and 14 (bands q23-q24)have recently been discovered to correspond to some phenotypic expressions of this disease. Autosomal dominant inheritance can occur, and approximately 30% of cases occur as a familial disorder.
Arrhythmogenic RV dysplasia affects men more often than women. The annual incidence rate of VF in this population is approximately 2%. Patients may present with signs and symptoms of RV hypertrophy and dilation, often with sustained monomorphic or polymorphic VT of the left bundle-branch block morphology with an axis usually between negative 90-100°.
Atrial arrhythmias may be present in up to 25% of patients. Syncope and sudden death are often associated with exercise. In many patients, sudden death is the first manifestation of the disease. Clinicians should be alerted to the epsilon wave finding on ECG studies (see following image). The epsilon wave can be present in up to 23% of patients after the first VT attack. The percentage of patients with the epsilon wave finding on ECG increases to 27% and 34% at 5 and 10 years, respectively, after the first VT event.


Epsilon wave in a patient with arrhythmogenic right ventricular dysplasia.
Uhl anomaly is a condition in which the RV wall is extremely thin secondary to apposition of endocardial and epicardial layers. Uhl anomaly usually manifests in the pediatric age group, while arrhythmogenic RV cardiomyopathy usually manifests in adults.
Valvular diseases: These include aortic stenosis and other valvular lesions.
Aortic stenosis
SCD was fairly common in patients with progressive aortic stenosis before the advent of surgical therapy for valvular heart disease.
Most deaths caused by aortic stenosis were sudden. In a 1980 study by Chizner et al of 42 patients who had isolated aortic stenosis and did not undergo valve replacement, up to 56% of deaths were sudden at 5-year follow-up. Of these 42 patients, 32 were symptomatic, and 10 were asymptomatic.9
The mechanism of sudden death is unclear, and both malignant ventricular arrhythmia and bradyarrhythmia have been documented.
VF accounts for up to 20% of deaths after aortic valve replacement and remains the second most common cause of postoperative death in this population. The incidence of VF after aortic valve surgery is highest in the first 3 weeks after the procedure and then plateaus at 6-month follow-up.
Other valvular lesions
Patients with aortic insufficiency usually present with signs of heart failure and progressive LV dilatation. As part of this process, reentrant or automatic ventricular foci may develop and ultimately lead to symptomatic ventricular arrhythmia. After valve replacement, LV wall tension can be expected to lessen and risk of arrhythmia can be expected to decrease.
Mitral stenosis is becoming increasingly uncommon in the United States because of widespread use of antibiotics in primary streptococcal infections. SCD due to mitral stenosis is very rare.
The incidence of VF is low in patients with mitral valve prolapse (MVP). MVP has a 5-7% incidence in the general population. In clinically significant MVP, the risk of VF seems to rise along with the total mortality rate. Kligfield et al estimated that the incidence of sudden death varies with the presence of symptoms and the severity of mitral regurgitation.10
Ventricular tachyarrhythmias are the most frequent arrhythmia in patients with VF. Risk factors for VF to consider in these patients include a family history of VF, echocardiographic evidence of a redundant mitral valve, repolarization abnormalities, and lengthening of the corrected QT interval (>420 milliseconds [ms] in women and >450 ms in men).
Congenital heart disease: In the pediatric and adolescent age groups, VF occurs with an annual incidence of 1.3-8.5 cases per 100,000 persons, accounting for approximately 5% of all deaths in this group. The causes of SCD are much more diverse in children than adults. In reviewing 13 studies involving 61 children and adolescents with VF, Driscoll and Edwards found 50% of cases were due to HCM; 25%, to anomalous origin of the left coronary artery; and the remaining, to aortic stenosis, cystic medial necrosis, and sinus node artery obstruction.11 The following is a classification of VF in the pediatric population:
Congenital causes of VF in patients with known, previously recognized (including repaired) heart disease include the following:
Tetralogy of Fallot
Transposition of the great arteries
Fontan operation
Aortic stenosis
Marfan syndrome
Eisenmenger syndrome
Congenital heart block
Ebstein anomaly
Acquired causes of VF in patients with known, previously recognized (including repaired) heart disease include the following:
Kawasaki syndrome
DCM or myocarditis
Causes of VF in patients with previously unrecognized heart disease who have structural heart disease include the following:
HCM
Congenital coronary artery abnormalities
Arrhythmogenic RV dysplasia
Causes of VF in patients with previously unrecognized heart disease who do not have structural heart disease include the following:
Long QT syndrome
WPW syndrome
Primary VT and VF
Primary pulmonary hypertension
Commotio cordis (traumatic blow to the chest wall causing VT/VF)
The predominant mechanism is ventricular arrhythmia. In patients with tetralogy of Fallot after postoperative correction of the anomaly, up to 10% have VT, and the incidence of sudden death is 2-3%. In the Fontan procedure to correct a physiologic single ventricle, even atrial arrhythmias can cause severe hemodynamic compromise and arrhythmic death. Patients who develop secondary pulmonary hypertension (Eisenmenger syndrome) despite attempted correction of the anatomic defects have a very poor prognosis. The terminal event may be bradycardia or VT progressing to VF.
Primary electrophysiologic abnormalities: These generally comprise a group of abnormalities in which patients have no apparent structural heart disease but have a primary electrophysiologic abnormality that predisposes them to VT or VF. Some imaging techniques have detected abnormal sympathetic neural function in these patients. An ECG study can provide clues to the diagnosis; consider a familial component to these conditions.
Long QT syndrome
Idiopathic long QT syndrome, in which patients have a prolonged QT interval with a propensity to develop malignant ventricular arrhythmias, is a rare familial disorder.
Two forms of congenital long QT syndrome have been described. The Jervell and Lange-Nielsen syndrome associated with deafness has an autosomal recessive pattern of inheritance. The Romano-Ward syndrome is not associated with deafness and has an autosomal dominant pattern of inheritance with variable penetration. This syndrome accounts for 90% of long QT syndrome cases. The Romano-Ward syndrome has been associated with gene mutations of SCN5A on chromosome 3, the HERG gene on chromosome 7, and the KVLTQT1 gene on chromosome 11.
The genetic alteration in a myocellular channel protein that regulates the potassium flux during electrical repolarization is thought to be the primary electrophysiologic abnormality. A relationship with sympathetic nervous system imbalance also appears to exist. The prolongation that occurs makes these patients susceptible for development of a specific form of VT called torsade de pointes.
The clinical course of patients with long QT syndrome is quite variable, with some patients remaining asymptomatic and others developing torsade de pointes with syncope and sudden death. Thirty percent of patients are identified while being evaluated for syncope or aborted sudden death. Patients at high risk for VF include those with deafness and first-degree relatives of patients with VF. VF in these patients is associated with emotional extremes, auditory auras or stimulation, and vigorous physical activity. Symptoms usually begin in childhood or adolescence.
Diagnosis of congenital long QT syndrome requires the presence of 2 major criteria or 1 major criterion and 2 minor criteria. Major criteria include (1) long QT interval (QTc >420 ms in females and >450 ms in males), (2) stress-induced syncope, and (3) a family history of long QT syndrome. Minor criteria include (1) congenital deafness, (2) T-wave alternans, and (3) bradycardia (in children).
The absence of long QT syndrome on a single resting ECG does not exclude the diagnosis or the possibility that the patient may have incomplete penetrance that may be accentuated by drugs or metabolic conditions.
Treatment for long QT syndrome includes beta-blockers, high thoracic left sympathectomy, and implanted cardioverter/defibrillators (ICDs). (See Treatment for more details)
Acquired long QT syndrome
A number of antiarrhythmics (especially class I-A and class III) and other medications, electrolyte abnormalities, cerebrovascular diseases, and altered nutritional states cause QT prolongation and put patients at risk for torsade de pointes. This usually occurs when QT prolongation is associated with a slow heart rate and hypokalemia.
The QT interval is prolonged in up 32% of patients with intracranial hemorrhage (especially in subarachnoid hemorrhages). Lesions in the hypothalamus are thought to lead to this phenomenon.
Sudden death due to ventricular arrhythmia has been reported in patients with hypocalcemia, hypothyroidism, and nutritional deficiencies associated with modified starvation diets and in patients who are obese and on severe weight-loss programs.
Class I-A antiarrhythmic drugs that cause acquired long QT syndrome include quinidine, disopyramide, and procainamide. Class III antiarrhythmic drugs that cause acquired long QT syndrome include sotalol, N-acetyl procainamide, bretylium, amiodarone, dofetilide, and ibutilide.
Other drugs that cause acquired long QT syndrome include bepridil, probucol, tricyclic and tetracyclic antidepressants, phenothiazines, haloperidol, antihistamines (eg, terfenadine, astemizole), antibiotics (eg, intravenous erythromycin, sulfamethoxazole/trimethoprim), chemotherapeutics (eg, pentamidine, anthracycline), serotonin antagonists (eg, ketanserin, zimeldine), and organophosphorous insecticides.
Electrolyte abnormalities that cause acquired long QT syndrome include hypokalemia, hypomagnesemia, and hypocalcemia.
Altered nutritional states and cerebrovascular disease that cause acquired long QT syndrome include intracranial and subarachnoid hemorrhages, stroke, and intracranial trauma.
Hypothyroidism and altered autonomic status (eg, diabetic neuropathy) can cause acquired long QT syndrome.
WPW syndrome
WPW syndrome is a rare cause of sudden death.
Most patients with WPW syndrome and VF develop atrial fibrillation with a rapid ventricular response over the accessory pathway, which induces VF (see image below). In a study by Klein et al of 31 patients with VF and WPW syndrome, a history of atrial fibrillation or reciprocating tachycardia was an important predisposing factor. The presence of multiple accessory pathways, posteroseptal accessory pathways, and a preexcited R-R interval of less than 220 ms during atrial fibrillation are associated with higher risk for VF.


Ventricular fibrillation appeared during rapid atrial fibrillation in a patient with Wolff-Parkinson-White syndrome.
In patients at high risk, preventing the occurrence of arrhythmias is possible by interrupting the anomalous pathway with surgery or radiofrequency ablation techniques.
Brugada syndrome
In 1992, Brugada and Brugada described a syndrome of a specific ECG pattern of right bundle-branch block and ST-segment elevation in leads V1 through V6 without any structural abnormality of the heart that was associated with sudden death.
The gene responsible for this syndrome has recently been discovered to be the cardiac sodium channel gene SCN5A on chromosome 3.
Patients with this syndrome are at high risk for VF. In a follow-up study of 63 patients with the syndrome in 33 centers worldwide, asymptomatic patients were found to have the same risk for arrhythmia as patients who had an episode of aborted sudden death. Treatment with amiodarone and/or beta-blockers did not confer a lesser risk of death, whereas the patients with ICDs had no deaths due to arrhythmia. Thus, placement of an ICD is considered the treatment of choice for Brugada syndrome.
Primary ventricular fibrillation
An estimated 3-9% of cases of VT and VF occur in the absence of myocardial ischemia. Up to 1% of patients with out-of-hospital cardiac arrest have idiopathic VF with no structural heart disease. Up to 15% of patients younger than 40 years who experience VF have no underlying structural heart disease. In a 1993 study, Belhassen and Viskin noted that 11 of 54 patients had histologic abnormalities on endomyocardial biopsy.12
VF usually has no preceding symptoms. The prognosis is unfavorable, and patients have a recurrence rate of as much as 33%. Conversely, idiopathic VT is generally associated with a benign prognosis.
The most common form of idiopathic VT originates from the RV outflow tract (RVOT) and has a left bundle-branch block/inferior or right axis morphology. Idiopathic VTs that originate from the LV outflow tract (LVOT), aortic root, or LV septum are less common. Idiopathic VT is often provoked by exercise.
Treatment has included beta-blockers or calcium channel blockers; however, at present, radiofrequency ablation of the VT focus is generally very effective for idiopathic VT. Patients with idiopathic VF are typically treated with ICDs.
RVOT tachycardia
RVOT tachycardia is the most common form of idiopathic VT, comprising 70-80% of all idiopathic VTs. RVOT tachycardia is a rare cause of VF. It has been referred to as exercise-induced VT, adenosine-sensitive VT, and repetitive monomorphic VT.
RVOT tachycardia occurs in patients without structural heart disease and arises from the RV outflow region. Current data suggest that triggered activity is the underlying mechanism of RVOT tachycardia. RVOT tachycardia is believed to be receptor mediated because exogenous and endogenous adenosine can terminate this process. Maneuvers that increase endogenous acetylcholine antagonize this process.
Symptoms typical of RVOT tachycardia include palpitations and presyncope or syncope, often occurring during or after exercise or emotional stress. VT can also occur at rest. The ECG during VT displays a left bundle-branch block/inferior axis morphology.
Treatment is based on frequency and severity of symptoms. The first line of therapy is a beta-blocker or calcium channel blocker. Patients with symptoms not relieved by medical therapy are best treated with radiofrequency catheter ablation. Successful ablation is reported in 83-100% of cases.
Lown-Ganong-Levine syndrome
This syndrome is characterized by tachyarrhythmias, short PR interval, and normal QRS duration.
Most of these patients appear to have enhanced atrioventricular (AV) nodal conduction and "typical" supraventricular tachycardia (usually AV nodal reentrant tachycardia or, less commonly, AV nodal tachycardia using a concealed accessory pathway).
Some patients may have a rapidly anterograde-conducting accessory AV connection, which theoretically poses a risk of extremely rapid rates and degeneration to VF.
Pulmonary embolism is a frequent cause of sudden death in people at risk. Risk factors include previous personal or family history of deep venous thromboembolism, malignancy, hypercoagulable states, and recent mechanical trauma such as hip or knee surgery. Patients with pulmonary embolism can develop fatal ventricular arrhythmias (eg, VF) due to hemodynamic collapse and/or severe hypoxia.
Aortic dissection or aneurysmal rupture is a rather uncommon but significant cause of out-of-hospital cardiac arrest. Predisposing factors for aortic dissection include genetic deficiencies of collagen such as Marfan syndrome, Ehlers-Danlos syndrome, and aortic cystic medial necrosis. VF may be an observed finding at the scene of an aortic aneurysmal rupture.

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