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In 1930, Wolff, Parkinson, and White described a series of young patients who had a bundle branch block pattern on electrocardiography (ECG) findings, a short PR interval, and paroxysms of tachycardia. Case reports began appearing in the literature in the late 1930s and early 1940s, and the term Wolff-Parkinson-White (WPW) syndrome was coined in 1940. In 1943, the existence of an accessory connection between atria and ventricles was confirmed, which is about 50 years after Kent's description of myocardial fibers that were believed to conduct from atria to ventricle.
The term preexcitation was first published by Ohnell in 1944 (the same year that the term delta wave was coined); Ohnell stated, "preexcitation indicates an additional excitatory spread in the ventricles of the heart, coupled to auricular excitation." WPW syndrome is not the only form of preexcitation but is the most common. The first surgical division of an accessory pathway (AP) was performed at Duke University by Will C. Sealy, MD, in 1968. The first catheter ablation was reported in 1983, using direct current (DC) energy; this was followed by the first successful RF ablation reported in 1987.
The current era of RF ablation has refined the understanding of the pathophysiology of WPW syndrome, providing elegant descriptions.
Pathophysiology
The underlying defect in WPW syndrome is the presence of an AP consisting of a myocardial connection at the atrioventricular (AV) junction. These are believed to be residual connections from the formation of the AV junction. The primary feature that differentiates WPW syndrome from other AP-mediated supraventricular tachycardias (SVTs) is the ability of the AP to conduct antegradely (ie, from atrium to ventricles) and retrogradely.
The amount of preexcitation present in a person with WPW pattern can be estimated by the width of the QRS and length of the PR interval. Thus, a wider or more preexcited QRS with a short PR interval with absent or nearly absent isoelectric component reveals that most (or all) of the ventricular depolarization occurs through the AP and not through the AV node. However, the QRS width may vary, becoming narrower during more rapid heart rates. This is possible because catecholamines permit the AV node to contribute more (or entirely) to ventricular depolarization by enhancing AV node conduction.
The presence of an AP allows a reentrant tachycardia circuit to be established. In orthodromic SVT, the conduction is through the AV node to the ventricles then back to the atria via the AP. Because the AP can conduct in both directions, experiencing antidromic tachycardia, in which the conduction from atrium to ventricle occurs via the AP, is also possible, resulting in a broad complex (ie, wide QRS) tachycardia.
The presence of an antegrade AV connection also allows atrial arrhythmias to be conducted to the ventricles without passing through the AV node. Patients with WPW syndrome can more frequently develop atrial fibrillation (AF), which can potentially be conducted to the ventricles rapidly (see Mortality/Morbidity).
The different patterns of preexcitation have produced various classification systems. Classification by type is largely obsolete, and, currently, classification by anatomic location of the AP is used (see Workup).
Family studies as well as recent molecular genetic investigations indicate that WPW syndrome and associated preexcitation disorders may have a genetic component. It may be inherited as a familial trait with or without associated congenital heart defects (CHDs).1
Frequency
International
WPW syndrome refers to preexcitation and paroxysms of tachycardia. The WPW pattern refers to the ECG pattern. The incidence of the WPW pattern is unknown but is estimated to be 1-2 cases per 1000 population. This may be an underestimate because it often represents an asymptomatic ECG finding. The incidence of newly diagnosed cases of WPW syndrome is approximately 4 cases per 100,000 population per year.
Mortality/Morbidity
Many individuals with WPW pattern remain asymptomatic throughout their lives. Approximately half of these individuals develop WPW syndrome.
The morbidity in WPW syndrome predominantly results from SVT. Even in the absence of rapid ventricular conduction, syncope is an occasional presenting symptom. However, in most patients, the SVT is well tolerated and is not life threatening. If a patient experiences incessant tachycardia, cardiomyopathy may develop.
Mortality in WPW syndrome is rare and is related to sudden cardiac death (SCD). The cause of SCD in WPW syndrome is rapid conduction of AF to the ventricles via the AP, resulting in ventricular fibrillation (VF).
* AF develops in one fifth to one third of patients with WPW syndrome; the reasons for this and the effects of AP ablation on its development are unclear. However, one study hypothesized that 2 mechanisms are involved in the pathogenesis of AF in patients with WPW syndrome: one is related to the AP that predisposes the atria to fibrillation, and the other is independent from the AP and is related to increased atrial vulnerability present in these individuals.2
* According to the literature, risk factors for the development of AF in the setting of WPW syndrome include advancing age (2 peak ages for AF occurrence are recognized, one at 30 years and the other at 50 years), male gender, and prior history of syncope.3
* Certain factors increase the likelihood of VF, including rapidly conducting APs and multiple pathways.4 Cases have also been reported in association with esophageal studies, digoxin, and verapamil. A few reports document spontaneous VF in WPW syndrome, and SVT may degenerate into AF, thus leading to VF;5 however, both scenarios are rare in pediatric patients.
* The incidence of SCD in WPW syndrome is approximately 1 in 100 symptomatic cases when followed for up to 15 years.
* Although relatively uncommon, SCD may be the initial presentation in as many as 4.5% of cases.
Sex
WPW pattern appears to equally affect both sexes. However, WPW syndrome has been found to be more frequent in males.
* A male-to-female ratio of approximately 2:1 has been documented in some series.
* In other series, the syndrome was found to be more frequent in men (1.4 cases per 1000 men) than in women (0.9 cases per 1000 women).
* A third study found a 3.5-fold higher prevalence of WPW syndrome in men.
Age
Patients with WPW syndrome may present at any age. However, an interesting bimodal age distribution has been reported in the pediatric population due to permanent or transitory loss of preexcitation during infancy in some patients and during late adolescence in others.
* Most patients with WPW syndrome present during infancy.
* A second peak of presentation is noted in school-aged children and in adolescents.
Clinical
History
The presentations of Wolff-Parkinson-White (WPW) syndrome are as diverse as an incidental finding to syncope or SCD. Patients usually present with symptomatic orthodromic supraventricular tachycardia (SVT), which accounts for approximately 95% of the SVT seen in children and infants with WPW syndrome. Antidromic SVT occurs in the remaining 5% of children and infants with WPW syndrome.
* Orthodromic SVT is usually well tolerated and not a high risk, especially in the pediatric population after young infancy.
* Antidromic SVT presents more frequently with dizziness and syncope. In addition, it may precipitate ventricular tachycardia and VF.
* The infant is often noted to be irritable, to not tolerate feedings, or to demonstrate evidence of congestive heart failure.
* Infants often have a history of not behaving as usual for 1-2 days.
* An intercurrent febrile illness is often observed.
* The verbal child usually reports chest pain, palpitations, or breathing difficulty.
* Most children are previously well, and a minority of children have a positive family history of this condition.
* Older patients can usually describe the sudden onset of a pounding heartbeat, which is regular and "too rapid to count." This is accompanied by a concomitant change in their tolerance for activity.
* An irregular rhythm may herald the presence of AF.
* In several series, the incidence of associated congenital heart disease is reported to be as high as 30%, most commonly Ebstein anomaly of the tricuspid valve and corrected transposition of the great arteries.
o Approximately 10% of patients with Ebstein anomaly of the tricuspid valve have WPW syndrome. They usually have more than one AP, and those are usually right sided.
o Patients with corrected transposition of the great arteries and left-sided Ebstein anomaly may also have WPW syndrome. In these patients, the AP is left sided or septal.
o Other congenital heart diseases associated with WPW syndrome include atrial and ventricular septal defects and coronary sinus diverticula.
* Preexcitation is believed to have a genetic substrate because 3.4% of those with WPW syndrome have first-degree relatives with preexcitation. The familial form is usually inherited as a Mendelian autosomal dominant trait. Although rare, mitochondrial inheritance has also been described. The syndrome may also be inherited with other cardiac and noncardiac disorders, such as familial atrial septal defects, familial hypokalemic periodic paralysis, and tuberous sclerosis. Clinicians have long recognized the association of WPW syndrome with autosomal dominant familial hypertrophic cardiomyopathy. However, only recently was a genetic substrate linking hypertrophic cardiomyopathy to WPW syndrome and skeletal myopathy described.
o Patients with mutations in the gamma 2 subunit of adenosine monophosphate (AMP)-activated protein kinase (PRKAG2) develop cardiomyopathy characterized by ventricular hypertrophy, WPW syndrome, AV block, and progressive degenerative conduction system disease. The mutation is believed to produce disruption of the annulus fibrosus by accumulation of glycogen within myocytes, which causes preexcitation. This is thought to be the case in Pompe disease, Danon disease, and other glycogen-storage diseases.
o Infantile Pompe disease or glycogen-storage disease type II is a fatal genetic muscle disorder that is caused by deficiency of acid alpha-glucosidase (GAA). These patients have a shortened PR interval, large left ventricular (LV) voltages, and an increased QT dispersion (QTd).
o Mutations in the lysosome-associated membrane protein 2 (LAMP2), which cause accumulation of cardiac glycogen, are thought to be the etiology of a significant number of hypertrophic cardiomyopathies in children, especially when skeletal myopathy, WPW syndrome, or both are present.
o For example, Danon disease is an X-linked lysosomal cardioskeletal myopathy; males are more often and more severely affected than females. It is caused by mutations in the LAMP2 that produce proximal muscle weakness and mild atrophy, left ventricle hypertrophy, WPW syndrome, and mental retardation.
Physical
* During an episode of SVT, the infant is usually tachypneic and irritable; pallor is common. The pulse is very rapid and diminished in volume. The ventricular rate typically is 200-250 beats per minute (bpm), and the blood pressure is decreased. If the episode has been untreated for several hours, the patient often has poor perfusion, hepatomegaly, and cardiac failure. The child is usually anxious but hemodynamically stable. Tachypnea often accompanies the tachycardia.
* Once the arrhythmia has been terminated, the physical examination findings are generally normal.
* In the presence of CHD or cardiomyopathy findings of the underlying condition often become apparent only after the SVT has been terminated, although the hemodynamic consequences may be poorly tolerated.
o Patients with Ebstein anomaly of the tricuspid valve may present with cyanosis, tachypnea, and other signs of congestive heart failure in presence of a rapid heart rate. The ECG may show either wide or narrow QRS, SVT, and, sometimes, QRS with changing morphology if more than one AP is present.
o Patients with glycogen-storage diseases have muscle weakness with normal or increased muscle bulk, macroglossia and hepatomegaly in the case of Pompe disease, and mental retardation in case of Danon disease.
Causes
* APs are considered congenital phenomena that are related to a failure of insulating tissue maturation within the AV ring. A proportion of patients with preexcitation may have a genetic predisposition, as outlined above.
* Preexcitation can be surgically created, such as in certain types of Bjork modifications of the Fontan procedure, if atrial tissue is flapped onto and sutured to ventricular tissue.
* Certain tumors of the AV ring, such as rhabdomyomas, may also cause preexcitation.
In 1930, Wolff, Parkinson, and White described a series of young patients who had a bundle branch block pattern on electrocardiography (ECG) findings, a short PR interval, and paroxysms of tachycardia. Case reports began appearing in the literature in the late 1930s and early 1940s, and the term Wolff-Parkinson-White (WPW) syndrome was coined in 1940. In 1943, the existence of an accessory connection between atria and ventricles was confirmed, which is about 50 years after Kent's description of myocardial fibers that were believed to conduct from atria to ventricle.
The term preexcitation was first published by Ohnell in 1944 (the same year that the term delta wave was coined); Ohnell stated, "preexcitation indicates an additional excitatory spread in the ventricles of the heart, coupled to auricular excitation." WPW syndrome is not the only form of preexcitation but is the most common. The first surgical division of an accessory pathway (AP) was performed at Duke University by Will C. Sealy, MD, in 1968. The first catheter ablation was reported in 1983, using direct current (DC) energy; this was followed by the first successful RF ablation reported in 1987.
The current era of RF ablation has refined the understanding of the pathophysiology of WPW syndrome, providing elegant descriptions.
Pathophysiology
The underlying defect in WPW syndrome is the presence of an AP consisting of a myocardial connection at the atrioventricular (AV) junction. These are believed to be residual connections from the formation of the AV junction. The primary feature that differentiates WPW syndrome from other AP-mediated supraventricular tachycardias (SVTs) is the ability of the AP to conduct antegradely (ie, from atrium to ventricles) and retrogradely.
The amount of preexcitation present in a person with WPW pattern can be estimated by the width of the QRS and length of the PR interval. Thus, a wider or more preexcited QRS with a short PR interval with absent or nearly absent isoelectric component reveals that most (or all) of the ventricular depolarization occurs through the AP and not through the AV node. However, the QRS width may vary, becoming narrower during more rapid heart rates. This is possible because catecholamines permit the AV node to contribute more (or entirely) to ventricular depolarization by enhancing AV node conduction.
The presence of an AP allows a reentrant tachycardia circuit to be established. In orthodromic SVT, the conduction is through the AV node to the ventricles then back to the atria via the AP. Because the AP can conduct in both directions, experiencing antidromic tachycardia, in which the conduction from atrium to ventricle occurs via the AP, is also possible, resulting in a broad complex (ie, wide QRS) tachycardia.
The presence of an antegrade AV connection also allows atrial arrhythmias to be conducted to the ventricles without passing through the AV node. Patients with WPW syndrome can more frequently develop atrial fibrillation (AF), which can potentially be conducted to the ventricles rapidly (see Mortality/Morbidity).
The different patterns of preexcitation have produced various classification systems. Classification by type is largely obsolete, and, currently, classification by anatomic location of the AP is used (see Workup).
Family studies as well as recent molecular genetic investigations indicate that WPW syndrome and associated preexcitation disorders may have a genetic component. It may be inherited as a familial trait with or without associated congenital heart defects (CHDs).1
Frequency
International
WPW syndrome refers to preexcitation and paroxysms of tachycardia. The WPW pattern refers to the ECG pattern. The incidence of the WPW pattern is unknown but is estimated to be 1-2 cases per 1000 population. This may be an underestimate because it often represents an asymptomatic ECG finding. The incidence of newly diagnosed cases of WPW syndrome is approximately 4 cases per 100,000 population per year.
Mortality/Morbidity
Many individuals with WPW pattern remain asymptomatic throughout their lives. Approximately half of these individuals develop WPW syndrome.
The morbidity in WPW syndrome predominantly results from SVT. Even in the absence of rapid ventricular conduction, syncope is an occasional presenting symptom. However, in most patients, the SVT is well tolerated and is not life threatening. If a patient experiences incessant tachycardia, cardiomyopathy may develop.
Mortality in WPW syndrome is rare and is related to sudden cardiac death (SCD). The cause of SCD in WPW syndrome is rapid conduction of AF to the ventricles via the AP, resulting in ventricular fibrillation (VF).
* AF develops in one fifth to one third of patients with WPW syndrome; the reasons for this and the effects of AP ablation on its development are unclear. However, one study hypothesized that 2 mechanisms are involved in the pathogenesis of AF in patients with WPW syndrome: one is related to the AP that predisposes the atria to fibrillation, and the other is independent from the AP and is related to increased atrial vulnerability present in these individuals.2
* According to the literature, risk factors for the development of AF in the setting of WPW syndrome include advancing age (2 peak ages for AF occurrence are recognized, one at 30 years and the other at 50 years), male gender, and prior history of syncope.3
* Certain factors increase the likelihood of VF, including rapidly conducting APs and multiple pathways.4 Cases have also been reported in association with esophageal studies, digoxin, and verapamil. A few reports document spontaneous VF in WPW syndrome, and SVT may degenerate into AF, thus leading to VF;5 however, both scenarios are rare in pediatric patients.
* The incidence of SCD in WPW syndrome is approximately 1 in 100 symptomatic cases when followed for up to 15 years.
* Although relatively uncommon, SCD may be the initial presentation in as many as 4.5% of cases.
Sex
WPW pattern appears to equally affect both sexes. However, WPW syndrome has been found to be more frequent in males.
* A male-to-female ratio of approximately 2:1 has been documented in some series.
* In other series, the syndrome was found to be more frequent in men (1.4 cases per 1000 men) than in women (0.9 cases per 1000 women).
* A third study found a 3.5-fold higher prevalence of WPW syndrome in men.
Age
Patients with WPW syndrome may present at any age. However, an interesting bimodal age distribution has been reported in the pediatric population due to permanent or transitory loss of preexcitation during infancy in some patients and during late adolescence in others.
* Most patients with WPW syndrome present during infancy.
* A second peak of presentation is noted in school-aged children and in adolescents.
Clinical
History
The presentations of Wolff-Parkinson-White (WPW) syndrome are as diverse as an incidental finding to syncope or SCD. Patients usually present with symptomatic orthodromic supraventricular tachycardia (SVT), which accounts for approximately 95% of the SVT seen in children and infants with WPW syndrome. Antidromic SVT occurs in the remaining 5% of children and infants with WPW syndrome.
* Orthodromic SVT is usually well tolerated and not a high risk, especially in the pediatric population after young infancy.
* Antidromic SVT presents more frequently with dizziness and syncope. In addition, it may precipitate ventricular tachycardia and VF.
* The infant is often noted to be irritable, to not tolerate feedings, or to demonstrate evidence of congestive heart failure.
* Infants often have a history of not behaving as usual for 1-2 days.
* An intercurrent febrile illness is often observed.
* The verbal child usually reports chest pain, palpitations, or breathing difficulty.
* Most children are previously well, and a minority of children have a positive family history of this condition.
* Older patients can usually describe the sudden onset of a pounding heartbeat, which is regular and "too rapid to count." This is accompanied by a concomitant change in their tolerance for activity.
* An irregular rhythm may herald the presence of AF.
* In several series, the incidence of associated congenital heart disease is reported to be as high as 30%, most commonly Ebstein anomaly of the tricuspid valve and corrected transposition of the great arteries.
o Approximately 10% of patients with Ebstein anomaly of the tricuspid valve have WPW syndrome. They usually have more than one AP, and those are usually right sided.
o Patients with corrected transposition of the great arteries and left-sided Ebstein anomaly may also have WPW syndrome. In these patients, the AP is left sided or septal.
o Other congenital heart diseases associated with WPW syndrome include atrial and ventricular septal defects and coronary sinus diverticula.
* Preexcitation is believed to have a genetic substrate because 3.4% of those with WPW syndrome have first-degree relatives with preexcitation. The familial form is usually inherited as a Mendelian autosomal dominant trait. Although rare, mitochondrial inheritance has also been described. The syndrome may also be inherited with other cardiac and noncardiac disorders, such as familial atrial septal defects, familial hypokalemic periodic paralysis, and tuberous sclerosis. Clinicians have long recognized the association of WPW syndrome with autosomal dominant familial hypertrophic cardiomyopathy. However, only recently was a genetic substrate linking hypertrophic cardiomyopathy to WPW syndrome and skeletal myopathy described.
o Patients with mutations in the gamma 2 subunit of adenosine monophosphate (AMP)-activated protein kinase (PRKAG2) develop cardiomyopathy characterized by ventricular hypertrophy, WPW syndrome, AV block, and progressive degenerative conduction system disease. The mutation is believed to produce disruption of the annulus fibrosus by accumulation of glycogen within myocytes, which causes preexcitation. This is thought to be the case in Pompe disease, Danon disease, and other glycogen-storage diseases.
o Infantile Pompe disease or glycogen-storage disease type II is a fatal genetic muscle disorder that is caused by deficiency of acid alpha-glucosidase (GAA). These patients have a shortened PR interval, large left ventricular (LV) voltages, and an increased QT dispersion (QTd).
o Mutations in the lysosome-associated membrane protein 2 (LAMP2), which cause accumulation of cardiac glycogen, are thought to be the etiology of a significant number of hypertrophic cardiomyopathies in children, especially when skeletal myopathy, WPW syndrome, or both are present.
o For example, Danon disease is an X-linked lysosomal cardioskeletal myopathy; males are more often and more severely affected than females. It is caused by mutations in the LAMP2 that produce proximal muscle weakness and mild atrophy, left ventricle hypertrophy, WPW syndrome, and mental retardation.
Physical
* During an episode of SVT, the infant is usually tachypneic and irritable; pallor is common. The pulse is very rapid and diminished in volume. The ventricular rate typically is 200-250 beats per minute (bpm), and the blood pressure is decreased. If the episode has been untreated for several hours, the patient often has poor perfusion, hepatomegaly, and cardiac failure. The child is usually anxious but hemodynamically stable. Tachypnea often accompanies the tachycardia.
* Once the arrhythmia has been terminated, the physical examination findings are generally normal.
* In the presence of CHD or cardiomyopathy findings of the underlying condition often become apparent only after the SVT has been terminated, although the hemodynamic consequences may be poorly tolerated.
o Patients with Ebstein anomaly of the tricuspid valve may present with cyanosis, tachypnea, and other signs of congestive heart failure in presence of a rapid heart rate. The ECG may show either wide or narrow QRS, SVT, and, sometimes, QRS with changing morphology if more than one AP is present.
o Patients with glycogen-storage diseases have muscle weakness with normal or increased muscle bulk, macroglossia and hepatomegaly in the case of Pompe disease, and mental retardation in case of Danon disease.
Causes
* APs are considered congenital phenomena that are related to a failure of insulating tissue maturation within the AV ring. A proportion of patients with preexcitation may have a genetic predisposition, as outlined above.
* Preexcitation can be surgically created, such as in certain types of Bjork modifications of the Fontan procedure, if atrial tissue is flapped onto and sutured to ventricular tissue.
* Certain tumors of the AV ring, such as rhabdomyomas, may also cause preexcitation.
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