Interuniversity Cardiology Institute of the Netherlands
Conduction reserve and arrhythmias M. Stein, M. Boulaksil, M.A. Engelen, T.A.B. van Veen, R.N.W. Hauer, J.M.T. de Bakker, H.V.M. van Rijen
The susceptibility of the heart to arrhythmias is determined by two components: 1) an arrhythmogenic substrate, i.e. the heart tissue must be able to accommodate arrhythmias, and 2) initiating triggers, to start the arrhythmia. Both factors are modulated by the autonomic nervous system.' A factor that plays an important role in the formation of the arrhythmogenic substrate is the impulse propagation. Major parameters for impulse propagation are cell-to-cell coupling and excitability. Slow and abnormal conduction is proarrhythmic, because it enhances the propensity for re-entrant arrhythmias. Normal propagation of the electrical impulse through the heart requires low resistance cell-to-cell coupling and proper excitability of the cardiac cells. The electrical coupling between myocytes is mediated by protein channels, called gap junctions, consisting of connexins (Cx, in the ventricle mainly Cx43). Sodium channels (SCN5a) are the major channel
M. Stein Departments of Cardiology and Medical Physiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, the Netherlands M. Boulaksil Department of Medical Physiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, the Netherlands and lnteruniversity Cardiology Institute of the Netherlands M.A. Engelen T.A.B. van Veen H.V.M. van RUjen Department of Medical Physiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, the Netherlands R.N.W. Hauer Department of Cardiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, the Netherlands J.M.T. de Bakker Department of Cardiology and Medical Physiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, Interuniversity Cardiology Institute of the Netherlands, and Cardiovascular Research Institute, Academic Medical Centre, Amsterdam, the Netherlands
Correspondence to: M. Stein Department of Medical Physiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, Yalelaan 50, 3584 CM Utrecht, the Netherlands E-mail: [email protected]
(Apl
Netherlands Heart Joural, Volume 14, Number 3, March 2006
proteins involved in excitability of the cardiac cells. Myocytes are embedded in a network of collagen fibres that provides the physical framework for transmission of force through the myocardium. In the normal heart the extracellular matrix consists of thin intertwining strands, allowing cell-to-cell contact between neighbouring cardiac cells. Cardiac pathologies, such as arterial hypertension and myocardial infarction, initiate a gene programme leading to myocardial remodelling. This includes structural and functional changes, which may finally lead to heart failure. Conduction velocity of the cardiac impulse is decreased with increasing severity of hypertrophy.2'3 In human heart, pathology reduces excitability by decreased sodium channel expression of up to 50%4'5 and electrical coupling is reduced by 30 to 50% due to decreased Cx43 expression.68 Intercellular collagen deposition (fibrosis) is increased from 5% up to 30%.9 These changes enhance the arrhythmogenic vulnerability of the heart, which is reflected by the high sudden death rate in patients with congestive heart failure. However, it is not clear how each alteration contributes to the arrhythmogenic substrate.
To investigate the effect of isolated alterations, mouse models with clinically relevant reductions in excitability, cell-to-cell coupling, or increased fibrosis were analysed and compared with wild-type littermates (figures 1A and B), in order to evaluate whether such changes in isolation alter ventricular conduction and enhance arrhythmogenesis. The reduction in cell-to-cell coupling was investigated using a mouse model, haploinsufficient for Cx43. When cardiac Cx43 expression was reduced by 50%, no effect on conduction velocity and anisotropic ratio was noticed, and no arrhythmias were inducible.'0"' Typical examples of conduction velocity measurements at a 50% Cx43 reduction are shown in figures IC and D. Similarly, the influence of reduced excitability on impulse propagation was studied by analysing a mouse, haploinsufficient for the cardiac sodium channel (SCN5a). These mice revealed a 50% reduction in sodium current, which resulted in a moderately reduced conduction velocity (both along and perpendicular to the fibre direction) exclusively in the right ventricle (figures 1E and F). The anisotropic ratio remained unchanged, and no arrhythmias were observed. These changes were expressed 113
Interuniversity Cardiology Institute of the Netherlands
'Woopo
-
....
.O..
:::" $01ON .4.
::::* :.**.:
O.:: 0 ...0
.
:::::::
:t::::: .0.
RV
LV
z
I _,
s
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.~~~~.* :::I:*@::: 12
Control
10
14 12 10 a B 4
50% Cx43
LI 50% CSN5a
5-fold Increase flbrosis
e:1
16
14 12 10
6
7lica4activation mapsfrom tlekftventrick (LV) and rigtventricle (RV) ofmoubeart, reord witha l9xl3multieectrode gi4d (elctrode spacing 0.3 mm), during pacingfrom two central elctrodes (Si-S1-150 ms). Tbe upper illustration shows the eletrode position. Tbe double-beaded blue arrow indicates epicardialfibre orientation. Isocbrone spacing in de activation maps 1 ms. A and B: Activation maps of contrl mice. C and D: Activation maps of mice expressing only 50% Cx43. Data redrawn from Van Rijen et al.1' E and F: Activation maps of mice exprsing only 50% SCN5a. On average, conduction velocity in RV is reduced by 19% parallel to myocardialfibre orentation and by 21% perpendicsar to fibre orentation. Data edrawn from Van Veen etal. G and H: Ativation maps of mice withfivefold increas in myocardial interstitialfibrosis. On average conduction velocity in RVperpendicular tofibre orientation is reduced by 25%. Data redrawn from Van Vean et al.U2
Figure
1.
114
Nedhcrands Heart Journal, Volume
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Mac
2006
v
Interuniversity Cardiology Institute of the Netherlands
(LV) and riqht ventrick (RV) ofcontrol hearts (A and B) and mouse hearts with a combined reduction of SCN5a expression and enhanced interstitial fibrosis (C and D). In RV, conduction velocity parallel and perpendKilar t myocardialfibre orientation was reduced by 35 and 50%, whik in LV these changes were 36 and 35%, respectively. Data redrawn Zfrom Van Veen et al.'2
Figure2. 7Tpical activation mapsfrom the kft ventrick
by a slightly prolonged QRS duration compared with wild-
type littermates.'2
The amount of interstitial fibrosis in mice was increased fivefold from about 0.5% in young wild type mice up to 2.5% by ageing mice up to 16 months. The old mice showed minor QRS widening, which was caused by slightly reduced conduction velocity in the right ventride perpendicular to the myocyte fibre orientation (figures 1G and H).'2"13 No arrhythmias were recorded. These data show that clinically relevant reductions of excitability, gap junction expression, or a moderate increase in interstitial fibrosis, are in themselves not responsible for significant conduction abnormalities or increased susceptibility to arrhythmias, albeit in mice. These studies show that the heart has conduction reserve. Conduction velocity can be maintained at near-normal values when either excitability or cell-cell coupling is reduced or fibrosis is increased. Thus, the heart might be affected up to a certain level without influencing impulse propagation or increasing its vulnerability to tachyarrhythmias. However, when we aged mice that were haploinsufficient for the SCN5a cardiac sodium channel, thus combining 9C
Netherlands Heart Journal, Volume 14, Number 3, March 2006
decreased excitability with increased interstitial fibrosis, conduction velocity was severely reduced both along and perpendicular to the fibre orientation, both in the right and in the left ventricle (figure 2). Interestingly, when two factors were impaired, the effect on conduction velocity was larger than was expected from the isolated impairments, showing clear synergism between the two factors. Overall it can be concluded that the heart has significant conduction reserve, which allows for moderate alterations in excitability, electrical coupling or interstitial fibrosis, especially when present in isolation. A combination of two or more impairments is needed to exceed the limits of conduction reserve and impair conduction. Conduction reserve was found to be less in the right ventricle, because impairments were predominantly located in the right ventricle. Conduction reserve is also expected to play a role in the human heart. This may be the case in Brugada syndrome and Lenegre disease which are both associated with loss offunction mutations of the SCN5a gene, encoding for the cardiac sodium channel.'4-'6 In these disorders, conduction reserve seems to play a role, because additional reduction ofsodium 115
Interuniversity Cardiology Institute of the Netherlands current (for example flecainide administration) is frequently needed for proper identification of the disease. In addition, the progressive nature of electrical abnormalities with age, strongly suggests that cofactors for arrhythmogeneity develop in time.'6"17 This is evidenced by recent reports that have shown that sodium channel mutations may lead to structural remodelling (increased fibrosis), thereby exhausting conduction reserve and enhancing arrhythmogeneity.'8
9
Studies were partly supported by NHS grant 2003B128.
12
References 1
2 3 4
5 6 7 8
Coumel P. The management of clinical arrhythmias. An overview on invasive versus non-invasive electrophysiology. Eur HeartJ 1987;8:92-9. Wmterton SJ, Turner MA, O'Gorman DJ, Flores NA, Sheridan DJ. Hypertrophy causes delayed conduction in human and guinea pig myocardium: accentuation during ischaemic perfusion. CardiovasRes 1994;28:47-54. Cooklin M, Wallis WRJ, Sheridan DJ, Fry CH. Changes in cell-to-cell electrical coupling associated with left ventricular hypertrophy. Circulation Res 1997;80:765-71. Borlak J, Thum T. Hallmarks of ion channel gene expression in end-stage heart failure. FasebJ2003;17:1592-608. Valdivia CR, Chu WW, Pu J, Foell JD, Haworth RA, Wolff MR, et al. Increased late sodium current in myocytes from a canine heart failure model and from failing human heart. JMol Cell Cardiol2005;38:475-83. Peters NS. New insights into myocardial arrhythmogenesis: Distribution of gap junctional coupling in normal ischemic and hypertrophied human hearts. Clin Sci 1996;90:447-52. Yamada KA, Rogers JG, Sundset R, Steinberg TH, Saffitz JE. Up-regulation ofconnexin45 in heart failure. JCardiovasc EleckropAysiol2003;14:1205-12. Kostin S, Dammer S, Hein S, Kiovekorn WP, Bauer EP, Schaper J. Connexin 43 expression and distribution in compensated and decompensated cardiac hypertrophy in patients with aortic stenosis. Cardiovasc Res 2004;62:426-36.
116
10 11
13
14
15 16 17
18
Kawara T, Derksen R, de Groot JR, Coronel R, Tasseron S, Linnenbank AC, et al. Activation delay after premature stimulation in chronically diseased human myocardium relates to the architecture of interstitial fibrosis. Circulation 2001;104:3069-75. Morley GE, Vaidya D, Samie FH, Lo C, Delmar M, Jalife J. Characterization of conduction in the ventricles ofnormal and heterozygous Cx43 knockout mice using optical mapping. JCardiovascElectrophysiol 1999;10:1361-75. Van Rijen HVM, Eckardt D, Degen J, Theis M, Ott T, Willecke K, et al. Slow conduction and enhanced anisotropy increase the propensity for ventricular tachyarrhythmias in adult mice with induced deletion of connexin43. Circulation 2004;109:1048-55. Van Veen TA, Stein M, Royer A, Le Quang K, Charpentier F, Colledge WH, et al. Impaired Impulse Propagation in Scn5a-Knockout Mice. Combined Contribution of Excitability, Connexin Expression, and Tissue Architecture in Relation to Aging. Circulation 2005;112(13):1927-35. Royer A, van Veen TA, Le Bouter S, Marionneau C, Griol-Charhbili V, Leoni AL, et al. Mouse model of SCN5A-linked hereditary Lenegre's disease: age-related conduction slowing and myocardial fibrosis. Circulation 2005;111:1738-46. Brugada P, Brugada J. Right bundle branch block, persistent ST segment elevation and sudden cardiac death: a distinct clinical and electrocardiographic syndrome. A multicenter report. J Am Coll Cardiol 1992;20: 1391-6. Antzelevitch C, Brugada P, Brugada J, Brugada R, Shimizu W, Gussak I, et al. Brugada syndrome: a decade of progress. Circ Res2002;91:1114-8. Probst V, Kyndt F, Potet F, Trochu JN, Mialet G, Demolombe S, et al. Haploinsufficiency in combination with aging causes SCN5A-linked hereditary Lenegre disease. JAm Coll Cardiol2003;41:643-52. Coronel R, Casini S, Koopmann TT, Wllms-Schopman FJ, VerkerkAO, de Groot JR, et al. Right ventricular fibrosis and conduction delay in a patient with clinical signs of Brugada syndrome: a combined electrophysiological, genetic, histopathologic, and computational study. Circulation 2005;112: 2769-77. Olson TM, Michels VV, Ballew JD, Reyna SP, Karst ML, Herron KJ, et al. Sodium channel mutations and susceptibility to heart failure and atrial fibrillation. JAMA 2005;293:447-54.
Netherlands Heart Jounal, Volume 14, Number 3, March 2006
¢l
Conduction reserve and arrhythmias M. Stein, M. Boulaksil, M.A. Engelen, T.A.B. van Veen, R.N.W. Hauer, J.M.T. de Bakker, H.V.M. van Rijen
The susceptibility of the heart to arrhythmias is determined by two components: 1) an arrhythmogenic substrate, i.e. the heart tissue must be able to accommodate arrhythmias, and 2) initiating triggers, to start the arrhythmia. Both factors are modulated by the autonomic nervous system.' A factor that plays an important role in the formation of the arrhythmogenic substrate is the impulse propagation. Major parameters for impulse propagation are cell-to-cell coupling and excitability. Slow and abnormal conduction is proarrhythmic, because it enhances the propensity for re-entrant arrhythmias. Normal propagation of the electrical impulse through the heart requires low resistance cell-to-cell coupling and proper excitability of the cardiac cells. The electrical coupling between myocytes is mediated by protein channels, called gap junctions, consisting of connexins (Cx, in the ventricle mainly Cx43). Sodium channels (SCN5a) are the major channel
M. Stein Departments of Cardiology and Medical Physiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, the Netherlands M. Boulaksil Department of Medical Physiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, the Netherlands and lnteruniversity Cardiology Institute of the Netherlands M.A. Engelen T.A.B. van Veen H.V.M. van RUjen Department of Medical Physiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, the Netherlands R.N.W. Hauer Department of Cardiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, the Netherlands J.M.T. de Bakker Department of Cardiology and Medical Physiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, Interuniversity Cardiology Institute of the Netherlands, and Cardiovascular Research Institute, Academic Medical Centre, Amsterdam, the Netherlands
Correspondence to: M. Stein Department of Medical Physiology, Heart Lung Centre Utrecht, University Medical Centre Utrecht, Yalelaan 50, 3584 CM Utrecht, the Netherlands E-mail: [email protected]
(Apl
Netherlands Heart Joural, Volume 14, Number 3, March 2006
proteins involved in excitability of the cardiac cells. Myocytes are embedded in a network of collagen fibres that provides the physical framework for transmission of force through the myocardium. In the normal heart the extracellular matrix consists of thin intertwining strands, allowing cell-to-cell contact between neighbouring cardiac cells. Cardiac pathologies, such as arterial hypertension and myocardial infarction, initiate a gene programme leading to myocardial remodelling. This includes structural and functional changes, which may finally lead to heart failure. Conduction velocity of the cardiac impulse is decreased with increasing severity of hypertrophy.2'3 In human heart, pathology reduces excitability by decreased sodium channel expression of up to 50%4'5 and electrical coupling is reduced by 30 to 50% due to decreased Cx43 expression.68 Intercellular collagen deposition (fibrosis) is increased from 5% up to 30%.9 These changes enhance the arrhythmogenic vulnerability of the heart, which is reflected by the high sudden death rate in patients with congestive heart failure. However, it is not clear how each alteration contributes to the arrhythmogenic substrate.
To investigate the effect of isolated alterations, mouse models with clinically relevant reductions in excitability, cell-to-cell coupling, or increased fibrosis were analysed and compared with wild-type littermates (figures 1A and B), in order to evaluate whether such changes in isolation alter ventricular conduction and enhance arrhythmogenesis. The reduction in cell-to-cell coupling was investigated using a mouse model, haploinsufficient for Cx43. When cardiac Cx43 expression was reduced by 50%, no effect on conduction velocity and anisotropic ratio was noticed, and no arrhythmias were inducible.'0"' Typical examples of conduction velocity measurements at a 50% Cx43 reduction are shown in figures IC and D. Similarly, the influence of reduced excitability on impulse propagation was studied by analysing a mouse, haploinsufficient for the cardiac sodium channel (SCN5a). These mice revealed a 50% reduction in sodium current, which resulted in a moderately reduced conduction velocity (both along and perpendicular to the fibre direction) exclusively in the right ventricle (figures 1E and F). The anisotropic ratio remained unchanged, and no arrhythmias were observed. These changes were expressed 113
Interuniversity Cardiology Institute of the Netherlands
'Woopo
-
....
.O..
:::" $01ON .4.
::::* :.**.:
O.:: 0 ...0
.
:::::::
:t::::: .0.
RV
LV
z
I _,
s
v-
.~~~~.* :::I:*@::: 12
Control
10
14 12 10 a B 4
50% Cx43
LI 50% CSN5a
5-fold Increase flbrosis
e:1
16
14 12 10
6
7lica4activation mapsfrom tlekftventrick (LV) and rigtventricle (RV) ofmoubeart, reord witha l9xl3multieectrode gi4d (elctrode spacing 0.3 mm), during pacingfrom two central elctrodes (Si-S1-150 ms). Tbe upper illustration shows the eletrode position. Tbe double-beaded blue arrow indicates epicardialfibre orientation. Isocbrone spacing in de activation maps 1 ms. A and B: Activation maps of contrl mice. C and D: Activation maps of mice expressing only 50% Cx43. Data redrawn from Van Rijen et al.1' E and F: Activation maps of mice exprsing only 50% SCN5a. On average, conduction velocity in RV is reduced by 19% parallel to myocardialfibre orentation and by 21% perpendicsar to fibre orentation. Data edrawn from Van Veen etal. G and H: Ativation maps of mice withfivefold increas in myocardial interstitialfibrosis. On average conduction velocity in RVperpendicular tofibre orientation is reduced by 25%. Data redrawn from Van Vean et al.U2
Figure
1.
114
Nedhcrands Heart Journal, Volume
14, Number 3,
Mac
2006
v
Interuniversity Cardiology Institute of the Netherlands
(LV) and riqht ventrick (RV) ofcontrol hearts (A and B) and mouse hearts with a combined reduction of SCN5a expression and enhanced interstitial fibrosis (C and D). In RV, conduction velocity parallel and perpendKilar t myocardialfibre orientation was reduced by 35 and 50%, whik in LV these changes were 36 and 35%, respectively. Data redrawn Zfrom Van Veen et al.'2
Figure2. 7Tpical activation mapsfrom the kft ventrick
by a slightly prolonged QRS duration compared with wild-
type littermates.'2
The amount of interstitial fibrosis in mice was increased fivefold from about 0.5% in young wild type mice up to 2.5% by ageing mice up to 16 months. The old mice showed minor QRS widening, which was caused by slightly reduced conduction velocity in the right ventride perpendicular to the myocyte fibre orientation (figures 1G and H).'2"13 No arrhythmias were recorded. These data show that clinically relevant reductions of excitability, gap junction expression, or a moderate increase in interstitial fibrosis, are in themselves not responsible for significant conduction abnormalities or increased susceptibility to arrhythmias, albeit in mice. These studies show that the heart has conduction reserve. Conduction velocity can be maintained at near-normal values when either excitability or cell-cell coupling is reduced or fibrosis is increased. Thus, the heart might be affected up to a certain level without influencing impulse propagation or increasing its vulnerability to tachyarrhythmias. However, when we aged mice that were haploinsufficient for the SCN5a cardiac sodium channel, thus combining 9C
Netherlands Heart Journal, Volume 14, Number 3, March 2006
decreased excitability with increased interstitial fibrosis, conduction velocity was severely reduced both along and perpendicular to the fibre orientation, both in the right and in the left ventricle (figure 2). Interestingly, when two factors were impaired, the effect on conduction velocity was larger than was expected from the isolated impairments, showing clear synergism between the two factors. Overall it can be concluded that the heart has significant conduction reserve, which allows for moderate alterations in excitability, electrical coupling or interstitial fibrosis, especially when present in isolation. A combination of two or more impairments is needed to exceed the limits of conduction reserve and impair conduction. Conduction reserve was found to be less in the right ventricle, because impairments were predominantly located in the right ventricle. Conduction reserve is also expected to play a role in the human heart. This may be the case in Brugada syndrome and Lenegre disease which are both associated with loss offunction mutations of the SCN5a gene, encoding for the cardiac sodium channel.'4-'6 In these disorders, conduction reserve seems to play a role, because additional reduction ofsodium 115
Interuniversity Cardiology Institute of the Netherlands current (for example flecainide administration) is frequently needed for proper identification of the disease. In addition, the progressive nature of electrical abnormalities with age, strongly suggests that cofactors for arrhythmogeneity develop in time.'6"17 This is evidenced by recent reports that have shown that sodium channel mutations may lead to structural remodelling (increased fibrosis), thereby exhausting conduction reserve and enhancing arrhythmogeneity.'8
9
Studies were partly supported by NHS grant 2003B128.
12
References 1
2 3 4
5 6 7 8
Coumel P. The management of clinical arrhythmias. An overview on invasive versus non-invasive electrophysiology. Eur HeartJ 1987;8:92-9. Wmterton SJ, Turner MA, O'Gorman DJ, Flores NA, Sheridan DJ. Hypertrophy causes delayed conduction in human and guinea pig myocardium: accentuation during ischaemic perfusion. CardiovasRes 1994;28:47-54. Cooklin M, Wallis WRJ, Sheridan DJ, Fry CH. Changes in cell-to-cell electrical coupling associated with left ventricular hypertrophy. Circulation Res 1997;80:765-71. Borlak J, Thum T. Hallmarks of ion channel gene expression in end-stage heart failure. FasebJ2003;17:1592-608. Valdivia CR, Chu WW, Pu J, Foell JD, Haworth RA, Wolff MR, et al. Increased late sodium current in myocytes from a canine heart failure model and from failing human heart. JMol Cell Cardiol2005;38:475-83. Peters NS. New insights into myocardial arrhythmogenesis: Distribution of gap junctional coupling in normal ischemic and hypertrophied human hearts. Clin Sci 1996;90:447-52. Yamada KA, Rogers JG, Sundset R, Steinberg TH, Saffitz JE. Up-regulation ofconnexin45 in heart failure. JCardiovasc EleckropAysiol2003;14:1205-12. Kostin S, Dammer S, Hein S, Kiovekorn WP, Bauer EP, Schaper J. Connexin 43 expression and distribution in compensated and decompensated cardiac hypertrophy in patients with aortic stenosis. Cardiovasc Res 2004;62:426-36.
116
10 11
13
14
15 16 17
18
Kawara T, Derksen R, de Groot JR, Coronel R, Tasseron S, Linnenbank AC, et al. Activation delay after premature stimulation in chronically diseased human myocardium relates to the architecture of interstitial fibrosis. Circulation 2001;104:3069-75. Morley GE, Vaidya D, Samie FH, Lo C, Delmar M, Jalife J. Characterization of conduction in the ventricles ofnormal and heterozygous Cx43 knockout mice using optical mapping. JCardiovascElectrophysiol 1999;10:1361-75. Van Rijen HVM, Eckardt D, Degen J, Theis M, Ott T, Willecke K, et al. Slow conduction and enhanced anisotropy increase the propensity for ventricular tachyarrhythmias in adult mice with induced deletion of connexin43. Circulation 2004;109:1048-55. Van Veen TA, Stein M, Royer A, Le Quang K, Charpentier F, Colledge WH, et al. Impaired Impulse Propagation in Scn5a-Knockout Mice. Combined Contribution of Excitability, Connexin Expression, and Tissue Architecture in Relation to Aging. Circulation 2005;112(13):1927-35. Royer A, van Veen TA, Le Bouter S, Marionneau C, Griol-Charhbili V, Leoni AL, et al. Mouse model of SCN5A-linked hereditary Lenegre's disease: age-related conduction slowing and myocardial fibrosis. Circulation 2005;111:1738-46. Brugada P, Brugada J. Right bundle branch block, persistent ST segment elevation and sudden cardiac death: a distinct clinical and electrocardiographic syndrome. A multicenter report. J Am Coll Cardiol 1992;20: 1391-6. Antzelevitch C, Brugada P, Brugada J, Brugada R, Shimizu W, Gussak I, et al. Brugada syndrome: a decade of progress. Circ Res2002;91:1114-8. Probst V, Kyndt F, Potet F, Trochu JN, Mialet G, Demolombe S, et al. Haploinsufficiency in combination with aging causes SCN5A-linked hereditary Lenegre disease. JAm Coll Cardiol2003;41:643-52. Coronel R, Casini S, Koopmann TT, Wllms-Schopman FJ, VerkerkAO, de Groot JR, et al. Right ventricular fibrosis and conduction delay in a patient with clinical signs of Brugada syndrome: a combined electrophysiological, genetic, histopathologic, and computational study. Circulation 2005;112: 2769-77. Olson TM, Michels VV, Ballew JD, Reyna SP, Karst ML, Herron KJ, et al. Sodium channel mutations and susceptibility to heart failure and atrial fibrillation. JAMA 2005;293:447-54.
Netherlands Heart Jounal, Volume 14, Number 3, March 2006
¢l
