Tahiaritmii ventriculare

1. Aritmiile ventriculare

Aritmiile ventriculare pot fi un eveniment izolat si complet benign la copii, un marker al unei afectiuni sistemice sau miopatii, sau un mecanism de sincopa si moarte subita. Tahicardia ventriculara sustinuta (TVS) este definita ca un ritm ventricular cu o durata de peste 30 de secunde si o frecventa de peste 110-120/min sau care necesita cardioversie urgenta. TV nesustinuta (TVNS) include 3 sau mai multe complexe ventriculare cu o durata de pina la 30 de secunde. Extrasistolele ventriculare de grad inalt includ cupletele si extrasistolele polimorfe sistematizate.

Extrasistolele ventriculare (ESV) sunt o tulburare de ritm comuna, care apare la aproximativ 40% dintre pacienti pe un cord aparent normal, frecventa lor zilnica fiind redusa. Din contra, in cardiopatiile congenitale operate, ele apar cu o frecventa crescuta, la peste 60% dintre pacienti1. Aritmiile ventriculare sustinute desi pot apare si pe un cord aparent normal, in peste 50% dintre pacienti exista un substrat precum miopatii sau cardiopatii congenitale.

Mecanismele clasice ale aritmiilor sunt implicate si in aritmiile ventriculare: reintrarea, automatismul si ectopiile.

Aritmiile prin reintrare depind de un circuit, adesea determinat de o cicatrice postoperatorie (corectia tetralogiei Fallot), fibroza sau degenerare grasoasa. Prezenta unei arii de tesut anormal functional cu o zona de conducere lenta generatoare a unei linii de bloc functional unidirectional in jurul careia apare un circuit de reintrare care se va perpetua este conditia esentiala de aparitie a aritmiei. In practica, circuitul de reintrare este "activat" frecvent de o extrasistola si intrerupt prin cardioversie electrica. De aceea, debutul brusc si frecventa in general stabila sunt alte caracteristici ale aritmiilor prin reintrare.

Automatismul celular anormal sunt cauza cea mai frecventa a aritmiilor la copii, pe un cord normal structural. Cresterea frecventei depolarizarilor spontane de faza 4 a potentialului de actiune, idiopatice sau in contextul unor tulburari metabolice (hipokaliemie, hipomagneziemie, etc) stau la baza automatismului anormal. Frecventele atriale inalte suprima dar nu inlatura aritmia ventriculara maligna de tip tahicardie

ventriculara (TV). Ritmul idioventricular accelerat este un exemplu de TV prin automatism (mecanism autonom).

Aritmiile ventriculare prin ectopii ("trigger") pot apare in intoxicatia digitalica (prin efectul batmotrop al digitalei) sau, de exemplu, in sindromul QT lung (TV polimorfa).

Mortalitatea

Riscul major al aritmiilor ventriculare este constituit de sincopa si moartea subita. Un rol esential il are prevenirea mortii subite la acesti pacienti. Acest risc este scazut, cu exceptia unui grup de pacienti cu afectare cardiaca organica si TVS, pentru care riscul anual de deces este de aproximativ 3% (inclusiv pentru populatia pediatrica). Astfel rata mortalitatii cardiace prin aritmii in populatia pediatrica este de 1-5 decese la 100.000 pacienti/an. La adulti aceasta este de 1-3 decese la 1000 pacienti pe an. Mortalitatea anuala la supravietuitorii unui infarct miocardic cu functie ventriculara stanga diminuata si TV inductibile si necontrolabile este de 20%.

La copiii aparent sanatosi incidenta aritmiilor ventriculare ectopice are 2 varfuri: unul care scade inainte de varsta prescolara si scoala primara si un altul in adolescenta. Desi 15% dintre copii si 40% dintre adolescenti au ectopii ventriculare, aritmiile ventriculare maligne sunt rare. Astfel, sincopa la copii are cel mai frecvent o etiologie vagala si foarte rar se datoreaza aritmiilor ventriculare. Din contra, la adolescentii mai mari si adultii tineri cu anomalii cardiace corectate chirurgical, incidenta acestor aritmii este semnificativ mai mare2.

Anamneza pacientilor trebuie sa evidentieze:

- prezenta si severitatea simptomelor;

- prezenta simptomelor la efort;

- diagnostice si proceduri cardiace interventionale anterioare;

- istoric familial de deces inainte de varsta de 40 de ani (chiar daca se datoreaza unui aparent accident de masina, poate ridica suspiciuni) si de afectiuni congenitale;

- medicamente (antidepresante triciclice, antiaritmice sau altele care afecteaza (repolarizarea) sau alte droguri potentiale (cocaina).

1. Mirowski M, Reid PR, Mower MM, et al. Termination of malignant ventricular arrhythmias with an implanted automatic defibrillator in human beings. N Engl J Med. 1980;303(6):322-4.

2. [Guideline] Epstein AE, DiMarco JP, Ellenbogen KA, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices) developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. J Am Coll Cardiol. 2008;51(21):1-62.

3. Kroll MW, Swerdlow CD. Optimizing defibrillation waveforms for ICDs. J Interv Card Electrophysiol. 2007;18(3):247-63.

4. The Antiarrhythmics versus Implantable Defibrillators (AVID) Investigators. A comparison of antiarrhythmic-drug therapy with implantable defibrillators in patients resuscitated from near-fatal ventricular arrhythmias. The Antiarrhythmics versus Implantable Defibrillators (AVID) Investigators. N Engl J Med. 1997;337(22):1576-83.

5. Connolly SJ, Gent M, Roberts RS, et al. Canadian implantable defibrillator study (CIDS) : a randomized trial of the implantable cardioverter defibrillator against amiodarone. Circulation. 2000;101(11):1297-302.

6. Kuck KH, Cappato R, Siebels J, Ruppel R. Randomized comparison of antiarrhythmic drug therapy with implantable defibrillators in patients resuscitated from cardiac arrest : the Cardiac Arrest Study Hamburg (CASH). Circulation. 2000;102(7):748-54.

7. Moss AJ, Hall WJ, Cannom DS, et al. Improved survival with an implanted defibrillator in patients with coronary disease at high risk for ventricular arrhythmia. Multicenter Automatic Defibrillator Implantation Trial (MADIT) Investigators. N Engl J Med. 1996;335(26):1933-40.

8. Buxton AE, Lee KL, Fisher JD, et al. A randomized study of the prevention of sudden death in patients with coronary artery disease. Multicenter Unsustained Tachycardia Trial (MUSTT) Investigators. N Engl J Med. 1999;341(25):1882-90.

9. Buxton AE, Lee KL, Hafley GE, et al. Relation of ejection fraction and inducible ventricular tachycardia to mode of death in patients with coronary artery disease: an analysis of patients enrolled in the multicenter unsustained tachycardia trial. Circulation. 2002;106(19):2466-72.

10. Fisher JD, Buxton AE, Lee KL, et al. Designation and distribution of events in the Multicenter Unsustained Tachycardia Trial (MUSTT). Am J Cardiol. 2007;100(1):76-83.

11. Moss AJ, Zareba W, Hall WJ. Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction (MADIT II). N Engl J Med. 2002;346(12):877-83.

12. Zwanziger J, Hall WJ, Dick AW, Zhao H, Mushlin AI, Hahn RM, et al. The cost effectiveness of implantable cardioverter-defibrillators: results from the Multicenter Automatic Defibrillator Implantation Trial (MADIT)-II. J Am Coll Cardiol. 2006;47(11):2310-8.

13. Bristow MR, Saxon LA, Boehmer J, et al. Cardiac-resynchronization therapy with or without an implantable defibrillator in advanced chronic heart failure. N Engl J Med. 2004;350(21):2140-50.

14. Bardy GH, Lee KL, Mark DB, et al. Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure. N Engl J Med. 2005;352(3):225-37.

15. Levy WC, Lee KL, Hellkamp AS, et al. Maximizing survival benefit with primary prevention implantable cardioverter-defibrillator therapy in a heart failure population. Circulation. 2009;120(10):835-42.

16. Kadish A, Dyer A, Daubert JP, et al. Prophylactic defibrillator implantation in patients with nonischemic dilated cardiomyopathy. N Engl J Med. 2004;350(21):2151-8.

17. Bansch D, Antz M, Boczor S, et al. Primary prevention of sudden cardiac death in idiopathic dilated cardiomyopathy: the Cardiomyopathy Trial (CAT). Circulation. 2002;105(12):1453-8.

18. Bigger JT Jr. Prophylactic use of implanted cardiac defibrillators in patients at high risk for ventricular arrhythmias after coronary-artery bypass graft surgery. Coronary Artery Bypass Graft (CABG) Patch Trial Investigators. N Engl J Med. 1997;337(22):1569-75.

19. Hohnloser SH, Kuck KH, Dorian P, et al. Prophylactic use of an implantable cardioverter-defibrillator after acute myocardial infarction. N Engl J Med. 2004;351(24):2481-8.

20. Strickberger SA, Hummel JD, Bartlett TG, et al. Amiodarone versus implantable cardioverter-defibrillator: randomized trial in patients with nonischemic dilated cardiomyopathy and asymptomatic nonsustained ventricular tachycardia--AMIOVIRT. J Am Coll Cardiol. 2003;41(10):1707-12.

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