Morte cardiaca improvvisa
Table of Contents
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Definizione
Con il termine “morte cardiaca improvvisa” si intende il decesso per cause naturali di origine cardiaca che consegue ad un’improvvisa perdita di coscienza entro un’ora dall’esordio dei sintomi.
Epidemiologia
Esistono due picchi di incidenza della morte improvvisa; il primo nei sei mesi di vita (Sudden infant Death Syndrome o SIDS) e il secondo tra i 45 e i 75 anni di età.La morte cardiaca improvvisa tra i 45 e 75 anni può essere dovuta a:
1.Tachiaritmia fatale (fibrillazione ventricolare primaria) è il modo più comune di morte cardiaca improvvisa.
2. Nel 10-15% dei casi la causa è un’asistolia (assenza di battito cardiaco);
3. Più raramente unadissociazione elettromeccanica (presenza di attività elettrica in assenza di contrazioni efficace del cuore).
4. Lapatologia coronarica è senz’altro la causa più frequente di morte cardiaca improvvisa negli adulti e per tale motivo sia la distribuzione sia i principali fattori di rischio sono comuni alle due condizioni. L’incidenza della morte cardiaca improvvisa mostra un ritmo circadiano con una prevalenza tra le ore 6 del mattino e mezzogiorno. Questo ritmo circadiano è molto simile a quello osservato per l’insorgenza di altri eventi cardiaci acuti quali l’infarto del miocardio ed ischemia miocardica transitoria.
Fisiopatologia
La genesi della morte cardiaca improvvisa coinvolge una serie di fattori con ruoli diversi. Un modello efficace di morte cardiaca improvvisa prevede l’esistenza di un substrato miocardico, di fattori scatenanti e di fattori modulanti o favorenti che interagiscono.
Con il terminesubstrato si intende la presenza di alterazioni strutturali o elettriche cardiache che favoriscano il rischio aritmico:
- alterazioni strutturali possono ad esempio essere rappresentate da una cardiopatia congenita, da alterazioni conseguenti all’ ipertrofia o alla fibrosi miocardica, e possono ad esempio seguire ad un infarto del miocardio;
- alterazioni elettriche sono tipicamente quelle presenti in cardiopatia aritmogena ereditarie, legate a difetti di canali ionici cardiaci, quali la sindrome del QT lungo o la Sindrome di Brugada.
Un fattore scatenante importante è costituito, ad esempio, da unepisodio ischemico acuto. La frequente assenza, nei vasi coronarici esaminate all’autopsia, di lesioni occlusive sottolinea la possibilità che a scatenare l’episodio di arresto cardiaco sia un ischemia miocardica solo transitoria.In accordo con questa ipotesi è il fatto che è solo una minoranza di soggetti che tornano in vita dopo arresto cardiaco sviluppa un infarto del miocardio.
Con il termine “fattore modulare” si intende un fattore variabile nel tempo, e possa in talune circostanze presentarsi con caratteristiche tali da favorire l’insorgenza, la perpetuazione o la degenerazione di un’ aritmia ventricolare minacciosa.
Esempi tipici sono:
- Alterazioni elettrolitichequali ipopotassiemia
- Farmacicon potenziale effetto proaritmico
- sistema nervoso autonomo. Un’ eccessiva attivazione adrenergica esercita una serie di effetti sfavorevoli nel senso di un aumento della gravità dell’ischemia.
Principali condizioni patologiche associate a morte cardiaca improvvisa
La cardiopatia ischemica è responsabile di circa l’80% delle morti improvvise nei paesi occidentali e le cardiomiopatie si rendono responsabili di un altro 10-15%. Tuttavia altre cause sebbene più rare (entità minori)sono tra le principali cause di morte improvvisa in adolescenti e giovani adulti. Ci sono inoltre dei casi in cui la causa della morte cardiaca improvvisa o della fibrillazione ventricolare resuscitata non riesce ad essere identificata e si parla quindi di “fibrillazione ventricolare idiopatica”. A 5 anni di follow-up questi pazienti hanno un rischio del 30% di avere un nuovo arresto. e, per tale motivo esistono indicazioni assolute all’impianto del defibrillatore automatico, un apparecchio simile ad un pacemaker, in grado di riconoscere e trattare attraverso shock elettrico le aritmie ventricolari maligne.
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