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DISPOSITIVO SUPERCONDUCTOR DE INTERFERENCIA CUÁNTICA (SQUID)

SQUID (por sus siglas en inglés) es una modalidad de diagnóstico por imágenes que emplea un campo magnético de muy baja potencia, con detectores sensibles que miden la interferencia del hierro dentro del campo. Se realiza una medición reduciendo el valor del paciente hasta un valor de campo magnético constante conocido y luego se detecta el cambio del flujo magnético en comparación con un medio acuoso de referencia. El sensor necesita un entorno criogénico, ya que debe ser superconductor para que funcione [47]. Aunque SQUID aún se considera un método en investigación, se han demostrado correlaciones lineales entre las mediciones mediante SQUID y los niveles de hierro obtenidos de biopsias hepáticas 48–50].

Técnica para tomar una medición de hierro con SQUID

Fischer [47]. © 1998 Wiley-VCH Verlag GmbH & Co KGaA, reimpreso con permiso.

Relación lineal entre SQUID y la biopsia hepática

Fischer [51]. © 1992 Elsevier Inc, reimpreso con permiso.

Aunque el método SQUID mide directamente la sensibilidad magnética de la ferritina y de la hemosiderina, al momento no posee suficiente resolución temporal o espacial para evaluar el hierro del corazón.  Actualmente el uso de SQUID es limitado, ya que sólo existen cuatro lugares en el mundo que cuentan con una máquina para SQUID disponible para realizar mediciones de niveles de hierro. Además, durante el desarrollo clínico de deferasirox, se mostró que los datos de LIC obtenidos mediante SQUID subestimaban lo valores de LIC obtenidos a través de biopsia, en un factor de 0,46 [52].

Uno de los cuatro centros mundiales que actualmente cuenta con SQUID

ECOCARDIOGRAFÍA, VENTRICULOGAMMAGRAFÍA

Se pueden proporcionar evaluaciones exactas de LVEF, de manera no invasiva, mediante ecocardiografía en reposo y con provocación [53, 54] o ventriculogammagrafía [55, 56]. Estas técnicas pueden resultar útiles en el diagnóstico de enfermedades tempranas cardiacas inducidas por hierro, ya que se ha mostrado que la disfunción diastólica tiene un valor pronóstico en el desarrollo de enfermedad cardiaca sintomática inducida por hierro [10, 57].

La ecocardiografía es la técnica más ampliamente usada para el diagnóstico y el pronóstico de la función sistólica del ventrículo izquierdo [58]. Sin embargo, una limitación importante de este enfoque es que las anomalías ecocardiográficas tienden a desarrollarse relativamente tarde en el transcurso de la cardiomiopatía. Además, la técnica depende de la habilidad del usuario y exige que se realicen suposiciones sobre la geometría ventricular, lo cual aumenta la probabilidad de variabilidad entre observadores. En consecuencia, las mediciones de la fracción de eyección en reposo por angiogammagrafía y resonancia magnética son más contundentes que las de ecocardiografía, y son mejores en cuanto al reconocimiento de la disfunción sistólica preclínica [59].

Resumen de los métodos primarios disponibles para la evaluación de la concentración de hierro corporal..

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Más información sobre la beneficios de la terapia de quelación en el tratamiento La sobrecarga de hierro transfusional.