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Scaring myocardial scars: new targets for the electrical fairy? (July/2012)

 

Myocardial scarring assessed by MRI is an independent predictor of poor outcomes in implantable cardioverter defibrillator (ICD) candidates with low left ventricular ejection fraction (LVEF), new trial results show.

Currently, measuring LVEF is the most common method for identifying which patients are most likely to need an implantable defibrillator to prevent sudden cardiac death, but sudden cardiac death is usually caused by ventricular tachyarrhythmia, so LVEF is only an indirect measure sudden cardiac death risk. About 70% of patients suffering sudden cardiac death have a preserved LVEF, and studies show that only one death is prevented for every 14 to 18 patients with ventricular dysfunction receiving an ICD, according to the study.
 
The study argues that previously, indirect measures with echocardiography or nuclear imaging techniques have been used, but MRI is a very high-resolution technique that can visualize myocardial scar the same way the pathologist sees the heart. It’s a very high-resolution test to directly visualize the scar, and this is the anatomical substrate that is responsible for the occurrence of ventricular arrhythmias in a fairly large number of patients.
 
The study used MRI to evaluate myocardial scarring in 137 patients being evaluated for possible ICD placement for prevention of sudden cardiac death.
Over a median follow up period of two years, among patients with LVEFs >30%, those with scarring over 5% of the left ventricle were 6.3 times as likely to die or suffer a sustained ventricular tachyarrhythmia as those with scarring under 5%. Among patients with an LVEF<30%, those with scarring greater than 5% were 3.9 times as likely to die or suffer a sustained ventricular tachyarrhythmia as those with minimal or no scarring.
 
Patients with an LVEF >30% but significant scarring had the same risk as all patients with an LVEF <30%. Patients with an LVEF <30% and minimal or no scarring had a similar risk to all patients with an LVEF >30%.