LVEF is almost the only parameter used to decide upon ICD implantation in patients for primary prevention, all this based upon MADIT and MADIT-affiliated trials. This strategy has led us to over-implant ICD devices in patients with significant consequences on health economics and patient morbidity.
Delayed enhancement, one of the most robust parameters brought to the table by MRI, has now heavy evidence backing up its predictive value on cardiac mortality and ventricular arrhythmias in various types of cardiomyopathies.
We need to re-do the MADIT trials implementing delayed enhancement in the therapeutic management decision.
Article Assessment of Myocardial Scarring Improves Risk Stratificati...
It's well known that the extent of scar and/or myocardial fibrosis [loss of viable tissue] is a strong predic tor of cardiac event as well as the extent of myocardial ischemia in CAD with preserved or LV dysfunction using Gated Spect and FDG-PET. In my experience myocardial innervation imaging with I123-MIBG adds further prognostic information by semiquantitative data [Heart/Mediastinum Ratio] and match/mismatch SPECT with perfusion, irrespectevely of severity of LV dysfunction, extent of scar, viability, and residual ischemia. So I think it's important to define adrenergic sympathic status of myocardium as an incremental prognostic index to identify pts with higher/lower risk of hard cardiac events[progressive heart failure, SCD, arrhythmyas
The most important contributions of CMR to the arrhitmic risk stratification is coming not only from LGE which is in relation to scarring but from T1 mapping which represents interstitial fibrosis and is a promising quantitative assessment of global LV fibrosis.
Besides the already complete observations. CMR with LGE is obviously the best and lighter way to address the issue of viability/scarring/recruitment. In addition MR is the gold standard for LVEF quantification (which is anyhow relevant as a criteria). CMR enhances the rate of responders and reduces the costs.
It is totally absurd if we think that identification of patients who require ICD is feasible only with one parameter such as Cardiac Delayed Enhancement. During the last years many methods have been introduced for risk stratification of patients who prone to SCD such as T-wave alternans (TWA), signal averaged EKG (SAEKG), Baroreceptor sensitivity reflex (BRSR), HRV, EF, family history, and so and so. But these temporary parameters separately, have not the ability to assess the risk of SCD and recommend ICD implantation in the reliable range of specificity and sensitivity; however most of them initially were introduced as a precise and effective method. Considering publications, it is evidence that a single parameter or method does not have this ability to identify implanting of the defibrillator. Therefore a combination of parameters and methods must be carried out to increase positive predictive value and negative predictive value. Maybe combining cardiac delayed enhancement with other parameters as a composite method would be more useful for assessing the risk of SCD and recommending ICD implantation.
I think CMR - Delayed gadolinium enhancement (GE) has definitely role in selecting appropriate patients for ICD implantation in primary prevention particularly of dilated cardiomyopathy ( DCM) . It has shown in various studies that appropriate therapy in patients with primary prevention particularly in (DCM) is very low and there is further risk stratification tools required. recently various small scale non randomized studies have shown that incidence of appropriate therapy is high in patients with delayed GE on CMR. One of the most recent study published in JAMA by gulati et al. I think to answer this question conclusively we need multicenter randomized study and will confirm that CMR has role in selection of patients for primary prevention in ICD implantation particularly DM as suggested by previous studies.
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