Reasons for ICD failure remain unclear after further investigation of IRIS
MedWire News: IRIS study investigators have found no evidence from a fresh analysis of their data to explain why early implantation with an implantable cardioverter defibrillator (ICD) following myocardial infarction (MI) increases rather than decreases patient mortality.
Although sudden cardiac death (SCD) was reduced in MI patients receiving ICDs during the first 2 years in the IRIS (Immediate Risk Stratification Improves Survival) study, this was outweighed by the increase in non-sudden cardiac death (NSCD) in those given an ICD, especially after 3 years of follow-up.
Older age, having three-vessel or main-stem disease, having a QRS interval of 120 ms or more, a New York Heart Association (NYHA) classification score of 3 or 4 versus 2 or less, or an ejection fraction of less than 35% all independently increased mortality in ICD and control groups. Having ST segment elevation MI (STEMI) and no reperfusion seemed to result in no initial reduction in NSCD with ICD use, but numbers were small.
"These preliminary data from this new analysis did not answer the question of why does the ICD not improve mortality early after a MI. So today we have no evidence to modify the current guidelines," said discussant Christophe Leclercq (Centre Cardio-Pneumologique, Rennes, France).
Results from the IRIS trial were originally published in 2009. The reasoning for the initial trial was that, although the European and US guidelines exclude ICD implantation for primary prevention within the first 40 days after initial MI, it is known that the risk for SCD is significantly raised immediately after an MI, especially in patients with a low left ventricular ejection fraction.
The current investigation was carried out to investigate why implantation with ICDs in IRIS increased the risk for NSCD. This question was not successfully answered, but the researchers identified risk factors associated with mortality and carried out further investigation of mortality trends in the IRIS study cohort.
The daily mortality risk of the ICD patients was lower than that of the control group for the first 2 years, owing to a reduction in SCD for most ICD patients over this period compared with controls. However, mortality then increased gradually in the ICD compared with the control group, largely because of the higher level of NSCD in the ICD group for the whole study.
Presenter Gerhard Steinbeck (Ludwig-Maximilian University, Munich, Germany) and colleagues carried out multivariate analysis with 30 baseline characteristics to assess whether they might influence mortality.
Seven of these factors significantly influenced mortality in both ICD patients and controls. Being 10 years older (hazard ratio [HR]=1.49), having three-vessel or main-stem disease (HR=1.48), having a QRS interval of 120 ms or more (HR=1.60), having a NYHA classification score of 3 or 4 versus 2 or less (HR=2.00), or an ejection fraction of less than 35% (HR=2.18) all increased risk for death, whereas being treated with an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker, or clopidogrel, significantly decreased risk (HR=0.54 and 0.64, respectively).
No factors were specific to the ICD group, but a subgroup of 91 patients with STEMI without reperfusion did not experience the initial 2-year benefit of ICDs on SCD.
Periods of increased risk for patients with ICDs were calculated to be those where both appropriate and non-appropriate shocks were given by the ICD and those of increased right ventricular pacing, said Steinbeck.
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By Helen Albert