Despite the improvement in treatment of coronary artery disease and myocardial infarction, survivors of a previous myocardial infarction are exposed to substantial risk of life-threatening ventricular tachyarrhythmias which has been the basis for use of ICD in post-infarction patients with left ventricular dysfunction
[4, 5, 17, 18].
There is a need to evaluate in routine practice, the outcome of patients with a previous MI, implanted with an ICD for primary prevention of sudden death. This is in accordance to the current approach proposed for a comprehensive validation of effective impact of innovative therapies, based on combination of high quality clinical trials and prospective registries
. Either the potentially worse outcome of patients with a profile similar to that of controlled trials but not selected according to trial’s exclusion criteria
, or the need to verify how treatments affect patient’s outcomes when applied in an unselected context, are at the basis of current interest on prospective registries
Our study, which is based on the final results of a prospective multicenter registry
, suggests that patients implanted with an ICD with remote myocardial infarction (7 years or more from last infarction) have higher chance of presenting an appropriate ICD activation, but do not present a worse outcome in terms of survival in comparison with post infarction patients who carry an ICD, but have a shorter time elapsed between last myocardial infarction and ICD implant. According to these data, the subgroup of patients with remote MI appears to include those patients who could get the greatest benefit from implant of a prophylactic ICD. However, these considerations should take into account that appropriate ICD shocks may occur more frequently than sudden death, as shown in patients with nonischemic cardiomyopathy
 and therefore some limitations exists in use of appropriate ICD shocks as a surrogate of sudden cardiac death. An increase in appropriate shocks with increasing time after MI has also been reported for the patients with previous MI enrolled in the SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial) study
In the context of use of ICDs, there is growing interest on determinants of appropriate ICD therapy in patients with reduced ventricular function after myocardial infarction. This as a way for assessing what patients may benefit most from implantation of a prophylactic ICD. This kind of analysis, combined with analysis of relationships between determinants of ICD therapy and death may be the basis for any attempts to improve patients targeting. As a matter of fact, in the “routine practice” it is possible that competing causes of death due to heart failure, comorbidities or any other cause when occurring without any prior appropriate ICD intervention, may preclude benefit from ICD therapy
Previously a post hoc analysis of the original MADIT II trial did not report any relationship between time from last MI and ICD activations, but showed that mortality rates in control patients increased as a function of time elapsed from most recent MI, with greater survival benefit associated with ICD implant when time elapsed from last MI was ≥18 months
Recently a post-hoc analysis of MUSTT trial found that the risk of 2- and 5-year arrhythmic death, cardiac arrest, and all-cause death did not vary as a function of time from the last recent MI
. However, interpretation of these data should consider that the MUSTT was non-randomized and that the published analysis was based only on patients who were not treated with an ICD and who were discharged without antiarrhythmic medications.
In our study we found that the rate of ventricular tachyarrhythmias and appropriately delivered ICD therapies increase significantly with the time between prior MI and ICD implant. This suggests that for high risk patients the longer the time elapsed from last MI the higher is the tendency to spontaneously develop ventricular tachyarrhythmias. Patients with a long survival after MI appear to have a higher probability of ventricular tachyarrhythmias (and ICD intervention) probably related to an extensive remodeling, more pronounced than in patients with a recent MI. The relationship between time from myocardial necrosis and arrhythmogenesis is confirmed by findings of the Maastricht study on out-of-hospital cardiac arrest in the 1990's
, where the mean interval between previous MI and occurrence of cardiac arrest was relatively long, being in average 6.5 years.
In daily clinical practice the question concerning what the optimal time would be for implanting an ICD in patients with previous MI and evidence of LV dysfunction is still open, and has public health implications. A recent modeling study indicates that benefits of ICD implantation in a relatively early phase after MI (ie, at 60 days) are really modest, when projected at 10 years of follow up, in comparison to delayed implantation at 6 months or 1 year
. Current practice guidelines recommend ICD implant in patients with previous MI and left ventricular dysfunction after at least 40 days from last MI, although the optimal time after the first 40 days remains undefined. It is unlikely that this question will be answered with a randomized controlled trial, therefore data from observational studies and registries play an important role. However we have to be cautious when interpreting the results because of possible selection bias and confounding factors.
Our registry, while limited to devices made by one manufacturer, included both single and dual chamber ICDs and devices with cardiac resynchronization therapy, a very effective therapeutic resource according to a series of controlled trials
. According to MADIT CRT trial cardiac resynchronization therapy will find a wider application in post infarction patients, since NYHA I-II patients will be candidate to resynchronization in the presence of wide QRS interval
. The MADIT CRT trial showed that devices with both defibrillation capabilities and cardiac resynchronization therapy have additional benefit with regard to heart failure hospitalization in comparison with ICD only therapy, but without advantages in terms of survival
Most recently a subanalysis of the MADIT-CRT
 demonstrated that among post MI patients the risk of life threatening ventricular arrhythmias increases as a function of time elapsed since revascularization procedure. With this regard we did not perform an analysis of the effects of revascularization and residual ischemia on ventricular tachyarrhythmias, ICD discharges and outcomes, since this is quite problematic in the setting of a registry. We cannot exclude that observed differences may be due to confounding factors that were not collected, including the number of previous MIs, the extent of myocardial scar, the exact time of revascularization and the evolution of revascularization practices and MI treatment over time (as suggested by the data in Table
1, patients with a more remote MI were treated differently from those with a more recent MI, with regard to use of CABG or PTCA). However, we need to consider that it is difficult in daily practice to obtain detailed information on previous revascularization procedures as the basis for individualized decision making. Similarly to MADIT II analysis
 we did not considered all the events corresponding to a MI, but we considered only most recent MI and this may be a limitation of the analysis.
Similarly to other registries we have to consider a series of limitations typical of study design. Although device programming according to PainFree study
 was suggested, differences in detection and therapy programming among the patient population could have influenced the results. Postmortem ICD interrogations were not recorded.