Outcomes After ICD Placement
Abstract & Commentary
By John P. DiMarco, MD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Synopsis: A risk score using simple clinical criteria may identify patients at high risk of early mortality after ICD implantation.
Source: Parkash R, et al. Predicting Early Mortality After Implantable Defibrillator Implantation: A Clinical Risk Score For Optimal Patient Selection. Am Heart J. 2006;151:397-403.
Parkash and colleagues from Brigham and Women's Hospital have developed a scoring system for predicting outcome after defibrillator implantation. Parkash and colleagues retrospectively reviewed data from 469 patients who underwent ICD implantation at their hospital between February, 1999 and March, 2002. The patients were randomly assigned to either a prediction or a validation cohort. Baseline clinical variables were chosen to be entered into a multivariate logistic regression model. The variables selected were: age greater than 80 years, primary vs secondary prevention use of ICD therapy, ejection fraction less than 35%, QRS duration greater than 120 m/sec, history of atrial fibrillation, New York Heart Association class III or IV, presence of coronary artery disease, renal insufficiency (creatinine greater than 1.8 mg/dL), and presence of significant co-morbid illness. The logistic regression model was used to assess the independent prognostic value of each of these variables for predicting mortality during one year after ICD implantation. Factors found to be significant were included in a risk score by assigning a value of 1 to the presence of the factor and 0 to its absence. The risk scoring system was then applied to the validation cohort to test its ability to protect 6 month and one year mortality.
There were 228 patients in the prediction cohort and 241 patients in the validation cohort. In the entire group, there were 46 deaths during the first year after the ICD implant. There were 27 deaths in the prediction cohort and 19 deaths in the validation cohort with one year mortalities of 11.8% and 7.9%, respectively. Total mortality over 3.2 years of follow-up was 18% in the entire group.
In the prediction cohort, the independent predictors of one year mortality were: age greater than 80 years, history of atrial fibrillation, renal insufficiency, and presence of New York Heart Association class III or IV. One year mortality significantly increased with higher risk scores. Mortality rates for patient groups with 0, 1, 2, and greater than or equal to 3 points were: 2.1%, 8.9%, 37.5%, and 42%, respectively. The Kaplan-Meier survival estimates for one year mortality risk showed a clear separation between the patients with a risk score less than 2 compared to those with a risk score greater than or equal to 2. Six months mortality rates showed a similar trend. The six month mortality rate for 0, 1, 2, and greater than 3 were: 1.1%, 3.3%, 34%, and 36%, respectively. In the validation cohort, the risk score showed similar results. A low risk score (0 to 1) predicted a one year survival of 96%, whereas risk score greater than or equal to 2 predicted a one year mortality of 21%.
Parkash et al conclude that their data provide the basis for a risk scoring system that may identify patients at increased risk of death in the first year after ICD implantation. They argue that given the high cost of ICD therapy and the ability to predict absence of long-term benefit should be an important consideration in ICD decision making.
Current indications for ICD implantation are quite liberal. Most patients with a history of a sustained ventricular arrhythmia who have structural heart disease are considered candidates for secondary prevention of sudden death. Heart failure or ventricular dysfunction are not criteria even though most benefit of the ICD over drug is seen in those with low ejection fractions. Indications for primary prevention ICDs, however, are based primarily on ventricular function and heart failure status. Both primary and secondary prevention indications are based on data from a large number of clinical trials.
In this paper, Parkash et al show that patients with early identifiable risk factors for pump failure death will still have significant mortality even with ICD implantation. This does not mean that these patients may not, as a group, derive benefit. In fact, many of these patients will receive an appropriate shock and have at least a small prolongation of life. However, the mortality benefit may be small and may not be enough to justify the expense of ICD implantation. This is true since in patients with advanced heart failure, the ratio of arrhythmic deaths to pump failure deaths is shifted to the latter mechanism. Even though the ICD therapy delivery rate in these patients is high, their mortality during chronic ICD therapy may still be substantial.
Optimal prescription of ICD therapy remains a challenge. One would hope that we could identify patients at high enough risk for arrhythmic death that they would have some chance of substantial prolongation of life after receiving the ICD. However, the ICD may not have a major effect on the long-term outcome in patients if their greatest risk is for a pump failure death. Unfortunately, predicting heart failure mortality in an individual patient can be quite difficult, but risk scores such as those outlined in this paper should prove to be helpful resources for physicians and patients.