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Shortcomings of the Lown grading system for observational or experimental studies in ischemic heart disease
Insights
The Lown grading system poorly predicts death in myocardial infarction patients and hinders analysis of ventricular arrhythmias. An alternative system is proposed but also has limitations in showing arrhythmia relationships.
Area of Science:
- Cardiology
- Clinical Electrophysiology
- Medical Statistics
Background:
- The Lown grading system is a hierarchical method for classifying ventricular arrhythmias.
- It uses frequency and complexity to predict mortality risk, particularly post-myocardial infarction.
Purpose of the Study:
- To evaluate the predictive accuracy of the Lown grading system for cardiac death in patients recovering from acute myocardial infarction.
- To assess the Lown system's utility in analyzing antiarrhythmic drug therapy effectiveness.
- To propose an improved grading system for ventricular arrhythmias.
Main Methods:
- Analysis of 400 patients convalescing from acute myocardial infarction.
- Evaluation of the Lown grading system's population distribution, risk gradient, and monotonicity.
- Assessment of the Lown system's compatibility with multivariate analyses.
- Examination of the Lown equation's ability to reflect drug therapy effects on ventricular premature depolarizations (VPDs).
Main Results:
- The Lown grading system showed poor population distribution and lacked a clear, monotonic increase in risk with higher grades.
- It failed to establish a substantial risk gradient and exhibited isometric properties in higher grades.
- The system hindered multivariate analysis of VPDs and cardiac death.
- It was ineffective in clearly demonstrating changes in VPDs related to antiarrhythmic drug dosage.
Conclusions:
- The Lown grading system has significant limitations in predicting mortality and analyzing antiarrhythmic treatments.
- An alternative, non-hierarchical grading system was proposed, offering better suitability for multivariate analyses.
- Neither system fully elucidates the complex relationships between ventricular arrhythmias, time, drug dose, and patient activity.
Abstract:
The Lown grading system uses three levels of frequency and four complex features to grade ventricular arrhythmias. The seven Lown grades are mutually exclusive (a patient can be in only one grade) and hierarchical (higher grades indicate increased likelihood of death). We evaluated the ability of the Lown arrhythmia grading system to predict death in 400 patients who were convalescing from acute myocardial infarction. Lown grading produced a poor distribution among grades of the population, lacked a monotonic increase in risk with increasing arrhythmia grade, lacked a substantial risk gradient between grades, and showed a lack of isometry in the higher grades. Also, the Lown grading system thwarts the use of standard multivariate techniques for relating the frequency and characteristics of ventricular premature depolarizations (VPDs) to cardiac death. We also examined the utility of the Lown arrhythmia equation for evaluating the results of antiarrhythmic drug therapy. The Lown grading system failed to reveal clearly the change in VPD frequency and characteristics as a function of drug dose. We propose an alternative grading system that is not mutually exclusive or hierarchical. This grading system lacks many of the flaws of the Lown grading system and is suitable for standard multivariate analyses but, like the Lown grading system, still fails to show the relationships among ventricular arrhythmias, time, drug dose, and activity.