Analysis of prognostic significance of ventricular arrhythmias after myocardial infarction. Shortcomings of Lown grading system.

Abstract

The Lown grading system for ventricular arrhythmias has been used in observational and experimental studies of ischaemic heart disease. This grading system uses three levels of ventricular premature depolarisation frequency and four complex features to assign patients to one of seven grades. We tested several of the major assumptions of the Lown grading system in a group of 400 patients who had recently experienced acute myocardial infarction. The Lown grading system assumes that the frequency of ventricular extrasystoles exerts a negligible risk force in patients who have complex ventricular extrasystoles. We found, however, that the frequency of ventricular extrasystoles contributed significant additional risk for cardiac death even in the three highest Lown grades, 4A, 4B, and 5. The Lown grading system assumes that, of the four complex features used, R on T ventricular extrasystoles have the greatest risk for subsequent cardiac death. We found that paired ventricular extrasystoles and ventricular tachycardia had more prognostic significance than R on T ventricular extrasystoles. It is important for prognostic stratification that subgroups which are merged into a given Lown grade should be relatively homogeneous with respect to outcome. We found a lack of homogeneity in the three highest Lown grades. Grade 5 contained 16 subgroups with a mortality risk which ranged from 0 to 75 per cent; statistically significant differences in subsequent mortality were found among these subgroups. Most of the shortcomings of the Lown grading system in our acute myocardial infarction population resulted from failure to give sufficient weight to ventricular extrasystoles frequency and to repetitive ventricular extrasystoles.

Clinical Applications of Ambulatory Electrocardiography

“…As noted by Bigger and Weld [95] with particular reference to early-cycle VPCs (Lown grade 5), these observations are of great importance in the design of therapeutic trials in the postinfarct population. Since substantial heterogeneity of risk clearly exists among presumed 'high-risk' population sub sets identified by VPC complexity alone, po tential harm to low-risk patients included in intervention trials must be weighed, and the effect of these patients on assessing the results of intervention must be considered.…”

“…and a very-high-risk subset was identified from the combination of these fea tures. Furthermore, stratification of mortal ity risk within Lown grade 5 (early-cycle VPCs) was extreme, ranging from 9% among patients with infrequent VPCs and no other 'complex' features, to as high as 59% when frequent VPCs and other complex patterns also occurred [95].…”

“…Emphasis on complexity of ventricular ectopy further implies that clinical outcome is accurately predicted within homogeneous study popula tions using this grading system. However, Bigger and Weld [95] have emphasized the marked heterogeneity of the 'complex' Lown grades (3-5), which in effect comprise 30 sub groups even when only one partition value for VPC frequency is used (30 VPCs/h). In 400 patients evaluated after myocardial in farction, the best predictors of death were found to be both VPC frequency and sequen tial VPCs.…”

Improvement of Risk-stratification by Use of a New Combination of Holter Variables in Survivors of Myocardial Infarction

“…Thus, reduced heart rate variability (HRV) measured 1-2 weeks after MI has been shown to be a powerful and independent predictor of short-and medium-term mortality (1)(2)(3). Ventricular tachycardia (VT) is known to identify patients at increased risk for future sudden death and ventricular brillation (4)(5)(6). Finally, episodes of transient ST-segment elevation (ST : ) during daily life early after MI appear to be associated with subsequent cardiac death (CD) (7).…”

Therapy for Late Post Infarction Ventricular Tachycardia

“…Of the 18 not referred for PES, there were 13 males and 5 females, with a mean age of 63 ± 9 years. The group referred for PES showed 15 % to have had a cardiac arrest, 62 % to have symptomatic VT and 23 % to have had asymptomatic VT on Holter monitoring (5)(6)(7)(8)(9)(10)(11)(12)(13)(14) days post infarction). In contrast, none of the patients in the non-referred group had a cardiac arrest, while half had symptomatic VT and half had asymptomatic VT on Holter.…”