Heart Rate Variability Density Analysis (Dyx) and Prediction of Long-Term Mortality after Acute Myocardial Infarction.

AIMS: The density HRV parameter Dyx is a new heart rate variability (HRV) measure based on multipole analysis of the Poincaré plot obtained from RR interval time series, deriving information from both the time and frequency domain. Preliminary results have suggested that the parameter may provide new predictive information on mortality in survivors of acute myocardial infarction (MI). This study compares the prognostic significance of Dyx to that of traditional linear and nonlinear measures of HRV. METHODS AND RESULTS: In the Nordic ICD pilot study, patients with an acute MI were screened with 2D echocardiography and 24-hour Holter recordings. The study was designed to assess the power of several HRV measures to predict mortality. Dyx was tested in a subset of 206 consecutive Danish patients with analysable Holter recordings. After a median follow-up of 8.5 years 70 patients had died. Of all traditional and multipole HRV parameters, reduced Dyx was the most powerful predictor of all-cause mortality (HR 2.4; CI 1.5 to 3.8; P < 0.001). After adjustment for known risk markers, such as age, diabetes, ejection fraction, previous MI and hypertension, Dyx remained an independent predictor of mortality (P = 0.02). Reduced Dyx also predicted cardiovascular death (P < 0.01) and sudden cardiovascular death (P = 0.05). In Kaplan-Meier analysis, Dyx significantly predicted mortality in patients both with and without impaired left ventricular systolic function (P < 0.0001). CONCLUSION: The new nonlinear HRV measure Dyx is a promising independent predictor of mortality in a long-term follow-up study of patients surviving a MI, irrespectively of left ventricular systolic function.

Heart rate variability density analysis (Dyx) for identification of appropriate implantable cardioverter defibrillator recipients among elderly patients with acute myocardial infarction and left ventricular systolic dysfunction.

AIMS: Dyx is a new heart rate variability (HRV) density analysis specifically designed to identify patients at high risk for malignant ventricular arrhythmias. The aim of this study was to test if Dyx can improve risk stratification for malignant ventricular tachyarrhythmias and to test if the previously identified cut-off can be reproduced. METHODS AND RESULTS: This study included 248 patients from the CARISMA study with ejection fraction ≤40% after an acute myocardial infarction and an analysable 24 h Holter recording. All patients received an implantable cardiac monitor, which was used to diagnose the primary endpoint of near-fatal or fatal ventricular tachyarrhythmias likely preventable by an implantable cardioverter defibrillator (ICD), during a period of 2 years. A Dyx ≤ 1.96 was considered abnormal. The secondary endpoint was cardiovascular death. At enrolment 59 patients (24%) had a Dyx ≤ 1.96 and 20 experienced a primary endpoint. A Dyx ≤ 1.96 was associated with a significantly increased risk for malignant arrhythmias [hazards ratio (HR) = 4.36 (1.81-10.52), P = 0.001] and cardiovascular death [HR = 3.47 (1.38-8.74), P = 0.008]. Compared with important clinical risk parameters (age >70 years and QRS > 120 ms), Dyx ≤ 1.96 significantly added predictive value (P = 0.0066). CONCLUSIONS: Dyx was a better predictor of ventricular tachyarrhythmias than the traditional measures of HRV and heart rate turbulence, particularly in the elderly. Dyx might be a useful tool for better selection of ICD candidates in the elderly population, since a normal Dyx in this group was associated with a very low risk for malignant ventricular arrhythmias.ClinicalTrials.gov Identifier NCT00145119.