title: Resting heart rate is a powerful predictor of arrhythmic events in patients with dilated cardiomyopathy and implantable cardioverter-defibrillator.
abstract: Patients with dilated cardiomyopathy and implantable cardioverter-defibrillator (ICD) are a high-risk group for arrhythmias. They regularly undergo cardiopulmonary exercise testing (CPET) to assess cardiac reserve and to guide clinical decisions or therapeutic adjustments. Data from previous studies demonstrate that prognosis in patients with heart failure (HF) worsens with the presence of appropriate shocks.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the value of CPET parameters to predict shocks and other arrhythmic events in HF patients with ICD, in order to identify a high-risk group for arrhythmias.
  
  
  METHODS
  This was a prospective single-center registry of 61 consecutive patients (mean age 55 +/- 15 years, 18% female), with dilated cardiomyopathy (ischemic etiology in 57%) and ICD, who underwent symptom-limited maximal CPET six months or less before device implantation. Minimum follow-up was 180 days. The primary endpoint was appropriate shock and the composite endpoint was appropriate shock and/or ventricular fibrillation (VF) and/or sustained ventricular tachycardia (VT), which were then correlated with hemodynamic variables (heart rate and blood pressure) and CPET parameters.
  
  
  RESULTS
  During a mean follow-up of 27 months, eight patients died (13%), two of them from arrhythmic cause (3.3%), and 16 (26%) patients received at least one appropriate ICD shock, eight (13%) due to VF. Sustained VT was recorded in 23 patients (38%) and nonsustained VT in 42 patients (69%). CPET showed that the group with the primary end point had lower peak VO2, anaerobic threshold and chronotropic reserve. On multivariate analysis, resting heart rate was the only independent predictor of appropriate shock (HR 1.06; 95% CI 1.01-1.10; p = 0.025). Univariate analysis identified peak VO2, anaerobic threshold, VE/VCO2 slope, resting heart rate and heart rate decrease during the first minute of recovery, and systolic blood pressure during exercise as predictive of the composite endpoint (shock/VF/sustained VT). Multivariate analysis identified resting heart rate and peak VO2 as independent predictors, with HR 1.04; 95% CI 1.00-1.09 (p = 0.050) and HR 0.88; 95% CI 0.78-0.98 (p = 0.026), respectively. The best cut-off for resting heart rate to predict the composite and primary endpoints was > 76 bpm (area under the ROC curve: 0.67; 95% CI 0.53-0.78 and 0.65; 95% CI 0.51-0.76, respectively).
  
  
  CONCLUSIONS
  Resting heart rate and peak VO2 were identified in multivariate analysis as good predictors of arrhythmic events and resting heart rate was the only independent predictor of appropriate shock in HF patients with ICD. Both advanced stage heart failure and sympathetic overdrive may be associated with the development of malignant arrhythmias.
authors.affiliation: Serviço de Cardiologia Hospital Santa Cruz, C.H.L.O., Lisboa, Portugal. ritacale@hotmail.com
authors.forename: Rita
authors.initials: R
authors.lastname: Calé
authors.forename: Miguel
authors.initials: M
authors.lastname: Mendes
authors.forename: João
authors.initials: J
authors.lastname: Brito
authors.forename: Pedro
authors.initials: P
authors.lastname: Sousa
authors.forename: Pedro
authors.initials: P
authors.lastname: Carmo
authors.forename: Sofia
authors.initials: S
authors.lastname: Almeida
authors.forename: Renata
authors.initials: R
authors.lastname: Gomes
authors.forename: António
authors.initials: A
authors.lastname: Ferreira
authors.forename: Katya Reis
authors.initials: KR
authors.lastname: Santos
authors.forename: Diogo
authors.initials: D
authors.lastname: Cavaco
authors.forename: Francisco
authors.initials: F
authors.lastname: Morgado
authors.forename: Pedro
authors.initials: P
authors.lastname: Adragão
authors.forename: João
authors.initials: J
authors.lastname: Calqueiro
authors.forename: José Aniceto
authors.initials: JA
authors.lastname: Silva
mesh_terms: D000328:Adult; D000368:Aged; D001145:Arrhythmias, Cardiac / Q000401:mortality / Q000503:physiopathology* / Q000628:therapy; D002311:Cardiomyopathy, Dilated / Q000401:mortality / Q000503:physiopathology* / Q000628:therapy; D002423:Cause of Death; D017147:Defibrillators, Implantable; D005080:Exercise Test; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D011379:Prognosis; D011446:Prospective Studies; D012146:Rest / Q000502:physiology*