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Background: Circulating endothelial progenitor cells (EPCs) might limit endothelial dysfunction in patients with microvascular angina (MVA). Endothelial colony-forming cells (ECFCs; displaying the CD34+/KDR+/CD45- phenotype) are currently regarded as true EPCs. The aim of this study was to evaluate exercise-induced ECFC mobilization and platelet reactivity in patients with MVA or with obstructive coronary artery disease (CAD)., Methods and Results: Exercise stress test (EST) was performed in 20 MVA patients, 20 CAD patients and 20 controls. Platelet reactivity was assessed before and after EST as formation of monocyte-platelet aggregates (MPAs) and CD41 platelet expression, without and with adenosine diphosphate (ADP) stimulation. ECFC number was measured before and 24h after EST. At rest, MPAs and CD41 platelet expression increased more with ADP in MVA patients (+71±11.0% and +37±7.5%, respectively), than in CAD patients (+37±8.6% and +19±4.5%, respectively) and controls (+29±3.5% and +21±3.1%, respectively; P<0.001 for both). At rest, ECFCs tended to be lower in CAD patients, compared to MVA patients and controls (4.1±5.0%, 7.2±6.0% and 7.3±7.0% cells/10(5), respectively; P=0.056). After EST, ECFCs increased less in MVA patients (+2.8±11) compared to CAD patients (+3.3±15; P<0.05) and controls (+7.4±24; P<0.01)., Conclusions: In MVA patients, EST is able to blunt the peculiar increase of platelet reactivity to ADP present at rest; in contrast, no potential protective response of ECFCs to exercise was seen in these patients.

Background: Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is associated with an increased risk of sudden cardiac death (SCD). Risk stratification of ARVC/D patients, however, remains an unresolved issue. In this study we investigated whether heart rate variability (HRV) can be helpful in identifying ARVC/D patients with increased risk of arrhythmic events., Methods and Results: We studied 30 consecutive patients (17 males; 45.4 ± 18 years) with ARVC/D, diagnosed according to guideline criteria; 15 patients (50%) had received an implantable cardioverter defibrillator (ICD) for primary SCD prevention. HRV was assessed on 24-h ECG Holter monitoring. The primary endpoint was the occurrence of major arrhythmic events (SCD, sustained ventricular tachycardia (VT), ICD therapy for sustained VT or ventricular fibrillation (VF)). During the follow-up period (19 ± 7 months), no deaths occurred, but 5 patients (17%) experienced arrhythmic events (4 VTs and 1 VF, all in the ICD group). All HRV parameters were significantly lower in patients with, compared with those without, arrhythmic events. Low-frequency amplitude was the most significant HRV variable associated with arrhythmic events in univariate Cox regression analysis (P=0.017), and was the only significant predictor of arrhythmic events in multivariable regression analysis (hazard ratio 0.88, P=0.047), together with unexplained syncope (hazard ratio 16.1, P=0.039)., Conclusions: Our data show that among ARVC/D patients HRV analysis might be helpful in identifying those with increased risk of major arrhythmic events.

Background: Drug-eluting stents (DES) have reduced restenosis following percutaneous coronary intervention (PCI), but they seem to be associated with increased coronary endothelial dysfunction compared to bare metal stents (BMS). No data are available about the prognostic value of exercise stress test (EST) in PCI patients in the DES era., Methods and Results: The 160 patients with coronary artery disease (CAD) who underwent PCI with either BMS (n=86) or DES (n=74) were studied. EST was performed 1 month after PCI. DES patients had a higher rate of positive EST compared to BMS patients (49% vs 32%; P=0.03). At a median follow-up of 18 months DES showed a lower rate of target vessel revascularization (TVR) (hazard ratio (HR) 0.37, P=0.07), but a higher rate of acute myocardial infarction (AMI) (HR 3.33, P=0.08). At multivariate Cox-regression time to 1 mm ST and low-workload ischemia were independent predictors of AMI (HR 0.96, P=0.03; and HR 6.24, P=0.009, respectively), as well as of TVR (HR 0.96, P=0.007; and HR 6.43, P=0.001, respectively)., Conclusions: DES implantation is associated with a higher rate of positive EST, compared to BMS, 1 month after PCI, likely due to a higher prevalence of endothelial dysfunction. EST seems to be helpful in predicting clinical outcome in patients with coronary stent implantation.