Patient characteristics and baseline BIN1 levels
There were no statistically significant differences between the 24 ARVC patients and 48 controls with respect to age, gender, or BMI (). Of the 24 ARVC patients, 21 met at least 2 major criteria and 3 patients met 1 Major and 2 minor criteria for diagnosis, as evaluated by modified Task Force Criteria [22
]. Eight (33%) had a confirmed family history of ARVC, defined as either autopsy confirmation of ARVC or clinically confirmed diagnosis of ARVC in a family member. Of the patients who underwent genotype analysis, 11/15 (73%) were gene positive ().
At the baseline blood sampling, 16 (70%) had at least one ventricular arrhythmia event, 7 (30 %) were NYHA class II or greater, and 4 (18%) were NYHA class III or IV. Four patients (18 %) had moderate to severe RV dysfunction. Twenty-three of the 24 patients had ICDs, with an average length of follow up after ICD placement of 4.4 ± 4.3 years to the time of the initial blood sampling. Of the patients with ICDs, 13 (57 %) were placed for primary prevention and 10 (43%) were placed for secondary prevention.
Plasma BIN1 did not significantly correlate with age, sex or BMI in the ARVC or control populations. As the metabolism kinetics and clearance of plasma BIN1 protein are not yet known, we analyzed plasma BIN1 against GFR to exclude the possibility of BIN1 changes with renal dysfunction. We found that BIN1 is not associated with renal function ().
BIN1 Correlation with Baseline Characteristics in ARVC Patients and Controls
The mean plasma BIN1 level in the ARVC population was 37 ± 1 with a median value of 17, as compared to controls with a mean of 60 ± 10 and a median of 27 (p < 0.05) (). As discussed below, the existence of clinical heart failure accounted for the lower BIN1 of ARVC patients.
Cross-sectional analysis of BIN1 in patients with heart failure and arrhythmia
Within the ARVC population, we explored measured BIN1 against the absence (NYHA class I) or presence (NYHA class II–IV) of symptomatic heart failure. In ARVC patients with symptomatic heart failure, the mean BIN1 level was 15 ± 7 (n=7), whereas in ARVC patients without clinical heart failure the mean BIN1 level was 60 ± 17 (n=15), (p <0.05). Results are in . Note plasma BIN1 levels were not different between control patients without failing hearts, and ARVC patients who did not have heart failure. This suggests BIN1 is not specific for ARVC, but may more generally indicate myocardial health. Spearman analyses were performed to assess for correlation of plasma BIN1 with baseline continuous clinical variables (). For patients with multiple samples, the first sample was used in this analysis. Plasma BIN1 levels inversely correlated with number of accumulated ventricular arrhythmia events (Rho of −0.61, p < 0.005) up to the point of the first plasma measurement (), but not with the length of ICD follow up, indicating an effect separate from an implanted ICD. To further control for the length of ICD implantation in each patient, the plasma BIN1 was analyzed against the average annual number of ventricular arrhythmia events. Consistently, plasma BIN1 inversely correlates with the average annual number of ventricular arrhythmia events (Rho of −0.47, p <0.05), independent of the presence of an ICD.
Plasma BIN1 is lower in ARVC with HF
To assess the ability of plasma BIN1 to distinguish between patients with severe and mild ARVC, a Receiver-Operator-Curve analysis was performed (). Severe ARVC was defined as either NYHA class III/IV heart failure or >1 ventricular arrhythmia event, and by default, mild ARVC was defined as NYHA class I/II and ≤1 ventricular arrhythmia event. At a cutoff value of less than 33, plasma BIN1 had an 82% sensitivity and an 82% specificity for predicting NYHA class III/IV heart failure status or >1 ventricular arrhythmia event (ROC AUC of 0.88 ± 0.07). Thus low plasma BIN1 correlates with the occurrence of severe ARVC.
Plasma BIN1 predicts disease severity
Analysis of plasma BIN1 as a predictor of future arrhythmia events
Mean follow up after initial blood sampling in the ARVC cohort was 3.3 ± 1.7 years. 23 of the 24 ARVC patients had ICDs. An event was defined as VT or VF requiring termination, as revealed and confirmed by subsequent ICD interrogation. BIN1<30 predicted a high future arrhythmia rate (>0.5 arrhythmia events/year, ) with a sensitively of 83%, specificity of 88% and an accuracy of 85 % (ROC AUC of 0.89 ± 0.09). Of the 23 patients with ICDs implanted, there were only 3 “failures” of the BIN1 test to classify patients in the appropriate high or low risk group. Two patients with BIN1 <30 did not have a high arrhythmia rate, and one patient with a BIN1 >30 continued to have high arrhythmias. Given the observed correlation of BIN1 with baseline heart failure and the known increase risk of arrhythmias in patients with heart failure, a stratified analysis was performed according to heart failure status at baseline. In patients with NYHA class I or II (n=20), BIN1< 30 predicted future arrhythmia event rate with a sensitivity of 83%, specificity of 80 % and an accuracy of 82 % (ROC AUC of 0.82 ± 0.14). In patients with NYHA class I (n=17), 10 of 17 had ICDs placed for primary prevention and 2 of them had recorded ventricular arrhythmias prior to the first blood sampling. A BIN1<30 predicted a future high arrhythmia event rate with a sensitivity of 82%, specificity 67% and an accuracy of 79% (ROC AUC of 0.76 ± 0.21). The relative risk for high future arrhythmia events for BIN1<30 is 8.56 (95% CI 1.27–57.26, p<0.01). In comparison, the relative risk for high future arrhythmia events for NYHA class II or greater heart failure at baseline alone is 3.61 (95 % CI 1.25–10.37, p<0.05). Thus low BIN1 is a stronger predictor of arrhythmia than the presence of heart failure.
Plasma BIN1 predicts future ventricular arrhythmias
BIN1 in ARVC patients with serial blood samples
Serial blood samples were available in seven ARVC patients and three controls (). Overall, BIN1 values decreased in patients with progressive ARVC. Patient 1 developed new RV dysfunction and had her first episode of VF. Patient 2 developed worsening RV dysfunction, and had multiple VF events. Patient 3 had a continued high arrhythmia (3.8 events/year) and developed new RV dysfunction. At the time of the initial blood sampling, patient 4 did not meet criteria for ARVC, however during follow up the patient developed new T wave inversion in ECG leads V1-V3 and an epsilon wave in V1, palpitations with a high non-sustained VT on Holter monitor. She has since had an ICD placed for confirmed ARVC but has not had sustained VT or VF, heart failure, or ventricular dysfunction. Patient 5 had a decrease in LV function from 70% to 49% and the progression from mild to moderate RV dysfunction. Patient 6 had mild RV dysfunction at baseline, but developed moderate RV dysfunction and 5 separate ventricular arrhythmia events. Patient 7 developed mild RV dysfunction during follow up and has had high ventricular arrhythmia rate (2.1events/year). In sum, patients with clinical progression had marked decreases in their plasma BIN1 levels (decrease of 63%, p<0.05). In contrast, in serial samples from the three healthy controls (), there was no significant change in BIN1 levels over a two year interval. In addition, in these healthy controls, plasma BIN1 remains the same when analyzed initially and repeated after two years storage in a −80°C freezer, indicating long term stability in cold storage.
Plasma BIN1 decreases with ARVC progression