Background:
Prolonged QTc interval is a known risk factor for adverse cardiac events, including sudden and non-sudden cardiac death. Understanding the determinants and physiologic correlates of QTc can guide the proper strategy for the primary prevention of sudden death in high risk patients.
Methods & Results:
This was an observational study that recruited ambulatory heart failure patients (NYHA I-III) from an outpatient clinic in NL, Canada. In supine resting position, consented participants underwent non-invasive 12-lead ECG and hemodynamic monitoring using BioZ Dx Impedance Cardiography (Sonosite Inc., WA, USA). ECGs were evaluated by a reviewer blinded to clinical data. Participants with pacing (n=12) or left bundle branch block (n=9) were excluded. Three measures of interest were automatically computed: (1) QTc interval (i.e., from QRS onset to T offset), (2) QRS duration (i.e., from QRS onset to QRS offset), and (3) JTc (i.e., QTc interval minus QRS duration). Effect sizes were computed using Pearson’s r coefficients. The final sample (n=23) was 62±13 years of age and 70% male with LVEF of 34±10%. The mean QTc was 441±39 milliseconds, and 10 patients (43%) had prolonged QTc (≥450 milliseconds). QTc interval negatively correlated with cardiac output (r= -0.57), and positively correlated with systemic vascular resistance (r= +0.57), as well as thoracic fluid content (r= +0.43). QRS duration alone was not specifically associated with any hemodynamic parameter, but JTc interval positively correlated with total arterial compliance (r=+0.42).
Conclusions:
In heart failure patients, we interestingly found that increased systemic vascular resistance results in QTc interval prolongation, where repolarization time is specifically influenced by arterial compliance. This suggests potential benefit from antihypertensive therapy targeted at lowering systemic vascular resistance in those with prolonged QTc/JTc. Nevertheless, these intervals need to be interpreted with caution in patients with thoracic fluid overload (e.g., pulmonary edema).
Quality of life and symptoms of depression in advanced heart failure patients and their partners