Abstract 2888: Evaluation of Ventricular Asynchrony Using Equilibrium Radionuclide Ventriculography: A Novel Approach
Background: Cardiac resynchronization therapy (CRT) is an important therapeutic modality in patients with heart failure (HF). Current indications presume that mechanical asynchrony occurs primarily in the context of left ventricular systolic dysfunction (LVEF ≤ 35%) in highly symptomatic patients (NYHA class III or IV) with electrical asynchrony (QRS duration >120ms). We describe a novel method of assessing mechanical asynchrony using equilibrium radionuclide ventriculography (RNV) and establish its correlation with standard clinical criteria.
Methods and Results: 97 patients underwent RNV in the context of pre-ICD assessment. Gated pool SPECT sequences were analyzed with 3D geometrical segmentation of the left ventricle using Fourier analysis. A Contraction Homogeneity Index (CHI) was calculated based on an algorithm relating the ratio of wall movement contributing to stroke volume to total wall movement. CHI was scaled from 0 to 100 (100 = total synchrony). Clinical characteristics including NYHA class and ECG parameters were collected from chart review. ROC curves were generated to determine the optimal CHI value predictive of a QRS ≥150ms, a well-correlated surrogate marker for mechanical asynchrony. CHI values ranged from 17.9 to 97.3 (median=75.1). CHI tended to be lower in NYHA III patients compared to I/II patients (66±4 vs. 74±2; p=0.07). It was lower in patients with an EF ≤ 35% versus >35% (67±2 vs. 82±2 p<0.01), and it was also lower in patients with a QRS ≥150ms compared to those with a QRS <120ms (62.1±3.6 vs. 76.2±2.2; p<0.01), or with a QRS of 120–150ms (76.1±2.9; p<0.05). A CHI cutoff value of 75 yielded the most favorable likelihood ratios. Overall, 30% of patients with a QRS<120ms, 42% with QRS 120–150ms, and 77% with QRS ≥ 150ms met this definition of asynchrony (p<0.01). These values increased to 56%, 43%, and 85% in analyses limited to patients with EF ≤ 35% (n=65).
Conclusion: CHI is a novel index of left ventricular mechanical asynchrony. A lower CHI is correlated with higher NYHA class, depressed LVEF, and prolonged QRS. CHI may potentially identify beneficiaries of CRT who do not meet standard criteria. Prospective validation of this promising index against other markers such as tissue Doppler imaging is currently under investigation.