Right Ventricular Electrogram Characteristics in a T1 Mapping-Validated Normal Population

Unipolar voltage mapping in right ventricular cardiomyopathy: pitfalls, solutions and advantages

AIMS

Endocardial unipolar and bipolar voltage mapping (UVM/BVM) of the right ventricle (RV) are used for transmural substrate delineation. However, far-field electrograms (EGMs) and EGM changes due to injury current may influence automatically generated UVM. Epicardial BVM is considered less accurate due to the impact of fat thickness (FT). Data on epicardial UVM are sparse. The aim of the study is two-fold: to assess the influence of the manually corrected window-of-interest on UVM and the potential role of epicardial UVM in RV cardiomyopathies.

METHODS AND RESULTS

Consecutive patients who underwent endo-epicardial RV mapping with computed-tomography (CT) integration were included. Mapping points were superimposed on short-axis CT slices and correlated with local FT. All points were manually re-analysed and the window-of-interest was adjusted to correct for false high unipolar voltage (UV). For opposite endo-epicardial point-pairs, endo-epicardial bipolar voltage (BV) and UV were correlated for different FT categories. A total of 3791 point-pairs of 33 patients were analysed. In 69% of endocardial points and 63% of epicardial points, the window-of-interest needed to be adjusted due to the inclusion of far-field EGMs, injury current components, or RV-pacing artifacts. The Pearson correlation between corrected endo-epicardial BV and UV was lower for point-pairs with greater FT; however, this correlation was much stronger and less influenced by fat for UV.

CONCLUSION

At the majority of mapping sites, the window-of-interest needs to be manually adjusted for correct UVM. Unadjusted UVM underestimates low UV regions. Unipolar voltage seems to be less influenced by epicardial fat, suggesting a promising role for UVM in epicardial substrate delineation.

Right ventricular outflow tract electroanatomical abnormalities in asymptomatic and high-risk symptomatic patients with Brugada syndrome: Evidence for a new risk stratification tool?

INTRODUCTION

Microstructural abnormalities at the epicardium of the right ventricular outflow tract (RVOT) may provide the arrhythmia substrate in Brugada syndrome (BrS). Endocardial unipolar electroanatomical mapping allows the identification of epicardial abnormalities. We evaluated the clinical implications of an abnormal endocardial substrate as perceived by high-density electroanatomical mapping (HDEAM) in patients with BrS.

METHODS

Fourteen high-risk BrS patients with aborted sudden cardiac death (SCD) (12 males, mean age: 41.9 ± 11.8 years) underwent combined endocardial-epicardial HDEAM of the right ventricle/RVOT, while 40 asymptomatic patients (33 males, mean age: 42 ± 10.7 years) underwent endocardial HDEAM. Based on combined endocardial-epicardial procedures, endocardial HDEAM was considered abnormal in the presence of low voltage areas (LVAs) more than 1 cm² with bipolar signals less than 1 mV and unipolar signals less than 5.3 mV. Programmed ventricular stimulation (PVS) was performed in all patients.

RESULTS

The endocardial unipolar LVAs were colocalized with epicardial bipolar LVAs (p = .0027). Patients with aborted SCD exhibited significantly wider endocardial unipolar (p < .01) and bipolar LVAs (p < .01) compared with asymptomatic individuals. A substrate size of unipolar LVAs more than 14.5 cm² (area under the curve [AUC]: 0.92, p < .001] and bipolar LVAs more than 3.68 cm² (AUC: 0.82, p = .001) distinguished symptomatic from asymptomatic patients. Patients with ventricular fibrillation inducibility (23/54) demonstrated broader endocardial unipolar (p < .001) and bipolar LVAs (p < .001) than noninducible patients. The presence of unipolar LVAs more than 13.5 cm² (AUC: 0.95, p < .001) and bipolar LVAs more than 2.97 cm² (AUC: 0.78, p < .001) predicted a positive PVS.

CONCLUSION

Extensive endocardial electroanatomical abnormalities identify high-risk patients with BrS. Endocardial HDEAM may allow risk stratification of asymptomatic patients referred for PVS.

Electrophysiologic and imaging evidence for an occult myopathic substrate in patients with idiopathic ventricular arrhythmias

BACKGROUND

Idiopathic VA are traditionally considered benign, although occasional patients develop an ectopy-mediated cardiomyopathy (EMC). It is unclear whether patients with idiopathic VA in the absence of left ventricular (LV) dysfunction harbor a subclinical cardiomyopathy. We aim to assess for cardiomyopathic substrate in patients with idiopathic ventricular arrhythmias (VA) using imaging and electrophysiologic markers of early fibrosis.

METHODS

Cardiac magnetic resonance (CMR) imaging and ventricular electroanatomic mapping was performed in 3 groups: patients undergoing ablation for idiopathic VA without (Group 1, n = 17) and with LV dysfunction (Group 2 [presumed EMC], n = 12) plus a control group undergoing ablation of supraventricular tachycardia (Group 3, n = 16). Global LV strain, T1 mapping and extended electrogram (EGM) characteristics were compared.

RESULTS

Global strain was impaired in patients with presumed EMC (Group 2, p < 0.001). Native T1 times did not differ between groups, however patients in both idiopathic VA groups (Groups 1 and 2) had shorter post-contrast T1 times at 8 min compared to SVT controls (Group 3, p = 0.04). Similarly, the duration of the bipolar EGM was subtly prolonged in both Group 1 and 2 compared to Group 3 (p = 0.002). There were no between group differences in unipolar or bipolar voltage, the no. of bipolar EGM deflections or the maximal unipolar EGM dV/dt.

CONCLUSION

Patients with idiopathic VAs and apparently structurally normal hearts may have subtle CMR and electrophysiologic changes similar in magnitude to that seen in frank presumed EMC, possibly suggestive of an occult cardiomyopathic process.