Endocardial unipolar voltage mapping to detect epicardial ventricular tachycardia substrate in patients with nonischemic left ventricular cardiomyopathy

Abstract

Background: Patients with nonischemic left ventricular cardiomyopathy (LVCM) and ventricular tachycardia (Vt) have complex 3-dimensional substrate with variable involvement of the endocardium (ENDO) and epicardium (EPI). The purpose of this study was to determine whether ENDO unipolar (UNI) mapping with a larger electric field of view could identify EPI low bipolar (BIP) voltage regions in patients with LVCM undergoing Vt ablation.

Methods and results: The reference value for normal ENDO unipolar voltage was determined from 6 patients without structural heart disease. Consecutive patients undergoing Vt ablation over an 8-year period with detailed (>100 points) LV ENDO and EPI mapping and normal LV ENDO BIP voltage were identified. From this cohort, we compared patients with structurally normal hearts and normal EPI BIP voltage (EPI-, group 1) with patients with LVCM and low LV EPI BIP voltage regions present (EPI+, group 2). Confluent regions of ENDO UNI and EPI BIP low voltage (>2 cm(2)) were measured. The normal signal amplitude was >8.27 mV for LV ENDO UNI electrograms. Detailed LV ENDO-EPI maps in 5 EPI- patients were compared with 11 EPI+ patients. Confluent ENDO UNI low-voltage regions were seen in 9 of 11 (82%) of the EPI+ (group 2) patients compared with none of 5 EPI- (group 1) patients (P<0.001). In all 9 patients with ENDO UNI low voltage, the ENDO UNI low-voltage regions were directly opposite to an area of EPI BIP low voltage (61% ENDO UNI-EPI BIP low-voltage area overlap).

Conclusions: EPI arrhythmia substrate can be reliably identified in most patients with LVCM using ENDO UNI voltage mapping in the absence of ENDO BIP abnormalities.

Figure 1

Images taken from two EPI- patients in the posterior-anterior (PA) projection: patient 1 (panel A) and patient 2 (panel B). The LV ENDO BIP (left), ENDO UNI (middle), and EPI BIP (right) voltage maps are normal.

Figure 2

Images taken from two EPI+ patients in the posterior-anterior (PA) projection: patient 5 (panel A) and patient 7 (panel B). The LV ENDO BIP voltage maps (left) are normal in both patients. Patient 5 has extensive LV ENDO UNI low voltage involving the entire lateral and inferior LV walls (A, middle). There is a large region of corresponding LV EPI BIP low voltage seen (A, right) corresponding spatially with the ENDO UNI abnormality. Patient 7 has two confluent low UNI voltage regions at the basal-mid lateral and apical LV segments (panel B, middle). The corresponding LV EPI BIP map shows two corresponding low voltage areas (panel B, right). See text for further discussion.

Figure 3

Images are taken from EPI+ patient 6. Panel A shows the LV ENDO UNI map in the left lateral (LL) projection with a confluent low voltage region involving the basal-mid lateral LV segment. The dotted region in panel A surrounds low UNI voltage directly overlapping a region of EPI BIP scar. The remaining low UNI voltage region in panel A (grey shading) did not have a corresponding area of BIP scar on the EPI map. Panel B shows a mesh overlay of the ENDO and EPI voltage maps with the ENDO UNI low voltage regions displayed (ENDO UNI and EPI BIP overlap region now shaded yellow). The dotted white line demarcates the apical extent of the EPI BIP voltage abnormality. Panel C shows a basal, short-axis image from the patient’s preoperative cardiac MR scan. There is a large region of predominantly mid-myocardial (M-M) delayed enhancement (DE) involving the anterolateral to the inferolateral LV and extending from the base to the mid-cavity. In this slice, normal ENDO and EPI enhancement (white arrows) are seen adjacent to the mid-myocardial scar. The shaded (non-overlapping) region of low ENDO UNI voltage likely represents detection of mid-myocardial scar with UNI mapping.