Relationship between voltage map "channels" and the location of critical isthmus sites in patients with post-infarction cardiomyopathy and ventricular tachycardia

Objectives: The goal of this study was to determine the relationship of the ventricular tachycardia (VT) isthmus to channels of preserved voltage on an electroanatomic voltage map in postinfarction cardiomyopathy.

Background: Substrate mapping in patients with postinfarction cardiomyopathy and VT may involve lowering the voltage cutoff that defines the scar (<1.5 mV) to identify "channels" of relative higher voltage within the scar. However, the prevalence of channels within the scar identified by using electroanatomic mapping and the relationship to the protected VT isthmus identified by entrainment mapping is unknown.

Methods: Detailed bipolar endocardial voltage maps (398 ± 152 points) from 24 patients (mean age 69 ± 9 years) with postinfarction cardiomyopathy (ejection fraction 33 ± 9%) and tolerated VT were reviewed. Endocardial scar was defined according to voltage <1.5 mV. Isolated late potentials (ILPs) were identified and tagged on the electroanatomic voltage map. The baseline voltage cutoffs were then adjusted until all channels were identified. The VT isthmus was identified using entrainment mapping.

Results: Inferior and anterior/lateral infarction was present by voltage mapping in 18 and 6 patients, respectively (scar area 44 ± 24 cm(2)). By adjusting voltage cutoffs, 37 channels were identified in 21 (88%) of 24 patients. The presence of ILPs within a channel was seen in 11 (46%) of 24 patients and 17 (46%) of 37 channels. A VT isthmus site was contained within a channel in only 11 of 24 patients or 11 of 37 channels. No difference in voltage characteristics was identified between clinical and nonclinical channels. Voltage channels with ILPs harbored the clinical isthmus with a sensitivity and specificity of 78% and 85%, respectively.

Conclusions: Channels were identified in 88% of patients with VT by adjusting the voltage limits of bipolar maps; however, the specificity of those channels in predicting the location of VT isthmus sites was only 30%. The presence of ILPs inside the voltage channel significantly increases the specificity for identifying the clinical VT isthmus.