High-resolution optical mapping of intramural virtual electrodes in porcine left ventricular wall

doi:10.1016/j.cardiores.2004.07.016

Cardiovascular Research 2004 64(3):448-456; doi:10.1016/j.cardiores.2004.07.016
© 2004 by European Society of Cardiology

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High-resolution optical mapping of intramural virtual electrodes in porcine left ventricular wall

Oleg F. Sharifov^a, Raymond E. Ideker^a^,b and Vladimir G. Fast^a^,*

^aDepartment of Biomedical Engineering, University of Alabama at Birmingham, 1670 University Boulevard, VH B126, Birmingham, Alabama 35294, United States
^bDepartment of Medicine and Physiology, University of Alabama at Birmingham, Birmingham, AL 35294, United States

^* Corresponding author. Tel.: +1 205 975 2119; fax: +1 205 975 4720. Email address: fast{at}crml.uab.edu

Objective: It is believed that shock-induced intramural virtualelectrodes (IVE) play a critical role in defibrillation. IVEwere recently demonstrated in the porcine left ventricle (LV),but their origin remains unknown. Macroscopic optical mappingshowed that strong shocks induce IVE of only one polarity, whichcontradicts theoretical predictions. It is hypothesized thatIVE have a microscopic origin and that microscopic positiveand negative IVE are spatially averaged during macroscopic opticalmapping. This hypothesis was examined by mapping V_m responsesat the transmural LV surface with increased optical resolution.

Methods: Rectangular shocks (strength=2–48 V/cm; duration=10ms) were applied across isolated coronary-perfused porcine LVpreparations (n=7) during the action potential plateau and diastole.Shock-induced V_m responses were measured at low resolution (LR;1.2 mm/diode) and high resolution (HR; 0.11 mm/diode).

Results: During plateau shocks with strength $≤$ 20 V/cm, LR recordingsdemonstrated only negative ${Delta}$ V_m extending to the cathodal preparationedge. In contrast, HR recordings from this area as well as fromintramural locations revealed both positive and negative ${Delta}$ V_mat all shock strengths. During diastolic shocks, only positivepolarizations were observed at LR, but both positive and negativepolarizations were detected at HR. In areas of negative polarization,large activation delays were found at HR, whereas LR recordingsat these locations demonstrated fast activation.

Conclusions: High- and low-resolution optical mapping producedradically different patterns of shock-induced polarization andactivation. The occurrence of positive and negative polarizationsduring plateau and diastolic shocks at high but not low resolutionprovides evidence for microscopic nature of IVE in LV wall.

KEYWORDS Defibrillation; Excitation; Virtual electrodes; Optical mapping; Voltage-sensitive dyes

Time for primary review 27 days

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