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Outer loop and isthmus in ventricular tachycardia circuits: Characteristics and implications
Antonio Frontera1, Stefano Pagani2, Luca Rosario Limite1
1Department of Arrhythmology, San Raffaele Hospital, Milan, Italy.
Heart Rhythm
|June 5, 2020
Summary
The outer loop (OL) significantly contributes to ventricular tachycardia (VT) circuits by featuring multiple slow conduction (SC) corridors. These SC areas, often with abnormal electrical activity, can be structural or functional, impacting VT reentry.
Area of Science:
- Cardiology
- Electrophysiology
- Medical Imaging
Background:
- Ventricular tachycardia (VT) circuits are often studied by focusing on the isthmus.
- Limited research exists on the role of the outer loop (OL) in VT circuits.
Purpose of the Study:
- To investigate and characterize the electrophysiological properties of the outer loop (OL) in ventricular tachycardia (VT) circuits.
Main Methods:
- High-density mapping was used for complete substrate activation during sinus rhythm (SR) and VT circuit mapping.
- Conduction velocities (CVs) were calculated, defining slow conduction (SC) as <50 cm/s.
- Electrograms were analyzed for fractionation, duration, and amplitude.
Main Results:
- The OL showed multiple corridors of SC during both VT and SR.
- SC in the OL was longer and faster than in the isthmus during SR.
- SC sites in the OL frequently exhibited local abnormal ventricular activity and low bipolar voltage.
Conclusions:
- The outer loop (OL) plays a crucial role in ischemic reentrant VT circuits through multiple SC corridors.
- These SC corridors can arise from structural or functional causes.
- VT circuit boundaries, including isthmuses, may be functional rather than fixed lines of block.
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