Key result
Selective perfusion with potassium to create slow conduction resulted in a completely sloped reset curve, allowing premature beats to terminate ventricular tachycardia in 19 of 24 rabbit hearts.
Why the study?
Does the nature of the area of slow conduction (potassium vs heptanol) affect the reset response and ability to terminate reentrant VT in rabbit hearts?
Does the nature of the area of slow conduction (potassium vs heptanol) affect the reset response and ability to terminate reentrant VT in rabbit hearts?
The nature of the area of slow conduction (depressed action potential vs electrical uncoupling) determines the type of reset response and the ability of premature beats to terminate ventricular tachycardia.
Findings in rabbit VT models highlight substrate-specific termination; extends mechanistic understanding but leaves open clinical relevance.
BACKGROUND: The purpose of this study was to compare differential effects of a segment of slow conduction during ventricular tachycardia (VT) due to depression of the action potential and electrical uncoupling. METHODS AND RESULTS: In 33 Langendorff-perfused rabbit hearts, a ring of anisotropic left ventricular subepicardium was created by a cryoprocedure. Reentrant VT was produced by incremental pacing. Slow conduction in a segment of the ring was created by selective perfusion of the LAD with 10 mmol/L potassium or 0.75 mmol/L heptanol. As a result, VT cycle length increased from 193+/-34 to 235+/-37 ms (potassium) and 227+/-42 ms (heptanol). Reset curves were made by applying premature stimuli proximal to the area of depressed conduction. In a ring of uniform anisotropic tissue, the reset curve was almost completely flat. Electrical uncoupling of part of the ring (nonuniform anisotropy) resulted in a mixed reset curve. In both substrates, early premature beats failed to terminate VT. Depression of part of the ring by increasing K+ resulted in a completely sloped reset curve, indicating a gap of partial excitability. Under these conditions, in 19 of 24 hearts, premature beats terminated VT by conduction block in the high K+ area. CONCLUSIONS: The nature of the area of slow conduction determines the type of reset response and the ability to terminate VT.
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Haberl et al. (1999) studied Reentrant Ventricular Tachycardia (n=33). Selective perfusion with potassium or heptanol vs. Baseline uniform anisotropic tissue was evaluated on Ventricular tachycardia cycle length and reset response. Selective perfusion with potassium to create slow conduction resulted in a completely sloped reset curve, allowing premature beats to terminate ventricular tachycardia in 19 of 24 rabbit hearts.
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