Subthreshold Stimulation of the Human Heart

Connelly, Derek Thomas (1994) Subthreshold Stimulation of the Human Heart. MD thesis, University of Glasgow.

Abstract

The effects of long duration subthreshold conditioning stimuli on refractory periods in the human heart have been studied in patients undergoing clinical electrophysiological studies. It has been shown that unipolar cathodal stimuli produce inhibition (lengthening of efifective refractory period), and unipolar anodal stimuli can produce either summation (shortening of effective refractory period) or inhibition, in both atrial and ventricular myocardium. Long duration conditioning stimuli produce much greater changes in refractory period than those shown in previous studies using short duration stimuli. Inhibitory effects can be produced 20 - 50 ms after the end of a subthreshold stimulus. Stimuli of shorter duration (20 ms or less) must have a greater amplitude to produce the same degree of inhibition as longer duration stimuli. The mechanism of the effect is uncertain, but may be related to sodium channel activation or inactivation by subthreshold electrical current. The spatial effects of subthreshold stimuli are very limited, inhibitory effects not being demonstrable 1 mm or more away from the site of delivery of the subthreshold pulses. Attempts to terminate reentrant arrhythmias were made using subthreshold pulses. Despite optimal mapping techniques, it was not possible to terminate any cases of atrioventricular reentrant tachycardia, atrioventricular nodal reentrant tachycardia or ventricular tachycardia using long duration cathodal conditioning stimuli. Higher amplitude pulses occasionally terminated the tachycardia, but only as a result of local capture. Thus it is likely that the spatial limitations of subthreshold stimuli preclude their routine use in the termination of tachycardias. Furthermore, the use of subthreshold stimulation as a mapping tool to identify suitable sites for catheter ablation for ventricular or supraventricular tachycardia seems to be impractical.

• Item Type: Thesis (MD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Edward Rowland
• Keywords: Medicine, Physiology
• Date of Award: 1994
• Depositing User: Enlighten Team
• Unique ID: glathesis:1994-75663
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 18:59
• Last Modified: 19 Nov 2019 18:59
• URI: https://theses.gla.ac.uk/id/eprint/75663