Ventricular reflex interactions during transmural myocardial ischemia

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System
• Myocardial Ischemia Research

Background:

• The role of left ventricular (LV) receptors with sympathetic afferent fibers in reflex responses to myocardial ischemia is debated.
• Previous studies suggested excitatory reflexes from LV sympathetic afferents during ischemia in sinoaortic denervated and vagotomized dogs.

Purpose of the Study:

• To investigate if reflex excitatory responses occur in dogs with intact LV vagal afferents.
• To elucidate the role of LV sympathetic afferents in mediating renal sympathetic nerve activity during myocardial ischemia.

Main Methods:

• Experiments conducted in 27 chloralose-anesthetized dogs with sinoaortic denervation.
• Measured efferent renal sympathetic nerve activity, arterial, and left atrial pressures during inferoposterior myocardial ischemia (transmural and non-transmural).
• Assessed responses before and after stellectomy (interruption of LV sympathetic afferents) and verified sympathetic deafferentation using epicardial bradykinin.

Main Results:

• Prior to stellectomy, 10 dogs showed excitatory responses and 9 showed inhibitory responses to ischemia.
• Stellectomy abolished excitatory renal nerve activity increases during ischemia in the excitatory group.
• In the inhibitory group, transmural ischemia after stellectomy elicited greater reflex inhibition, suggesting sympathetic afferent attenuation of vagal inhibitory reflexes.

Conclusions:

• Reflex excitatory responses mediated by LV receptors with sympathetic afferent fibers can be elicited in dogs with intact vagal afferents.
• These excitatory responses are most evident during transmural myocardial ischemia.
• LV sympathetic afferent activation during transmural ischemia may attenuate inhibitory reflexes mediated by LV vagal afferents.