Altered ventricular repolarization in central sympathetic dysfunction associated with spinal cord injury

Area of Science:

• Cardiology
• Neurology
• Autonomic Function

Background:

• Complete cervical spinal cord injury (SCI) disrupts central sympathetic outflow.
• The impact of cervical sympathectomy on ventricular repolarization is not well understood.
• Autonomic dysfunction significantly influences cardiac repolarization.

Purpose of the Study:

• To investigate the effects of disrupted central sympathetic outflow on electrocardiogram (ECG) ST-segment height in individuals with chronic complete cervical SCI.
• To compare ST-segment changes during rest, exercise, and pharmacologic stimulation between high-level SCI patients and controls.

Main Methods:

• Prospective study of 40 subjects with complete chronic SCI, divided into high-level (C5-C8, disrupted sympathetic outflow) and control (T10-L1, intact sympathetic innervation) groups.
• Autonomic dysfunction verified using the cold pressor response.
• Resting and exercise (arm ergometry) surface ECGs analyzed for ST-segment height.
• Response to exogenous sympathomimetic amine (isoproterenol) infusion assessed.

Main Results:

• High-level SCI group exhibited significant multilead ST-segment elevation at rest compared to controls (131 ± 21 vs 47 ± 8 μV; p=0.0005).
• Exercise failed to decrease ST-segment height in the high-level SCI group, unlike controls (ΔST = -3 ± 6 vs -43 ± 14 μV; p=0.02).
• Isoproterenol infusion markedly decreased ST-segment height in the high-level SCI group (mean ΔST = -84 ± 26 vs -17 ± 18 μV; p=0.04).

Conclusions:

• Central sympathetic dysfunction in high-level SCI regularly results in multilead ST-segment elevation.
• ST-segment height is influenced by central sympathetic nervous activity at rest and during stress.
• Unlike normal subjects, ST-segment height in SCI is not altered by exercise but decreases with isoproterenol, indicating sympathetic influence.