Abstract and Introduction
Abstract
Aims To determine whether the magnitude of post-acute myocardial infarction (AMI) sympathetic activation is greater in women (F-AMI) than men (M-AMI).
Methods and results Both sympatho-humoral activation and female gender are associated with worse outcome in the early phase following AMI. However, women have lower sympathetic output than men. We therefore examined matched groups of F-AMI (18) and M-AMI (18) patients 2–4 days following uncomplicated AMI, then 3 monthly to 9 months; matched normal control (NC) groups comprised M-NC (18) and F-NC (18). Muscle sympathetic nerve activity (MSNA) was measured by microneurography. Muscle sympathetic nerve activity was lower in the F-NC than M-NC (at least P < 0.05) and greater in the two AMI groups than their corresponding NC groups (at least P < 0.001). Muscle sympathetic nerve activity was similar in the F-AMI and M-AMI groups indicating a post-AMI increase in women of about twice that in men (P < 0.0001). Both AMI groups returned to corresponding NC (lower in women) levels by 9 months.
Conclusion Following uncomplicated AMI, women developed a relatively greater magnitude of sympathetic activation lasting until its resolution at 9 months. This is consistent with reports of their worse prognosis observed during this time period, with important potential clinical implications.
Introduction
Sympatho-humoral activation occurs following acute myocardial infarction (AMI) and has long been related to the extent of myocardial damage and associated mortality and morbidity. It is also known that a protracted sympathetic activation occurs following AMI, in both normotensive and hypertensive subjects, persisting for at least 6 months, until returning to the level of matched control groups at 9 months.
The mortality and morbidity in the acute phase following AMI have been reported to be greater in women than men, and to occur despite advances in the medical management of AMI that have led to improved prognosis. This increased risk in women has been attributed both independently to female gender and at least partly to the fact that, at the time of infarction, women are generally older and have a higher prevalence of hypertension, heart failure, and diabetes mellitus. It is notable that these conditions have themselves been associated with sympathetic activation, which in turn has been related to increased cardiovascular risk following AMI. Despite these considerations, we and others have found that normal women have lower resting sympathetic output than men, and it has been proposed that such reduced sympathetic drive in women may confer a degree of protection against cardiovascular risk. These issues have remained unresolved because the level of sympathetic nerve activity and the extent of its activation after AMI in women relative to men are as yet unknown.
The present study was therefore planned to determine whether the magnitude of the sympathetic neural activation in the acute phase following uncomplicated AMI was greater in women than in men, and to investigate its behaviour over time. In order to achieve this, a prospective comparison of muscle sympathetic nerve activity (MSNA) between four matched groups was made: female (F-AMI) and male (M-AMI) patients following uncomplicated AMI and female normal control (F-NC) and male normal control (M-NC).