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Cross-bridge activation rate constant determined from systolic time intervals in patients with systemic lupus
1Department of Medicine, Dokkyo University School of Medicine, Tochigi.
Insights
Systemic lupus erythematosus (SLE) patients show increased cardiac adrenergic activity, specifically in left ventricular (LV) myocardium. This heightened adrenergic tone may contribute to cardiovascular complications in SLE.
Area of Science:
- Cardiology
- Rheumatology
- Physiology
Background:
- Systemic lupus erythematosus (SLE) is associated with increased cardiovascular risk.
- Cardiac adrenergic activity plays a crucial role in cardiovascular function.
- Assessing adrenergic tone in SLE patients is important for understanding disease mechanisms.
Purpose of the Study:
- To investigate cardiac adrenergic activity in patients with SLE.
- To evaluate the adrenergic tone of the working left ventricular (LV) myocardium.
- To assess sinus node adrenergic tone using heart rate.
Main Methods:
- Utilized a new index for adrenergic tone of the LV myocardium.
- Calculated the corrected cross-bridge activation rate constant (Kac) using echocardiography, ECG, phonocardiogram, and carotid pulse wave tracing.
- Divided 38 SLE patients into normal (n=26) and high (n=12) Kac groups based on calculated values.
Main Results:
- A subset of SLE patients (n=12) exhibited a high Kac, indicating increased adrenergic tone of the LV myocardium.
- This increase in adrenergic tone occurred without significant changes in heart rate.
- The Kac index demonstrated variability in SLE patients compared to normal individuals.
Conclusions:
- Patients with SLE may have elevated cardiac adrenergic activity.
- Increased adrenergic tone in the LV myocardium could be a contributing factor to cardiovascular issues in SLE.
- Further research is needed to explore the clinical implications of these findings.
Abstract:
Cardiac adrenergic activity was investigated in 38 patients with systemic lupus erythematosus (SLE) who were not receiving cardiovascular agents using a new index of the adrenergic tone of the working left ventricular (LV) myocardium and using the heart rate to represent sinus node adrenergic tone. According to the active cross-bridge model employed in this study, the cross-bridge activation rate constant (Ka) of the LV myocardium, corresponding to the rate constant for the binding of Ca2+ to troponin C, can be approximately expressed as Ka = 3/electromechanical systole (sec-1). The Ka value corrected for heart rate (Kac) remains nearly constant in normal individuals, but is increased without change of the heart rate by dobutamine infusion. Fifty patients who fulfilled the American Rheumatism Association criteria for SLE underwent echocardiography, as well as simultaneous recording of the electrocardiogram, phonocardiogram, and carotid pulse wave tracing. Kac was calculated from the interval between the onset of the QRS complex to the second heart sound (QS2 interval) and the heart rate (HR) as follows: Kac = 3/QS2 + 0.0249 (66-HR). The 38 SLE patients were divided into a normal Kac group (n = 26, 6.9 < Kac < 8.3 sec-1) and a high Kac group (n = 12, Kac > or = 8.3 sec-1).(ABSTRACT TRUNCATED AT 250 WORDS)