Diurnal variation in exercise responses in angina pectoris

Area of Science:

• Cardiology
• Chronobiology
• Exercise Physiology

Background:

• Stable angina patients exhibit diurnal variations in cardiovascular responses to exercise.
• Understanding these circadian rhythms is crucial for accurate patient assessment and treatment comparison.

Purpose of the Study:

• To investigate diurnal variations in exercise electrocardiography (ECG) responses in patients with stable angina.
• To explore the influence of propranolol on these diurnal variations.
• To assess potential training effects from repeated exercise testing.

Main Methods:

• Symptom-limited exercise ECG was performed on male patients with stable angina at different times of day (0800, 1200, 1600 hours).
• Patients were grouped based on treatment (no treatment or propranolol).
• Normal subjects were included as controls to assess diurnal heart rate variation and propranolol effects.

Main Results:

• Significant diurnal variation in heart rate and ST segment displacement was observed in untreated angina patients tested on the same day.
• This circadian variation in ST segment response persisted even with propranolol treatment.
• Repeated exercise testing on the same day suggested a possible training effect on heart rate.
• Normal subjects showed no diurnal heart rate variation, but propranolol reduced their heart rate response.

Conclusions:

• A circadian variation in the ST segment response to exercise exists in angina patients, influenced by reduced vagal parasympathetic tone.
• This diurnal variation must be considered when assessing angina patients and comparing treatment responses.
• Potential training effects from serial exercise testing warrant further investigation.