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Determinants of variable exercise performance among patients with severe left ventricular dysfunction.

M B Higginbotham, K G Morris, E H Conn

The American Journal of Cardiology

|January 1, 1983

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Patients with heart failure have lower exercise capacity due to reduced cardiac output, not ejection fraction. Heart rate and arteriovenous oxygen difference changes predict performance in heart failure patients.

Area of Science:

Cardiology
Exercise Physiology

Background:

Heart failure (HF) significantly impairs cardiovascular function and exercise capacity.
Understanding the determinants of exercise performance in HF is crucial for management.

Purpose of the Study:

To assess the relationship between bicycle exercise performance and central/peripheral cardiovascular function in patients with moderate to severe heart failure.
To identify predictors of exercise capacity in heart failure.

Main Methods:

17 patients with class II-III heart failure and 9 healthy controls performed bicycle exercise to exhaustion.
Cardiovascular function was assessed using radionuclide angiography to measure ejection fraction (EF), stroke volume, and cardiac output (CO).
Oxygen consumption (VO2) and arteriovenous oxygen difference (A-VO2) were measured; exercise capacity was quantified as maximal VO2 (Mets).

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Main Results:

Maximal VO2 was significantly lower in heart failure patients compared to controls.
Reduced exercise performance in patients was attributed to a blunted cardiac output response, not impaired oxygen extraction (A-VO2).
The reduced CO response stemmed from a failure of EF to increase or an attenuated heart rate response, or both.
In patients, exercise capacity (Mets) correlated with changes in heart rate, CO, and A-VO2, but not with EF or stroke volume changes.
Resting EF and exercise-induced changes in EF did not correlate with exercise performance in patients.

Conclusions:

In heart failure, exercise capacity is primarily limited by a reduced cardiac output response during exercise, influenced by heart rate and stroke volume.
Left ventricular ejection fraction and stroke volume changes during exercise are not reliable predictors of exercise performance in severe left ventricular dysfunction.
Variable exercise performance in heart failure is mainly driven by inconsistent heart rate and arteriovenous oxygen difference responses.