How to assess contractile reserve and transporting flow rate with dobutamine (Dobutamine) stress echocardiography (DSE)?

Assessment of Contractile Reserve and Flow Rate with Dobutamine Stress Echocardiography (DSE)

Contractile reserve and transporting flow rate during dobutamine stress echocardiography are best assessed by measuring stroke volume changes (>20% increase from baseline indicates contractile reserve) and monitoring valve hemodynamics throughout the stress protocol.

Protocol for Low-Dose Dobutamine Stress Echocardiography

• Start with a low-dose protocol, beginning at 2.5 or 5 μg/kg/min with incremental increases every 3-5 minutes to a maximum dose of 10-20 μg/kg/min 1
• Continuous ECG and blood pressure monitoring is essential throughout the procedure 2
• The test should be terminated when:
  • A positive result is obtained (>20% increase in stroke volume from baseline) 1
  • The heart rate increases >10-20 bpm over baseline or exceeds 100 bpm 1
  • Significant arrhythmias, symptoms, or blood pressure fall occurs 1

Assessment of Contractile Reserve

• Contractile reserve is present when there is >20% increase in stroke volume (SV) from baseline 1, 3
• Measure biplane ejection fraction at baseline and peak stress to assess improvement in LV contractile function 1
• Absence of contractile reserve (failure to increase SV by >20%) predicts high surgical mortality and poor long-term outcome 1
• In patients with aortic stenosis, contractile reserve assessment helps distinguish between true severe stenosis and pseudo-severe stenosis 3

Measurement of Transporting Flow Rate

• Record Doppler data at each stage, including LVOT velocity from the apical approach 1
• Measure the LVOT diameter at baseline and use the same diameter to calculate continuity-equation valve area at each stage 1
• Calculate stroke volume at each stage to quantify flow rate changes 1
• Track the dimensionless index (velocity ratio) during stages as an alternate measure to corroborate changes in valve area 1

Interpretation of Results in Aortic Stenosis

• True severe aortic stenosis: Fixed valve area (<1.0 cm²) despite increased flow, with significant increase in gradient (mean gradient >30-40 mmHg) 1, 3
• Pseudo-severe aortic stenosis: Increase in effective valve area to >1.0 cm² with increased flow 1, 3
• Severe stenosis is suggested by an aortic jet velocity ≥4.0 m/s or mean gradient >30-40 mmHg provided that valve area does not exceed 1.0 cm² at any flow rate 1

Common Pitfalls and Caveats

• Hypertension can alter peak velocity/gradient measurements and should be recorded for every examination 1
• Underestimation of LVOT area can lead to underestimation of flow rate, causing diagnostic errors 1
• Risk of arrhythmia increases with higher dobutamine doses; medical supervision is required throughout the test 1, 2
• At higher plasma concentrations of dobutamine, stroke volume may remain stable or even decrease, with cardiac output increases driven primarily by heart rate 4
• Dobutamine may be ineffective if the patient has recently received beta-blocking medications 2

Documentation Requirements

• The report should include aortic stenosis velocity, mean gradient, stroke volume, and valve area at each stage 1
• Ejection fraction should be measured at least at baseline and peak effect 1
• For prosthetic valves, record transprosthetic gradients and effective orifice areas at each stage 1

By following this systematic approach to DSE, clinicians can accurately assess contractile reserve and transporting flow rate, which are crucial for clinical decision-making in patients with valvular heart disease and cardiomyopathies.