Echocardiographic Ramp test for continuous-flow left ventricular assist devices: do loading conditions matter?

Area of Science:

• Cardiology
• Medical Devices
• Echocardiography

Background:

• Ramp speed tests assess left ventricular assist device (LVAD) function by measuring left ventricular end-diastolic diameter (LVEDD) changes with increasing device speeds.
• Failure to reduce LVEDD indicates potential pump obstruction, a critical complication in LVAD patients.
• Aortic insufficiency (AI) and elevated mean arterial pressure (MAP) can impair the ability to effectively unload the left ventricle during ramp tests.

Purpose of the Study:

• To determine if continuous aortic insufficiency (AI) or elevated mean arterial pressure (MAP) are associated with false positive results for flow obstruction in echocardiographic ramp speed tests.
• To evaluate the impact of abnormal loading conditions on the interpretation of LVAD ramp tests.
• To identify predictors of device obstruction in continuous-flow LVADs.

Main Methods:

• Echocardiographic ramp speed tests were performed on patients with continuous-flow LVADs.
• Left ventricular end-diastolic diameter (LVEDD) was plotted against device speed, and the slope of the linear function was calculated.
• Receiver-operator characteristic (ROC) curves were used to assess the predictive value of LVEDD slope and other parameters for device obstruction, with device thrombosis confirmed by direct visualization.

Main Results:

• Abnormal LVEDD slopes (≥-0.16), indicative of obstruction, were observed in 36 out of 78 ramp tests (46%), with 18 true positives and 18 false positives.
• Patients with AI exhibited significantly flatter LVEDD slopes (-0.14 ± 0.17) compared to those without AI (-0.25 ± 0.11), suggesting obstruction despite similar lactate dehydrogenase levels.
• Elevated MAP (≥85 mm Hg) also correlated with abnormal LVEDD slopes, and combining LVEDD slope with lactate dehydrogenase concentration yielded a high area under the ROC curve (0.96) for predicting device obstruction.

Conclusions:

• Abnormal loading conditions, specifically AI and elevated MAP, can lead to false positive interpretations of flow obstruction during LVAD ramp speed tests.
• These findings highlight the importance of considering hemodynamic factors when interpreting ramp test results in LVAD patients.
• Accurate assessment of LVAD function requires accounting for conditions that affect left ventricular filling and unloading.