Acoustic and afterload evaluation of left ventricular assist devices

Methods: Two different mock loops, with the possibility to insert artificial thrombus and to adjust preload and afterload were created to facilitate recording of the left ventricular assist devices. An iPhone/iPodTM was used as recording device since remote monitoring is desirable. The sounds from HeartMate IITM during different conditions were studied. The iPhone/iPod was evaluated in comparison to dedicated recording equipment, and the mock loop recordings to clinical situation. The sound from HeartMate 3TM was studied, compared between in vivo and in vitro recordings, and the use of an electronic stethoscope was evaluated. The impact of afterload on left ventricular assist devices was studied in a mock loop circuit with different changes in preload and afterload.

Results: Mock loop circuit is a promising method to safely change the surrounding conditions as the pump is working. The sound from both HeartMate IITM and HeartMate 3TM can be recorded and analyzed in frequency and time domain. When inserting artificial thrombus in a HeartMate IITM the frequency spectrum is altered. The use of dedicated recording devices is superior to both electronic stethoscope and iPhone/iPodTM, but these handheld devices can be used in clinical settings. The recordings from mock loop circuit and patients appear similar for both HeartMate IITM and HeartMate 3TM. The flow of the devices is affected by the afterload. The HeartMate 3TM is more resistant to increased clot analogs within the pump. For both pumps, best efficacy is seen for clean circuits. The flow rate from the monitor might be misleading since the measured flow rate and the flow rate from monitor can differ due to surrounding conditions. The estimated flow might be adjusted by fitting a parabolic curve.

Conclusion: The use of mock loop circuit to study both flow and sound under different conditions is valid. It is possible to record and study the sound from both HeartMate IITM and HeartMate 3TM. The sound holds information of pump function and appears similar in vivo and in vitro. All recording devices can be used, but dedicated equipment is superior to the more handheld devices, although these might have a function as a screening device. The flow measurement on the monitor might not be valid and optimization of fluid status and afterload can further increase pump efficiency.