Contemporary Ventricular Assist Devices: Hemodynamic Consequences

Courtesy of Dr. Agustín Vecchia.

Despite current technological advancements and improvement in reperfusion rates in a setting of infarction, cardiogenic shock still is a relatively frequent complication with a mortality rate close to 50%. The need to augment cardiac output in these patients and the fact that the popular intraaortic balloon counterpulsation has not been able to improve patient outcomes in randomized studies have renewed the interest on the development of new technology in this field.

The following study compares two of the most used ventricular assist devices and assesses their performance. To that end, 7 Yorkshire swine (average weight: 76 ± 2 kg; n = 7) received a left ventricular (LV) pressure-volume catheter and were subjected to a 2-hour balloon circumflex artery occlusion in order to create a model of infarction with reperfusion. Impella CP (ICP) and TandemHeart (TH) devices were implanted in randomized order at comparable flow rates, and hemodynamic parameters and ventricular performance indexes were measured 30 minutes after reperfusion and during support.

Induced infarction caused a rightward shift in the pressure-volume loop and provoked a significant increase in the LV end-diastolic pressure (from 9 ± 2 mmHg to 15 ± 2 mmHg; p = 0.04).

After reperfusion, both devices managed to maintain aortic pressure, shifted the pressure-volume loop to the left, and decreased LV end-diastolic pressure (ICP vs. TandemHeart; 11 ± 1 mmHg vs. 7 ± 4 mmHg; p = 0.04).

Only TandemHeart achieved significant reductions in the following:

• systolic volume (from 75 ± 7 mL to 39 ± 7 mL; p < 0.01),
• dP/dtmax (from 988 ± 77 mmHg/s to 626 ± 42 mmHg/s; p < 0.01),
• stroke work (from 0.70 ± 0.03 J to 0.26 ± 0.05 J; p < 0.01),
• pressure-volume loop area (from 0.95 ± 0.11 J to 0.47 ± 0.10 J; p < 0.01),
• pre-load-recruitable stroke work slope (from 41.7 ± 2.8 J/mL to 30.6 ± 3.9 J/mL; p = 0.05).

Authors conclude that, at similar flow rates, TandemHeart decreases LV pre-load, stroke volume, and myocardial contractility more than Impella CP. Reductions observed in load-independent indexes of ventricular performance (pre-load-recruitable stroke work) suggest favorable effects on myocardial oxygen balance and support further study of TandemHeart as support in a setting of infarction.

Editorial

This article describes one of the few studies comparing ventricular assist devices. Its findings are particularly interesting because they contradict previous papers (Novel Percutaneous Cardiac Assist Devices, Circulation 2011) favoring Impella CP in computerized simulations. In this in vivo study, both left atrial blood withdrawal by TandemHeart and LV blood withdrawal by Impella reduced pre-load and maintained aortic pressure. However, only the former device managed to decrease stroke work and improve myocardial contractility and oxygen consumption.

One practical difference is that these animal models did not present low flow rates. This means that animals were not in cardiogenic shock, a setting in which device performance may vary individually. As a precedent, Kapur et al. published in 2015 the first paper comparing directly these same devices in animal models. Although the study was carried out at a scale smaller than this one, results were similar.

Courtesy of Dr. Agustín Vecchia. Buenos Aires German Hospital, Argentina.

Original title: Comparative Hemodynamic Effects of Contemporary Percutaneous Mechanical Circulatory Support Devices in a Porcine Model of Acute Myocardial Infarction.

Autors: Brian R. Weil, PHD, Filip Konecny, DVM, PHD, Gen Suzuki, MD, PHD, Vijay Iyer, MD, PHD, John M. Canty, JR, MD.

Reference: J Am Coll Cardiol Intv. 2016.

Doi: 10.1016/j.jcin.2016.08.037.

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