Ventricular Assist Device Therapy in Advanced Heart Failure


Common Misconceptions

  • Left ventricular recovery is common after placement of left ventricular assist devices (LVAD).

  • Patients who are candidates for heart transplantation should never have an LVAD placed.

  • Palliative care consultation is inappropriate for patients being considered for a destination therapy LVAD.

  • The development of reliable left ventricular assist devices (LVADs) has revolutionized heart failure (HF) management.

  • In the cardiac intensive care unit (CICU) context, LVADs are encountered in three situations:

    • Selection of the appropriate patient with heart failure for mechanical circulatory support (MCS) and preoperative evaluation

    • Treatment of these patients perioperatively

    • Treatment of complications and prevention of adverse events.

Technology of Left Ventricular Assist Devices

  • The initial LVADs were volume displacement pumps known as pulsatile-flow devices.

  • However, pumps had multiple moving parts, including bearings, valves, and pusher plates that were subject to failure.

  • A paradigm shift in the field of assisted circulation occurred with the introduction of durable, implantable continuous-flow devices.

  • The rationale for continuous flow was the observation that the initial pulsatile flow in the aorta is progressively dampened, transforming into continuous nonpulsatile flow at the level of the capillary ( Fig. 25.1 ).

    Fig. 25.1, Pressure and pulsatility distribution in the systemic circulation. Caps ., Capillaries; Lg. art ., large artery; Lt. vent ., left ventricle; Pulm. art ., pulmonary artery; Rt. vent ., right ventricle; Sm. art ., small artery.

  • Continuous-flow LVADs have only a single moving part and propel blood forward in a steady, continuous fashion with an axial or centrifugal rotor or an impeller.

  • With this simplified design, the risk of mechanical failure has been greatly reduced.

  • Currently, the HeartMate II (St. Jude Medical) and the HeartWare HVAD (HeartWare) are the only US Food and Drug Administration (FDA)–approved continuous-flow LVADs ( Fig. 25.2 ).

    Fig. 25.2, Axial St. Jude HeartMate II ( A ) and centrifugal HeartWare HVAD ( B ) left ventricular assist devices.

  • The HeartMate II is capable of providing up to 10 L/min of support and is surgically inserted into a preperitoneal pocket (See Fig. 25.2A ).

  • Blood is pulled out of the LV into the LV inflow cannula, accelerated by a rotor, and then ejected into the outflow graft, which is anastomosed to the ascending aorta.

  • A percutaneous driveline exits in the upper abdomen and connects the device with a portable controller and two batteries for mobile operation, or to a power base unit and a wall outlet when a patient is stationary for several hours (e.g., while sleeping).

  • The device provides a constant flow of blood with one backup speed used in case of a sudden drop of preload.

  • The typical operating speed range is 8600 to 9600 rpm.

  • Despite antithrombotic coating with titanium microbeads, anticoagulation with a target international normalized ratio (INR) of 2.0 to 3.0 and aspirin are recommended.

  • In distinction to the axial-flow HeartMate II, the HVAD is a miniaturized centrifugal pump (see Fig. 25.2B ).

  • The smaller size of this device allows implantation into the pericardial space and, often, a shorter operation.

  • The housing contains an impeller suspended by magnets and the device is capable of providing 10 L/min of flow.

  • The usual operating speed range is 2400 to 2800 rpm.

  • The presence of a continuous-flow device does not necessarily eliminate the presence of a palpable pulse on physical examination.

  • This has an important consequence when measuring a patient's blood pressure.

  • In the absence of a palpable pulse, mean arterial pressure (MAP) is measured via Doppler.

    • The blood pressure cuff is inflated above where the Doppler tones are heard, and then the return of sounds auscultated via Doppler is taken as the MAP.

    • MAP measured by Doppler overestimates pressure in the presence of palpable pulse and should not be reported.

    • Instead, auscultation of the Korotkoff sounds should be performed.

Bridge to Transplantation (BTT) LVAD

  • BTT refers to the implantation of a durable LVAD in a patient with end-stage HF with the intent of improving the hemodynamics and clinical course until a donor heart is available.

  • As the donor shortage has worsened, the proportion of transplant recipients who required bridging with a durable LVAD increased from 26% in 2004 to more than 50% in 2014.

  • Early studies in patients with a BTT have proven that prompt implantation of an LVAD is the only meaningful chance for survival available to the sickest patients.

  • These studies also demonstrated a substantial reversibility of organ damage: that is, implantation of LVADs was followed by a significant improvement in biochemical markers of kidney and liver injury.

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