LVAD Hemodynamics — #2 When LVAD Flow <100%

Date
November 6, 2025
URL
https://x.com/WithAScalpel/status/1986417730291982672
Categories
VAD

LVAD Hemodynamics — When LVAD Flow <100%

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What “<100% flow” means

On contemporary consoles, the LVAD “flow” readout is an estimate inferred from speed, power, and pump hydraulics. A value below the patient’s expected total systemic cardiac output indicates that the native LV still contributes a meaningful portion of forward flow (often with intermittent aortic valve opening). In this mixed-support zone, the system is highly preload-sensitive (RV ➜ lungs ➜ LVAD inflow) and vulnerable to any mechanical resistance at the inflow or outflow cannulae. A practical bedside framework tracks three pressures:

  • RAP (right-atrial pressure) → RV preload / pulmonary supply
  • LAP (left-atrial pressure or PCWP) → LV filling / left-sided congestion
  • LVAD inlet pressure (or surrogates: console PI/suction events, power) → local inflow conditions

Why a structured approach matters. Echocardiographic ± invasive ramp testing separates physiology from mechanics, guides speed titration, and screens for device problems [1]. In a prospective cohort, only ~43% of patients at their “usual” RPM had normal CVP/PCWP—underscoring the value of objective ramp-guided adjustment [2]. Ramp interpretation must account for loading conditions, since elevated MAP or aortic insufficiency can mimic outflow or pump obstruction by blunting LV size reduction with speed [3]. When available, Doppler signals in the outflow cannula (VTI, systolic/diastolic slope) predict PCWP, CO, and SVR and may reduce invasive testing [4]. Targets commonly pursued during optimization include CVP <12 mmHg, PCWP <18 mmHg, and CI >2.2 L·min⁻¹·m⁻², which are associated with fewer readmissions [5].

Below are four canonical patterns when displayed flow is <100%, with typical pressure behavior and practical cues.

1) Inflow obstruction

Signature: RAP ↑, LAP ↑, Inlet P ↓

Mechanism. Venous return is adequate (RAP/LAP rise), but the pump cannot ingest blood efficiently because the inflow cannula is limited—transient suction from relative hypovolemia, cannula malposition (septal/apical contact), kinking or thrombus at the inlet, pericardial compression, or leftward septal shift that narrows the LV cavity [1,2].

Clues. PI/suction alarms, brief power dips, abrupt pulsatility spikes, positional variability, echo showing a small, over-unloaded LV or cannula abutting myocardium; ramp testing that fails to show appropriate LVEDD decrease with speed, after excluding high MAP/AI confounders [1–3].

Immediate actions. Temporarily lower RPM to abort suction; correct volume/positioning; treat tamponade if present; image for thrombus/kink; reduce RV afterload to mitigate septal shift [1–3,5].

2) Outflow obstruction

Signature: RAP ↑, LAP ↑, Inlet P ↑

Mechanism. Inlet is well supplied, but the pump faces downstream resistance—outflow graft kink/torsion, extrinsic compression (e.g., bio-debris between HM3 graft and bend relief), anastomotic stenosis, intragraft thrombus, or simply severe hypertension [2,6–9].

Clues. Rising power at fixed speed (working against afterload), dampened arterial pulsatility, and imaging evidence of graft angulation/stenosis—with CTA particularly helpful when echo is nondiagnostic [7–9].

Immediate actions. Treat blood pressure first (afterload acts like a “pinch” on the outflow) [6]. If suspicion persists, obtain graft imaging (CTA ± cath). Mechanical lesions typically require endovascular stenting or surgical correction; antithrombotic escalation is center-specific [7–9].

3) Right-ventricular failure

Signature: RAP ↑, LAP ↓, Inlet P ↓

Mechanism. The RV fails to deliver preload to the lungs/LV—ischemia, high PVR, inadequate contractility, or excessive LV unloading with leftward septal shift. The LVAD becomes preload-starved, and flow falls despite an unobstructed circuit [2,5].

Clues. High CVP with hepatovenous congestion, low PI without suction, reduced pulmonary venous inflow, echo showing RV dilation/dysfunction with a small LV; ramp testing shows limited augmentation of CO with speed [2,4,5].

Immediate actions. Optimize oxygenation/ventilation, correct acidosis, treat PVR (inhaled or systemic vasodilators), give judicious volume, consider inotropes, and often lower RPM to reduce septal shift. Escalate to temporary RVAD if refractory [2,5].

4) Inadequate RPM (under-support)

Signature: RAP ↓/N, LAP ↑, Inlet P ↑

Mechanism. Speed is below physiologic demand. The native LV continues to fill and transmit pressure to the LA (LAP↑) without right-sided congestion (RAP N/↓). Inlet conditions are generous; AV opening is usually preserved [1,2,5].

Clues. Low estimated flow with relatively low power, symptoms/signs of pulmonary congestion, no evidence of inflow/outflow pathology, and improvement in hemodynamics when speed is increased during a controlled ramp [1,2,4,5].

Immediate actions. Titrate RPM upward while monitoring MAP, PI/pulsatility, suction alarms, and end-organ perfusion; reassess echo for septal position and AV opening [1,2,5].

Practical pearls for the bedside team

  • Treat speed changes as diagnostic tests. A deliberate ramp protocol that tracks CVP, PCWP/LAP, MAP, console power/PI, and echo (LV size, septal position, AV behavior) cleanly separates inflow from outflow pathology and distinguishes RV failure from under-support [1,2,5].
  • Echo + Doppler add precision. Outflow-cannula Doppler metrics can noninvasively predict PCWP/CO/SVR and support real-time decisions [4].
  • The pressure triad beats any single number. Interpreting RAP/LAP/Inlet together prevents misattribution (e.g., RHF misread as inflow obstruction) [2,5].
  • Control afterload early. Hypertension increases adverse events on CF-LVAD support and can masquerade as mechanical obstruction during ramp; prompt afterload reduction often restores flow without a scalpel [3,6].
  • Don’t miss blended etiologies. RHF plus mild inflow malposition—or a graft kink compounded by hypertension—can blend patterns; address all contributors to restore safe pump–patient coupling [2,3,7–9].
  • Know your console. Understanding device-specific power/PI behavior and alarm logic (e.g., HeartMate 3) improves troubleshooting and safety during ramps and speed changes [10].

References

[1] Uriel N, Morrison KA, Garan AR, Kato TS, Yuzefpolskaya M, Latif F, et al. Development of a novel echocardiography ramp test for speed optimization and diagnosis of device thrombosis in continuous-flow left ventricular assist devices: the Columbia ramp study. J Am Coll Cardiol. 2012;60(18):1764–1775. PubMed

[2] Uriel N, Sayer G, Addetia K, Fedson S, Kim GH, Rodgers D, et al. Hemodynamic Ramp Tests in Patients With Left Ventricular Assist Devices. JACC Heart Fail. 2016;4(3):208–217. PubMed

[3] Adatya S, Holley CT, Roy SS, Yarmohammadi H, Feng A, Eckman P, et al. Echocardiographic Ramp Test for Continuous-Flow Left Ventricular Assist Devices: Do Loading Conditions Matter? JACC Heart Fail. 2015;3(4):291–299. PubMed

[4] Grinstein J, Imamura T, Kruse E, Kalantari S, Rodgers D, Adatya S, et al. Echocardiographic Predictors of Hemodynamics in Patients Supported With Left Ventricular Assist Devices. J Card Fail. 2018;24(9):561–567. PubMed

[5] Imamura T, Jeevanandam V, Kim G, Raikhelkar J, Sarswat N, Kalantari S, et al. Optimal Hemodynamics During Left Ventricular Assist Device Support Are Associated With Reduced Readmission Rates. Circ Heart Fail. 2019;12(2):e005094. PubMed

[6] Saeed O, Jermyn R, Kargoli F, Madan S, Mannem S, Gunda S, et al. Blood pressure and adverse events during continuous-flow left ventricular assist device support. Circ Heart Fail. 2015;8(3):551–556. PubMed

[7] Peters CJ, Zhang RS, Vidula MK, Giri J, Atluri P, Acker MA, et al. Durable Left Ventricular Assist Device Outflow Graft Obstructions: Clinical Characteristics and Outcomes. J Clin Med. 2023;12(6):2430. PubMed

[8] Agrawal A, Parikh V, Silva Enciso J, Eudailey KW, Adatya S, Reed GW, et al. Outflow graft obstruction after left ventricular assist device implantation: a poorly recognized complication. Eur Heart J. 2021;42(20):1970–1980. PubMed+1

[9] Nathan S, Schubach SL, Patel AK, Joseph J, Stamos TD, Vorovich EE, et al. Left Ventricular Assist Device Outflow Graft Obstruction. ASAIO J. 2020;66(10):e158–e163. PubMed

[10] Belkin MN, Imamura T, Tedford RJ, Uriel N, Sayer G. Physiology and Clinical Utility of HeartMate 3 Left Ventricular Assist Device Pump Parameters. ASAIO J. 2022;68(4):465–472. PubMed

[11] International Society for Heart and Lung Transplantation (ISHLT) Guidelines for Mechanical Circulatory Support—Executive Summary. Feldman D, Pamboukian SV, Teuteberg JJ, et al. J Heart Lung Transplant. 2013;32(2):157–187. PubMed