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CardioNerds (Amit Goyal & Karan Desai) join Dr. Matthew Delfiner (Cardiology fellow, Temple University Hospital) and Dr. Katie Vanchiere (Internal medicine resident, Temple University Hospital) in the beautiful Fairmount Park in Philadelphia. They discuss a case of a 53-year-old man with an LVAD who presents with progressive dyspnea since LVAD implant due to right-to-left shunting due to a PFO. Dr. Val Rakita (Assistant professor of medicine and advanced heart failure and transplant specialist at Temple University Hospital) provides the E-CPR for this episode. Episode introduction by CardioNerds Clinical Trialist Dr. Anthony Peters (Duke Heart Center). This case has been published by Circulation: Heart failure. See Invasive Hemodynamic Study Unmasks Intracardiac Shunt With Ventricular Assist Device.
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Disclosures: None
Jump to: Pearls – Notes – References
Case Summary – Dyspnea with an LVAD: A Tale of Hypoxia and Hemodynamics
A 53-year-old man with an LVAD placed 3 months prior presents with progressive dyspnea since LVAD implant, though it has acutely worsened over the past 2 weeks. Two weeks ago, he had a hemodynamic and echocardiographic ramp study, where the LVAD speed was increased. By increasing the speed, his LV was more adequately decongested, and flow improved. In the Emergency Department, he was hypoxic on room air, and remained so with escalation ultimately with intubation. Even then he remained severely hypoxic requiring cannulation to veno-venous ECMO.
Chest imaging was normal, and LVAD parameters were normal without any alarms. An astute clinician noticed that when the patient became hypertensive, his oxygen saturation improved. A subsequent echocardiogram revealed a patent foramen ovale, with right to left shunting. The patient then went to the cath lab, where simultaneous right atrial and left atrial pressures and oxygen pressures were measured, along with trans-esophageal echocardiography, while adjusting LVAD speed. It became evident that right-to-left shunting occurred only when there was high LVAD speed and low peripheral blood pressure. Essentially, faster LVAD speeds (sucking blood from the LV) and low systemic blood pressure (reducing LV afterload) increased right to left shunting by decreasing the left atrial pressure relative to the right atrial pressure. The PFO was closed at that time, drastically improving oxygenation. He was decannulated and extubated the following day.
Episode Teaching -Dyspnea with an LVAD: A Tale of Hypoxia and Hemodynamics
Pearls
- PFOs are present in up to 25% of individuals, including those with LVADs.
- LV unloading, and therefore LA decompression, depends on both LVAD speed and systemic vascular resistance.
- Blood pressure dependent hypoxia may be suggestive of a right-to-left intracardiac shunt.
- Hypoxia refractory to mechanical ventilation should raise suspicion for intracardiac shunt.
- Patients with LVADs can suffer from the same diseases that anyone can.
Notes – Dyspnea with an LVAD: A Tale of Hypoxia and Hemodynamics
1. What factors influence LVAD flow?
Factors that influence LVAD flow include pump speed, blood pressure, volume status, RV function, cardiac rhythm, and some other variables. The faster the pump is spinning, the more flow you should provide (to an extent). However, if your LV is underfilled, either from systemic hypovolemia or an RV not providing the needed LV preload, then you have no blood to flow! If you have high systemic vascular resistance, then you will have less forward flow, just as a native heart would. We must always think about the interaction between a patient and the LVAD, not just the machine settings.
2. What can cause dyspnea and hypoxia in LVAD patients?
The same things that cause dyspnea in any other patient! But also… inadequate unloading of the LV due to the above factors in addition to possible suction events. Aortic regurgitation can cause an endless loop of flow from: LV > LVAD > aorta > AV > LV. Pump malfunction must always be considered, including inflow/outflow obstruction and pump thrombosis. Anemia may also contribute, as patients with LVAD are prone to both bleeding and hemolysis.
3. What are the ideal LVAD settings?
There are no standard settings for LVADs, especially because there are different manufacturers. But most importantly, every patient is different, and therefore the patient-LVAD interaction is different. Overall, the ideal LVAD speed would decongest the heart while preserving RV function, maintaining the interventricular septum midline, and having intermittent aortic valve opening.
4. Explain how PFOs can result in hypoxemia.
PFOs, or any septal defect, allow intra-cardiac flow from one side of the heart to the other. Flow will follow a pressure gradient. Usually, the left heart will have higher pressures than the right heart, but if the right heart pressure exceeds the left, then de-oxygenated venous blood can bypass the pulmonary circulation and enter the left heart and systemic circulation, causing hypoxemia.
5. List the methods that are used to diagnose and evaluate the severity of intra-cardiac shunts.
Doppler color flow and bubble study with TTE or TEE. Blood gas measurement across various chambers can be used as well.
For an in-depth review of LVADs, enjoy Ep #15. LVAD 101 with Dr. Steve Hsu.
References
CardioNerds Case Report Production Team
