Conference Coverage

STS: Minimizing LVAD pump thrombosis poses new challenges

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Field of mechanical circulatory support awaits new technology

Dr. Hossein Almassi, FCCP, comments: With improvements in technology and development of rotary pumps, there has been a significant growth in the use of mechanical circulatory support (MCS) for treatment of end stage heart failure with a parallel improvement in patients’ survival and the quality of life.

Dr. Hossein Almassi

The authors of this report presented at the 2016 annual meeting of the STS, are authorities in the field of MCS outlining the observed increase in pump thrombosis noted in 2012. The sharp increase in the thrombosis rate is different from the lower incidence seen in the preapproval stage of the pump trial.

It should be noted that the report is related mainly to the HeatMate II left ventricular assist device (LVAD) and not the more recently implanted HeartWare device.

The diagnostic algorithm outlined in the accompanying reference (J Heart Lung Transplant. 2013 July;32[7]:667-70) regarding the diagnosis and management of suspected pump thrombosis is worth reading with the main criteria heralding a potential pump thrombosis being 1)sustained pump power elevation, 2) elevation of cardiac LDH or plasma-free hemoglobin, 3) hemolysis, and 4) symptoms of heart failure.

With further refinements in technology, the field of MCS is awaiting the development of newer LVAD devices that would mitigate the serious problem of pump thrombosis.


 

EXPERT ANALYSIS FROM THE STS ANNUAL MEETING

References

PHOENIX – Cardiothoracic surgeons who implant left ventricular assist devices in patients with failing hearts remain at a loss to fully explain why they started seeing a sharp increase in thrombus clogging in these devices in 2012, but nevertheless they are gaining a better sense of how to minimize the risk.

Three key principles for minimizing thrombosis risk are selecting the right patients to receive left ventricular assist devices (LVAD), applying optimal management strategies once patients receive a LVAD, and maintaining adequate flow of blood through the pump, Dr. Francis D. Pagani said in a talk at a session devoted to pump thrombosis at the annual meeting of the Society of Thoracic Surgeons.

Dr. Francis D. Pagani Mitchel L. Zoler/Frontline Medical News

Dr. Francis D. Pagani

Other critical aspects include optimal implantation technique, quick work-up of patients to rule out reversible LVAD inflow or outflow problems once pump thrombosis is suspected, and ceasing medical therapy of the thrombosis if it proves ineffective and instead progress to surgical pump exchange, pump explantation, or heart transplant when necessary, said Dr. Ahmet Kilic, a cardiothoracic surgeon at the Ohio State University, Columbus.

Another key issue is that, now that the pump thrombosis incidence is averaging about 10% of LVAD recipients, with an incidence rate during 2-year follow-up as high as 24% reported from one series, surgeons and physicians who care for LVAD patients must have a high index of suspicion and routinely screen LVAD recipients for early signs of pump thrombosis. The best way to catch pump thrombosis early seems to be by regularly measuring patients’ serum level of lactate dehydrogenase (LDH), said Dr. Robert L. Kormos, professor of surgery and director of the artificial heart program at the University of Pittsburgh.

Dr. Ahmet Kilic Mitchel L. Zoler/Frontline Medical News

Dr. Ahmet Kilic

“We measure LDH on most clinic visits, whether or not the patient has an indication of pump thrombosis. We need to screen [LDH levels] much more routinely than we used to,” he said during the session. “Elevated LDH is probably the first and most reliable early sign, but you need to also assess LDH isoenzymes because we’ve had patients with an elevation but no sign of pump thrombosis, and their isoenzymes showed that the increased LDH was coming from their liver,” Dr. Kormos said in an interview.

Although serial measurements and isoenzyme analysis can establish a sharp rise in heart-specific LDH in an individual patient, a report at the meeting documented that in a series of 53 patients with pump thrombosis treated at either of two U.S. centers, an LDH level of at least 1,155 IU/L flagged pump thrombosis with a fairly high sensitivity and specificity. This LDH level is roughly five times the upper limit of normal, noted Dr. Pagani, professor of surgery and surgical director of adult heart transplantation at the University of Michigan, Ann Arbor, and a senior author on this report.

Dr. Robert L. Kormos

Dr. Robert L. Kormos

But prior to this report Dr. Kormos said that he regarded a LDH level of 600-800 IU/L as enough of an elevation above normal to prompt concern and investigation. And he criticized some LVAD programs that allow LDH levels to rise much higher.

“I know of clinicians who see a LDH of 1,500-2,000 IU/L but the patient seems okay and they wonder if they should change out the pump. For me, it’s a no brainer. Others try to list a patient like this for a heart transplant so they can avoid doing a pump exchange. I think that’s dangerous; it risks liver failure or renal failure. I would not sit on any LVAD that is starting to produce signs of hemolysis syndrome, but some places do this,” Dr. Kormos said in an interview.

“Pump thrombosis probably did not get addressed in as timely a fashion as it should have been” when it was first seen on the rise in 2012, noted Dr. James K. Kirklin, professor of surgery and director of cardiothoracic surgery at the University of Alabama, Birmingham. “It is now being addressed, and we realize that this is not just a pump problem but also involves patient factors and management factors that we need to learn more about. We are quite ignorant of the patient factors and understanding their contributions to bleeding and thrombosis,” said Dr. Kirklin. He also acknowledged that whatever role the current generation of LVAD pumps play in causing thrombosis will not quickly resolve.

Dr. James K. Kirklin

Dr. James K. Kirklin

“I’m looking forward to a new generation of pumps, but the pumps we have today will probably remain for another 3-5 years.”

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