New Percutaneous Left Ventricular Assist Device: The TandemHeart PTVA® System

As Roy pushed his Lawn Boy up the gradual incline of his lawn, his heart rate began to climb to 168 and his blood pressure rose to 190/118. The coronary arteries to his heart dilated in response to the physiologic demand for more blood to supply his heart muscle with the needed oxygen. A series of events began to unfold that would be catastrophic. Roy had suffered a myocardial infarction (MI) four years ago and had lost some of his function in the inferior aspect of his myocardium. He had led an uneventful course after recovery, despite his borderline medical compliance, but at this moment, lying in his proximal left anterior descending artery was an area of vulnerable plaque. As he strained to push his lawn mower up a slight hill, the increasing inner luminal pressure in his coronary arteries caused the thin fibrous cap at the site in his left anterior descending coronary artery (LAD) to develop fissures and crack open. Macrophages accompanied by platelets rushed to the site, trying to do their job of forming fibrin over the injured site. Thrombus began to form as the platelets grabbed onto one another like loose bushes in a flowing streambed. Suddenly, occlusion of Roy’s LAD occurred. May saw Roy fall to his knees clutching his chest from the kitchen window. As he fell face forward onto the lawn, she rushed towards him, yelling at their son to call 911. Joyce, her next-door neighbor, and part-time RN, observed the event from her yard and ran to his side to begin CPR. The EMTs arrived ten minutes later and took over transport of Roy to the nearest Medical Center Emergency Room. At this moment, Roy’s left ventricle had taken a large hit. Due to the lack of oxygenated blood flow to the myocardium of his heart, systolic pumping action was failing, as erosion of the muscle elasticity spread across the anterior surface of the heart and the ischemic zone continued to spread. Failing in pumping ability, the left ventricle was unable to empty its volume and the excess blood began to backup through the left atrium and into the pulmonary veins. As his breathing became labored, Roy’s lips and nail beds began to become cyanotic as the lungs failed to adequately exchange oxygen into the blood. The downward spiral of cardiogenic shock (CS) had started. Physicians in the emergency room assessed the situation quickly and summoned the cardiologist on call. Roy would need to be taken to the cardiac cath lab so that an assessment could be made. An intra aortic balloon pump was inserted into the right femoral artery and placed on 1:2 augmentations, while inotropic drugs and antithrombotics were given intravenously. Frantic efforts were made to stabilize Roy and as his breathing became more labored, he was intubated. His gurney, along with the IABP, IVs, two nurses and an ER doc, were squeezed into the small elevator on the way to the third floor cath lab. In the elevator, Roy went into ventricular fibrillation, as erratic electrical impulses tried to find pathways; his heart was counter shocked back into a normal sinus rhythm. He was going downhill fast. Pressure in the right side of the heart was rising as the right atrium strained to push against the rising backpressure and try to force blood into already congested lungs. This fictional case is one example of an all-too-familiar series of events unfolding daily in patients who suffer a massive myocardial infarction accompanied by ischemic left heart failure. Cardiogenic Shock (CS) remains overwhelmingly lethal, developing in 7% to 10% of cases after acute myocardial infarction, with some statistics stating a mortality rate of 70-80% in patients with large anterior infarcts.1,2 Little in the way of mechanical support or pharmacological therapy has changed in recent times. The current use of the intra aortic balloon pump (IABP) and inotropic therapy remains the main defense from the offensive onslaught of acute heart failure. The IABP, combined with pharmacological support, may serve as a buttress to coronary revascularization such as coronary artery bypass grafts (CABG),3,4 percutaneous coronary intervention (PCI),5 or a permanent left ventricular assist device (LVAD). However, supporting patients through the dire straits of ischemic heart failure when currently accepted aggressive therapy fails still poses a significant dilemma. The Tandem Heart PTVA® System A new device, called the TandemHeart PTVA® System (CardiacAssist, Inc., Pittsburgh, PA), recently received FDA 510(k) clearance for clinical use as a short-term circulatory support system. It is a completely percutaneous ventricular assist device (pVAD), which can be inserted in the catheterization laboratory and maintained by trained nurses and technologists. The system opens up an opportunity for cardiologists to have a means of stabilizing patients hemodynamically and assist in gaining time to alternative treatments when conventional means are not considered adequate. The TandemHeart PTVA System is comprised of a pump for circulating the blood, a cannulae for achieving the percutaneous access, and a micro processing controller for operating the pump and providing operator interface. The system allows for a simple, relatively inexpensive left atrial to femoral artery bypass to be completed in less than 30 minutes, within the cath lab environment, through a traditional transseptal puncture. The TandemHeart pVAD is a palm-sized, dual-chambered, centrifugal, continuous-flow pump with specifically designed inflow and outflow ports. A preformed 21F cannulae is attached to the inflow port of the pump after a traditional transseptal puncture (Brockenbrough needle, Mullen sheath) has been performed, across the septum into the left atrium, via the femoral vein. The outflow port is connected to a commercially available wire-reinforced aortic cannula (usually 15F or 17F) and used to return the blood into the patient’s systemic circulation by way of a rotating impeller inside the lower housing of the pump via the femoral arterial system. The device is held in place, usually on the thigh, by a holster, where it resides outside the body until discontinued. Driving the pump is the controller, resembling a typical IV pole. It is a computer-driven systems monitor containing an infusate system used to keep the pump lubricated with a heparinized solution. The controller has extensive self-diagnostics and backup features to ensure patient support without the need for constant operator surveillance. The controller generates the signals to drive and maintain the TandemHeart pVAD operation and adjusting a control knob on the front panel regulates the pump speed. The TandemHeart System is capable of providing up to 4.0 liters of oxygenated blood per minute. The anticoagulant drip infusate solution is fed into the lower chamber of the pump and serves as a lubricant and dissuades fibrin build up in the chamber of the pump. Built-in batteries allow up to 60 minutes of patient transport time without the need for continuous a/c power. As we resume our adventure with Roy, we may see the TandemHeart System can serve as a span to therapy for such an extremely ill patient: After moving Roy to the cath lab table, hemodynamic measurements showed a left ventricular ejection fraction of 20%, Swan-Ganz readings gave a Cardiac Index of 1.8 L/min, with a mean pulmonary pressure of 46 mmHg, and mean arterial pressure of 56 mmHg. Angiography documented a totally occluded LAD with additional severe 90% stenosis of his RCA. Feeling that the IABP and inotropic therapy was providing inadequate support, and Roy being too unstable to undergo CABG, it was felt that a PCI was the only option for his declining condition. Additionally the physician was concerned that the procedure had the potential to induce further hemodynamic deterioration that could be life-threatening. The physician and hospital were participating in a clinical trial of the TandemHeart System for the treatment of cardiogenic shock. Roy met all the criteria, was consented for the trial, and was randomly assigned to the TandemHeart System treatment group. To initiate the TandemHeart System support, a needle puncture was made into the right femoral vein, a standard Brockenbrough catheter was inserted into the inferior vena cava, and the inter-atrial septum was punctured at the site of the fossa ovalis. Using an exchange wire technique, the transseptal puncture site was dilated with a 2-stage dilator and followed by insertion of the 21F side hole venous inflow cannula. This transseptal cannula was sutured to the skin and cross-clamped with a vascular clamp and additional heparin was given to raise the ACT to >400 sec. A 15F arterial perfusion catheter was inserted into the right common iliac artery and cross-clamped. During the procedure, the cath lab technologists had turned on the controller so that the microprocessor could run the self-check. During this 5 minutes, the scrub tech had prepped the pVAD pump with heparinized saline and handed the connecting infusate line and power cord off the sterile field back to the controller tech. Heparin-coated Tygon pre-cut tubing was used for connection of the device, first to the arterial, then venous cannulae, and after careful de-airing and back bleeding had been accomplished, the pump was started. The TandemHeart PTVA System was initiated at low speed, after the clamps had been removed from the input and output cannulae, and the pump started with a low hum. Flow through the input tubing was measured by a transonic flow meter and with the pump speed set at 6000 rpm, was shown to deliver 3.0 L/min of cardiac output. Immediately upon starting initiation of support with the system, improvement could be seen. Cardiac output stabilized at 4.8 L/min (with a native output of 1.8 L/min), the mean pulmonary arterial pressure (PAp) fell to a level of 24 mmHg, and the mean arterial pressure (MAP) increased to 96 mm hg. At this point, the IABP was discontinued. Oxygenated blood was being withdrawn from the left atrium and recirculated by the rotating impeller in the TandemHeart pVAD and directed into the systemic circulation by way of the cannula in the right femoral artery. The left ventricle, relieved of 80-85% of its burden, was allowed to rest and to stabilize the oxygen demand of the jeopardized myocardium. Outflow resumed from the lungs by way of the pulmonary veins and the backpressure to the right atrium started to resolve. Demonstration of this could be seen by significant drop in the PAP and reduction of cyanosis in the patient’s extremities. Now that Roy’s condition had been stabilized, the cardiologists and staff in the cath lab had the necessary time to start revascularization of his coronary arteries. Balloon dilatation was done on his LAD and a 3.0 x 20mm stent was placed with good results. In his mid right coronary artery (RCA), at the site of his old infarct, mechanical rotational artherectomy (PTRA) was performed using a series of burrs. After the PTRA, a 3.5 x 25mm drug-eluting stent was deployed and fully expanded. Roy was transferred to the CCU where inotropes were suspended over time and he was extubated and gradually weaned from the TandemHeart, as steadily improving hemodynamic measurements showed that his native left ventricle was recovering sufficiently to support the workload. After two days of support, the pump was stopped and the arterial and transseptal cannulae were removed. Although direct pressure closure is possible, the attending cardiologist decided to have the puncture site surgically repaired to facilitate early mobilization. That same day, Roy enjoyed a belated piece of his son’s birthday cake. The preceding case shows the potential for supporting the systemic circulation and perfusion of patients with cardiogenic shock by using the TandemHeart PTVA System. Use of a centrifugal pump to unload the left ventricle by diverting blood from the left atrium to the systemic circulation is possible in the setting of the cardiac catheterization laboratory by means of a relatively simple percutaneous transseptal procedure. The TandemHeart System is commercially available in the United States under 510(k) clearance as a short-term ventricular assist device, and is currently under investigation for the treatment of cardiogenic shock. Transient circulatory support has long been of interest to cardiologists for facilitation of precarious percutaneous interventions as a span to other therapies, or as a potential post cardiac surgery support.6 As clinical indications for the TandemHeart continue to evolve, it may prove to be helpful in the management of patients such as Roy. Acknowledgement The author wishes to thank Irene Cooper, RN, SICU, Brigham & Women’s Hospital, Boston, MA. David M. Venesy, MD, Dept. of Cardiovascular Medicine, Lahey Clinic, Burlington, MA. Douglas Smith, PhD, Tim Krauskopf and David H.J. Wang, PhD at CardiacAssist, Inc. for their assistance in reviewing this article for medical and technical accuracy. About the author: Kent Riddle is the Director of Clinical Marketing for CardiacAssist, Inc., Pittsburgh, PA. He holds a Bachelors Degree in Health Sciences and an Associate of Sciences in Nursing. He has worked in the medical device industry for over 20 years and participated in the introduction, marketing and sales of some of the original devices for coronary angioplasty and coronary stenting. Previously he has been Manager of a Cardiac Cath Lab in Madison, Wisconsin, has served as an Officer in the U.S. Air Force where he was Head Nurse of a Coronary Care Unit, also working in Aeromedical Evacuation and Intensive Care. He currently resides in Chapel Hill, North Carolina. Kent can be contacted at: kriddle@cardiacassist.com

1. Goldberg RJ, Samad NA, Yarzebski J, et al. Temporal trends in cardiogenic shock complicating acute myocardial infarction. <i>N Engl J Med </i>1999;340:1162-1168.<p>2. Holmes DR Jr. Bates ER, Kleiman NS, et al. Contemporary reperfusion therapy for cardiogenic shock: the GUSTO-I trial experience. <i>J Am Coll Cardiol </i>1995;26:668-674. </p><p>3. Lund O, Johansen G, Allermand H, et al. Intraaortic balloon pumping in the treatment of low cardiac output following open heart surgery-immediate results and long term-prognosis. <i>Thoracic Cardiovasc Surg </i>1988;36:332-337</p><p>4. Campbell CD, Tolitano DJ, Weber KT, et al. Mechanical support for postcardiotomy heart failure. <i>J Cardiac Surg</i> 1988;3:181-191. </p><p>5. Brodie BR, Stuckey TD, Hansen C, Muncy D. Intra-aortic balloon counterpulsation before primary percutaneous transluminal coronary angioplasty reduces catheterization laboratory events in high-risk patients with acute myocardial infarction. <i>Am J Cardiol</i> 1999;84:18-23. </p><p>6. Vranckx P, Foley DP, de Feijter P, Vos J, Smits P, Serruys P. Effective use of the TandemHeart during high-risk percutaneous coronary intervention. <i>Intl J Cardiovasc Inter</i> 2003;5:35-39. Reprinted in A compendium of Clinical Reports-Vol. 2-2003. CardiacAssist, Inc. Pittsburgh, Pa.</p>