Ventricular Assist Device-Main project-2012

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Ventricular Assist Device-Main project. A panacea for end stage cardiac patients.

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Ventricular Assist Device-Main project-2012

  1. 1. INTRODUCTIONA Ventricular Assist Device (VAD) is a mechanical circulatory device that isused to partially or completely replace the pumping action of a failing human heart.Unlike artificial heart, which completely takes over all the functions of the human heart,a Ventricular Assist Device, as the name suggests, aids the functioning of the ventriclesof the heart. Any abnormality present in the ventricles can be effectively dealt by aVentricular Assist Device.Cardiac problems are a very common ailment in today’s world. People fromall walks of life suffer from a plethora of cardiac complications. Ventricular malfunctionis a common disease which leads to several problems viz. Lower Cardiac output, AnginaPectoris, poor circulation of oxygen and nutrients to the body, poor supply ofdeoxygenated blood to the lungs, etc. which leads to further physiological diseases.Ventricular Assist Device can effectively treat all such problems by treating the rootcause of such ailments, the Ventricles. Proper contraction of Ventricular muscles willlead to a higher Cardiac output, which helps in delivering a higher volume of blood tothe lungs, followed by proper delivery of oxygenated blood from the Left Ventricle.Thereby solving all the problems related to insufficient supply of oxygen and nutrientsto the body.All such aspects, classifications, working mechanisms, presently usedVentricular Assist Devices in the surgical arena, future of Ventricular Assist Devicesand their shortcomings will be elaborated in the following pages. Although VentricularAssist Devices have been in the world of cardiac surgery for more than a decade, thisseminar work will stress upon Advanced Ventricular Assist Devices, which aretechnologically different from the conventional Ventricular Assist Devices. Technicaldetails and methodology will be discussed as you browse through the pages to follow.Happy reading and discovery!1
  2. 2. HISTORY AND PRESENT STATE OF VENTRICULAR ASSIST DEVICESThe very first Ventricular Assist Device was manufactured in the year 1994, thename coined was “HeartMate IP LVAS”. This device and its sister devices emulated theheart by using a pulsatile action where blood is alternately sucked into the pump fromthe left ventricle and then forced out of the aorta. FDA in the US had approved of suchdevices in October 1994. Such devices were termed as “First Generation VADs”.Currently used Ventricular Assist Devices employ continuous flow pumps whichcan be classified into 2 types: Centrifugal pumps and Axial flow impeller driven pumps.These pumps have advantage over the former pulsatile action pumps because of theirsimplicity in working mechanism. Due to simplicity their sizes are also smaller. Thesedevices are popularly known as “Second Generation VADs” or Advanced VentricularAssist Devices. Working mechanism and classifications of Advanced Ventricular AssistDevices will be explained in details in the subsequent sections.Ventricular Assist Devices are implanted to patients who have practically lost theability of contraction of ventricles. The entire contraction mechanism of heart is takenover by this device, be it the right ventricle, the left ventricle or both. Since it takes overa major functionality of the normal heart, one might ask what is the difference betweenan artificial heart and a Ventricular Assist Device? The answer is, an artificial heart is adevice that carries out all the functions of a healthy heart: intake of deoxygenated bloodfrom the Vena Cavae, sending it to the lungs through pulmonary artery, receivingoxygenated blood from the pulmonary veins and finally releasing it through the aorta.The normal heart merely has a physical existence in this case. Ventricular Assist Deviceon the other hand performs with the impaired heart, it only assists the releasing/pumpingof oxygenated blood from the impaired right ventricle to the aorta or pumping out thedeoxygenated blood from right ventricle to the pulmonary artery. Basically, aVentricular Assist Device is provided to support mere existence of the normal heart.Patients being implanted with Ventricular Assist Device must have their hearttransplanted sooner or later because their heart has been severely damaged. PermanentVentricular Assist Device do not have a huge utility because heart transplantation is thebest solution for such an ailment rather than living on an artificial life support system.2
  3. 3. CLASSIFICATION OF VENTRICULAR ASSIST DEVICESAdvanced Ventricular Assist Devices can be classified under the following heads:1) On the basis of period of useTemporary Ventricular Assist Device: Ventricular Assist Devices which aremeant for short term use, i.e when a patient is undergoing cardiac surgery orrecovering from any cardiac ailment.Permanent Ventricular Assist Device: Ventricular Assist Devices which arepermanently transplanted into the human body for proper functioning ofventricles.2) On the basis of impaired ventricleLeft Ventricular Assist Device ( LVAD): Ventricular Assist Device which helpsin restoring the proper functioning of left ventricle.Right Ventricular Assist Device (RVAD): Ventricular Assist Device which helpsin restoring the proper functioning of right ventricle.Bi- Ventricular Assist Device (BiVAD): Ventricular Assist Device which helpsin restoring the proper functioning of both the left and right ventricles.3) On the basis of Pumping MechanismPulsatile Ventricular Assist Device: Ventricular Assist Devices which mimic thepumping action of the ventricles are termed as Pulsatile Ventricular AssistDevices.Non-pulsatile Ventricular Assist Device: Centrifugal pumps or Axial flow pumpsare employed to carry out the blood circulation through the ventricles.3
  4. 4. 4) On the basis of suspension of rotorsRotors are an important component of Ventricular Assist Device’s pump. Thisclassification is of relevance to Advanced Ventricular Assist Devices onlybecause the earlier versions did not propel the blood using rotors.Bearing suspension: Advanced Ventricular Assist Devices use such rotorsuspension technique where the rotor is suspended in the pumping chamber overa bearing chamber. As the rotor rolls over the bearings it creates a translatorymotion in the chamber which pumps the blood out.Electromagnetic or Hydrodynamic suspension: These technologies are still underresearch and has not been implemented in the device.NEED OF VENTRICULAR ASSIST DEVICESAs mentioned in the introduction, cardiac ailments have become a major cause ofmortality in the recent times, out of which ventricular problems find a great percentage.Invention of the Ventricular Assist Device has been able to solve this problem quitelargely. Statistics of the US regarding cardiac ailments are listed below: 5 million people suffer from Congestive Heart Failure (CHF). 2,50,000 patients are in the advanced stage of CHF 5,00,000 new cases arrive each year 50,000 deaths are caused due to ventricular failure alone Only-effective treatment for end stage ventricular failure is total Heart transplant.But in the year 2008-2009: 7318 patients required a heart 2210 received one 623 perished waiting4
  5. 5. ADVANCED VENTRICULAR ASSIST DEVICEAdvanced Ventricular Assist Device is also termed as “Non-pulsatile Ventricular AssistDevice”, because the main difference between the puslatile ones and the advanced is thepumping mechanism. Pulsatile Ventricular Assist Devices used positive displacementpumps to circulate blood which almost emulated the real contraction phenomenon ofventricles. But Advanced Ventricular Assist Devices uses continuous flow pumps whichare of two types: Centrifugal and Axial flow pumps. The replacement of pulsatiletechnology with non-pulsatile technology was due to a few factors:1) Irregular Haemodynamic flow of blood through the pulsatile pump.Such a turbulent flow lead to haemolysis of blood corpuscles which lead to severecomplications like clotting, emboli formation, thrombus formation. All such undesirableside effects lead to abandonment of the technology.2) Large sizeLarge size of the pulsatile Ventricular Assist Device was undesirable as it had tobe implanted within the body (most cases). Non pulsatile ones have smaller size.3) Operating soundPulsatile Ventricular Assist Devices emitted sound during their operation whichhad an unaesthetic appeal. Non pulsatile have practically no sound duringoperation or at most may have a faint humming sound.4) Large sized batteryOwing to its primitive design and working mechanism, the power consumptionof pulsatile Ventricular Assist Device was high, thereby requiring a larger batteryfor its supply. Non pulsatile ones do not suffer from this problem.Due to such positive desirable factors Non-pulsatile Ventricular Assist Devices becamepopular and are widely used now.5
  6. 6. Key features of Advanced Ventricular Assist Device: Enabled with Continuous flow pumps ECG independent LVADs are the most popular Advanced Ventricular Assist Devices Operation is practically soundless Patient generally has a weak or non palpable pulse owing to the continuouspumping mechanism of the Ventricular Assist Device. Patient may have a narrow pulse pressure and may not be measurable by normalblood pressure measuring instruments. Mean arterial pressure is in the range of 65 to 90 mm Hg.Although the systolic pressure is quite below the normal range of a healthy humanbeing, one must not compare the blood pressure with that of a healthy human becausethe patient who is being put on a Ventricular Assist Device has practically lost his heartcontraction ability. A mean blood pressure of 65 to 90 mm Hg is sufficient to circulatethe blood through the entire body because the pumping action is continuous rather thanpulse variant.Components of an Advanced Ventricular Assist Device: Outflow tube: attached to aorta Inflow tube: attached to the apex (bottom) of left ventricle Power source: driving the continuous flow pump, placed outside the body. Driveline: connects the pump to the controller, placed outside the body.6
  7. 7.  Controller: controls the pump’s functioning, displays the status of the system andhas alarm system.Fig1: Arrangement of Advanced VAD (Axial Pump) and its external components.7
  8. 8. 8
  9. 9. Fig 2: Arrangement of Advanced VAD (Centrifugal Pump) and its external components.The Pump:This is the heart of the Advanced Ventricular Assist Device. These devices useContinuous flow pumps, which are of two types:1) Centrifugal flow pumps:A central rotor is present which is suspended on bearings inside the pumpchamber. Controlled electric currents running through coils contained in thepump housing apply forces to the electromagnets which causes the rotors to spin.9
  10. 10. Fig 3.: Centrifugal flow pump.2) Axial flow pump:10
  11. 11. This type of pumps are mostly preferred in manufacturing Advanced Ventricularassist devices. Similar to the centrifugal ones, the rotors are suspended over abearing set but here the blades are helical in shape and are parallely aligned withthe rotor’s axis.Fig. 4: Axial flow pump.Key features of the continuous flow pumps:11
  12. 12. 1) Flow: Measured in liters per minute (lpm): General range: (3-10)lpm Flow is directly proportional to pump speed: Higher the pump speed greater isthe flow rate.2) Speed: Measured in revolutions per minute (rpm): General range: (8000-15000) rpm Flow speed is determined and fixed by the surgeons and cannot be manipulated.If, however this speed changes, it indicates thrombus formation inside the pump.3) Power: The amount of power a VAD consumes to run continuously at the set speed.4) Pulsatility Index (PI):It is the measure of the pressure difference inside the Ventricular Assist Devicepump and the heart’s ventricle(s) if it is functioning partially. Patients sufferingfrom severe cardiac problem have a PI of Zero.Such important parameters are displayed on the Ventricular Assist Device’s console orcontroller.LIST OF VENTRICULAR ASSIST DEVICES USED:12
  13. 13. Device Manufacturer TypeApproval Status as ofJuly 2009Novacor World Heart Pulsatile.Was approved for use inNorth America, EuropeanUnion and Japan. Nowdefunct and no longersupported by themanufacturer.HeartMate XVE Thoratec Pulsatile.FDA approval for BTT in2001 and DT in 2003. CEMark Authorized. Rarelyused anymore due toreliability concerns.HeartMate II ThoratecRotor driven continuousaxial flow, ball and cupbearings.Approved for use in NorthAmerica and EU. CE MarkAuthorized. FDA approvalfor BTT in April 2008.Recently approved by FDAin the US for DestinationTherapy (as at January2010).HeartMate III ThoratecContinuous flow drivenby a magneticallysuspended axial flowrotor.Clinical trials yet to start,uncertain future.Incor Berlin HeartContinuous flow drivenby a magneticallysuspended axial flowrotor.Approved for use inEuropean Union. Used onhumanitarian approvals oncase by case basis in theUS. Entered clinical trialsin the US in 2009.Jarvik 2000 Jarvik HeartContinuous flow, axialrotor supported byceramic bearings.Currently used in theUnited States as a bridge toheart transplant under anFDA-approved clinical13
  14. 14. investigation. In Europe,the Jarvik 2000 has earnedCE Mark certification forboth bridge-to-transplantand lifetime use. Childversion currently beingdeveloped.MicroMedDeBakey VADMicroMedContinuous flow drivenby axial rotor supportedby ceramic bearings.Approved for use in theEuropean Union. The childversion is approved by theFDA for use in children inUSA. Undergoing clinicaltrials in USA for FDAapproval.VentrAssist VentracorContinuous flow drivenby a hydrodynamicallysuspended centrifugalrotor.Approved for use inEuropean Union andAustralia. Companydeclared bankrupt whileclinical trials for FDAapproval were underway in2009. Company nowdissolved and intellectualproperty sold to Thoratec.MTIHeartLVADMiTiHeartCorporationContinuous flow drivenby a magneticallysuspended centrifugalrotor.Yet to start clinical trials.C-Pulse Sunshine HeartPulsatile, driven by aninflatable cuff around theaorta.Currently in clinical trialsin the US and Australia.HVAD HeartWareMiniature "thirdgeneration" device withcentrifugal blood pathand hydromagneticallysuspended rotor that maybe placed in thepericardial space.Obtained CE Mark fordistribution in Europe,January 2009. Initiated USBTT trial in October 2008(completed February 2010)and US DT trial in August2010.14
  15. 15. DuraHeart TerumoMagnetically levitatedcentrifugal pump.CE approved, US FDAtrials underway as atJanuary 2010.Thoratec PVAD(ParacorporealVentricular AssistDevice)ThoratecPulsatile system includesthree major components:Blood pump, cannulaeand pneumatic driver(dual drive console orportable VAD driver).CE Mark Authorized.Received FDA approval forBTT in 1995 and for post-cardiotomy recovery (openheart surgery) in 1998.IVAD -ImplantableVentricular AssistDeviceThoratecPulsatile system includesthree major components:Blood pump, cannulaeand pneumatic driver(dual drive console orportable VAD driver).CE Mark Authorized.Received FDA approval forBTT in 2004. Authorizedonly for internal implant,not for paracorporealimplant due to reliabilityissues.COMPLICATIONS AND SIDE EFFECTSLike every technology, this technology too has its share of shortcomings. Some of thecomplications are:15
  16. 16. 1) Coagulation and Thrombosis:This is one of the most predominant side effects of the Advanced VentricularAssist Device. This happens mainly due to the flow of blood over non-biologicalsurfaces. This problem has been eliminated by constructing the pumpcomponents with anticoagulant coated materials viz. Heparin or a fibrin basedcompound and polyurethane compounds.2) Haemolysis:It is a phenomenon where red blood corpuscles are destroyed due to non-laminarflow of blood. The non-laminar flow occurs across various sections of theVentricular Assist Device viz. the pump, the conduits carrying the blood fromthe ventricles or to the aorta. Such a problem is eliminated by using elasticconduits which more or less resemble the elastic nature of normal blood vesselsand by using blood straightener devices before and after the pump which createsa laminar flow.3) Infection:Ventricular Assist Devices infections can be caused by a large number ofdifferent organisms viz.: Gram positive bacteria (Staphylococci, etc) Gram negative bacteria (Pseudomonas aeruginosa, etc) Fungi (Candida, etc)Treatment of Ventricular Assist Device related infection is very difficult despiteoptimal treatment. But every effort is made to contain proliferation of suchorganisms. Practicing sterile procedures during every step of the operation andalso during maintenance is necessary.4) Portability:This remains one of the major disadvantages of this technology. The majority ofthe Advanced Ventricular Assist Devices present today are somewhat bulky,therby rendering normal movement of human a bit difficult and uneasy. The16
  17. 17. smallest device, the HeartMate II weighs about 0.45 kg and measures 7.6 cm.This has been proven the best device for women and children for whom otherdevices would be bulky. As technology progresses we hope to see even morecompact and reliable devices being discovered and used.CONCLUSION17
  18. 18. Advanced Ventricular Assist Devices have been a boon to cardiac patientssuffering from severe ventricular failure. It has been a long time since this device wasfirst designed, the device has evolved and through extensive research and development ithas reached almost a supreme state. But as other technologies and methodologies woulddevelop this present technology would gradually become outdated. For instance, thelatest form of Ventricular Assist Devices, still under development, employsHydrodynamic suspension of the rotor and its blades within the pump. This technologywould drastically decrease the power consumption of the device, probably wouldeliminate the usage of blood flow straighteners, thereby making the devices morecompact. FDA and other medical bodies would be there to ascertain the credibility ofsuch a technology and its implications. Till then, this present technology would continueto serve innumerable patients suffering from ventricular ailments and gift them betterlives.REFERENCES18
  19. 19. 1) www.thoratec.com2) www.jarvikheart.com3) www.google.com4) Google Scholar19

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