The ppt is on VAD and IABP

1. Circulatory Assist Devices
Shane A. Yates, M.D.
Anesthesia Svc.
Brooke Army Medical Center

2. Intra-aortic Balloon Pump
Ventricular Assist Devices
*Cardiopulmonary Bypass

3. Intra-aortic Balloon Pump
(IABP)
 IABP first successfully used by Kantrowitz et al.
in 1967
 Able to reverse pharmacologically refractory Post
MI cardiogenic shock using this technique
 Kantrowitz et al. Initial clinical experience with
intraaortic balloon pumping in cardiogenic shock.
JAMA 203:135, 1968

4. Basics of Cardiac Physiology
Determinants of myocardial O2 delivery
Determinants of myocardial O2
consumption
Determinants of Cardiac Output
Windkessel Effect

5. Determinants of Myocardial DO2
 CBF X CaO2
 heart has near maximal extraction at rest. Increased needs
are met by increased O2 delivery.
 O2 delivery is regionally controlled by autoregulation,
 Ischemic heart has maximally dilated arteries. Perfusion is
then directly related to perfusion pressure.
 Coronary perfusion occurs predominately during diastole
 Increasing diastolic time increases coronary blood flow

6. Determinants of Myocardial DO2
(cont’)
 Major resistance to (subendocardial) coronary blood flow
during diastole is LVEDP such that...
 CPP=AoDP-LVEDP
 AoDP and LVEDP are dynamic values
 Overlapping the aortic pressure and LV pressure curves
gives a visual representation of the pressure gradient.
 This gradient over the diastolic time cycle is described as
the Diastolic Pressure Time Index (DPTI)
 Area within the DPTI is directly correllated with O2
availability to the myocardium (supply)

8. Determinants of MVO2
 HR, contractility, wall tension (50% of MVO2 at rest).
 Laplace’s law T=Pr/2h
 Intraventricular pressure is a modifiable variable.
 IVP greatest during systole (LVSP).
 LVSP is a dynamic value continually changing throughout
systole and altering wall tension as this occurs.
 Area under the LVSP tracing is represented by the Tension
Time Index (TTI) and is directly correllated to wall tension
and MVO2.

9. Determinants of MVO2
(cont’)
 Increasing systole time (HR) or peak LV systolic pressure
increases the TTI and subsequently MVO2
 Conversely, lowering the AoEDP (decreased afterload)
decreases the pressure the LV must overcome to eject
blood and lowers the TTI
 The Endocardial Viability Ratio relates the relationship
between myocardial O2 supply and demand and is defined
by EVR=DPTI/TTI (supply/demand).

11. Determinants of Cardiac Output
 CO=SV X HR
 Stroke Volume
*preload (AV synchrony, volume, RV function...)
*afterload
*contractility
 HR

12. Windkessel Effect
 Potential energy stored in aortic root during
systole
 Converted to kinetic energy with elastic recoil of
aortic root
 Increases diastolic pressure/flow during early
diastole
 Less affect with hypovolemia or noncompliant
aortas
 Noted on the A-line tracing as the dicrotic notch.

13. IABP- how does it work?
 IABP does not ‘pump’ blood per se in contrast to a
VAD.
 Requires a functioning, beating heart.
 IABP serves as an external source of energy to
allow the sick heart to pump more efficiently.
 Does this via afterload reduction and diastolic
augmentation.
 Net result is an increased DO2, decreased MVO2,
and an increased CO.

14. Concepts of Counterpulsation
 The balloon is phasically pulsed in
counterpulsation to the patient’s cardiac cycle
(IABC)
 IABP has no ‘inotropic’ action; does not directly
increase contractility.
 Primarily benefits the left ventricle, although the
diastolic augmentation may improve coronary
flow to both ventricals.

15. Components
 Double lumen cathater with a distal sausage shaped non-
thrombogenic polyurethane balloon with standard 30-40cc
displacement volumes.
 Pump, equipped with a console display to view the ECG,
aortic and balloon pressure waveforms.
 Central lumen extends to the cathater tip. Serves as a
transducer to measure aortic pressure.
 Central lumen is concentric with and situated inside the
helium channel which is used for balloon inflation.

17. Placement
 Placed percutaneously or surgically with or without a
sheath via the femoral artery.
 Advanced into aorta under flouroscopy until the tip is
about 1cm distal to the origin of the left subclavian a.
 Cathater locations more proximal than this compromise
flow to the vessels of the aortic arch.
 More distal locations attenuate the hemodynamic benefits
of the IABP and can potentially compromise renal blood
flow.

19. Diastolic Augmentation
 Balloon inflation at the onset of diastole which is
correllated to aortic valve closure (mechanical event).
 Displacement of blood within the aorta to areas proximal
and distal to the balloon. Termed “compartmentilization”.
 Proximal compartment consists of branches of aortic arch
(carotids) and coronary vasculature.
 Diastolic balloon inflation augments cerebral and coronary
perfusion.
 Increased DPTI and EVR.
 ‘Exaggerated’ Windkessel Effect.

21. Afterload Reduction
 Optimal balloon deflation occurs just prior to the opening
of the aortic valve; during early isovolemic contraction.
 Abruptly decreases intraaortic volume
 AoEDP is acutely decreased (afterload reduction).
 AoV opens sooner during cardiac cycle lending more time
for ventricular ejection
 Overall result is a larger SV (CO).
 A lower peak LVSP decreases the TTI which leads to a
decrease MVO2 and an icrease in the EVR.

23. Indications
 Pump failure (reversible)
*AMI
-progressive deterioration despite pharmacologic support
-frank cardiogenic shock
*Cardiac transplant patient
-as a bridge to transplantation
-post transplant support
 Acute MV regurgitation
 Aide to separate from CPB
 ? other indications

24. Contraindications
 Thoracic or abdominal aortic aneurysm
 Aortic dissection
 Aortic insufficiency
 ? Severe pre-existing vascular disease, presence of
iliofemoral grafts.
 ? Prosthetic aortic graft

25. Determinants of IABP efficiency
 Ideal balloon volume causes maximal emptying of LV
without causing retrograde flow from the coronary
vasculature and vessels of the aortic arch.
 Balloon should occlude 75-90% of the aortic cross-
sectional area during inflation.
 CO2 vs Helium
 Efficiency if IABC is critically dependent on the timing of
both inflation and deflation.
 Improper timing can worsen a patient’s condition.

26. IAPB Timing
 IABP requires a trigger to determine systole and diastole.
 ECG or arterial waveform.
 ECG directly from the patient to the pump or the pump can
slave off the bedside monitor.
 T-wave default. Electrical index of diastole. Deflation
occurs prior to the next QRS (during PR interval).
 Timing is manually fine-tuned according to the aortic
pressure waveform (more representative of mechanical
events).

27. Early inflation

28. Late Inflation

29. Early Deflation

30. Late Deflation

31. Limitations of IABC
Heart Rate
Arrhythmias (non-sinus rhythms)
Hypovolemia

33. Effects of IABP on BP
 Normal BP has two reference points- SBP & DBP
 With a pump set at 1:2 you have 5 different reference
points.
 Net effect:
*SBP following an augmented beat will be lower than SBP
following an unassisted beat.
*AoEDP following an augmented beat will be lower than
AoEDP following an unassisted beat.
*Peak diastolic augmented pressure will be integrated into
the pressure reading on the arterial line. Overall BP as
read by A-line (number you see) should increase.

35. Bottom Line WRT BP & IABPs
Follow mean pressures
Ensure adequate C.O. (flow)
You can have an ‘adequate’ pressure with
very little flow.

36. Weaning
Frequency ratio weaning (1:1, 1:2, 1:3,
etc.).
Volume weaning (more physiologic?)

37. Risk of IABC
 Reported complication rates vary, but in general
range about 20-30% of all IABP’s placed.
 Factors which predispose to a higher complication
rate include age, pre-existing vascular disease,
duration of IABC, DM, HTN, obesity, and
vasopressor therapy.

38. Complications of IABP
 Loss of pulse
 Limb ischemia
 Thromboembolism (extremity, visceral, cerebral, etc.)
 Compartment syndrome
 Aortic dissection
 Local vascular injury
 Infection
 Balloon rupture with secondary gas emboli (loss of IABC
augmentation, blood in helium channel)

39. Ventricular Assist Devices
Provide either partial (parallel pump) or full
(ventricular bypass) systemic and/or pulmonary
perfusion

40. Technique
 Blood is passively drained via a large cathater
from either the left atrium or left ventrical, passes
through the pump chamber and is returned via an
outflow cathater to the aorta.
 Cannula placement varies according to the
surgery, the pump being used and the ventrical(s)
being supported.

41. Indications
 Bridge to cardiac transplantation- to sustain life,
organ perfusion while awaiting donor.
 Thoracic aortic surgery- to bypass flow to areas of
the body distal to a high aortic crossclamp.
Decreases workload on the heart, decreased
incidence of renal and spinal cord ischemia.
 Post-cardiotomy cardiogenic shock

42. Classifications of VADS
Type of pump used
ventrical assisted (LVAD vs RVAD vs
BVAD)
BVAD vs TAH

43. Centrifugal Pumps
(BioMedicus)
 Identical to pump on CPB machine.
 Disposable plastic housing with internal rotating cones
 Pressure sensitive, with flow determined by pump head
speed as well as inflow and outflow pressures.
 Electromagnetic flowmeter to indicate flow rate.
 Pump mounted to machine housing and connected to pt via
drainage and outflow cannulas.
 Can be equipped with membrane oxygenator to provide
ECMO or CPS.
 For shortterm use only (<7days).

47. Placement
 Surgically placed
 Drainage cannula from left (right) atrium and outflow
cannula to ascending aorta (pulmonary a., descending
aorta)
 Drainage is dependent on pressure gradient, gravity.
 Flow rate used depends on the indication for the pump, and
is gradually decreased as the patient is weaned from the
pump.
 Flow rates in general are 3-5L/min

48. Heart physiology with ventricular
assist
 Pump functions independently of native cardiac cycle.
 Normal RV function must be maintained with LVAD use.
*must maintain functional rhythm
*loss of interventricular dependence
 Diversion of flow through the VAD decompresses the LV.
*decreases LV radius, wall tension, MVO2
*AoV may not open (Heartmate and Novocor)

49. VAD for thoracic aortic surgery
 Usually centrifugal pump - simplicity, availability, cost
 Drainage LA, return to aorta distal to operative site.
 Must monitor BP proximally and distally to operative site
to ensure ‘balanced flows’.
 Decrease afterload prevent ischemic spinal cord injury.
 U. of Wash. A. Forbes et al. Arch Surg. 1994;129:494-498.
30 patients surviving thoracic aortic surg. MCS n=21,
CC n=9. SCI confirmed in 4 of 9 patients (44%) in the CC
group. All patients in the MCS group were neurologically
intact. Lower incidence of ARF and shorter hosp stay with
MCS.

50. VAD for Post Cardiotomy
Support (Indications)
 Theory is to ‘rest’ the heart to allow for metabolic
and functional recovery of stunned myocardium.
 Complete and adequate surgical procedure.
 Correction of all metabolic problems.
 Inability to wean from CPB despite maximal
pharmacologic therapy and IABP.

51. Contraindications
(post-cardiotomy)
 Non-remediable heart condition
 Pre-op EF<35%
 evidence of extensive myocardial necrosis
 uncontrolled bleeding
 age>60
 ongoing infection/sepsis
 severe cerebrovascular disease or neuro deficit
 ?aortic insufficiency

52. Inotropes
 Generally stopped when on VAD support.
 Increase MVO2
 Some degree of inotropic support may be
necessary during LVAD support when RV function
is suboptimal.
 Used to assist in weaning.

53. Anticoagulation
 VAD is a ‘closed’ system. Lower ACT than for CPB.
 Because thromboembolism is a major source of M&M
during VAD use, some anticoagulation is necessary.
 Anticoagulation is not initiated until hemostasis is
achieved.
 ACT >150
 Flows 1.5-2L/min, ACT 200-250
 Flows <.5L/M contraindicated due to high incidence of
thrombogenesis.

54. Anesthetic considerations with
VAD use
 Direct negative inotrope effects on the supported ventricle
are of limited concern.
 Anesthetic effects on VAD preload
*cardiac depressent effects on non-supported ventricle
*vasodilation effects on preload
 Ventilation effects
 Pulmonary vascular resistance.
 Peripheral vascular resistance.

55. Displacement Pumps
 Provide pulsatile flow via a filling chamber
 Pneumatic or electrically powered.
 Have unidirectional inflow and outflow valves.
 Either sit on the abdomen or are implanted in the LUQ.
 Pump is tethered to the power source/console.
 Require full anticoagulation due to valves (except
Heartmate)
 Approved for longterm use.
 Some are designed for outpatient use.

56. Thoratec VAD
 Right, left or biventricular assist.
 Most commonly used as a bridge to transplantation; has
also been used for post-cardiotomy cardiogenic shock.
 Non-portable, however patients can ambulate (unlike
centrifugal pumps). Inpatient use only.
 Pneumatic drive unit can be synchronized to the patient’s
ECG or run at a fixed rate.
 Pulsatile pump consists of a smooth polyurethane inner sac
in a rigid case. Lays on abdomenal wall.
 65cc SV, 6.5L/min max flow rate.
 Very expensive!

60. Heartmate
 Pneumatically or electrically driven pulsatile pump.
 For use as a bridge to transplant only.
 Implanted in the LUQ with the drive line exiting the LLQ.
 Electrical version can be connected to a portable battery.
 Max SV 85cc and max flow rate of 12L/M.
 Internal sensor measures filling volume and pump output.
 Pusher plate covered with sintered polyurethane and
housing surface sintered titanium therefore anticoagulation
not necessary.

63. Novocor
 For use as bridge to transplantation only.
 Implanted in abdomen similar to Heartmate.
 Electronically powered pulsatile pusher plate pump.
 Has portable battery.
 Inner surface is smooth polyurethane.
 Max SV 70cc, max flow rate 10L/M.
 Anticoagulation with coumadin.

65. Complications with VADS
 Uncontrolled hemorrhage (most common early comp)
 Thrombosis and emboli (CVA)
 MOFS (encephalopathy, ARDS, ARF, etc.)
 Infection
 Failure to maintain pump flow.
*RV failure
*volume
*drainage cannula obstruction
*pulmonary HTN

66. VADs
 Centrifugal (BioMedicus, Sarns Delphin)
 Non-pulsatile Rotary (Hemopump)
 Pulsatile pneumatic (Thoratec,ABIOMED BVS 5000,
Symbion AVAD)
 Pulsatile pneumatic implantable (TCI Heartmate)
 Pulsatile electrical implantable (Novocor LVAS, TCI
Heartmate)

67. BVAD vs TAH
 BVADs are ‘heterotopic’ pump which assist the working
ventrical.
 TAH are ‘orthotopic’ pumps which take the place of the
heart both physiologically and anatomically. Single pump.

68. Outcome- postcardiotomy VAD
support with Thoratec pump
 Ruhr U. of Bochum. R Korfer et al. Ann Thorac Surg
1996;61:314-6.
 Oct 1992- Sept 1994
 Reported on 9 patients with postcardiotomy cardiogenic
shock supported with Thoratec VAD.
 4 patients (44%) survived to hospital discharge. In 3of 4
patients VAD placed in OR due to inability to wean from
CPB, remaining pt had thoratec placed later on after
unsuccessful CPR in ICU.

69. Outcome- postcardiotomy VAD
support with centrifugal pump
 U. of Missouri. J. Curtis et al. Ann Thorac Surg
1996;61:296-300.
 65 consecutive pts requiring BioMedicus VAD (R, L & B)
to wean from CPB.
 Looked to see if experience improved outcome.
 Divided into early and late group n=33 & n=32
 Early group
*weaned 11 (33%), survived hospitalization 5 (15%)
 Recent group
*weaned 17 (53%), survived hopitalization 9 (28%)

70. ASAIO-ISHT
 Volunteer registry through 1992.
 LVAD for postcardiotomy support (N=436)
*50% weaned
*27% discharged
 RVAD for postcardiotomy support (N=117)
*36% weaned
*25% discharged
 BVAD for postcardiotomy support (N=306)
*37% weaned
*20% discharged