Cardiac catheterization

1. VENTRICULAR ASSIST DEVICE

2. TRANSVALVULAR LEFT VENTRICULAR-
TO-AORTIC PUMPS (IMPELLA)
• With recognition of the hemodynamic limitations of IABP especially for the
treatment of severe cardiogenic shock, there has been long-standing interest in
developing catheter based, percutaneous devices to pump blood directly from the
left ventricle to the aorta.
• The first such device was the Hemopump (Medtronic, Inc., Minneapolis , MN)
which was introduced in the late l980s. This device was a catheter based device
the principle of operation of which was based on the principles of the Archimedes
screw.
• A rotating screw within a covered housing pulled blood from a distal inlet port
positioned in the left ventricle and pumped it through the housing to an outlet
port positioned in the proximal aorta. The catheter head, which consisted of the
screw and covered housing, was positioned across the aortic valve.
• The rotation of the screw was accomplished by an external rotating motor that
connected to the screw via a long metal shaft running through the center of the
catheter.
• In theory, it allowed for percutaneous implantation and provided a high degree of
flow, significant unloading of the left ventricle (thus reducing myocardial oxygen
demand and protecting against myocardial ischemia and necrosis) , and
augmentation of coronary flow by increasing diastolic aortic pressure.

4. EXTRACORPOREAL LEFT ATRIAL-TO-
ARTERIAL PUMP (TANDEM HEART)
• Another device currently approved for short-term (6 hours) support
is the TandemHeart percutaneous ventricular assist device consists
of an extracorporeal, nonpulsatile centrifugal (continuous flow)
pump that withdraws blood from the left atrium (via a 21F trans-
septal cannula) , introduced via the femoral vein.
• Blood is then pumped by the device (typically at approximately 3.5
to 5.0 Umin) and delivered into one or both femoral arteries
through l5 F to l8 F cannulae.
• This device thus functions in parallel with the left ventricle in
pumping blood from the left atrium to the aorta. Owing to the
nature of centrifugal, non pulsatile flow of blood, the arterial line
tracing may be "flat" with no evidence of the aortic valve opening
or ejection from the left ventricle if the flow rate exceeds that of
the native heart.

5. TANDEM HEART
• The degree of pulsatility seen on the arterial waveform will
therefore be mainly dependent on the amount of residual blood
flow from the native left ventricle.
• Since Tandem Heart pumps blood from the left atrium, there are
significant reductions in left atrial pressure and, therefore,
reductions in left ventricular end-diastolic pressure and volume .
• The increase in total flow is accompanied by increases in arterial
pressure, both during systole and more significantly during diastole,
because of the continuous, asynchronous pumping throughout the
cardiac cycle.
• With the decrease in preload and the increase in afterload
pressure, intrinsic cardiac output decreases, and this is reflected as
a decrease in the width of the pressure-volume loop.

6. Indications
• The TandemHeart system is generally indicated to provide
temporary circulatory support in conditions such as
• cardiogenic shock in the setting of acute myocardial infarction or
• decompensated chronic heart failure
• pulmonary edema
• Post cardiotomy shock.
• It has been used successfully as a bridge to recovery or as a bridge
to a bridge in patients with cardiogenic shock secondary to
myocardial infarction, acute myocarditis , or end-stage
cardiomyopathy.

7. Contraindications
• The system is generally contraindicated for patients with any
of the following:
• primary right heart failure,
• high-grade aortic valve regurgitation,
• or any condition that prevents extracorporeal blood
circulation.
• As with any extracorporeal support system, caution should be
exercised in cases of mitral or aortic mechanical heart valves.

8. Insertion Technique
• The TandemHeart system utilizes a 2lF trans-septal cannula
inserted percutaneously through the femoral vein to the
inferior vena cava, into the right atrium, and across the atrial
septum into the left atrium.
• Blood is withdrawn via this cannula from the left atrium by
the pump.
• The transseptal puncture can be made by various means ,
including via a Brockenbrough needle after positioning its tip
in the fossa ovalis and via a radiofrequency puncture system.
• After puncture, a guide wire is inserted into the left atrium
and a multistage dilator is used to dilate the opening from
right atrium into left atrium until the trans-septal cannula can
be slid into the left atrium.

9. Insertion Technique
• The cannula is then fixed by placing a suture at the femoral
access site.
• Further fixation is provided by the curvature in the cannula
which assists in securing lodgment of the cannula tip.
• The trans-septal cannula is backfilled with blood and clamped
on the clear portion near the tubing connector.
• The placement of the trans-septal cannula should be verified
by fluoroscopy or, when inserted in the operating room, by
direct visualization.

10. Initiation of Support
• the trans-septal cannula and arterial cannulae are attached
to the pump's inflow and outflow ports , respectively.
• The arterial cannula is inserted, backfilled and clamped,
and the pump is primed with saline.
• Using wet-to-wet connection, the tubing and pump are
connected and de-aired.
• Alternatively, in view of the low volume required for
priming, the pump is first connected to the arterial cannula
and primed with blood, and a wet-to-wet connection is
then made to the left atrial cannula.
• After ensuring that all air is removed from the system, the
clamps are released and the "start" button on the
controller is pressed to initiate pumping.

11. Pump Adjustments
• The only parameter that can be controlled on the system is pump
speed, and change of speed will cause a change of flow as indicated
in the controller display screen.
• Though maximum support is often desirable, there are conditions
that result in reduced supply of blood to the left atrium (and
therefore reduced left atrial pressure) that necessitate a reduction
in pump speed.
• Examples of such conditions include hypovolemia; reduced right
ventricular output (e.g. , primary RV dysfunction as can occur in
dilated cardiomyopathy or RV infarction); obstructed right heart
outflow (e.g. , saddle pulmonary embolism) ; primary or secondary
lung diseases with increased pulmonary vascular resistance; cardiac
tamponade; and arrhythmias that compromise right ventricular
output.

12. Pump Adjustments
• If reduced left atrial filling is traced to one of these conditions, pump
speed can be reduced until that condition is corrected, with the
understanding that optimal pump performance occurs with left atrial
pressure (LAP) or pulmonary capillary wedge pressure (PCWP) in the range
between 10 and 20 mmHg .
• Specific signs of inadequate blood supply to the pump from the left atrium
include unusual vibrations of the trans-septal cannula or the pump, low
infusion pressures or infusion pressure alarms, and kinking of the trans-
septal cannula.
• If patient factors can be excluded, another factor to consider in low-flow
conditions is inflow or outflow cannula kinks, especially at the skin exit
sites.
• The general practice is to adjust the pump speed to a level that still allows
a minimum of pulsatile flow across the native aortic valve in order to
prevent stasis of blood in the left ventricle, which could result in thrombus
formation and subsequent embolization.

13. Management During Support
• Patients on the Tandem Heart system typically undergo
standard ICU monitoring, including EKG and measurement
of arterial blood pressure, pulmonary artery pressures
(PAP), pulmonary capillary wedge pressure (PCWP) , central
venous pressures (CVP) , and cardiac output (CO) .
• Arterial and mixed venous blood gases and other
laboratory values are monitored according to hospital
policy.
• The flow displayed on the controller display panel is a
measured value if the controller is used in conjunction with
the Tandem Heart flow sensor or is an estimated value
based on parameters measured in the pump.
• Since the TandemHeart system pumps in parallel to the
native heart, the total cardiac output is the summation of
TandemHeart flow and native heart output.

14. Management During Support
• Total flow (the sum of TandemHeart and native heart flows)
can be measured as usual by standard thermodilution
methodology.
• The TandemHeart system requires that the patient be
anticoagulated.
• It is recommended that the ACT should be 400 seconds for
insertion of the device but only after puncture of the
septum in the catheterization lab or operating room.
• The ACT should be > 200 seconds during the support
period.
• If ACT is unavailable, PTT can be used. During support, PTT
should be maintained between 65 and 80 seconds (21/2 to
3 times normal range) .

15. Weaning and Device Removal
• Initiation of weaning is accomplished by reducing pump speed.
Typically, flow rate can initially be reduced by approximately 50%
for approximately l hour; however, physician discretion in the rate
of speed reduction should always prevail.
• In any event, however, flow rate should never be reduced to < l L
per min because of the increased risk of pump thrombosis and
stoppage.
• If the patient tolerates weaning, the device can be removed. Device
removal can be accomplished at the bedside, in the catheterization
lab, or in the operating room at the physician's discretion.
• The femoral access site is usually managed by compression.
Management of the arterial site depends on the caliber of cannulae
used and may involve manual compression, use of preclose
techniques, or surgical repair.
• In any event, management of anticoagulation must be considered
and is similar to that described above for IABP removal.

16. Complications
• The main complications associated with use of the Tandem Heart system
include
• Bleeding
• complications associated with trans-septal puncture (e.g. , accidental
puncture of aorta, myocardial perforation, arrhythmias).
• Dislocation of the trans-septal cannula, stroke, vascular access
complications, dislocation of the arterial cannulae, leg ischemia, and
hemolysis.
• Bleeding is a potential risk for all circulatory support devices , particularly
when these devices are used to support patients with postcardiotomy
shock, or after revascularization procedures.
• These risks are increased in the presence of prolonged anticoagulation
which is required during the period of support.
• ACT values of 200 seconds are typically adequate for proper pump
operation. Antiplatelet therapy following coronary interventions may also
contribute to bleeding complications.

17. • Minimized manipulation of cannulae at the insertion sites reduces risk of
bleeding as well as vascular complications.
• The trans-septal cannula is positioned across the atrial septum and, once
in place, should be promptly secured to the skin so as not to allow
migration.
• Signs of cannula dislocation include change in color of blood in the pump
from bright red to dark red (indicating that desaturated venous blood is
being pumped) , decreased arterial oxygen saturation, or an
echocardiogram or chest x-ray indicating dislocation.
• Development of leg ischemia is a potential hazard for all percutaneous
vascular access procedures, and appropriate arterial cannula size for a
patient should be selected prior toinitiation of support.
• Distal flow cannulation is also available for use in situations requiring
additional flow to be delivered distally.

18. • Usual measures should be taken for early detection of an
impending problem, such as monitoring pulses (using Doppler if
necessary) , temperature, and capillary refill to check for changes in
peripheral flow.
• If distal leg ischemia develops while a patient is on Tandem Heart
system support, there are several measures that can be considered
to reestablish perfusion to the lower extremity.
• A single large arterial cannula can be replaced with one or even two
smaller-bore cannulae; for the latter, a "Y" connector can be used
on the outflow tubing.
• Finally, an additional small-gauge antegrade catheter can be
inserted to directly perfuse the distal limb using the side port of the
arterial cannula.

19. • The practice of inserting an antegrade sheath distally to the arterial
cannula and connected via the side arm to the arterial cannula can
also be instituted as a preventive measure at the time of initial
arterial access.
• If distal perfusion cannot be established by any of these means ,
consideration should be given to surgical intervention to provide
distal perfusion or removal of the Tandem Heart system.
• Dislocation of the arterial cannula is another extremely rare
complication, which unfortunately can be fatal as it is associated
not only with bleeding at the arterial site but also with bleeding
from the pump if the pump is not shut off immediately.
• Right-to-left shunting following removal of the left atrial cannula
resulting in systemic desaturation, and requiring percutaneous
closure of the iatrogenic atrial septal defect.