Transcript Cardiochirurgia universitaria

Terapie chirurgiche dell’Insufficienza
Cardiaca
Contropulsazione aortica
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Intra Aortic Balloon Pump
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IABP- History
In 1958 Harken described for the first time a method to treat left ventricular failure by
using counterpulsation or diastolic augmentation. He suggested removing a certain blood
volume from the femoral artery during systole and replacing this volume rapidly during
diastole. By increasing coronary perfusion pressure this concept would therefore augment
cardiac output and unload the functioning heart simultaneously. This method of treatment
was limited because of problems with access (need for arteriotomies of both femoral
arteries), turbulence and development of massive hemolysis by the pumping apparatus.
Even experimental data showed that no augmentation of coronary blood flow was
obtained.
Then in the early 1960s Moulopoulus et al. from the Cleveland Clinic, developed an
experimental prototype of the intra-aortic balloon (IAB) whose inflation and deflation were
timed to the cardiac cycle. In 1968 the initial use in clinical practice of the IABP and it`s
further improvement was realized resp. continued by A. Kantrowiz`s group.
In its first years, the IABP required surgical insertion and surgical removal with a balloons
size of 15 French. In 1979 after subsequent development in IABP technology a dramatic
headway with the introduction of a percutaneous IAB with a size of 8,5 to 9,5 French was
achieved. This advance made it for even nonsurgical personnel possible, to perform an IAB
insertion at the patient’s bedside. In 1985 the first prefolded IAB was developed.
Today continued improvements in IABP technology permit safer use and earlier
intervention to provide hemodynamic support. All these progresses have made the IABP a
mainstay in the management of ischemic and dysfunctional myocardium.
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Physiologic Effects of IABP Therapy
After correct placement of the IAB in the
descending aorta with it`s tip at the distal
aortic arch (below the origin of the left
subclavian artery) the balloon is connected
to a drive console. The console itself
consists of a pressurized gas reservoir, a
monitor for ECG and pressure wave
recording,
adjustments
for
inflation/deflation
timing,
triggering
selection switches and battery back-up
power sources. The gases used for inflation
are either helium or carbon dioxide . The
advantage of helium is its lower density
and therefore a better rapid diffusion
coefficient. Whereas carbon dioxide has an
increased solubility in blood and thereby
reduces the potential consequences of gas
embolization following a balloon rupture.
Inflation and deflation are synchronized to
the patients’ cardiac cycle. Inflation at the
onset of diastole results in proximal and
distal displacement of blood volume in the
aorta. Deflation occurs just prior to the
onset of systole.
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Hemodynamic effects of IABP Therapy
The primary goals of IABP treatment are to increase myocardial oxygen supply and decrease myocardial
oxygen demand. Secondary, improvement of cardiac output (CO), ejection fraction (EF), an increase of
coronary perfusion pressure, systemic perfusion and a decrease of heart rate, pulmonary capillary wedge
pressure and systemic vascular resistance occur.
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Determinants of Myocardial
Supply and Demand
Oxygen
In particular systolic wall tension uses approximately 30% of myocardial oxygen demand. Wall tension
itself is affected by intraventricular pressure, afterload, end-diastolic volume and myocardial wall
thickness.
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Schematic representation of coronary blood flow, aortic and left
ventricular pressure wave form with / without IABP
TTI (= tension-time index ), is an important
determinant of myocardial oxygen consumption. On
the other hand, the integrated pressure difference
between the aorta and left ventricle during diastole
(DPTI = diastolic pressure time index) represents
the myocardial oxygen supply (i.e. hemodynamic
correlate of coronary blood flow)
1.
2.
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Inflation of the balloon during diastole (=
augmentation of the aortic diastolic pressure)
increases coronary blood flow ( DPTI ).
Deflation of the balloon occurs just prior to the
onset of systole and reduces impedance to left
ventricular ejection (TTI ). This results in less
myocardial work, decreased myocardial oxygen
consumption and increased cardiac output
Control of the IABP (1)
• TRIGGERING
– To achieve optimal effect of counterpulsation, inflation and
deflation need to be correctly timed to the patient’s cardiac cycle.
This is accomplished by either using the patient’s ECG signal, the
patient’s arterial waveform or an intrinsic pump rate. The most
common method of triggering the IAB is from the R wave of the
patient’s ECG signal. Mainly balloon inflation is set automatically
to start in the middle of the T wave and to deflate prior to the
ending QRS complex. Tachyarrhythmias, cardiac pacemaker
function and poor ECG signals may cause difficulties in obtaining
synchronization when the ECG mode is used. In such cases the
arterial waveform for triggering may be used.
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Control of the IABP (2)
• TIMING and WEANING
– It is important that the inflation of the IAB occurs at the beginning
of diastole, noted on the dicrotic notch on the arterial waveform.
Deflation of the balloon should occur immediately prior to the
arterial upstroke. Balloon synchronization starts usually at a beat
ratio of 1:2. This ratio facilitates comparison between the patient’s
own ventricular beats and augmented beats to determine ideal IABP
timing. Errors in timing of the IABP may result in different
waveform characteristics and a various number of physiologic
effects
– If the patient’s cardiac performance improves, weaning from the
IABP may begin by gradually decreasing the balloon augmentation
ratio (from 1:1 to 1:2 to 1:4 to 1:8) under control of hemodynamic
stability . After appropriate observation at 1:8 counterpulsation the
balloon pump is removed.
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IABP Indications and Contraindications
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Complications of IABP counterpulsation
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