Ramp Test Protocol
All patients underwent a ramp test using hemodynamic monitoring with a
Swan Ganz catheter after an average period of 6.4 ± 1.2 months after
LVAD implantation. The ramp test consisted of three stages. First,
clinical parameters were reviewed to ensure safety. Appropriate
anticoagulation was defined as INR >1.8 or PTT
>60. If inadequate anticoagulation was demonstrated, 60
u/kg of Heparin was administered intravenously before the test.
Transthoracic echocardiography confirmed absence of an intraventricular
or aortic root thrombus. If a thrombus was identified, the ramp study
was not performed due to the possibility of thrombus dislodgement. After
this initial safety pre-test screening, a pulmonary artery catheter was
inserted via the right internal jugular vein. Baseline right heart
catheterization and estimation of cf-LVAD flows were performed, followed
by baseline echocardiographic images. The hemodynamic parameters
included central venous pressure (CVP), systolic (SPAP), diastolic
(DPAP) and mean pulmonary artery pressures (MPAP) and pulmonary
capillary wedge pressure (PCWP). Blood samples were obtained from the
pulmonary artery for measurement of mixed venous oxygen saturation.
Cardiac output (CO) and cardiac index (CI) were calculated by
thermodilution. Hemoglobin was measured from the venous blood gas and
arterial oxygen saturation measured using pulse oximetry.
Echocardiographic parameters included Left ventricular end-diastolic and
end-systolic dimensions (LVEDD and LVESD), measured from the parasternal
long-axis view. Percent aortic valve (AV) opening and qualitative
estimation of the severity of aortic and mitral regurgitation (AR and
MR, respectively) were noted. Preload and afterload were optimized. Mean
blood pressure between 75 and 85 mmHg was maintained. If the patient
experienced mean blood pressure greater than 100 mmHg, an infusion of
nitroprusside was started and the test was deferred to a later time when
blood pressure was under better control. A CVP between 8 and 10 mmHg was
considered optimal to start the test. If the patient had a CVP less than
8 mmHg, an infusion of 250 ml/h physiological solution was administered.
After completion of baseline measurements, HM3 patients’ device speeds
were lowered to 5200 Revolutions per Minute (RPM) or the lowest
tolerated speed. After at least a 2-minute stabilization period,
echocardiographic and hemodynamic parameters, and device flows were
repeated. Device speeds were then increased by 200 RPM. Another two
minutes were allowed for stabilization, and all parameters were again
recorded. This procedure was repeated until one of the following
occurred:
1) Reaching the maximum of 6400 RPM.
2) Occurrence of suction events.
3) LVEDD decreased to less than 3.0 cm.
Doppler ultrasound blood pressure (BP) measurements were obtained using
a calibrated sphygmomanometer. The doppler probe was placed over the
brachial artery, and the examiner verified that the brachial pulse could
be auscultated. Then the cuff, placed proximal to the doppler probe, was
inflated until the doppler identified no signal. The cuff was then
slowly deflated (2-3 mmHg/s), allowing the reestablishment of blood flow
and a reading was taken when the pulse became audible again. Once an
adequate balance between preload and afterload and RPM was obtained,
hemodynamic data were estimated and then a new hemodynamic index was
calculated for all patients based on the following formula:
\(\mathbf{\text{HI}}\mathbf{=}\mathbf{\text{MAP}}\mathbf{\ }\mathbf{x}\mathbf{\ }\frac{\mathbf{\text{PCWP}}}{\mathbf{\text{CVP}}}\)\(\mathbf{x}\mathbf{\ }\frac{\mathbf{\text{RPM}}\mathbf{\ }\mathbf{\text{set}}}{\mathbf{\text{RPM}}\mathbf{\ }\mathbf{\max}}\)