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Ann Thorac Surg 2004;77:143-149
© 2004 The Society of Thoracic Surgeons

Original article: cardiovascular

Left ventricular pressure and volume unloading during pulsatile versus nonpulsatile left ventricular assist device support

Stefan Klotz, MDa*, Mario C. Deng, MDb, Joerg Stypmann, MDc, Juergen Roetker, MDa, Markus J. Wilhelm, MDa, Dieter Hammel, MDa, Hans H. Scheld, MDa, Christof Schmid, MDa

a Department of Thoracic and Cardiovascular Surgery, University Hospital, Muenster, Germany
b Heart Failure Center, Columbia University, New York, New York, USA
c Department of Cardiology and Angiology, University Hospital, Muenster, Germany

Accepted for publication June 25, 2003.

* Address reprint requests to Dr Klotz, Department of Thoracic and Cardiovascular Surgery, University Hospital Muenster, Albert-Schweitzer-Str 33, 48129 Muenster, Germany.
e-mail: stefan.klotz{at}thgms.uni-muenster.de


   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Comment
 References
 
BACKGROUND: Nonpulsatile axial or centrifugal pumps are the latest generation of left ventricular assist devices (LVAD). Whether left ventricular (LV) unloading and outcome in these devices is similar to pulsatile LVADs during long-term support has not been investigated. We compared LV unloading and mortality between different types of LVAD support (pulsatile versus nonpulsatile).

METHODS: In 31 patients undergoing long-term LVAD implantation (nonpulsatile = 10, pulsatile = 21) preoperative and postoperative echocardiographic and hemodynamic assessment with right heart catheterization had been obtained.

RESULTS: All patients had similar echocardiographic, hemodynamic, and clinical heart failure characteristics at baseline. The degree of LV pressure unloading was the same in both device types, caused by similar reduction of mean pulmonary pressure (18.6 ± 5.1 versus 18.3 ± 7.5 mm Hg) and pulmonary capillary wedge pressure (8.9 ± 4.4 versus 8.0 ± 7.0 mm Hg). Left ventricular volume unloading was pronounced with a pulsatile device owing to a statistically significant higher pump output (5.1 ± 1.0 L/min) in comparison with nonpulsatile LVADs (3.6 ± 0.9 L/min, p < 0.001). Echocardiographic-determined end-systolic indicators confirm this augmentation in pulsatile LVADs. Etiology or the time interval of hemodynamic reassessment had no impact in left ventricular pressure unloading, but LV volume unloading decreased between day 60 and 120 in patients with nonpulsatile LVADs. The preoperative and postoperative transplant mortality was comparable in both groups.

CONCLUSIONS: Left ventricular pressure unloading is similar in patients with nonpulsatile as compared with pulsatile implantable long-term assist devices. Left ventricular volume unloading is pronounced in pulsatile LVADs.


   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Comment
 References
 
In patients with end-stage heart failure support by a left ventricular assist device (LVAD) as a bridge to transplant or bridge to recovery is a well-known therapeutic option. It leads to an improvement of cardiac function, which sometimes offers the opportunity to wean from LVAD support. The intracorporeal pulsatile flow devices such as Novacor LVAS (World Heart, Oakland, CA) and TCI HeartMate VE LVAS (Thermo Cardiosystems, Woburn, MA) cannot be implanted into small adults and children except for the extracorporeal Thoratec VAD (Thoratec, Pleasanton, CA). In recent years, continuous flow pumps have become clinically available [1]. They operate as centrifugal flow pumps, for example the AB-180 Circulatory Support System (Cardiac Assist, Pittsburgh, PA), HeartMate III LVAS (Thermo Cardiosystems, Woburn, MA), and CorAid LVAS (Cleveland Clinic, Cleveland, OH); or as axial flow pumps, for example the Nimbus/TCI IVAS (Thermo Cardiosystems, Woburn, MA), Jarvik 2000 IVAS (Jarvik Heart , New York, NY), and MicroMed DeBakey VAD (MicroMed, Houston, TX) [1, 2]. In contrast to pulsatile LVADs the nonpulsatile LVAD produces a nonpulsatile continuous flow with an axial or centrifugal flow pump and fills not only during the systolic phase but also during diastole.

Improvement of cardiac function with pulsatile LVADs is well described [3–7]. Pulsatile LVADs provide profound LV volume and pressure unloading while simultaneously restoring adequate systemic blood flow in end-stage congestive heart failure patients [6]. However, comparison of LV pressure and volume unloading between nonpulsatile axial flow pumps and pulsatile pumps has not been investigated. While early studies with nonpulsatile blood flow in calves [8] suggest no adverse impact on nonphysiological blood flow pattern the debate regarding the effect of nonpulsatile flow on organ function and neurohormonal activation remains controversial [9, 10].

To address the question of left ventricular pressure and volume unloading we compared preoperative to postoperative echocardiographic and hemodynamic measurements in patients with implantable pulsatile and nonpulsatile long-term LVADs.


   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Comment
 References
 
Patients
We retrospectively included 31 patients (29 men, 2 women) undergoing LVAD implantation between July 1994 and September 2001 who fulfilled the inclusion criteria of our LVAD and transplantation program [11]. The inclusion criteria for this study were as follows: (1) LVAD support for more than 30 days either with a pulsatile (Novacor LVAS or TCI-HeartMate VE LVAS) or a nonpulsatile LVAD (MicroMed DeBakey VAD); (2) availability of preoperative and postoperative hemodynamic and echocardiographic measurements corresponding to the protocol of this study

Pulsatile LVAD implantations were performed from July 1994 to January 2000 and implantations of nonpulsatile LVADs began in February 2000. The LVAD allocation was based on an identical clinical algorithm [12] and the clinical characteristics were identical in both groups at baseline, despite the two varying time frames.

Devices
MicroMed DeBakey VAD.
The MicroMed DeBakey VAD is an electromagnetically actuated, implantable titanium axial flow pump that connects to the left ventricular apex and ascending aorta [13]. Because of the continuous flow properties of the axial flow pump no valves are needed in the system (Fig 1). The axial flow motor is small and contains rotary blades that spin at 7,500 to 12,500 rpm and can pump approximately 5 to 6 L/min against 100 mm Hg pressure [14]. The DeBakey VAD was first implanted in our department in February 2000 [15].



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  		Fig 1. The pulsatile Novacor left ventricular assist system (LVAS), TCI HeartMate LVAS, and the nonpulsatile MicroMed DeBakey ventricular assist system (IVAS).

 
TCI HeartMate VE LVAS.
The TCI HeartMate VE LVAS is an electrically vented pusher-plate device with a maximum stroke volume of 85 mL and weighs approximately 1 kg. The sintered-titanium microspheres on the pump housing and the integrally textured polyurethane on the flexing pusher-plate diagram allow formation of a tenacious thrombus that evolves into a stable pseudointimal layer that does not embolize. The device is implanted with an inflow cannula inserted to the ventricular apex and a Dacron (CR Bard, Haverhill, PA) outflow graft anastomized to the ascending aorta. Both conduits contain a 25-mm porcine valve to ensure unidirectional blood flow. The maximum possible blood flow is 9.6 L/min [16, 17].

Novacor LVAS.
The Novacor LVAS differs significantly from the TCI HeartMate in its method of pump actuation and use of a smooth blood-containing surface. During pump systole two opposing pusher plates compress a seamless polyurethane blood sac, causing ejection of blood. The inflow and outflow connections are similar to those described for the TCI HeartMate except for two 21-mm bioprosthetic valves to achieve unidirectional blood flow [16].

Hemodynamic protocol
Preoperative and postoperative hemodynamic measurements were done under the same conditions by using a Swan-Ganz catheter (Baxter Healthcare, Irvine, CA) through the left or right jugular vein, inserted with local anesthesia. Cardiac output was measured by thermodilution using rapid 10 mL bolus injections of cold saline. The averages of five measurements were used. Mean arterial pressure was measured noninvasively with the Dinamap XL (Johnson & Johnson Medical, Arlington, TX) or by invasive methods if noninvasive measurements were not possible in patients with nonpulsatile devices.

Transpulmonary gradient (TPG), pulmonary vascular resistance (PVR) and systemic vascular resistance (SVR) were calculated using the following formulas:



The postoperative hemodynamic assessment was done as part of a standardized exercise protocol that has been described previously [18, 19] during the reevaluation for heart transplant candidates. Hemodynamic and LVAD sensor measurements were made at rest in a supine position with full device support. The Novacor and the TCI HeartMate LVAS were set at automode and the MicroMed DeBakey VAD ran at approximately 10,000 rpm. These settings were not changed during or before hemodynamic assessment. Left ventricular pressure unloading was defined as the significant lowering of mean pulmonary artery pressure and pulmonary capillary wedge pressure in comparison with the values of the preoperative hemodynamics. Left ventricular volume unloading (LVVU) was defined as the percentage from pump output to cardiac output during the postoperative hemodynamic measurement (LVVU = [pump output*100]/cardiac output). The LVVU gives a good impression of the effects of left ventricular unloading because cardiac output in patients with LVAD support, measured by the thermodilution method, consists of the device flow (pump output) plus the output from the native heart across the aortic valve.

During the postoperative assessment every patient was either in the normal ward or in our LVAD outpatient program. No patient was on inotropic agents, intraaortic balloon pump, or ventilation. All patients were on standard congestive heart failure medication titrated upward as clinically appropriate. Furthermore all patients were fully rehabilitated on their LVAD and able to perform a bicycle exercise protocol up to 50 W.

The time interval between preoperative hemodynamics and LVAD implantation was 29.6 ± 35.8 days (range, 0 to 120). The time of the postoperative hemodynamic measurements was 111.5 ± 44.9 days (range, 46 to 220) after LVAD implantation.

Echocardiographic measurements
In addition to the hemodynamic protocol we used two-dimensional echocardiography data to determine LV end-diastolic and end-systolic dimension, fractional shortening, end-diastolic and end-systolic volume, and flow pattern across the aortic valve (during LVAD support). Left ventricular ejection fraction was determined by radionuclide ventriculography or angiography. All preoperative measurements were done 6.1 ± 7.7 days before LVAD implantation; the postoperative measurements were performed during the time of the hemodynamic protocol (±15 days).

Statistical analysis
A paired Student's t test was used to compare groups. All data are expressed as mean ± SD. A p-value of less than 0.05 was considered statistically significant. For all pair-wise comparisons the Wilcoxon signed-rank test was employed to assess significance. The follow-up period ended on July 31, 2002.


   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Comment
 References
 
Patient population
Thirty-one patients were included in this study: 21 patients with a pulsatile device (19 Novacor LVAS and 2 TCI-HeartMate VE LVAS) and 10 patients with a nonpulsatile device (MicroMed DeBakey VAD). Reasons for LVAD implantation were mostly on an urgent basis owing to clinical deterioration on the waiting list with increasing doses of inotropic agents according to predefined criteria [11, 20]. Emergency implantations due to cardiogenic shock and elective implantations were less frequent (Table 1). The distributions between elective, urgent, and emergency were similar in both groups. The mean age of the patients in the nonpulsatile group was 33.7 ± 15.0 years (range, 18 to 55); the mean age in the pulsatile group was 43.5 ± 12.5 years (range, 23 to 67; p = not significant). End-stage coronary artery disease (ischemic cardiomyopathy) was the underlying etiology for roughly one third of the patients and dilative cardiomyopathy accounted for roughly two thirds of the patients. Demographic data for all patients are shown in Table 1.


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  		Table 1. Demographic Data for All Patients (n = 31)

 
During preoperative hemodynamic assessments 7 patients were on inotropic support, 3 were ventilated, and 2 were under support of an intraaortic balloon pump in the nonpulsatile group. In the pulsatile group 16 patients were on inotropic support, 3 were ventilated, and 1 was under support with an intraaortic balloon pump immediately before LVAD implantation (all p = not significant; Table 1). During the postoperative hemodynamic assessment all patients were in the normal recovery ward or in the outpatient rehabilitation program without inotropic support.

Hemodynamics
Hemodynamic baseline values (preoperative values) for the nonpulsatile versus the pulsatile group are shown in Table 2. Mean pulmonary artery pressure and pulmonary capillary wedge pressure were elevated in both the nonpulsatile and pulsatile groups (mean pulmonary artery pressure, 40.2 ± 11.0 versus 33.7 ± 8.0 mm Hg, p = not significant; pulmonary capillary wedge pressure, 30.6 ± 9.5 versus 23.1 ± 7.6 mm Hg, p = 0.03) as was mean right atrial pressure (6.8 ± 5.9 versus 7.8 ± 8.1 mm Hg, p = not significant). The relatively high preoperative values of cardiac output were intensified by inotropic support or intraaortic balloon pump.


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  		Table 2. Hemodynamic and Echocardiographic Data Before and After Left Ventricular Assist Device

 
After LVAD implantation mean pulmonary artery pressure decreased to 18.6 ± 5.1 versus 18.3 ± 7.5 mm Hg and pulmonary capillary wedge pressure dropped to 8.9 ± 4.4 versus 8.0 ± 7.0 mm Hg (all p = not significant; Fig 2). We found no differences in left ventricular pressure unloading dependent on etiology (ischemic versus dilated cardiomyopathy) or the time interval of hemodynamic reassessment (<100 versus >100 days).



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  		Fig 2. Left ventricular pressure unloading (decrease of mean pulmonary artery pressure [mPA] and pulmonary capillary wedge pressure [PCWP]) during different left ventricular assist device (LVAD) support. Versus nonpulsatile LVAD: *p = 0.03; {dagger}p = not significant. Open bars = nonpulsatile LVAD; solid bars = pulsatile LVAD.

 
With pulsatile LVAD support systemic vascular resistance increased to 1,579 ± 550 dyne x s-1 x cm-5 (21% increase) whereas with nonpulsatile support, systemic vascular resistance decreased to 1,215 ± 363 dyne x s-1 x cm-5 (2% decrease; p = 0.08). The postoperative values for mean arterial pressure showed a similar trend. Mean arterial pressure increased to 104.6 ± 13.6 mm Hg in the pulsatile group (27% increase) versus a decrease to 77.7 ± 6.2 mm Hg in the nonpulsatile group (3% decrease; p < 0.001; Fig 3). Cardiac output increased to 5.1 ± 1.0 L/min in the pulsatile group versus 5.6 ± 1.3 L/min in the nonpulsatile group (p = not significant; Fig 4). The pump output measured with the LVAD flow sensor was 5.1 ± 1.0 L/min in the pulsatile LVAD group and 3.6 ± 0.9 L/min in the nonpulsatile LVAD group (p < 0.001). The LVVU was 90.9% ± 9.3% with a pulsatile device and 72.3% ± 17.1% with a nonpulsatile device (p < 0.001). A time-dependent decrease in LV volume unloading in the nonpulsatile group was found during the time interval between days 60 and 120 after LVAD implantation (R2 = 0.699 for the nonpulsatile group versus R2 = 0.248 for the pulsatile group; Fig 5).



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  		Fig 3. Course of mean arterial pressure (mAP) and systemic vascular resistance (SVR) in pulsatile and nonpulsatile left ventricular assist devices (LVAD). Pulsatile LVAD versus nonpulsatile LVAD: *p = not significant; {dagger}p less than 0.001; {ddagger}p = 0.08. Open bars = nonpulsatile LVAD; solid bars = pulsatile LVAD.

 


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  		Fig 4. Improvement of cardiac output with different left ventricular assist devices (LVAD) support. Pulsatile LVAD versus nonpulsatile LVAD: *p = not significant; {dagger}p less than 0.001. Open bars = nonpulsatile LVAD; solid bars = pulsatile LVAD.

 


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  		Fig 5. Time dependence of left ventricular volume unloading (LVVU) with different left ventricular assist devices (LVAD) support.

 
Echocardiography
The measurements of the preoperatively performed echocardiography (LV end-diastolic dimension, end-systolic dimension, fractional shortening, end-diastolic volume, and end-systolic volume) were comparable in both LVAD-groups (all p = not significant; Table 2). With LVAD support LV end-diastolic dimension and volume were decreased about 7% and 16% respectively (Table 2). Despite slightly different pre-LVAD values there were no significant differences in end-diastolic measurements between both LVAD groups (Fig 6). End-systolic measurements (dimension and volume) were reduced by 11% and 14% respectively during nonpulsatile LVAD support. However reduction was more pronounced with a pulsatile LVAD (17% versus 59%, respectively). An antegrade flow across the aortic valve was observed in 2 patients with a pulsatile device (10%) and in 5 patients with a nonpulsatile LVAD (50%). Noninvasive blood pressure measuring was possible in 2 patients with a nonpulsatile LVAD to confirm pulsatile flow patterns.



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  		Fig 6. (Top) Left ventricular (LV) end-diastolic parameter: improvement of echocardiographic-determined end-diastolic dimension (EDD) and volume (EDV) during different left ventricular assist devices (LVAD) support. Solid boxes = LVEDD, pulsatile LVAD; open boxes = LVEDD, nonpulsatile LVAD; solid triangles = LVEDV, pulsatile LVAD; open triangles = LVEDV, nonpulsatile LVAD. (Bottom) LV end-systolic parameter: improvement of LV echocardiographic-determined end-systolic dimension (ESD) and volume (ESV) during different LVAD support. Solid boxes = LVESD, pulsatile LVAD; open boxes = LVESD, nonpulsatile LVAD; solid triangles = LVESV, pulsatile LVAD; open triangles = LVESV, nonpulsatile LVAD.

 
Outcome
The duration of LVAD support in the nonpulsatile group was 249 ± 111 days (range, 74 to 438). Eight patients underwent heart transplantation, 1 patient died of intracerebral bleeding before transplant on postoperative day 131, and 1 patient was still on LVAD support at the end of the follow-up period awaiting transplantation. Two patients died during the first year after heart transplantation because of intracerebral bleeding and acute right ventricular failure (Table 1).

In the pulsatile group LVAD duration was 189 ± 71 days (range, 53 to 309; p = not significant versus nonpulsatile group). One patient died of multiorgan failure during LVAD support on postoperative day 53, another patient on postoperative day 116 owing to intracerebral bleeding, and a third patient on postoperative day 244 of unknown reason (the patient was found dead at home). In all other patients cardiac transplantation was performed. Four patients died after transplantation from multi organ failure, acute rejection, and acute right ventricular failure (n = 2).


   Comment
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
References
 
The optimal degree of LV unloading during device support has not been studied. The LVAD was originally designed to entirely off-load the heart while restoring systemic blood pressure. Complete resting of the myocardium was presumed to be beneficial for myocardial recovery and to maximize myocardial perfusion [6].

Hemodynamic improvement with pulsatile assist devices has been studied extensively. The Berlin group [4] observed that optimal improvement in left ventricular size and function occurred within a few weeks (89 ± 79 days) after LVAD implantation. In another study from Columbia University the maximal benefits of LVAD support for reverse remodeling were between 80 and 120 days [21]. These investigators also noted that pulmonary capillary wedge pressure and mean arterial pressure decreased significantly after 30 days during LVAD support [5]. But there is a lack of comparison between pulsatile and nonpulsatile LVADs. In two studies concerning biochemical markers for brain injury or activation of the inflammatory system no differences were found in the early phases after LVAD surgery [9, 10].

Our postoperative assessment was made 112 ± 45 days after LVAD implantation and confirmed similar LV improvement as previously reported. Despite differing LVAD implantation time points in our hospital owing to availability and clinical trials both groups were similar in clinical heart failure status and hemodynamic and echocardiographic measurements. With LVAD support pulmonary vascular resistance, mean pulmonary pressure, and capillary wedge pressure reduction were highly significant in comparison with the preoperative values in failing hearts. The degree of reduction was independent of the type of device, etiology, and time of reassessment. Systemic vascular resistance and mean arterial pressure showed no improvement with a nonpulsatile LVAD, which is most likely due to the lack of pulsatile flow properties. While cardiac output increases with pulsatile and nonpulsatile LVAD support, we found a significant difference in LVAD output (p < 0.001). Pulsatile LVADs generate nearly complete LV volume unloading. In contrast nonpulsatile devices produce only a partial unloading of the left ventricle. These findings with pulsatile LVADs were supported by a pronounced decrease in end-systolic dimension and volume in comparison with nonpulsatile support. Furthermore we found a time-dependent decrease of LVVU between days 60 and 120 in these devices.

The impact of complete or partial LV volume unloading on cardiac recovery is not clear. However morbidity and mortality rates with a nonpulsatile device are similar to those of patients with a pulsatile device. Hemodynamic and echocardiographic data suggest that the completely unloaded ventricle could contract easier (without any pressure gradient) whereas the heart connected to a nonpulsatile device utilizes a part of its own contractility to create an antegrade flow. While partial unloading of the left ventricle seems to be sufficient enough for LVAD bridge to transplantation, the impact of a bridge to recovery with the goal to wean the patient from the device is not clear and further studies are warranted.

Study limitations
The small number of patients enrolled in this study limits our ability to make conclusions with respect to LV unloading or the etiology of LVAD support. Background medical management after LVAD implantation may have varied during the time period. In addition all reported values were determined under full device support (automode in both pulsatile devices, fixed speed at 10,000 rpm in the nonpulsatile device). Hence changes in hemodynamic and echocardiographic measurements with reduced LVAD flow were not determined and are warranted.

In conclusion nonpulsatile devices show left ventricular pressure unloading and pretransplant and posttransplant outcomes comparable with those of pulsatile devices. Nonpulsatile LVADs generate only partial LV volume unloading whereas pulsatile LVADs produce complete volume unloading. Further studies on the impact of weaning from the device depending on the device type are warranted.


   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 

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  6. Mancini D.M., Beniaminovitz A., Levin H., et al. Low incidence of myocardial recovery after left ventricular assist device implantation in patients with chronic heart failure. Circulation 1998;98:2383-2389.[Abstract/Free Full Text]
  7. Mueller J., Wallukat G., Weng Y., et al. Weaning from mechanical support in patients with dilated cardiomyopathy. Circulation 1997;96:542-549.[Abstract/Free Full Text]
  8. Johnston G.G., Hammill F., Marczec U., et al. Prolonged pulseless perfusion in unanesthetized calves. Arch Surg 1976;111:1225-1230.[Abstract/Free Full Text]
  9. Loebe M., Koster A., Sanger S., et al. Inflammatory response after implantation of a left ventricular assist device: comparison between the axial flow MicroMed DeBakey VAD and the pulsatile Novacor device. ASAIO J 2001;47:272-274.[Medline]
  10. Potapov E.V., Lobe M., Abdul-Khaliq H., et al. Postoperative course of S-100B protein and neuron-specific enolase in patients after implantation of continuous and pulsatile flow LVADs. J Heart Lung Transplant 2001;20:1310-1316.[Medline]
  11. Deng M.C., Weyand M., Hammel D., et al. Selection and management of ventricular assist device patients: the Muenster experience. J Heart Lung Transplant 2000;19:77-82.
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