- Email: [email protected]
Fracture of the total artificial heart pneumatic driveline after transition to the portable driver
http://www.jhltonline.org
RESEARCH CORRESPONDENCE Fracture of the total artificial heart pneumatic driveline after transition to the portable driver Keyur B. Shah, MD,a Regina A. Volman, NP,a Suzanne Harton, NP,a Daniel G. Tang, MD,b and Vigneshwar Kasirajan, MDb From the aDivision of Cardiology, Richmond, Virginia; and the b Division of Cardiothoracic Surgery, Virginia Commonwealth University, Richmond, Virginia
The CardioWest (SynCardia Systems Inc, Tucson, AZ) total artificial heart (TAH) consists of polyurethane ventricles with pneumatically driven diaphragms and 4 mechanical tilting disk valves that replace the entire heart. A polyvinyl chloride wire–reinforced pneumatic conduit (permanent driveline) attaches to each pump. The drivelines are tunneled through the left rectus muscle to the left upper quadrant and are covered with velour to promote tissue ingrowth. The permanent drivelines are attached via connecters to longer tubing that attaches to the pneumatic driver and is replaceable. Although rehabilitation and mobility are feasible with the TAH, implantation of the device until recently required patients to remain tethered to a 418-pound inpatient driver until a heart transplant donor became available.1 With the introduction the TAH portable Freedom Driver (SynCardia Systems), which has not yet been approved by the Food and Drug Administration, patients may look forward to increased mobility and potential discharge from the hospital.2 Although improving patient quality of life, increased patient mobility could increase stress and torque
on the conduit and driveline. In this report, we describe the incidence and risk factors of driveline fracture after implantation of the TAH. This single-center retrospective study evaluated 66 consecutive patients who received the CardioWest TAH from 2006 through 2012. The Virginia Commonwealth University School of Medicine Institutional Review Board reviewed and approved this project. Patient clinical data were abstracted from the medical record. Fracture of the driveline was defined as any air leak of a conduit or driveline requiring repair. For the different sub-groups (hospital driver vs portable driver), the 2-sample independent Student’s t-test was used to compare continuous variables, and the chi-square test was used for categoric variables. Six of the 66 patients (9%) implanted with the TAH sustained fractures of the conduit that required repair. All fractures occurred only in patients transitioned to the portable driver (38% vs 0% of hospital driver patients, p o 0.001; Table 1). The rate of fracture per patient-year was 0.11 ⫾ 0.42 and was increased in patients on the portable driver vs those that remained on the hospital driver (0.46 ⫾ 0.77 vs 0.0 ⫾ 0.0 fractures/patient-year, p ¼ 0.03). Patients on the portable driver were supported with the TAH for longer durations (308 ⫾ 234 vs 84 ⫾ 70 days, p ¼ 0.002), and the initial fracture occurred at a median of 228 days (range, 168–430 days) after TAH implantation and 178 days (range, 33–401 days) after transition to the portable driver. Figure 1 depicts the relationship of driver type, time on TAH support, and occurrence of driveline fracture.
Table 1 Clinical Characteristics, Pre-operative Laboratory Data, and Outcomes for Patients Transitioned to the Portable Driver and Those Who Remained on the In-Hospital Driver Variablesa
Hospital (n ¼ 50)
Age, years Male Body mass index, kg/m2 Body surface area, m2 Serum creatinine, mg/dl Hemoglobin, mg/dl Total bilirubin, mg/dl INTERMACS Ischemic cardiomyopathy Fracture Days on device
48.0 94% 28.8 2.1 1.7 10.6 1.6 63 76 0 84
⫾ 12.1 ⫾ ⫾ ⫾ ⫾ ⫾
5.9 0.3 1.8 1.8 1.1
⫾ 70
Portable (n ¼ 16)
p-value
⫾ 11.1
0.9 0.01 0.9 0.9 0.5 0.3 0.3 0.8 0.3 o0.001 0.002
48.6 63% 29.9 2.1 1.2 11.0 1.9 58 88 38 308
⫾ ⫾ ⫾ ⫾ ⫾
5.8 0.2 0.5 2.5 0.9
⫾ 234
INTERMACS, Interagency Registry for Mechanically Assisted Circulatory Support. a Continuous data are shown as mean ⫾ standard deviation and categoric data as the percentage of patients.
1053-2498/$ - see front matter r 2013 International Society for Heart and Lung Transplantation. All rights reserved. http://dx.doi.org/10.1016/j.healun.2013.06.014
1042
The Journal of Heart and Lung Transplantation, Vol 32, No 10, October 2013
Figure 1 The dot plot depicts the days free from driveline fracture for patients who remained on the in-hospital driver compared with those who were transitioned to the portable driver. Patients who developed a driveline fracture are represented with a red “X.”
The 6 patients with fractures all presented with audible air leaks, and 1 of these patients was experiencing fault alarms for low flows from the driver. As shown in Figure 2A, the fractures occurred near transition zones, where the conduit interfaces with the driveline connectors (Patients 1, 4, 5, and 6) or where the conduit exits the velour/skin (Patients 2 and 3). Torque, strain, and bending forces on the conduit likely caused stress at these points where the tubing is fixed.
The fractures in 4 patients were initially managed with silicone vulcanizing tape, and 2 of these patients later required mechanical excision of fractured portions of the driveline. In the 2 remaining patients, the fractures were mechanically excised as primary treatment. Patients 3 and 6 had additional conduit fractures associated with discoloration and increased brittleness of the driveline, possibly related to the adhesive tapes (Figure 2B). None of the fractures resulted in acute hemodynamic compromise, stroke, or death. One patient, who underwent extensive excision of both drivelines, eventually required replacement of her TAH for persistently decreased pump output. Examination of the explanted components of the device did not identify a cause of device malfunction. Fractures of the TAH conduits were observed only in patients converted to the portable driver and in no patients who remained exclusively on the hospital driver. The occurrence of fractures was probably related to (1) increased patient mobility resulting in torque and stress on the conduit at transition points and (2) increased waiting time to transplantation for patients discharged from the hospital. Although most were clinically managed, 1 patient with extensive driveline excisions eventually had malfunction of the TAH. This report was formulated to raise awareness of a complication observed with utilization of a novel technology and has several limitations. This is a single-center retrospective analysis, and due to the non-randomized nature of the study, unmeasured patients characteristics (such as patient functional capacity) that favor transition to the portable driver may play a role in the development of fractures. Multivariate analysis for interaction of covariates was not possible due to small sample size. When repairing the driveline, an organized methodical approach is necessary. The pneumatic air leak is often readily apparent to the patient and can be associated with a mild symptomatic decrease in cardiac output. Depending on the degree of air loss, the driver may have low flow alarms, and patients are often quite anxious. Manual stabilization of the driveline by hand and/or wrapping the driveline with tape is
Figure 2 (A) The venous and arterial conduits (permanent driveline) are shown exiting the skin and attaching to connectors to the extension driveline tubing. The initial driveline fracture in each patient (noted by the numbers) was located near the conduit–connector interface or near the exit site near the skin. (B) Shown is a driveline segment that developed linear fractures after a tape repair of the initial fracture. (C) During repair of a fracture, the driveline is cut proximal to the perforation and immediately attached to a driveline connector attached to the second driver. (D) The fractured portion of the driveline and original connector is shown.
Research Correspondence often sufficient to minimize the air leak as the patient is transported to the hospital. Repair of the drivelines should occur in a monitored setting with backup drivers readily available. Steps in excising damaged portions of the pneumatic driveline: 1. Prepare a second driver with a set of driveline extension tubing and set the second driver to an identical ejection rate as the patient’s driver. During the repair, the affected pump will be temporarily supported by the second driver. 2. The operator exposes the air leak and divides any associated ties between the drivelines. The air leak is often readily apparent, although soapy water can be applied to help identify the site. 3. Use heavy shears to cut the driveline proximal to the fracture site (closer to the patient) and immediately attach the driveline conduit to the second driver to a fracture free portion of the driveline attached to the TAH (Figure 2C and D). 4. While the left and right ventricles are being separately supported by 2 different drivers, the patient should be warned to expect an alarm on the old driver. Once the repair is complete, reconnect the patient to the primary driver. Significant resection of the patient’s driveline can alter the pneumatic balance and affect the effective stroke volume delivered. In our experience, fracture of the pneumatic conduit was common after conversion to the portable TAH driver, occurring in 38% of patients. Patients and clinicians must be
1043 educated on surveillance for this potentially serious complication. Considering that most observed fracture occurred near the connection of the conduit to the driveline extension, changes to the driveline design, such as a continuous, fully integrated driveline without intermediate connectors, may decrease fracture rates. With the current design, however, driveline fractures may limit the long-term durability of the TAH for the ambulatory and active patient.
Disclosure statement The authors thank Joyce Hager for her data collection that contributed to this study. K.B.S. has received institutional grants from Thoratec Corp. V.K. is a consultant for SynCardia Systems, manufacturer of the CardioWest TAH. None of the other authors has a financial relationship with a commercial entity that has an interest in the subject of the presented manuscript or other conflicts of interest to disclose.
References 1. Kohli HS, Canada J, Arena R, et al. Exercise blood pressure response during assisted circulatory support: comparison of the total artificial heart with a left ventricular assist device during rehabilitation. J Heart Lung Transplant 2011;30:1207-13. 2. Jaroszewski DE, Anderson EM, Pierce CN, Arabia FA. The SynCardia freedom driver: a portable driver for discharge home with the total artificial heart. J Heart Lung Transplant 2011;30:844-5.
RESEARCH CORRESPONDENCE Fracture of the total artificial heart pneumatic driveline after transition to the portable driver Keyur B. Shah, MD,a Regina A. Volman, NP,a Suzanne Harton, NP,a Daniel G. Tang, MD,b and Vigneshwar Kasirajan, MDb From the aDivision of Cardiology, Richmond, Virginia; and the b Division of Cardiothoracic Surgery, Virginia Commonwealth University, Richmond, Virginia
The CardioWest (SynCardia Systems Inc, Tucson, AZ) total artificial heart (TAH) consists of polyurethane ventricles with pneumatically driven diaphragms and 4 mechanical tilting disk valves that replace the entire heart. A polyvinyl chloride wire–reinforced pneumatic conduit (permanent driveline) attaches to each pump. The drivelines are tunneled through the left rectus muscle to the left upper quadrant and are covered with velour to promote tissue ingrowth. The permanent drivelines are attached via connecters to longer tubing that attaches to the pneumatic driver and is replaceable. Although rehabilitation and mobility are feasible with the TAH, implantation of the device until recently required patients to remain tethered to a 418-pound inpatient driver until a heart transplant donor became available.1 With the introduction the TAH portable Freedom Driver (SynCardia Systems), which has not yet been approved by the Food and Drug Administration, patients may look forward to increased mobility and potential discharge from the hospital.2 Although improving patient quality of life, increased patient mobility could increase stress and torque
on the conduit and driveline. In this report, we describe the incidence and risk factors of driveline fracture after implantation of the TAH. This single-center retrospective study evaluated 66 consecutive patients who received the CardioWest TAH from 2006 through 2012. The Virginia Commonwealth University School of Medicine Institutional Review Board reviewed and approved this project. Patient clinical data were abstracted from the medical record. Fracture of the driveline was defined as any air leak of a conduit or driveline requiring repair. For the different sub-groups (hospital driver vs portable driver), the 2-sample independent Student’s t-test was used to compare continuous variables, and the chi-square test was used for categoric variables. Six of the 66 patients (9%) implanted with the TAH sustained fractures of the conduit that required repair. All fractures occurred only in patients transitioned to the portable driver (38% vs 0% of hospital driver patients, p o 0.001; Table 1). The rate of fracture per patient-year was 0.11 ⫾ 0.42 and was increased in patients on the portable driver vs those that remained on the hospital driver (0.46 ⫾ 0.77 vs 0.0 ⫾ 0.0 fractures/patient-year, p ¼ 0.03). Patients on the portable driver were supported with the TAH for longer durations (308 ⫾ 234 vs 84 ⫾ 70 days, p ¼ 0.002), and the initial fracture occurred at a median of 228 days (range, 168–430 days) after TAH implantation and 178 days (range, 33–401 days) after transition to the portable driver. Figure 1 depicts the relationship of driver type, time on TAH support, and occurrence of driveline fracture.
Table 1 Clinical Characteristics, Pre-operative Laboratory Data, and Outcomes for Patients Transitioned to the Portable Driver and Those Who Remained on the In-Hospital Driver Variablesa
Hospital (n ¼ 50)
Age, years Male Body mass index, kg/m2 Body surface area, m2 Serum creatinine, mg/dl Hemoglobin, mg/dl Total bilirubin, mg/dl INTERMACS Ischemic cardiomyopathy Fracture Days on device
48.0 94% 28.8 2.1 1.7 10.6 1.6 63 76 0 84
⫾ 12.1 ⫾ ⫾ ⫾ ⫾ ⫾
5.9 0.3 1.8 1.8 1.1
⫾ 70
Portable (n ¼ 16)
p-value
⫾ 11.1
0.9 0.01 0.9 0.9 0.5 0.3 0.3 0.8 0.3 o0.001 0.002
48.6 63% 29.9 2.1 1.2 11.0 1.9 58 88 38 308
⫾ ⫾ ⫾ ⫾ ⫾
5.8 0.2 0.5 2.5 0.9
⫾ 234
INTERMACS, Interagency Registry for Mechanically Assisted Circulatory Support. a Continuous data are shown as mean ⫾ standard deviation and categoric data as the percentage of patients.
1053-2498/$ - see front matter r 2013 International Society for Heart and Lung Transplantation. All rights reserved. http://dx.doi.org/10.1016/j.healun.2013.06.014
1042
The Journal of Heart and Lung Transplantation, Vol 32, No 10, October 2013
Figure 1 The dot plot depicts the days free from driveline fracture for patients who remained on the in-hospital driver compared with those who were transitioned to the portable driver. Patients who developed a driveline fracture are represented with a red “X.”
The 6 patients with fractures all presented with audible air leaks, and 1 of these patients was experiencing fault alarms for low flows from the driver. As shown in Figure 2A, the fractures occurred near transition zones, where the conduit interfaces with the driveline connectors (Patients 1, 4, 5, and 6) or where the conduit exits the velour/skin (Patients 2 and 3). Torque, strain, and bending forces on the conduit likely caused stress at these points where the tubing is fixed.
The fractures in 4 patients were initially managed with silicone vulcanizing tape, and 2 of these patients later required mechanical excision of fractured portions of the driveline. In the 2 remaining patients, the fractures were mechanically excised as primary treatment. Patients 3 and 6 had additional conduit fractures associated with discoloration and increased brittleness of the driveline, possibly related to the adhesive tapes (Figure 2B). None of the fractures resulted in acute hemodynamic compromise, stroke, or death. One patient, who underwent extensive excision of both drivelines, eventually required replacement of her TAH for persistently decreased pump output. Examination of the explanted components of the device did not identify a cause of device malfunction. Fractures of the TAH conduits were observed only in patients converted to the portable driver and in no patients who remained exclusively on the hospital driver. The occurrence of fractures was probably related to (1) increased patient mobility resulting in torque and stress on the conduit at transition points and (2) increased waiting time to transplantation for patients discharged from the hospital. Although most were clinically managed, 1 patient with extensive driveline excisions eventually had malfunction of the TAH. This report was formulated to raise awareness of a complication observed with utilization of a novel technology and has several limitations. This is a single-center retrospective analysis, and due to the non-randomized nature of the study, unmeasured patients characteristics (such as patient functional capacity) that favor transition to the portable driver may play a role in the development of fractures. Multivariate analysis for interaction of covariates was not possible due to small sample size. When repairing the driveline, an organized methodical approach is necessary. The pneumatic air leak is often readily apparent to the patient and can be associated with a mild symptomatic decrease in cardiac output. Depending on the degree of air loss, the driver may have low flow alarms, and patients are often quite anxious. Manual stabilization of the driveline by hand and/or wrapping the driveline with tape is
Figure 2 (A) The venous and arterial conduits (permanent driveline) are shown exiting the skin and attaching to connectors to the extension driveline tubing. The initial driveline fracture in each patient (noted by the numbers) was located near the conduit–connector interface or near the exit site near the skin. (B) Shown is a driveline segment that developed linear fractures after a tape repair of the initial fracture. (C) During repair of a fracture, the driveline is cut proximal to the perforation and immediately attached to a driveline connector attached to the second driver. (D) The fractured portion of the driveline and original connector is shown.
Research Correspondence often sufficient to minimize the air leak as the patient is transported to the hospital. Repair of the drivelines should occur in a monitored setting with backup drivers readily available. Steps in excising damaged portions of the pneumatic driveline: 1. Prepare a second driver with a set of driveline extension tubing and set the second driver to an identical ejection rate as the patient’s driver. During the repair, the affected pump will be temporarily supported by the second driver. 2. The operator exposes the air leak and divides any associated ties between the drivelines. The air leak is often readily apparent, although soapy water can be applied to help identify the site. 3. Use heavy shears to cut the driveline proximal to the fracture site (closer to the patient) and immediately attach the driveline conduit to the second driver to a fracture free portion of the driveline attached to the TAH (Figure 2C and D). 4. While the left and right ventricles are being separately supported by 2 different drivers, the patient should be warned to expect an alarm on the old driver. Once the repair is complete, reconnect the patient to the primary driver. Significant resection of the patient’s driveline can alter the pneumatic balance and affect the effective stroke volume delivered. In our experience, fracture of the pneumatic conduit was common after conversion to the portable TAH driver, occurring in 38% of patients. Patients and clinicians must be
1043 educated on surveillance for this potentially serious complication. Considering that most observed fracture occurred near the connection of the conduit to the driveline extension, changes to the driveline design, such as a continuous, fully integrated driveline without intermediate connectors, may decrease fracture rates. With the current design, however, driveline fractures may limit the long-term durability of the TAH for the ambulatory and active patient.
Disclosure statement The authors thank Joyce Hager for her data collection that contributed to this study. K.B.S. has received institutional grants from Thoratec Corp. V.K. is a consultant for SynCardia Systems, manufacturer of the CardioWest TAH. None of the other authors has a financial relationship with a commercial entity that has an interest in the subject of the presented manuscript or other conflicts of interest to disclose.
References 1. Kohli HS, Canada J, Arena R, et al. Exercise blood pressure response during assisted circulatory support: comparison of the total artificial heart with a left ventricular assist device during rehabilitation. J Heart Lung Transplant 2011;30:1207-13. 2. Jaroszewski DE, Anderson EM, Pierce CN, Arabia FA. The SynCardia freedom driver: a portable driver for discharge home with the total artificial heart. J Heart Lung Transplant 2011;30:844-5.