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Intraaortic Balloon Pump Insertion through the Subclavian Artery.
CASE REPORT
Case Report
Intraaortic Balloon Pump Insertion through the Subclavian Artery. Subclavian Artery Insertion of IABP Constantin B. Marcu, MD a,∗ , Thomas J. Donohue, MD, FACC b , Antoine Ferneini, MD b and Andre E. Ghantous, MD, FACC b a
Vrije University Medical Center, Department of Cardiology, Room 6D 120, De Boelelaan 1117 1081 HV, Amsterdam, The Netherlands b Hospital of Saint Raphael – Yale University, New Haven, CT, USA
The intraaortic balloon pump (IABP) is frequently used in the management of cardiac failure in the setting of myocardial infarction or as a bridge for coronary revascularisation surgery. The IABP is usually inserted through the femoral artery. Occasionally severe aorto-iliac occlusive disease prevents the retrograde passage of the balloon, in which case an anterograde route, usually through the ascending aorta is used. We describe four patients in whom an IABP was placed through the subclavian artery by the joint efforts of cardiologists and vascular surgeons. (Heart Lung and Circulation 2006;15:148–150) © 2005 Australasian Society of Cardiac and Thoracic Surgeons and the Cardiac Society of Australia and New Zealand. Published by Elsevier Inc. All rights reserved. Keywords. Subclavian artery; Insertion; Intraaortic counterpulsation
Introduction
A
graft anastomosed to the subclavian artery in an end-toside fashion.
n intraaortic balloon pump is frequently used in cardiogenic shock of different etiologies in an effort to reduce left ventricular afterload and improve diastolic coronary and subendocardial perfusion.1 The intraaortic balloon counterpulsation technique has been shown to be effective in reducing mortality and morbidity when used for cardiogenic shock after acute myocardial infarction,2 in stabilizing patients who are undergoing angioplasty,3 and after coronary artery bypass surgery (CABG).4 Placement of the IABP is usually achieved through the femoral artery using a modified Seldinger technique. Occasionally, the retrograde safe passage of the intraaortic balloon is prevented by severe aorto-iliac occlusive disease in which case an anterograde route has to be used. At the time of cardiac surgery the ascending aorta can be used as a point of access, a method that requires a median sternotomy. This method does not solve the problem of IABP insertion in patients with severe aortic occlusive disease who need the therapy preoperatively and implies repeat sternotomy for patients who need it postoperatively. Insertion of an IABP through the subclavian artery has the advantage of avoiding a median sternotomy and increasing the patient’s mobility.5,6 We present four cases in which a balloon was successfully passed into the descending aorta through a
After preparation of the pectoral and neck regions, a 6cm incision was made, under local anaesthesia, in the infraclavicular region. The right or left subclavian/axillary arteries were identified and the patient received an intravenous bolus of 5000 IU of unfractionated heparin followed by proximal and distal control of the artery. A 1-cm longitudinal incision of the arterial wall was performed after which a 6–8 mm Gore-Tex® graft was anastomosed end to side. The free end of the synthetic graft was sutured shut. The proximal graft portion was tunneled under the skin to the exterior and sutured to the skin of the ipsilateral shoulder. The graft was punctured with a Cook® needle, and under fluoroscopy a 145-cm 0.03 in. J guide-wire was introduced through the graft and was directed to the descending aorta by a 6-French diagnostic multipurpose catheter. An 8-French sheathless IABP was exchanged anterogradely for the diagnostic catheter in the descending thoracic aorta and the tip was placed above the aorto-iliac bifurcation (Fig. 1). The synthetic grafts were removed at the same time or on the day after the balloon pump removal.
Available online 20 October 2005
Case 1
∗
A 62-year-old woman with a history of systemic hypertension presented with congestive heart failure. A
Corresponding author. Tel.: +31 20 4442244; fax: +31 20 4442446. E-mail address: [email protected] (C.B. Marcu).
Method
© 2005 Australasian Society of Cardiac and Thoracic Surgeons and the Cardiac Society of Australia and New Zealand. Published by Elsevier Inc. All rights reserved.
1443-9506/04/$30.00 doi:10.1016/j.hlc.2005.08.008
Marcu et al. Intraaortic balloon pump insertion through the subclavian artery. Subclavian artery insertion of IABP
149
Case 3 A 59-year-old man with a prior history of diabetes mellitus and peripheral vascular disease was hospitalised with gangrene of his left lower extremity. An emergent below the knee amputation was complicated by an inferior wall myocardial infarction and congestive heart failure. Cardiac catheterisation performed through a left brachial approach demonstrated a LVEF of 25% and severe three vessel coronary disease. An aortogram showed complete infrarenal occlusion. The patient underwent CABG surgery with saphenous vein grafts to the posterior descending artery, diagonal and marginal branches and a left thoracic artery graft to the left anterior descending coronary artery. An IABP was inserted through the right subclavian artery preoperatively and successfully removed after surgery. The patient had an uneventful postoperative course.
Case 4
Figure 1. Diagram of subclavian insertion of an IABP. Synthetic graft anastomosed end to side to the right subclavian artery (arrow). Intra-aortic balloon pump placed through the graft into the descending thoracic aorta (arrow-head).
transthoracic echocardiogram revealed a left ventricular ejection fraction (LVEF) of 25% and severe mitral valve regurgitation due to a flail posterior leaflet. Cardiac catheterisation demonstrated a 90% diameter stenosis of the right coronary artery, 4+ mitral regurgitation and significant occlusive aortic disease. An IABP was placed through a left subclavian approach for circulatory support prior to the valvular surgery. The patient underwent mitral valve replacement surgery and coronary revascularisation with a saphenous vein graft to the right coronary artery. The IABP was successfully discontinued one day after surgery.
Case 2 A 75-year-old man with known critical calcific aortic stenosis, coronary artery and peripheral vascular disease was hospitalised for aortic valve replacement and CABG surgery. The LVEF was 30% on ventriculography. Because of the severe peripheral vascular disease and signs of left subclavian stenosis (the systolic blood pressure was 30 mm Hg lower in the left arm compared to the right arm), an IABP was placed through the right subclavian artery prior to cardiac surgery. Aortic valve replacement and CABG surgery were performed and the IABP was successfully removed on postoperative day 1. His hospital course was complicated by respiratory failure requiring prolonged mechanical ventilation and a tracheostomy. The patient was eventually transferred to a specialised facility for pulmonary rehabilitation.
A 72-year-old woman, who presented with cardiogenic shock due to an acute anterior wall myocardial infarction, underwent emergent cardiac catheterisation. The cardiac catheterisation, initially unsuccessful from a femoral approach, was performed through the left radial artery and revealed severe triple coronary vessel disease with a decreased LVEF. Significant stenosis of the distal aorta was demonstrated on aortography, precluding the retrograde insertion of an IABP. She underwent emergent CABG surgery. Because the patient remained in cardiogenic shock despite maximum inotropic support, an IABP was placed in the descending thoracic aorta via a left subclavian arterial approach. Her hospital course was complicated by acute renal failure and she died on postoperative day three.
Discussion The American College of Cardiology/American Heart Association guidelines suggest the use of IABP in patients with ST elevation myocardial infarction and cardiogenic shock unresponsive to pharmacological therapy, acute mitral regurgitation or ventricular septal defect, recurrent ischaemia or intractable ventricular arrhythmias with haemodynamic instability, and in patients with refractory pulmonary congestion.7 While the frequency of IABP use in cardiac surgical patients has increased over time,8–10 the decision of whether and when to use an IABP is often not clear. A recent review by Baskett et al. classified the evidence for the efficacy of IABP in cardiac surgical patients using a similar system to the ACC/AHA guidelines.8 Class I indications for the use of an IABP in the perioperative period were ongoing ischaemia or a LVEF <25% before non-elective or repeat CABG and the use of IABP if needed for weaning from cardiopulmonary bypass. Patients without ongoing ischemia who have low LVEF or left main disease or are undergoing procedures other than isolated CABG received a class II indication for the preoperative use of an IABP.
CASE REPORT
Heart Lung and Circulation 2006;15:148–150
150
Marcu et al. Intraaortic balloon pump insertion through the subclavian artery. Subclavian artery insertion of IABP
CASE REPORT
During the use of IABP complications such as limb ischaemia, bleeding, infection, balloon leak, stroke and death may arise. A registry study describing the trend of IABP use in cardiac surgery during the late 1990s10 showed an overall complication rate of 6.5% (with 2.1% major complications) compared to historical rates of up to 33%.8 The decrease in the rate of IABP related major complications such as severe limb ischaemia or bleeding requiring surgery over the last 10 years may be explained by the increased use of smaller size catheters, sheathless insertion, percutaneous approach and improved physician experience.9 Patients with severe peripheral vascular disease who require IABP support are not infrequently encountered in clinical practice. In such patients it is often impossible to pass even a guide-wire retrograde from the femoral artery, in which case an alternative approach is to place an IABP through the ascending aorta.11 This method requires a median sternotomy under general anaesthesia. Complications of ascending aortic IABP insertion such as graft infection, aberrant cannulation of the left subclavian artery, left coronary artery embolism, and inability to close the sternum due to mechanical tamponade have been described.11 It appears, however, that the insertion of an IABP in the ascending aorta is not associated with a significant increase in complications or mortality compared to femoral insertion when other comorbidities are considered.8,12 Subclavian arterial IABP insertion under local anaesthesia is easier and safer to perform and allows increased patient mobility. In deciding which subclavian artery to use for IABP access one has to consider the presence of signs and symptoms of subclavian stenosis (difference between blood pressure measurements in the arms, presence of vertebral steal syndrome or arm claudication), and if needed obtain a computed tomographic or magnetic resonance angiogram of the aortic arch vessels. If the left internal thoracic artery is to be used for CABG, one might consider placing the IABP through the right subclavian artery and avoid, at least in theory, interfering with the left thoracic artery blood flow. A subclavian IABP approach should be strongly considered in patients with severe left ventricular systolic
Heart Lung and Circulation 2006;15:148–150
dysfunction where an IABP is indicated and there is severe aorto-iliac atherosclerotic disease.
References 1. Maccioli GA, Lucas WJ, Norfleet EA. The intra-aortic balloon pump: a review. J Cardiothorac Anesth 1988;2:365–73. 2. Waksman R, Weiss AT, Gotsman MS, Hassin Y. Intra-aortic balloon counterpulsation improves survival in cardiogenic shock complicating acute myocardial infarction. Eur Heart J 1993;14:71–4. 3. Ohman EM, et al., The Randomized IABP Study Group. Use of aortic counterpulsation to sustain coronary artery patency during acute myocardial infarction. Results of a randomized trial. Circulation 1994;90(2):792–9. 4. Christenson JT, Buswell L, Velebit V, Maurice J, Simonet F, Schmuziger M. The intraaortic balloon pump for postcardiotomy heart failure. Experience with 169 intraaortic balloon pumps. Thorac Cardiovasc Surg 1995;43:129–33. 5. Mayer JH. Subclavian artery approach for insertion of intraaortic balloon. J Thorac Cardiovasc Surg 1978;76:61–3. 6. Rubenstein RB, Karhade NV. Supraclavicular subclavian technique of intra-aortic balloon insertion. J Vasc Surg 1984;1:577–8. 7. Antman EM, Anbe DT, Armstrong PW, Bates ER, Green LA, Hand M, et al. ACC/AHA guidelines for the management of patients with ST-elevation myocardial infarction: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Revise the 1999 Guidelines for the Management of patients with acute myocardial infarction). J Am Coll Cardiol 2004;44(3):E1–211. 8. Baskett RJ, Ghali WA, Maitland A, Hirsch GM. The intraaortic balloon pump in cardiac surgery. Ann Thorac Surg 2002;74(4):1276–87. 9. Elahi MM, Chetty GK, Kirke R, Azeem T, Hartshorne R, Spyt TJ. Complications related to intra-aortic balloon pump in cardiac surgery: a decade later. Eur J Vasc Endovasc Surg 2005;29(6):591–4. 10. Christenson JT, Cohen M, Ferguson 3rd JJ, Freedman RJ, Miller MF, Ohman EM, et al. Trends in intraaortic balloon counterpulsation complications and outcomes in cardiac surgery. Ann Thorac Surg 2002;74(4):1086–90. 11. Meldrum-Hanna WG, Deal CW, Ross DE. Complications of ascending aortic intraaortic balloon pump cannulation. Ann Thorac Surg 1985;40(3):241–4. 12. Hazelrigg S, Auer J, Seifert P. Experience in 100 transthoracic balloon pumps. Ann Thorac Surg 1992;54:528–32.
Case Report
Intraaortic Balloon Pump Insertion through the Subclavian Artery. Subclavian Artery Insertion of IABP Constantin B. Marcu, MD a,∗ , Thomas J. Donohue, MD, FACC b , Antoine Ferneini, MD b and Andre E. Ghantous, MD, FACC b a
Vrije University Medical Center, Department of Cardiology, Room 6D 120, De Boelelaan 1117 1081 HV, Amsterdam, The Netherlands b Hospital of Saint Raphael – Yale University, New Haven, CT, USA
The intraaortic balloon pump (IABP) is frequently used in the management of cardiac failure in the setting of myocardial infarction or as a bridge for coronary revascularisation surgery. The IABP is usually inserted through the femoral artery. Occasionally severe aorto-iliac occlusive disease prevents the retrograde passage of the balloon, in which case an anterograde route, usually through the ascending aorta is used. We describe four patients in whom an IABP was placed through the subclavian artery by the joint efforts of cardiologists and vascular surgeons. (Heart Lung and Circulation 2006;15:148–150) © 2005 Australasian Society of Cardiac and Thoracic Surgeons and the Cardiac Society of Australia and New Zealand. Published by Elsevier Inc. All rights reserved. Keywords. Subclavian artery; Insertion; Intraaortic counterpulsation
Introduction
A
graft anastomosed to the subclavian artery in an end-toside fashion.
n intraaortic balloon pump is frequently used in cardiogenic shock of different etiologies in an effort to reduce left ventricular afterload and improve diastolic coronary and subendocardial perfusion.1 The intraaortic balloon counterpulsation technique has been shown to be effective in reducing mortality and morbidity when used for cardiogenic shock after acute myocardial infarction,2 in stabilizing patients who are undergoing angioplasty,3 and after coronary artery bypass surgery (CABG).4 Placement of the IABP is usually achieved through the femoral artery using a modified Seldinger technique. Occasionally, the retrograde safe passage of the intraaortic balloon is prevented by severe aorto-iliac occlusive disease in which case an anterograde route has to be used. At the time of cardiac surgery the ascending aorta can be used as a point of access, a method that requires a median sternotomy. This method does not solve the problem of IABP insertion in patients with severe aortic occlusive disease who need the therapy preoperatively and implies repeat sternotomy for patients who need it postoperatively. Insertion of an IABP through the subclavian artery has the advantage of avoiding a median sternotomy and increasing the patient’s mobility.5,6 We present four cases in which a balloon was successfully passed into the descending aorta through a
After preparation of the pectoral and neck regions, a 6cm incision was made, under local anaesthesia, in the infraclavicular region. The right or left subclavian/axillary arteries were identified and the patient received an intravenous bolus of 5000 IU of unfractionated heparin followed by proximal and distal control of the artery. A 1-cm longitudinal incision of the arterial wall was performed after which a 6–8 mm Gore-Tex® graft was anastomosed end to side. The free end of the synthetic graft was sutured shut. The proximal graft portion was tunneled under the skin to the exterior and sutured to the skin of the ipsilateral shoulder. The graft was punctured with a Cook® needle, and under fluoroscopy a 145-cm 0.03 in. J guide-wire was introduced through the graft and was directed to the descending aorta by a 6-French diagnostic multipurpose catheter. An 8-French sheathless IABP was exchanged anterogradely for the diagnostic catheter in the descending thoracic aorta and the tip was placed above the aorto-iliac bifurcation (Fig. 1). The synthetic grafts were removed at the same time or on the day after the balloon pump removal.
Available online 20 October 2005
Case 1
∗
A 62-year-old woman with a history of systemic hypertension presented with congestive heart failure. A
Corresponding author. Tel.: +31 20 4442244; fax: +31 20 4442446. E-mail address: [email protected] (C.B. Marcu).
Method
© 2005 Australasian Society of Cardiac and Thoracic Surgeons and the Cardiac Society of Australia and New Zealand. Published by Elsevier Inc. All rights reserved.
1443-9506/04/$30.00 doi:10.1016/j.hlc.2005.08.008
Marcu et al. Intraaortic balloon pump insertion through the subclavian artery. Subclavian artery insertion of IABP
149
Case 3 A 59-year-old man with a prior history of diabetes mellitus and peripheral vascular disease was hospitalised with gangrene of his left lower extremity. An emergent below the knee amputation was complicated by an inferior wall myocardial infarction and congestive heart failure. Cardiac catheterisation performed through a left brachial approach demonstrated a LVEF of 25% and severe three vessel coronary disease. An aortogram showed complete infrarenal occlusion. The patient underwent CABG surgery with saphenous vein grafts to the posterior descending artery, diagonal and marginal branches and a left thoracic artery graft to the left anterior descending coronary artery. An IABP was inserted through the right subclavian artery preoperatively and successfully removed after surgery. The patient had an uneventful postoperative course.
Case 4
Figure 1. Diagram of subclavian insertion of an IABP. Synthetic graft anastomosed end to side to the right subclavian artery (arrow). Intra-aortic balloon pump placed through the graft into the descending thoracic aorta (arrow-head).
transthoracic echocardiogram revealed a left ventricular ejection fraction (LVEF) of 25% and severe mitral valve regurgitation due to a flail posterior leaflet. Cardiac catheterisation demonstrated a 90% diameter stenosis of the right coronary artery, 4+ mitral regurgitation and significant occlusive aortic disease. An IABP was placed through a left subclavian approach for circulatory support prior to the valvular surgery. The patient underwent mitral valve replacement surgery and coronary revascularisation with a saphenous vein graft to the right coronary artery. The IABP was successfully discontinued one day after surgery.
Case 2 A 75-year-old man with known critical calcific aortic stenosis, coronary artery and peripheral vascular disease was hospitalised for aortic valve replacement and CABG surgery. The LVEF was 30% on ventriculography. Because of the severe peripheral vascular disease and signs of left subclavian stenosis (the systolic blood pressure was 30 mm Hg lower in the left arm compared to the right arm), an IABP was placed through the right subclavian artery prior to cardiac surgery. Aortic valve replacement and CABG surgery were performed and the IABP was successfully removed on postoperative day 1. His hospital course was complicated by respiratory failure requiring prolonged mechanical ventilation and a tracheostomy. The patient was eventually transferred to a specialised facility for pulmonary rehabilitation.
A 72-year-old woman, who presented with cardiogenic shock due to an acute anterior wall myocardial infarction, underwent emergent cardiac catheterisation. The cardiac catheterisation, initially unsuccessful from a femoral approach, was performed through the left radial artery and revealed severe triple coronary vessel disease with a decreased LVEF. Significant stenosis of the distal aorta was demonstrated on aortography, precluding the retrograde insertion of an IABP. She underwent emergent CABG surgery. Because the patient remained in cardiogenic shock despite maximum inotropic support, an IABP was placed in the descending thoracic aorta via a left subclavian arterial approach. Her hospital course was complicated by acute renal failure and she died on postoperative day three.
Discussion The American College of Cardiology/American Heart Association guidelines suggest the use of IABP in patients with ST elevation myocardial infarction and cardiogenic shock unresponsive to pharmacological therapy, acute mitral regurgitation or ventricular septal defect, recurrent ischaemia or intractable ventricular arrhythmias with haemodynamic instability, and in patients with refractory pulmonary congestion.7 While the frequency of IABP use in cardiac surgical patients has increased over time,8–10 the decision of whether and when to use an IABP is often not clear. A recent review by Baskett et al. classified the evidence for the efficacy of IABP in cardiac surgical patients using a similar system to the ACC/AHA guidelines.8 Class I indications for the use of an IABP in the perioperative period were ongoing ischaemia or a LVEF <25% before non-elective or repeat CABG and the use of IABP if needed for weaning from cardiopulmonary bypass. Patients without ongoing ischemia who have low LVEF or left main disease or are undergoing procedures other than isolated CABG received a class II indication for the preoperative use of an IABP.
CASE REPORT
Heart Lung and Circulation 2006;15:148–150
150
Marcu et al. Intraaortic balloon pump insertion through the subclavian artery. Subclavian artery insertion of IABP
CASE REPORT
During the use of IABP complications such as limb ischaemia, bleeding, infection, balloon leak, stroke and death may arise. A registry study describing the trend of IABP use in cardiac surgery during the late 1990s10 showed an overall complication rate of 6.5% (with 2.1% major complications) compared to historical rates of up to 33%.8 The decrease in the rate of IABP related major complications such as severe limb ischaemia or bleeding requiring surgery over the last 10 years may be explained by the increased use of smaller size catheters, sheathless insertion, percutaneous approach and improved physician experience.9 Patients with severe peripheral vascular disease who require IABP support are not infrequently encountered in clinical practice. In such patients it is often impossible to pass even a guide-wire retrograde from the femoral artery, in which case an alternative approach is to place an IABP through the ascending aorta.11 This method requires a median sternotomy under general anaesthesia. Complications of ascending aortic IABP insertion such as graft infection, aberrant cannulation of the left subclavian artery, left coronary artery embolism, and inability to close the sternum due to mechanical tamponade have been described.11 It appears, however, that the insertion of an IABP in the ascending aorta is not associated with a significant increase in complications or mortality compared to femoral insertion when other comorbidities are considered.8,12 Subclavian arterial IABP insertion under local anaesthesia is easier and safer to perform and allows increased patient mobility. In deciding which subclavian artery to use for IABP access one has to consider the presence of signs and symptoms of subclavian stenosis (difference between blood pressure measurements in the arms, presence of vertebral steal syndrome or arm claudication), and if needed obtain a computed tomographic or magnetic resonance angiogram of the aortic arch vessels. If the left internal thoracic artery is to be used for CABG, one might consider placing the IABP through the right subclavian artery and avoid, at least in theory, interfering with the left thoracic artery blood flow. A subclavian IABP approach should be strongly considered in patients with severe left ventricular systolic
Heart Lung and Circulation 2006;15:148–150
dysfunction where an IABP is indicated and there is severe aorto-iliac atherosclerotic disease.
References 1. Maccioli GA, Lucas WJ, Norfleet EA. The intra-aortic balloon pump: a review. J Cardiothorac Anesth 1988;2:365–73. 2. Waksman R, Weiss AT, Gotsman MS, Hassin Y. Intra-aortic balloon counterpulsation improves survival in cardiogenic shock complicating acute myocardial infarction. Eur Heart J 1993;14:71–4. 3. Ohman EM, et al., The Randomized IABP Study Group. Use of aortic counterpulsation to sustain coronary artery patency during acute myocardial infarction. Results of a randomized trial. Circulation 1994;90(2):792–9. 4. Christenson JT, Buswell L, Velebit V, Maurice J, Simonet F, Schmuziger M. The intraaortic balloon pump for postcardiotomy heart failure. Experience with 169 intraaortic balloon pumps. Thorac Cardiovasc Surg 1995;43:129–33. 5. Mayer JH. Subclavian artery approach for insertion of intraaortic balloon. J Thorac Cardiovasc Surg 1978;76:61–3. 6. Rubenstein RB, Karhade NV. Supraclavicular subclavian technique of intra-aortic balloon insertion. J Vasc Surg 1984;1:577–8. 7. Antman EM, Anbe DT, Armstrong PW, Bates ER, Green LA, Hand M, et al. ACC/AHA guidelines for the management of patients with ST-elevation myocardial infarction: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Revise the 1999 Guidelines for the Management of patients with acute myocardial infarction). J Am Coll Cardiol 2004;44(3):E1–211. 8. Baskett RJ, Ghali WA, Maitland A, Hirsch GM. The intraaortic balloon pump in cardiac surgery. Ann Thorac Surg 2002;74(4):1276–87. 9. Elahi MM, Chetty GK, Kirke R, Azeem T, Hartshorne R, Spyt TJ. Complications related to intra-aortic balloon pump in cardiac surgery: a decade later. Eur J Vasc Endovasc Surg 2005;29(6):591–4. 10. Christenson JT, Cohen M, Ferguson 3rd JJ, Freedman RJ, Miller MF, Ohman EM, et al. Trends in intraaortic balloon counterpulsation complications and outcomes in cardiac surgery. Ann Thorac Surg 2002;74(4):1086–90. 11. Meldrum-Hanna WG, Deal CW, Ross DE. Complications of ascending aortic intraaortic balloon pump cannulation. Ann Thorac Surg 1985;40(3):241–4. 12. Hazelrigg S, Auer J, Seifert P. Experience in 100 transthoracic balloon pumps. Ann Thorac Surg 1992;54:528–32.