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Non-invasive Determination of Cardiac Output by the Inert Gas Rebreathing Method in a Patient With an Axial-flow Left-ventricular Assist Device
The Journal of Heart and Lung Transplantation Volume 28, Number 5
journal.1 This is always an important clinical problem given the diagnostic challenges and therapeutic dilemmas it presents. We would like to make an important correction and a few comments that we believe are important. On page 1160, second column, line 17, the word “concordant” is erroneously used. The invasive hemodynamic feature that characterizes constrictive pericarditis is the presence of ventricular interdependence, characterized by the discordant behavior of the left ventricular (LV) and right ventricular (RV) peak systolic pressure during respiration. In the presence of constrictive pericarditis, during inspiration there is an increase in RV filling until the constrictive process limits further RV expansion. This phenomenon will cause a dislocation of the interventricular septum toward the left ventricle, compromising proper LV filling. Although RV peak systolic pressure increases during inspiration, simultaneous recording of LV pressure will show a decrease in LV peak systolic pressure. This simultaneous, discordant change in RV and LV peak systolic pressure during respiration is the most specific hemodynamic characteristic of constrictive pericarditis. The Mayo Clinic group has published most of the studies utilizing a high-fidelity, micromanometer-tipped catheter in the invasive hemodynamic assessment of constrictive pericarditis versus restrictive myocardial disease.2 In a recent article, the same group proposed a new, invasive criterion for the diagnosis of constrictive pericarditis. Instead of using the aforementioned changes in RV and LV peak systolic pressure, they used the systolic area index, which takes into account the area under the RV and LV pressure curve during respiration. The systolic area index had a sensitivity of 97% and a specificity of 100% for the identification of patients with surgically proven constrictive pericarditis.3 It is important to mention that the validation of this hemodynamic technique for diagnosis of constrictive pericarditis was obtained with the use of high-fidelity, micromanometer-tipped catheters placed in the right and left ventricles, simultaneously. The use of diagnostic pigtail catheters with fluid-filled pressure systems available in most catheterization laboratories have not been validated for this indication. It is not unreasonable to speculate that the sensitivity and specificity of this technique with our routine cath lab tools may be significantly less accurate. Over the last few years, we have seen an increase in the use of proliferating signal inhibitors (PSIs) in the management of de novo heart transplant patients, particularly in the presence of renal dysfunction. However, there are also growing concerns regarding the incidence of rejection, infection and wound-healing issues with PSI utilization. In our program we have had a few clinical issues with
Letters to the Editor
533
post-transplant pericardial effusion requiring intervention in patients taking a PSI. Our preliminary data are sparse and inconclusive, but we wonder if the increased use of PSIs will contribute to an increase in the number of cases such as the one presented by Kumar et al. Eduardo R. Azevedo, MD Heather Ross, MD Diego Delgado, MD Department of Medicine University of Toronto Toronto, ON, Canada REFERENCES 1. Kumar R, Entrikin DW, Ntim WO, et al. Constrictive pericarditis after cardiac transplantation: a case report and literature review. J Heart Lung Transplant 2008;27:1158 – 61. 2. Hurrell DG, Nishimura RA, Higano ST, et al. Value of dynamic respiratory changes in left and right ventricular pressures for the diagnosis of constrictive pericarditis. Circulation 1996;93: 2007–13. 3. Talreja DR, Nishimura RA, Oh JK, et al. Constrictive pericarditis in the modern era: novel criteria for diagnosis in the cardiac catheterization laboratory. J Am Coll Cardiol 2008;51:315–9.
NON-INVASIVE DETERMINATION OF CARDIAC OUTPUT BY THE INERT GAS REBREATHING METHOD IN A PATIENT WITH AN AXIAL-FLOW LEFT-VENTRICULAR ASSIST DEVICE To the Editor: Cardiac output (CO) is an important parameter in heart failure therapy. Usually, optimal adjustment of the axialflow left ventricular assist device (LVAD) is performed by echocardiography and by estimation of CO based on a computerized algorithm incorporated into the device. The inert gas rebreathing method (IGR), using the Innocor device, has recently been proposed as a feasible, noninvasive method for the determination of CO, based on the Fick principle. The Innocor device uses the soluble nitrous oxide and the insoluble sulfur hexafluoride as test gases, with their concentrations measured online by a photo-magnetoacoustic gas analyzer.1 In a 67-year-old man receiving a HeartMate II (Thoratec Corp., Pleasanton, CA) for destination therapy, we assessed the feasibility of determining CO by IGR. We increased the rotation speed of the device bidirectionally in steps of 400, from 8,600 to 11,400 rotations per minute (rpm), and determined CO simultaneously by three different methods at each level. CO by echocardiography was measured using the Doppler-derived continuity equation. For this purpose, Doppler-derived stroke volume was averaged from three consecutive beats and multiplied by the heart rate. According to recommendations by Damgaard et al,2 the rebreathing maneuver of the IGR was started after normal expiration at a rate of 20 breaths/min. Between repeated
534
Letters to the Editor
The Journal of Heart and Lung Transplantation May 2009
Table 1. Hemodynamic Parameters rpm 8,600 9,000 9,400 9,800 10,200 10,600 11,000 11,400
COHeartMate 4.5 5.0 5.8 6.1 6.0 6.3 6.3 6.5
COIGR 4.6 4.5 5.0 5.2 5.1 5.6 5.9 5.5
COEcho 4.6 4.7 5.0 5.3 5.3 5.4 5.8 5.7
IGR and echocardiographic measurements are both feasible in detecting the proper rotation speed for optimal CO. An LVAD delivery rate in excess of the patient’s individual optimum, did not result in a further increase in CO. Our echocardiographic observations further suggest that setting the device flow too high will pump the left ventricle dry and prevent it from generating forward flow through the native aortic valve.3
measurements, an interval of 5 minutes was strictly adhered to in order to guarantee complete elimination of the test gases. The volume of the rebreathing bag was calculated by the IGR system as a function of the patient’s height and age. Estimates of CO based on the HeartMate II computerized algorithm were also recorded at each step and constituted the third method of measuring CO. The investigators were blinded to the results obtained by either echocardiography, IGR or device-based estimates of CO. Hemodynamic parameters are shown in Table 1. There was a significant correlation between CO values as determined by echocardiography and the devicebased algorithm (r ⫽ 0.91, p ⬍ 0.01) or IGR (r ⫽ 0.96,
p ⬍ 0.001). We also found a significant correlation between CO values determined by IGR and the devicebased algorithm (r ⫽ 0.88, p ⬍ 0.01). An increasing rotation speed led to a linear increase in CO for rpm values between 8,600 and 9,800. A further increase resulted only in a small effect on CO, reaching a maximum value of 6.5 liters/min with the device-based algorithm, 5.8 with echocardiography and 5.9 liters/min with IGR, respectively. The patient’s heart rate remained unchanged at 80 beats/min with mean arterial blood pressure rising significantly from 80 to 100 mm Hg. Joachim Saur, MD Frederik Trinkmann Ursula Hoffmann, MD Jens J. Kaden, MD Dariusch Haghi, MD First Department of Medicine University Hospital Mannheim, Germany REFERENCES 1. Clemensen P, Christensen P, Norsk P, et al. A modified photo- and magnetoacoustic multigas analyzer applied in gas exchange measurements. J Appl Physiol 1994;76:2832–9. 2. Damgaard M, Norsk P. Effects of ventilation on cardiac output determined by inert gas rebreathing. Clin Physiol Funct Imag 2005;25:142–7. 3. Haghi D, Suselbeck T, Saur J. Aortic regurgitation during left ventricular assist device support. J Heart Lung Transplant 2007; 26:1220 –1.
journal.1 This is always an important clinical problem given the diagnostic challenges and therapeutic dilemmas it presents. We would like to make an important correction and a few comments that we believe are important. On page 1160, second column, line 17, the word “concordant” is erroneously used. The invasive hemodynamic feature that characterizes constrictive pericarditis is the presence of ventricular interdependence, characterized by the discordant behavior of the left ventricular (LV) and right ventricular (RV) peak systolic pressure during respiration. In the presence of constrictive pericarditis, during inspiration there is an increase in RV filling until the constrictive process limits further RV expansion. This phenomenon will cause a dislocation of the interventricular septum toward the left ventricle, compromising proper LV filling. Although RV peak systolic pressure increases during inspiration, simultaneous recording of LV pressure will show a decrease in LV peak systolic pressure. This simultaneous, discordant change in RV and LV peak systolic pressure during respiration is the most specific hemodynamic characteristic of constrictive pericarditis. The Mayo Clinic group has published most of the studies utilizing a high-fidelity, micromanometer-tipped catheter in the invasive hemodynamic assessment of constrictive pericarditis versus restrictive myocardial disease.2 In a recent article, the same group proposed a new, invasive criterion for the diagnosis of constrictive pericarditis. Instead of using the aforementioned changes in RV and LV peak systolic pressure, they used the systolic area index, which takes into account the area under the RV and LV pressure curve during respiration. The systolic area index had a sensitivity of 97% and a specificity of 100% for the identification of patients with surgically proven constrictive pericarditis.3 It is important to mention that the validation of this hemodynamic technique for diagnosis of constrictive pericarditis was obtained with the use of high-fidelity, micromanometer-tipped catheters placed in the right and left ventricles, simultaneously. The use of diagnostic pigtail catheters with fluid-filled pressure systems available in most catheterization laboratories have not been validated for this indication. It is not unreasonable to speculate that the sensitivity and specificity of this technique with our routine cath lab tools may be significantly less accurate. Over the last few years, we have seen an increase in the use of proliferating signal inhibitors (PSIs) in the management of de novo heart transplant patients, particularly in the presence of renal dysfunction. However, there are also growing concerns regarding the incidence of rejection, infection and wound-healing issues with PSI utilization. In our program we have had a few clinical issues with
Letters to the Editor
533
post-transplant pericardial effusion requiring intervention in patients taking a PSI. Our preliminary data are sparse and inconclusive, but we wonder if the increased use of PSIs will contribute to an increase in the number of cases such as the one presented by Kumar et al. Eduardo R. Azevedo, MD Heather Ross, MD Diego Delgado, MD Department of Medicine University of Toronto Toronto, ON, Canada REFERENCES 1. Kumar R, Entrikin DW, Ntim WO, et al. Constrictive pericarditis after cardiac transplantation: a case report and literature review. J Heart Lung Transplant 2008;27:1158 – 61. 2. Hurrell DG, Nishimura RA, Higano ST, et al. Value of dynamic respiratory changes in left and right ventricular pressures for the diagnosis of constrictive pericarditis. Circulation 1996;93: 2007–13. 3. Talreja DR, Nishimura RA, Oh JK, et al. Constrictive pericarditis in the modern era: novel criteria for diagnosis in the cardiac catheterization laboratory. J Am Coll Cardiol 2008;51:315–9.
NON-INVASIVE DETERMINATION OF CARDIAC OUTPUT BY THE INERT GAS REBREATHING METHOD IN A PATIENT WITH AN AXIAL-FLOW LEFT-VENTRICULAR ASSIST DEVICE To the Editor: Cardiac output (CO) is an important parameter in heart failure therapy. Usually, optimal adjustment of the axialflow left ventricular assist device (LVAD) is performed by echocardiography and by estimation of CO based on a computerized algorithm incorporated into the device. The inert gas rebreathing method (IGR), using the Innocor device, has recently been proposed as a feasible, noninvasive method for the determination of CO, based on the Fick principle. The Innocor device uses the soluble nitrous oxide and the insoluble sulfur hexafluoride as test gases, with their concentrations measured online by a photo-magnetoacoustic gas analyzer.1 In a 67-year-old man receiving a HeartMate II (Thoratec Corp., Pleasanton, CA) for destination therapy, we assessed the feasibility of determining CO by IGR. We increased the rotation speed of the device bidirectionally in steps of 400, from 8,600 to 11,400 rotations per minute (rpm), and determined CO simultaneously by three different methods at each level. CO by echocardiography was measured using the Doppler-derived continuity equation. For this purpose, Doppler-derived stroke volume was averaged from three consecutive beats and multiplied by the heart rate. According to recommendations by Damgaard et al,2 the rebreathing maneuver of the IGR was started after normal expiration at a rate of 20 breaths/min. Between repeated
534
Letters to the Editor
The Journal of Heart and Lung Transplantation May 2009
Table 1. Hemodynamic Parameters rpm 8,600 9,000 9,400 9,800 10,200 10,600 11,000 11,400
COHeartMate 4.5 5.0 5.8 6.1 6.0 6.3 6.3 6.5
COIGR 4.6 4.5 5.0 5.2 5.1 5.6 5.9 5.5
COEcho 4.6 4.7 5.0 5.3 5.3 5.4 5.8 5.7
IGR and echocardiographic measurements are both feasible in detecting the proper rotation speed for optimal CO. An LVAD delivery rate in excess of the patient’s individual optimum, did not result in a further increase in CO. Our echocardiographic observations further suggest that setting the device flow too high will pump the left ventricle dry and prevent it from generating forward flow through the native aortic valve.3
measurements, an interval of 5 minutes was strictly adhered to in order to guarantee complete elimination of the test gases. The volume of the rebreathing bag was calculated by the IGR system as a function of the patient’s height and age. Estimates of CO based on the HeartMate II computerized algorithm were also recorded at each step and constituted the third method of measuring CO. The investigators were blinded to the results obtained by either echocardiography, IGR or device-based estimates of CO. Hemodynamic parameters are shown in Table 1. There was a significant correlation between CO values as determined by echocardiography and the devicebased algorithm (r ⫽ 0.91, p ⬍ 0.01) or IGR (r ⫽ 0.96,
p ⬍ 0.001). We also found a significant correlation between CO values determined by IGR and the devicebased algorithm (r ⫽ 0.88, p ⬍ 0.01). An increasing rotation speed led to a linear increase in CO for rpm values between 8,600 and 9,800. A further increase resulted only in a small effect on CO, reaching a maximum value of 6.5 liters/min with the device-based algorithm, 5.8 with echocardiography and 5.9 liters/min with IGR, respectively. The patient’s heart rate remained unchanged at 80 beats/min with mean arterial blood pressure rising significantly from 80 to 100 mm Hg. Joachim Saur, MD Frederik Trinkmann Ursula Hoffmann, MD Jens J. Kaden, MD Dariusch Haghi, MD First Department of Medicine University Hospital Mannheim, Germany REFERENCES 1. Clemensen P, Christensen P, Norsk P, et al. A modified photo- and magnetoacoustic multigas analyzer applied in gas exchange measurements. J Appl Physiol 1994;76:2832–9. 2. Damgaard M, Norsk P. Effects of ventilation on cardiac output determined by inert gas rebreathing. Clin Physiol Funct Imag 2005;25:142–7. 3. Haghi D, Suselbeck T, Saur J. Aortic regurgitation during left ventricular assist device support. J Heart Lung Transplant 2007; 26:1220 –1.