Changes
in Plasma
Atria1 Natriuretic Peptide Heart Transplantation
Concentration
During
Tetsuhiro Sakai, MD, Terry W. Latson, MD, Charles W. Whitten, MD, David N. O’Flaherty, MB, Dac Vu, MS Ill, Satya Krishnan, MS, James M. Lipton, PhD, and W. Steves Ring, MD Examination of changes in plasma atrial natriuretic peptide (ANP) concentrations during heart transplantation may provide important information about factors influencing plasma ANP in patients with severe heart failure. Serial changes in plasma ANP during heart transplantation, and atrial content of ANP in native and donor atria, were measured in 12 patients. Preoperative plasma ANP was elevated in all patients (387 f 77 pg/mL), whereas atrial content of ANP in native atria was reduced (0.36 f 0.082 Fg/mg protein). Preoperative plasma ANP did not correlate with hemodynamics, but was negatively correlated with creatinine clearance (r = -0.76, P < .Ol). lntraoperative plasma ANP prior to transplantation was strongly correlated with intraoperative plasma ANP after transplantation (r = 0.84, P < .OOl). Although postoperative plasma ANP was reduced from preoperative plasma ANP by 75%. these two measurements were also significantly correlated (r = 0.70, P < .02). Postoperative plasma ANP was not correlated with hemodynamics, but was negatively correlated with both creatinine clearance (r = -0.65, P < .05) and content of ANP in the native atria (r = -0.75, P < .Ol). Multiple linear regression analysis sug-
A
TRIAL natriuretic peptide (ANP) is a potent hormone with natriuretic, vasodilatory, and neuroregulatory actions.‘,? This hormone may play an important role in the regulation of blood pressure, blood volume, and sodium excretion. Plasma concentrations of ANP (plasma ANP) are elevated in patients with congestive heart failure (CHF).2-X The primary etiology of this increase in plasma ANP is thought to be increased atria1 secretion of ANP in response to atria1 stretch. However, several investigators have suggested that other factors may also play a role in the elevations in plasma ANP observed in patients with severe CHF. These factors include: (1) alterations in metabolic clearance; (2) cellular adaptations in atria1 myocytes to maximize ANP synthesis and secretion; and (3) recruitment of ventricular myocytes to synthesize additional ANP. Heart transplantation represents a unique clinical event during which hemodynamics, atria1 chamber size, and myocardial function are abruptly changed. Examinations of changes in plasma ANP during this event might provide additional insight into factors influencing plasma ANP. Strong correlations between pretransplant and posttransplant plasma ANP would provide important evidence that factors other than acute changes in hemodynamics and atria1 stretch play a significant role in determining plasma ANP. The goal of this study was to investigate these perioperative changes in plasma ANP in heart transplant patients. Possible correlations between plasma ANP and
From the Departments of Anesthesiology and Surgev, University of Texas Southwestern Medical Center at Dallas. Address reprint requests to Terry W. Latson, MD, CJ.T. Southwestern Medical Center, Department of Anesthesiology, 5323 Hany Hines Blvd, Dallas, TX 75235-8894. Copyright 0 I992 by W.B. Saunders Company 1053-077019210606-0009$03.00/O 686
Journalof
Cardiothoraoc
gested that up to 85% of the variability of early postoperative plasma ANP could be accounted for by the variability in these latter two parameters. The decrease in native atrial ANP content, in the context of elevated plasma ANP concentration, is consistent with prior animal studies suggesting that severe heart failure induces cellular adaptations favoring accelerated ANP synthesis and secretion (with resultant reduction in tissue content). The significant correlations between pretransplant and posttransplant measurements of plasma ANP suggest that factors that influence variability in plasma ANP between patients prior to heart transplantation remain important determinants of variability in plasma ANP in the first 24 hours after transplantation. These factors appear to be independent of the acute changes in atrial size and myocardial function that accompany heart transplantation, and may involve more slowly adapting biologic mechanisms regulating ANP synthesis, secretion, and clearance in patients with severe heart failure. Copyright 0 1992 by W. B. Saunders Company KEY WORDS: heart surgery, anesthesia, atrium, hormone
tissue concentrations of ANP in both the native and donor atria were also examined. METHODS After institutional Review Board approval, 12 heart transplant patients ranging in age from 43 to 65 years were studied. Informed written consent was obtained from all patients. The patients were sedated with midazolam, 0.03 to 0.05 mgikg, IV, upon arrival in the operating room. Following insertion of a radial artery catheter. anesthesia was induced with sufentanil, 1.5 to 8.5 kg/kg, and/or etomidate, 0.1 to 0.25 mgikg, along with vecuronium, 0.14 to 0. IX mgikg, for muscle relaxation. A pulmonary artery catheter (PAC) was inserted in all patients after induction of anesthesia. Anesthesia was maintained with sufentanil, supplemental isoflurane (0.2% to I%), and muscle relaxants (vecuronium or pancuronium). Ventilation was mechanically controlled using a rate of X to 10 breathsimin and a tidal volume of approximately 10 ml/kg. adjusted to maintain PaC02 at 35 + 5 mmHg. Blood samples for the measurements of plasma ANP levels were drawn from the arterial catheter at the following sampling points: Pl) before induction; P2) after induction; P3) after incision; P4) immediately before cardiopulmonary bypass (CPB); P.5) on CPB, immediately before removal of the old heart: P6) on CPB. immediately before reperfusion of the new heart; P7) on CPB. immediately before weaning from CPB; P8) 10 minutes after discontinuing CPB; P9) 60 minutes after discontinuing CPB; PlO) 24 hours postoperatively. Measurements of central venous pressure (CVP) and pulmonary artery pressure (PAP) were recorded at sample points P3 (the first sample point after insertion of the PAC), P8 (first sample point after CPB), and PlO (first postoperative day). All 4 mL samples of arterial blood were collected in chilled tubes containing EDTA and 100 FL of aprotinin (0.67 trypsin inhibiting units per mL of blood). The samples were immediately placed in ice and centrifuged within 10 minutes (3,000 rpm, 4”C, 15 minutes). After transferral of the platelet-rich plasma to polypropylene Eppendorf tubes (Brinkman. Westbury, NY), the samples were centrifuged in a microfuge for 1 minute. The plasma was stored at and
Vascular Anesthesia,
Vol6, No 6 (December),
1992: pp 686-691
PLASMA ANP AND HEART TRANSPLANTATION
-70°C until the assay was performed. Immunoreactive ANP was measured by radioimmunoassay (Peninsula Laboratories, Belmont, CA). Cross-reactivities of this assay with a-hANP, P-hANP, and r-hANP are lOO%, 94%, and 40%, respectively. Interassay variation with this technique was between 5% and 10%. Atria1 tissue samples were obtained from the nonauricular free wall of the right atrium for both native (n = 11) and donor (n = 8) hearts. In donor hearts, this sample was taken when the excised heart was brought into the operating room (donor hearts were perfused with cardioplegia solution before excision, and then immediately placed in iced saline). For the native heart, this sample was taken within minutes after the native heart (ie, both ventricles and approximately 25% of the atria) was excised. Tissue samples were immediately placed in iced saline, and subsequently frozen in liquid nitrogen and stored at -70°C until assays were performed. For measurements of ANP tissue concentration, the tissue samples were placed in an ice-cold solution of 0.1 mol/L acetic acid with 0.02N HCI and homogenized with a Polytron (VirTishear, Virtis Co, Gardiner, NY) for six 30-second intervals.9 Tissue homogenates were then sonicated for three 20-second intervals using a Virsonic 50 (Virtis Co). ANP in tissue homogenates was then measured using the same radioimmunoassay used for plasma ANP. ANP concentrations are reported as microgram of ANP per milligram of protein. Total protein was assessed by comparing the optical density of dyed tissue homogenates with the density of known standards (Biorad Laboratories, Richmond, CA). Significance of changes in plasma ANP measured at different sample times was assessed with the Wilcoxon signed-ranks test. Correlations between plasma ANP at different sample times, and between tissue ANP and plasma ANP, were assessed using least squares linear regression. The significance of differences in tissue concentrations of ANP in native and donor atria was assessed using the Mann-Whitney II test. For all statistical comparisons, P values less than 0.05 were considered significant. All values are reported as mean 2 SEM. RESULTS
Preinduction plasma ANP (387 ? 77 pg/mL) was elevated in all patients relative to normal values for this assay technique (10 to 50 pg/mL). However, there was considerable variation among patients (range, 177 to 940 pg/mL). No significant correlation was found between plasma ANP and hemodynamics at any of the three sample times for which simultaneous hemodynamic measurements were recorded (P3, P8, PlO). Similarly, there was no correlation between preinduction plasma ANP and hemodynamic parameters (CVP, PAP, pulmonary capillary wedge pressure [PCWP], cardiac index) recorded during prior cardiac catheterization. However, there was a significant negative correlation between preinduction plasma ANP and creatinine clearance (r = -0.76, P < .Ol; Fig 1). This correlation between creatinine clearance and plasma ANP was also present in the postoperative period (r = -0.65, P < .05). There were clear changes in plasma ANP at certain points during transplant surgery (Fig 2). Although there was no significant change in plasma ANP immediately after induction (Pl v P2), there was an approximate 35% decrease during maintenance of anesthesia prior to CPB (P3 and P4). With onset of CPB (P5), plasma ANP decreased to 23% of control level. After excision of the native heart, plasma ANP decreased to only 4% of control
PreTransplant Plasma ANP
I-=-0.76 p
in Plasma
Atria1 Natriuretic Peptide Heart Transplantation
Concentration
During
Tetsuhiro Sakai, MD, Terry W. Latson, MD, Charles W. Whitten, MD, David N. O’Flaherty, MB, Dac Vu, MS Ill, Satya Krishnan, MS, James M. Lipton, PhD, and W. Steves Ring, MD Examination of changes in plasma atrial natriuretic peptide (ANP) concentrations during heart transplantation may provide important information about factors influencing plasma ANP in patients with severe heart failure. Serial changes in plasma ANP during heart transplantation, and atrial content of ANP in native and donor atria, were measured in 12 patients. Preoperative plasma ANP was elevated in all patients (387 f 77 pg/mL), whereas atrial content of ANP in native atria was reduced (0.36 f 0.082 Fg/mg protein). Preoperative plasma ANP did not correlate with hemodynamics, but was negatively correlated with creatinine clearance (r = -0.76, P < .Ol). lntraoperative plasma ANP prior to transplantation was strongly correlated with intraoperative plasma ANP after transplantation (r = 0.84, P < .OOl). Although postoperative plasma ANP was reduced from preoperative plasma ANP by 75%. these two measurements were also significantly correlated (r = 0.70, P < .02). Postoperative plasma ANP was not correlated with hemodynamics, but was negatively correlated with both creatinine clearance (r = -0.65, P < .05) and content of ANP in the native atria (r = -0.75, P < .Ol). Multiple linear regression analysis sug-
A
TRIAL natriuretic peptide (ANP) is a potent hormone with natriuretic, vasodilatory, and neuroregulatory actions.‘,? This hormone may play an important role in the regulation of blood pressure, blood volume, and sodium excretion. Plasma concentrations of ANP (plasma ANP) are elevated in patients with congestive heart failure (CHF).2-X The primary etiology of this increase in plasma ANP is thought to be increased atria1 secretion of ANP in response to atria1 stretch. However, several investigators have suggested that other factors may also play a role in the elevations in plasma ANP observed in patients with severe CHF. These factors include: (1) alterations in metabolic clearance; (2) cellular adaptations in atria1 myocytes to maximize ANP synthesis and secretion; and (3) recruitment of ventricular myocytes to synthesize additional ANP. Heart transplantation represents a unique clinical event during which hemodynamics, atria1 chamber size, and myocardial function are abruptly changed. Examinations of changes in plasma ANP during this event might provide additional insight into factors influencing plasma ANP. Strong correlations between pretransplant and posttransplant plasma ANP would provide important evidence that factors other than acute changes in hemodynamics and atria1 stretch play a significant role in determining plasma ANP. The goal of this study was to investigate these perioperative changes in plasma ANP in heart transplant patients. Possible correlations between plasma ANP and
From the Departments of Anesthesiology and Surgev, University of Texas Southwestern Medical Center at Dallas. Address reprint requests to Terry W. Latson, MD, CJ.T. Southwestern Medical Center, Department of Anesthesiology, 5323 Hany Hines Blvd, Dallas, TX 75235-8894. Copyright 0 I992 by W.B. Saunders Company 1053-077019210606-0009$03.00/O 686
Journalof
Cardiothoraoc
gested that up to 85% of the variability of early postoperative plasma ANP could be accounted for by the variability in these latter two parameters. The decrease in native atrial ANP content, in the context of elevated plasma ANP concentration, is consistent with prior animal studies suggesting that severe heart failure induces cellular adaptations favoring accelerated ANP synthesis and secretion (with resultant reduction in tissue content). The significant correlations between pretransplant and posttransplant measurements of plasma ANP suggest that factors that influence variability in plasma ANP between patients prior to heart transplantation remain important determinants of variability in plasma ANP in the first 24 hours after transplantation. These factors appear to be independent of the acute changes in atrial size and myocardial function that accompany heart transplantation, and may involve more slowly adapting biologic mechanisms regulating ANP synthesis, secretion, and clearance in patients with severe heart failure. Copyright 0 1992 by W. B. Saunders Company KEY WORDS: heart surgery, anesthesia, atrium, hormone
tissue concentrations of ANP in both the native and donor atria were also examined. METHODS After institutional Review Board approval, 12 heart transplant patients ranging in age from 43 to 65 years were studied. Informed written consent was obtained from all patients. The patients were sedated with midazolam, 0.03 to 0.05 mgikg, IV, upon arrival in the operating room. Following insertion of a radial artery catheter. anesthesia was induced with sufentanil, 1.5 to 8.5 kg/kg, and/or etomidate, 0.1 to 0.25 mgikg, along with vecuronium, 0.14 to 0. IX mgikg, for muscle relaxation. A pulmonary artery catheter (PAC) was inserted in all patients after induction of anesthesia. Anesthesia was maintained with sufentanil, supplemental isoflurane (0.2% to I%), and muscle relaxants (vecuronium or pancuronium). Ventilation was mechanically controlled using a rate of X to 10 breathsimin and a tidal volume of approximately 10 ml/kg. adjusted to maintain PaC02 at 35 + 5 mmHg. Blood samples for the measurements of plasma ANP levels were drawn from the arterial catheter at the following sampling points: Pl) before induction; P2) after induction; P3) after incision; P4) immediately before cardiopulmonary bypass (CPB); P.5) on CPB, immediately before removal of the old heart: P6) on CPB. immediately before reperfusion of the new heart; P7) on CPB. immediately before weaning from CPB; P8) 10 minutes after discontinuing CPB; P9) 60 minutes after discontinuing CPB; PlO) 24 hours postoperatively. Measurements of central venous pressure (CVP) and pulmonary artery pressure (PAP) were recorded at sample points P3 (the first sample point after insertion of the PAC), P8 (first sample point after CPB), and PlO (first postoperative day). All 4 mL samples of arterial blood were collected in chilled tubes containing EDTA and 100 FL of aprotinin (0.67 trypsin inhibiting units per mL of blood). The samples were immediately placed in ice and centrifuged within 10 minutes (3,000 rpm, 4”C, 15 minutes). After transferral of the platelet-rich plasma to polypropylene Eppendorf tubes (Brinkman. Westbury, NY), the samples were centrifuged in a microfuge for 1 minute. The plasma was stored at and
Vascular Anesthesia,
Vol6, No 6 (December),
1992: pp 686-691
PLASMA ANP AND HEART TRANSPLANTATION
-70°C until the assay was performed. Immunoreactive ANP was measured by radioimmunoassay (Peninsula Laboratories, Belmont, CA). Cross-reactivities of this assay with a-hANP, P-hANP, and r-hANP are lOO%, 94%, and 40%, respectively. Interassay variation with this technique was between 5% and 10%. Atria1 tissue samples were obtained from the nonauricular free wall of the right atrium for both native (n = 11) and donor (n = 8) hearts. In donor hearts, this sample was taken when the excised heart was brought into the operating room (donor hearts were perfused with cardioplegia solution before excision, and then immediately placed in iced saline). For the native heart, this sample was taken within minutes after the native heart (ie, both ventricles and approximately 25% of the atria) was excised. Tissue samples were immediately placed in iced saline, and subsequently frozen in liquid nitrogen and stored at -70°C until assays were performed. For measurements of ANP tissue concentration, the tissue samples were placed in an ice-cold solution of 0.1 mol/L acetic acid with 0.02N HCI and homogenized with a Polytron (VirTishear, Virtis Co, Gardiner, NY) for six 30-second intervals.9 Tissue homogenates were then sonicated for three 20-second intervals using a Virsonic 50 (Virtis Co). ANP in tissue homogenates was then measured using the same radioimmunoassay used for plasma ANP. ANP concentrations are reported as microgram of ANP per milligram of protein. Total protein was assessed by comparing the optical density of dyed tissue homogenates with the density of known standards (Biorad Laboratories, Richmond, CA). Significance of changes in plasma ANP measured at different sample times was assessed with the Wilcoxon signed-ranks test. Correlations between plasma ANP at different sample times, and between tissue ANP and plasma ANP, were assessed using least squares linear regression. The significance of differences in tissue concentrations of ANP in native and donor atria was assessed using the Mann-Whitney II test. For all statistical comparisons, P values less than 0.05 were considered significant. All values are reported as mean 2 SEM. RESULTS
Preinduction plasma ANP (387 ? 77 pg/mL) was elevated in all patients relative to normal values for this assay technique (10 to 50 pg/mL). However, there was considerable variation among patients (range, 177 to 940 pg/mL). No significant correlation was found between plasma ANP and hemodynamics at any of the three sample times for which simultaneous hemodynamic measurements were recorded (P3, P8, PlO). Similarly, there was no correlation between preinduction plasma ANP and hemodynamic parameters (CVP, PAP, pulmonary capillary wedge pressure [PCWP], cardiac index) recorded during prior cardiac catheterization. However, there was a significant negative correlation between preinduction plasma ANP and creatinine clearance (r = -0.76, P < .Ol; Fig 1). This correlation between creatinine clearance and plasma ANP was also present in the postoperative period (r = -0.65, P < .05). There were clear changes in plasma ANP at certain points during transplant surgery (Fig 2). Although there was no significant change in plasma ANP immediately after induction (Pl v P2), there was an approximate 35% decrease during maintenance of anesthesia prior to CPB (P3 and P4). With onset of CPB (P5), plasma ANP decreased to 23% of control level. After excision of the native heart, plasma ANP decreased to only 4% of control
PreTransplant Plasma ANP
I-=-0.76 p
