Thyroid Hormone Treatment after Coronary-Artery Bypass Surgery
John D. Klemperer, M.D., Irwin Klein, M.D., Maureen Gomez, R.N., Robert E. Helm, M.D., Kaie Ojamaa, Ph.D., Stephen J. Thomas, M.D., O. Wayne Isom, M.D., and Karl Krieger, M.D.
Background Thyroid hormone has many effects on the cardiovascularsystem. During and after cardiopulmonary bypass, serum triiodothyronineconcentrations decline transiently, which may contribute topostoperative hemodynamic dysfunction. We investigated whetherthe perioperative administration of triiodothyronine (liothyroninesodium) enhances cardiovascular performance in high-risk patientsundergoing coronary-artery bypass surgery.
Methods We administered triiodothyronine or placebo to 142 patientswith coronary artery disease and depressed left ventricularfunction. The hormone was administered as an intravenous bolusof 0.8 µg per kilogram of body weight when the aorticcross-clamp was removed after the completion of bypass surgeryand then as an infusion of 0.113 µg per kilogram per hourfor six hours. Clinical and hemodynamic responses were seriallyrecorded, as was any need for inotropic or vasodilator drugs.
Results The patients' preoperative serum triiodothyronine concentrationswere normal (mean [±SD] value, 81±22 ng per deciliter[1.2±0.3 nmol per liter]), and they decreased by 40 percent(P<0.001) 30 minutes after the onset of cardiopulmonary bypass.The concentrations in patients given intravenous triiodothyroninebecame supranormal and were significantly higher than thosein patients given placebo (P<0.001). However, the concentrationswere once again similar in the two groups 24 hours after surgery.The mean postoperative cardiac index was higher in the triiodothyroninegroup (2.97±0.72 vs. 2.67±0.61 liters per minuteper square meter of body-surface area, P = 0.007), and systemicvascular resistance was lower (1073±314 vs. 1235±387dyn · sec · cm-5, P = 0.003). The two groups didnot differ significantly in the incidence of arrhythmia or theneed for therapy with inotropic and vasodilator drugs duringthe 24 hours after surgery, or in perioperative mortality andmorbidity.
Conclusions Raising serum triiodothyronine concentrations inpatients undergoing coronary-artery bypass surgery increasescardiac output and lowers systemic vascular resistance but doesnot change outcome or alter the need for standard postoperativetherapy.
Poor cardiac performance is a major cause of morbidity and deathin patients who undergo open-heart surgery, especially olderpatients and those with extensive disease or poor ventricularfunction.1 Physicians therefore are challenged to improve perioperativemanagement. Because of recent evidence that cardiopulmonarybypass results in altered thyroid hormone metabolism,2,3 interesthas focused on the relation between decreased serum triiodothyronineconcentrations and hemodynamic variables after cardiopulmonarybypass.4 There are similarities between hypothyroid patientsand those undergoing cardiac surgery with respect to both serumtriiodothyronine concentrations and decreased cardiac contractilityand elevated peripheral vascular resistance5,6; prior studieshave suggested that perioperative triiodothyronine supplementationmay improve outcome in patients with postoperative cardiovasculardysfunction.7,8 We now report the results of a trial in whichtriiodothyronine (liothyronine sodium) was administered to high-riskpatients undergoing coronary-artery bypass surgery.
Methods
Enrollment of Patients
We enrolled patients who underwent coronary-artery bypass surgerybetween April 1994 and February 1995 at New York HospitalCornellUniversity Medical Center in New York City. Patients under 85years of age, of either sex, were eligible if their ejectionfractions had been 40 percent or less during cardiac catheterizationwithin the preceding two months. Criteria for exclusion includeda planned concomitant valve procedure, a history of thyroiddisease or thyroid hormone therapy, treatment with amiodarone,or ongoing inotropic support or use of an intraaortic balloonpump at the time of surgery. The protocol was approved by theinstitution's Committee on Human Rights in Research, and allpatients gave informed consent.
Study Design
Immediately before surgery, the patients were randomly assignedto receive either triiodothyronine or placebo and were stratifiedaccording to their preoperative ejection fractions (less than25 percent or 25 to 40 percent). All physicians and nurses involvedin the patients' care were unaware of the treatment assignments,and with the exception of administration of the study drug,care during and after surgery did not differ between the twogroups. Patients assigned to triiodothyronine received an intravenousbolus of 0.8 µg per kilogram of body weight (Triostat,SmithKline Beecham Pharmaceuticals, Philadelphia), given fortwo minutes at the time of removal of the aortic cross-clamp;an intravenous infusion of 0.113 µg per kilogram per hourfor six hours; and a tapered final dose, decreased by 50 percenteach hour and then stopped. The patients in the placebo groupreceived 5 percent dextrose solution at the same infusion rates.Samples of arterial blood, for determination of serum triiodothyronineconcentrations, were drawn after the induction of anesthesia(base line), 30 minutes after the start of cardiopulmonary bypass,30 minutes and 6 hours after the infusion of the study drugbegan, and, in the last 22 patients enrolled, 15 hours afterthe end of the infusion. Serum thyroxine and thyrotropin concentrationswere measured at base line. Serum thyroxine and triiodothyronineconcentrations were determined by standard radioimmunoassays,and serum thyrotropin concentrations were measured by immunofluorescence.The coefficients of variation for each assay were less than5 percent, and all samples from an individual patient were analyzedsimultaneously.
Surgery and Anesthesia
The operation was performed by a group of six cardiothoracicsurgeons using a standardized protocol for anesthesia and surgery.All the patients had invasive hemodynamic monitoring. Anesthesiawas induced with thiopental (1 to 2 mg per kilogram) and fentanyl(25 µg per kilogram) and was maintained with a combinationof fentanyl and midazolam or isoflurane. Pancuronium was administeredfor muscle relaxation.
Cardiopulmonary bypass was performed with aortic and right atrialcannulation, priming with an asanguineous solution, membraneoxygenation, and nonpulsatile flow. Mean arterial pressure wasmaintained between 55 and 65 mm Hg. Moderate hypothermia (bladdertemperature, 30 to 32°C) was routinely induced. Cardioplegicarrest was produced by the initial administration of a cold-blood,high-potassium solution and maintained with additional dosesadministered at approximately 20-minute intervals.
After grafting, the patients were rewarmed to 36°C and separatedfrom cardiopulmonary bypass by the gradual reduction of venousreturn to the bypass circuit. Intravenous inotropic support,with either epinephrine (2 to 4 µg per minute) or dobutamine(333 to 500 µg per minute), was initiated if poor cardiaccontractility or ventricular distension became obvious duringseparation or if the cardiac index was less than 2.1 litersper minute per square meter. An additional supportive agent(amrinone) was given or an intraaortic balloon pump was putin place if initial therapy was inadequate. Electric pacingwas instituted when needed to maintain a heart rate above 70beats per minute.
Postoperative Management
The patients were continuously monitored in a cardiothoracicintensive care unit. The cardiac index was maintained above2.1 liters per minute per square meter by the administrationof epinephrine and dobutamine. Vasodilator (sodium nitroprusside)and vasopressor (norepinephrine) drugs were administered asneeded to maintain arterial systolic blood pressure between90 and 140 mm Hg. Sustained and nonsustained ventricular tachycardiaand premature contractions that were more frequent than sixper minute or multifocal were treated with lidocaine. For eachpatient, the total doses of the individual inotropic and vasodilatordrugs administered, in micrograms per kilogram, were recordedduring the six-hour period of study-drug infusion, and the meantotal dose was calculated for all the patients who requiredsupport. Patients were weaned from mechanical ventilation whenthey were hemodynamically stable and alert, and they were usuallydischarged from the cardiothoracic intensive care unit afterextubation and the discontinuation of all vasoactive-drug infusions.
Hemodynamic Measurements
Base-line hemodynamic measurements (heart rate, mean arterialpressure, central venous pressure, and pulmonary-capillary wedgepressure) were recorded in the operating room before the startof surgery and then 2, 4, 6, 12, and 16 hours after removalof the aortic cross-clamp. Mixed venous oxygen saturation wasdetermined by standard blood gas analysis of pulmonary arterial-bloodsamples. Cardiac output the average of three measurements was determined by thermodilution. Derived measurementsincluded the cardiac index (cardiac output divided by body-surfacearea) and systemic vascular resistance, calculated as (meanarterial pressure minus central venous pressure times 80) dividedby cardiac output.
Measures of Clinical Outcome
Data on clinical outcome, including the need for and quantityof inotropic and vasodilator drugs, were obtained from flowsheets from the intensive care unit and from the patients' medicalrecords by a research assistant who was unaware of the treatmentassignments. Cardiac rhythm was monitored continuously in theintensive care unit with bedside monitors and, after discharge,with telemetry. Twelve-lead electrocardiograms were obtainedimmediately after the operations and on the first three morningsafter surgery. Supraventricular and ventricular arrhythmias,and their treatment, were documented by the nurses. All physicians'notes were reviewed to determine the incidence of postoperativecomplications. Postoperative mortality was defined as the rateof death during hospitalization or within 30 days after surgery.Major morbid events were defined as adverse events that prolongedthe patient's postoperative stay in the intensive care unitor the hospital or that led to clinical deterioration.
Statistical Analysis
All analyses were performed on an intention-to-treat basis.All enrolled patients were randomized, and none were excludedfrom the analysis. The demographic, base-line, and one-timeoutcome variables in the two groups were compared by two-samplet-test. Categorical variables were compared by chi-square testor, where applicable, Fisher's exact test. The values for continuousoutcome variables at different points in time were comparedby repeated-measures analysis of variance. We also used repeated-measuresanalysis to compare binary outcomes between groups at differentpoints. Since several analyses were performed, a Bonferronicorrection was made to minimize the possibility of a type Ierror. All statistical tests were two-sided. Statistical analysiswas performed with SAS software (Cary, N.C.).
Results
Study Population
The characteristics of the 142 patients with coronary arterydisease who were randomly assigned to receive triiodothyronineor placebo are shown in Table 1. There were no significant differencesbetween the two groups with respect to any of the characteristicslisted.
Table 1. Preoperative Characteristics of Patients Undergoing Coronary-Artery Bypass Surgery and Intraoperative Data, According to Treatment Group.
Administration of Triiodothyronine
In both groups, the mean serum triiodothyronine concentrationwas in the low-normal range before the start of surgery andhad decreased significantly by approximately 40 percent 30 minutes after the start of cardiopulmonary bypass(Figure 1). In the placebo group, the concentrations remainedlow throughout the 24-hour period after removal of the cross-clamp.In the triiodothyronine group, they increased quickly to wellabove normal and remained high throughout the drug infusion.By the end of 24 hours the concentrations had returned to thepreoperative range.
Figure 1. Mean (±SE) Serum Triiodothyronine Concentrations in Patients Who Received Triiodothyronine or Placebo during Coronary-Artery Bypass Surgery.
Base-line serum samples were drawn in the operating room after the induction of anesthesia. Zero denotes the time when the aortic cross-clamp was removed and infusion of the study drug was begun. At 24 hours, serum triiodothyronine was measured in 11 patients in each study group. To convert values for triiodothyronine to nanomoles per liter, multiply by 0.015. Asterisks indicate P<0.001 for the comparison with the base-line value. CPB denotes cardiopulmonary bypass.
In both groups, the occurrence of at least one episode of supraventriculararrhythmia, including sinus tachycardia, was common. Duringthe first 6 hours after removal of the cross-clamp, 71 percentof the treated group and 66 percent of the placebo group hadsuch arrhythmias; in the next 18 hours the proportions were40 percent and 35 percent, respectively. Similar numbers ofpatients in each group received pharmacologic treatment (39percent and 34 percent, respectively) for these arrhythmias.The proportions of patients having any ventricular arrhythmiaduring the first 6 hours (42 percent in the triiodothyroninegroup and 44 percent in the placebo group) and the next 18 hours(24 percent and 24 percent) were also similar, as were the proportionstreated for ventricular arrhythmias (22 percent and 21 percent).
Therapy
There were no significant differences between groups in theinterventional support needed to separate patients from cardiopulmonarybypass. Three patients in the triiodothyronine group and sevenin the placebo group were returned to bypass because of hemodynamicinstability (P = 0.19). In each group, 56 percent of the patientsrequired inotropic support in order to be separated from bypass,including five patients in the triiodothyronine group and twoin the placebo group who were treated with counterpulsationby an intraaortic balloon pump. Eight patients in each groupreceived amrinone. Vasopressor drugs were administered to 70percent of the patients in the triiodothyronine group and to65 percent of those in the placebo group at the time of separationfrom bypass. The proportions of patients requiring pacing immediatelyafter removal of the cross-clamp were similar (50 percent inthe treated group and 49 percent in the placebo group).
The percentages of patients in each group who required postoperativetherapy with inotropic or vasodilator drugs were similar, aswere the doses given (Figure 2). During the six-hour periodof study-drug infusion, 37 patients in the triiodothyroninegroup received a mean (±SD) total dose of epinephrineof 9.1±7.3 µg per kilogram, as compared with 8.9±6.8µg per kilogram in 42 patients in the placebo group. Themean total (six-hour) dose of dobutamine administered to 14patients in the triiodothyronine group was 1708±1222µg per kilogram, as compared with 1402±980 µgper kilogram in 17 patients in the placebo group. Fifteen patientsin the triiodothyronine group required inotropic drugs for longerthan six hours, as compared with 21 patients in the placebogroup (P = 0.22). The mean total doses of sodium nitroprussidegiven over a period of six hours 5.2±4.5 µgper kilogram in 46 patients treated with triiodothyronine and6.5±5.6 µg per kilogram in 49 patients in the placebogroup were also similar. Fifteen percent of the patientsin the triiodothyronine group received norepinephrine duringthe study-drug infusion, as compared with 18 percent of thosein the placebo group (P = 0.64). The need for temporary cardiacpacing in the two groups did not differ significantly, eitherduring the first 6 hours (17 percent in the triiodothyroninegroup and 25 percent in the placebo group, P = 0.56) or thenext 18 hours (8 percent and 13 percent, P = 0.7).
Figure 2. Patients in the Triiodothyronine and Placebo Groups Who Required Inotropic or Vasodilator Drugs after Coronary-Artery Bypass Surgery.
Zero denotes the time when the aortic cross-clamp was removed and infusion of the study drug was begun. No statistically significant differences between groups were detected.
Hemodynamic Measurements
There were no significant differences between the groups inheart rate, mean arterial blood pressure, central venous pressure,pulmonary-capillary wedge pressure, cardiac output, cardiacindex, or systemic vascular resistance, either before the startof surgery or for most of these variables atany time after surgery (Table 2). Two hours after removal ofthe aortic cross-clamp, the cardiac index was higher in thetriiodothyronine group (2.88±0.73 liters per minute persquare meter, as compared with 2.61±0.60 liters per minuteper square meter in the placebo group), and it remained higherfour hours and six hours after removal (Figure 3). Because themean heart rates of the two groups were not significantly different,the increased cardiac output in the triiodothyronine group canbe attributed to an increase in stroke volume. Systemic vascularresistance was lower in the triiodothyronine group two hours(1151±369 vs. 1311±389 dyn · sec ·cm-5), four hours, and six hours after the start of infusion(Figure 3).
Table 2. Perioperative Hemodynamic Variables in the Triiodothyronine and Placebo Groups, According to Length of Time after Removal of the Aortic Cross-Clamp.
Figure 3. Cardiac Index and Systemic Vascular Resistance in the Triiodothyronine and Placebo Groups at Base Line and at Specified Intervals after Removal of the Aortic Cross-Clamp and Initiation of the Study-Drug Infusion.
Clinical Outcome
There was no difference between the two groups in the durationof postoperative mechanical ventilation, the length of stayin the intensive care unit or the hospital, or perioperativemortality from either cardiac causes or all causes. The incidenceof major postoperative complications was also similar in thetwo groups (Table 3).
Table 3. Postoperative Outcome and Complications in the Tri-iodothyronine and Placebo Groups.
Discussion
The low serum concentrations of triiodothyronine and impairedcardiovascular hemodynamics in patients with hypothyroidismand patients who have undergone cardiopulmonary bypass,9 alongwith recent evidence that triiodothyronine may have acute inotropicand vasodilative effects,4,10 provided a rationale for investigatingwhether the perioperative administration of triiodothyroninemight enhance cardiovascular performance. Experimental studieshave found improvement in post-ischemic cardiac function iftriiodothyronine is administered during reperfusion,11-13 andseveral, largely uncontrolled, studies of patients undergoingcoronary-artery bypass surgery7,8 or heart transplantation14have suggested that the administration of triiodothyronine decreasesperioperative mortality and the need for traditional inotropicagents. The results of our trial, however, do not support theseconclusions.
The mechanism by which serum triiodothyronine concentrationsdecrease in patients undergoing cardiac surgery is uncertain,but it is probably associated with hypothermia, hemodilution,and the activation of inflammatory-response mediators.5,15 Thedecrease in serum triiodothyronine concentrations in these patientsis considerably more rapid than that which occurs if the extrathyroidalconversion of thyroxine to triiodothyronine is inhibited, thusimplicating in the surgical patients an increasedvolume of distribution of triiodothyronine and an increase inits clearance as contributing factors. The half-life of thetriiodothyronine administered in our trial was about half aslong as normal,16 as estimated by the decline in serum triiodothyronineconcentrations between 6 and 24 hours after the start of infusion.Although not measured separately in this study, serum concentrationsof free triiodothyronine changed in parallel with those of totaltriiodothyronine in another study of patients undergoing bypasssurgery.4
It has been suggested that the changes in thyroid function thatoccur in nonthyroidal illness are an adaptive physiologic responseto illness.17-19 In our study, the administration of triiodothyronineprovided hemodynamic benefits similar to those that occur duringthe treatment of hypothyroidism.5 The administration of thyroidhormone to patients with underlying cardiac illness, however,has been associated with untoward responses.20 We noted no adversecardiovascular effects including any tachycardia orsupraventricular arrhythmia of the administration oftriiodothyronine in doses that raised serum triiodothyronineconcentrations transiently to well above the normal range. Althoughoxygen consumption was not measured, the enhanced cardiac performanceduring the administration of triiodothyronine, with no evidenceof increased ischemia, does not point to a harmful shift inthe relation between oxygen consumption and delivery. Experimentaldata have suggested that the acute inotropic effects of triiodothyronineafter myocardial ischemiareperfusion injury are accomplishedwithout oxygen wasting.12
Our results confirm that triiodothyronine can act acutely asa cardiotonic agent. It increases cardiac output while loweringsystemic vascular resistance. Whether the hemodynamic enhancementduring the administration of triiodothyronine was related primarilyto direct, positive cardiac inotropism or to peripheral vasodilationis not known. Thyroid hormone has an acute effect on vascularresistance.21 In our experience, the acute cardiovascular effectsof triiodothyronine appear moderate, as compared with thoseof commonly used -adrenergic agonists and nitrovasodilator drugs,and were not independently sufficient to ensure adequate postoperativehemodynamics in patients with preexisting impairment of ventricularfunction. Although a molecular basis for the acute effects oftriiodothyronine cannot be inferred from this study, the rapidityof those effects is consistent with putative nongenomic or extranuclearmechanisms.22 The potentiation of the effects of -adrenergicagonists, either endogenous or pharmaceutical, may also havea role in the process.23-25 Finally, triiodothyronine has directrelaxant effects on vascular smooth muscle.21
In this study the administration of triiodothyronine duringcardiac surgery was safe and enhanced cardiovascular performancein the early postoperative period. Since it is difficult toidentify patients who will have cardiovascular dysfunction,a low threshold for starting the use of inotropic drugs duringweaning from cardiopulmonary bypass and tight pharmacologiccontrol of postoperative cardiac and vascular function are standardsof care at our institution; they were adhered to in the courseof this study. Although triiodothyronine improved postoperativecardiovascular performance, we found no decrease in the requirementsfor traditional inotropic support. Therefore, our findings donot support the use of triiodothyronine as a substitute forstandard drug therapy to maintain hemodynamic stability aftercardiopulmonary bypass in patients with impaired ventricularfunction.
Supported by a grant from SmithKline Beecham Pharmaceuticals.
We are indebted to Dr. Nasser K. Altorki, Dr. Jeffrey P. Gold,Dr. Samuel Lang, and Dr. Todd K. Rosengart, the cardiothoracicsurgeons of New York Hospital whose patients were enrolled inthe study; to Dr. Martin Lesser and Dr. Barbara Napolitano fortheir statistical consultation; to Ms. Beverly Woytowich forher assistance as a research pharmacist; and to Mr. RichardKung and the hospital's nuclear-medicine laboratory staff.
Source Information
From the Departments of Cardiothoracic Surgery (J.D.K., M.G., R.E.H., O.W.I., K.K.) and Anesthesiology (S.J.T.), New York HospitalCornell University Medical College, New York; and the Division of Endocrinology, Department of Medicine, North Shore University HospitalCornell University Medical College, Manhassett, N.Y. (I.K., K.O.).
Address reprint requests to Dr. Klemperer at the Department of Cardiothoracic Surgery, New York Hospital, 525 E. 68th St., New York, NY 10021.
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