Effects of triiodothyronine supplementation after myocardial ischemia

Euthyroid sick syndrome in paediatric and adult patients requiring extracorporeal circulatory support and the role of thyroid hormone supplementation: a review

Non-thyroid disorders may modify thyroid hormone metabolism, resulting in an 'euthyroid sick syndrome'. Studies determining the association of cardiopulmonary bypass to thyroid function showed changes in line with this euthyroid sick syndrome. In some cases, cardiovascular dysfunction after cardiac surgery with cardiopulmonary bypass is comparable to that noticed in hypothyroidism associated with low cardiac output and elevated systemic vascular resistance. Numerous lines of research have proposed that triiodothyronine can behave acutely as a positive inotropic and vasodilator agent. The aim of this review is to present an update on the current literature about in what clinical situations the use of thyroid supplementation during the perioperative period of extracorporeal circulation in the adult and paediatric populations may impact outcome to any appreciable degree. The contribution of thyroid function in patients undergoing a ventricular assist device implantation is additionally reviewed and future study directions are proposed. This is a narrative review, where the search strategy consisted on retrieving the articles through an extensive literature search performed using electronic databases from January 1978 up to September 2019. All controlled trials randomly allocating to perioperative thyroid hormone administration in children and adults undergoing extracorporeal circulation for cardiac surgery were considered. Thyroid hormone supplementation may be recommended particularly in selected paediatric sub-populations. There is currently no firm evidence regarding the benefits of routine use of thyroid hormone administration in cardiac adult patients. Further studies are required to assess the beneficial effect of thyroid hormone on patients with end-stage heart failure supported by ventricular assist devices.

Transient Secondary Hypothyroidism and Thyroid Hormone Replacement Therapy in Pediatric Postoperative Cardiopulmonary Bypass

Background:

To develop an understanding of current practices in the management of transient secondary hypothyroidism in pediatric postoperative cardiopulmonary bypass (CPB) patients.

Methods:

Electronic survey comprising a 10-item questionnaire was sent to sixty-four high volume pediatric heart centers in the United States and United Kingdom. Survey participants included cardiologists, intensivists, cardiothoracic surgeons, and advanced practice providers. A retrospective chart review was also performed at a large regional referral center in the Midwest on subjects 0-18 years old who underwent CPB from 2005-2015. Information obtained included a unique identifier, date of birth, age, procedure performed, CPB time, date of surgery and date and type of Thyroid Function Test (TFT) ordered.

Results:

1,153 individuals from 64 congenital heart centers were contacted via email to participate in the electronic survey. In the 3-month response window, 129 completed surveys were received from cardiologists (55%), intensivists (17%), surgeons (15%), “other” (8%), and advanced practice providers (5%). This yielded a response rate of 11.2%. Of the 129 respondents, only 10 providers routinely order TFTs prior to (n=7) and after (n=1) CPB or when clinically indicated (n=2). All 10 providers order thyroid stimulating hormone test, 7 order thyroxine, and 3 order triiodothyronine. Only 1 provider routinely treats children with prophylactic thyroid hormone replacement therapy after CPB. Our retrospective review included 502 CPB events with 442 unique patients. Of the events, 20 patients received preoperative TFT testing while 11 received postoperative testing.

Conclusions:

There is a general lack of uniformity in the evaluation, diagnosis, and treatment of transient secondary hypothyroidism in pediatric postoperative CPB patients.

Molecular and biochemical evidences on the protective effects of triiodothyronine against phosphine-induced cardiac and mitochondrial toxicity

AIM

Aluminum phosphide (AlP) is a widely used fumigant and rodenticide. While AlP ingestion leads to high mortality, its exact mechanism of action is unclear. There are ample evidences suggesting cardioprotective effects of triiodothyronine (T3). In this study, we aimed to examine the potential of T3 in the protection of a rat model of AlP induced cardiotoxicity.

MAIN METHODS

In order to induce AlP intoxication animals were intoxicated with AlP (12 mg/kg; LD50) by gavage. In treatment groups, T3 (1, 2 and 3 μg/kg) was administered intra-peritoneally 30 min after AlP administration. Animals were connected to the electronic cardiovascular monitoring device simultaneously after T3 administration. Then, electrocardiogram (ECG), blood pressure (BP), and heart rate (HR) were monitored for 180 min. Additionally, 24h after AlP intoxication, rats were deceased and the hearts were dissected out for evaluation of oxidative stress, cardiac mitochondrial function (complexes I, II and IV), ATP/ADP ratio, caspases 3 & 9, and apoptosis by flow cytometry.

KEY FINDINGS

The results demonstrated that AlP intoxication causes cardiac toxicity presenting with changes in ECG patterns such as decrement of HR, BP and abnormal QRS complexes, QTc and ST height. T3 at a dose of 3 μg/kg significantly improved ECG and also oxidative stress parameters. Furthermore, T3 administration could increase mitochondrial function and ATP levels within the cardiac cells. In addition, administration of T3 showed a reduction in apoptosis through diminishing the caspase activities and improving cell viability.

SIGNIFICANCE

Overall, the present data demonstrate the beneficial effects of T3 in cardiotoxicity of AlP.

Impact of thyroid hormone administration on fluid requirements and hepatic injury markers in hemorrhagic shock due to liver trauma

INTRODUCTION

The aim of the present study was to evaluate the effect of triiodothyronine (T3) administration in a porcine model of hemorrhagic shock due to liver surgery, in terms of hemodynamic stability, acid-base status, and hepatic injury markers.

MATERIALS AND METHODS

Hemorrhagic shock was induced in swine by left lobe liver resection and allowed bleeding to a mean arterial pressure of 35-40 mmHg for 40 min. Animals were randomly assigned into a sham group (n = 5), a fluid-resuscitated group (n = 7), and a fluid plus T3-resuscitated group (n = 7). T3 was given by continuous intravenous infusion from the beginning of the experiment. After the 40 min of shock animals were resuscitated with the aim of restoring mean arterial pressure (±10% from baseline). Resuscitation lasted for 1 hr and then swine were followed for another 460 min (total 6 hr). Blood loss, hamodynamic parameters, fluids administered, acid-base status, and liver enzymes were measured.

RESULTS

Blood loss was similar in both groups. Animals treated with T3 required less fluids than swine resuscitated with crystalloids and colloids only (N/S 0.9%: 1071 ± 189 ml vs. 2429 ± 535 ml, Voluven 6%: 550 ± 96 ml vs. 1000 ± 289 ml, p < .05), plus they were less acidotic at the end of the observing period (7.38 ± 0.08 vs. 7.26 ± 0.12, p < .05). Tachycardia was not associated with T3 administration. Hepatic enzymes did not exhibit differences between groups.

CONCLUSION

Our study demonstrates the beneficial impact of T3 administration during controlled hemorrhagic shock and resuscitation. Animals resuscitated with T3 necessitate less amounts of fluids to maintain hemodynamic stability and acid-base status. Moreover, T3 administration does not seem to aggravate blood loss or harm the hepatic tissue.

Acute myocardial infarction and thyroid function: new pathophysiological and therapeutic perspectives

In the post-reperfusion era, molecular and genetic mechanisms of cardioprotection and regeneration represent new therapeutic challenges to limit infarct size and minimize post-ischemic remodeling after acute myocardial infarction (AMI). Activation of cell survival mechanisms can be promoted by the administration of external drugs, stimulation of internal mechanisms, and genetic manipulation to delete or replace pathological genes or enhance gene expression. Among internal cardiovascular regulatory mechanisms, thyroid hormones (THs) may play a fundamental role. TH has a critical role in cardiovascular development and homeostasis in both physiological and pathological conditions. In experimental AMI, TH has been shown to affect cardiac contractility, left ventricular (LV) function, and remodeling. Several experimental studies have clearly shown that THs participate in the regulation of molecular mechanisms of angiogenesis, cardioprotection, cardiac metabolism, and ultimately myocyte regeneration, changes that can reverse left ventricular remodeling by favorably improving myocyte shape and geometry of LV cavity, thus improving systolic and diastolic performance. This review is focused on the role of thyroid on AMI evolution and on the potential novel option of thyroid-related treatment of AMI.

Thyroid hormone as a therapeutic option for treating ischaemic heart disease: from early reperfusion to late remodelling

Thyroid hormone (TH), apart from its "classical" actions on cardiac contractility and heart rhythm, appears to regulate various intracellular signalling pathways related to response to stress and cardiac remodelling. There is now accumulating experimental and clinical evidence showing a beneficial effect of TH on limiting myocardial ischaemic injury, preventing/reversing post infarction cardiac remodelling and improving cardiac hemodynamics. Thyroid analogs have already been developed and may allow TH use in clinical practice. However, the efficacy of TH in the treatment of cardiac diseases is now awaiting to be tested in large clinical trials.

Cardiovascular effects of oral tri-iodothyronine in patients undergoing valvular cardiac surgery

BACKGROUND

Cardiopulmonary bypass produces a state of functional hypothyroidism characterized by low levels of circulating tri-iodothyronine (T3). Theoretically, supplementing T3 should result in improved hemodynamics as well as patients' outcome. The aim of the present study was to determine whether pretreatment with single oral T3 could prevent serum T3 reduction, and improve hemodynamics and clinical outcome.

METHODS

Forty-seven patients undergoing valvular heart surgery were included in the study. Patients were randomly assigned into two groups (T = T group; C = control group) the day before surgery and received single oral T3 40 microg or placebo before operation. Blood samples were collected for determination of serum levels of total T3, T4 and TSH before administration of oral T3 or placebo (baseline), 1, 6 and 18 hour after weaning of cardiopulmonary bypass. Hemodynamic parameters and medication were recorded during the intraoperative period and throughout the first 24 h after arrival at the intensive care unit.

RESULTS

T3 levels were significantly higher in the T group 1 hr after weaning of cardiopulmonary bypass. T3 levels in the T group were all maintained within the normal range throughout the study period, whereas it was decreased to below normal level in the C group at 18 hr after weaning of cardiopulmonary bypass. In the T group, vasoactive agent requirements were reduced during and after cardiopulmonary bypass.

CONCLUSIONS

Pretreatment with single oral T3 prevented the reduction in T3 level after valvular heart surgery, with subsequent reduction in vasoactive agent requirement.

Thyroid hormone improves postischaemic recovery of function while limiting apoptosis: a new therapeutic approach to support hemodynamics in the setting of ischaemia-reperfusion?

Although it has long been recognized that thyroid hormone is an effective positive inotrope, its efficacy in supporting hemodynamics in the acute setting of ischaemia and reperfusion (R) without worsening reperfusion injury remains largely unknown. Thus, we investigated the effects of triiodothyronine (T3) on reperfusion injury in a Langendorff-perfused rat heart model of 30 min zero-flow ischaemia and 60 min of (R) with or without T3 (40 microg/l) at R, T3-R60, n = 11 and CNT-R60, n = 10, respectively. Furthermore, phosphorylated levels of intracellular kinases were measured at 5, 15 and 60 min of R. T3 markedly improved postischaemic recovery of left ventricular developed pressure (LVDP%); 56.0% (SEM, 4.4) in T3-R60 versus 38.8% (3.1) in CNT-R60, P < 0.05. Furthermore, LDH release was significantly lower in T3-R60. Apoptosis detection by fluorescent probe optical imaging showed increased fluorescent signal in CNT-R60 hearts, while the signal was hardly detectable in T3-R60 hearts. Similarly, caspase-3 activity was found to be 78.2 (8.2) in CNT-R60 vs 40.5 (7.1) in T3-R60 hearts, P < 0.05. This response was associated with significantly lower levels of phospho-p38 MAPK at any time point of R. No significant changes in phospho- ERK1/2 and JNK levels were observed between groups. Phospho-Akt levels were significantly lower in T3 treated group at 5 min and no change in phospho-Akt levels were observed at 15 and 60 min between groups. In conclusion, T3 administration at reperfusion can improve postischaemic recovery of function while limiting apoptosis. This may constitute a paradigm of a positive inotropic agent with anti-apoptotic action suitable for supporting hemodynamics in the clinical setting of ischaemia-reperfusion.

Thyroid hormone and myocardial ischaemia

Thyroid hormone has various effects on the cardiovascular system and its effects on cardiac contractility, heart rhythm and vascular function has long been recognized. However, new evidence is emerged on the importance of thyroid hormone in the response of the myocardium to ischaemic stress and cardiac remodelling following myocardial infarction. Based on this new information, this review highlights the role of thyroid hormone in myocardial ischaemia and cardiac remodelling, the possible underlying mechanisms and the potential therapeutic implications. Thyroid hormone or analogs may prove new therapeutic agents for treating ischaemic heart disease.

Protection of the abnormal heart

Myocardial ischemia and reperfusion injury have been extensively investigated in the laboratory mainly in healthy tissues. However, in clinical settings, ischemic heart disease coexists with certain illnesses, which could potentially influence the response of the myocardium to ischemia and reperfusion. Recent research has revealed that the abnormal heart may not be always vulnerable to ischemic injury. Furthermore, the effect of powerful means of protection, such as ischemic preconditioning, may not be in operation under certain pathological conditions. With this evidence in mind, the present review will focus on the response of the abnormal heart to ischemia and reperfusion, the possible underlying mechanisms, and potential cardioprotective strategies.

Myocardial and coronary sinus purines as indicators of pig heart energy metabolism during reperfusion after extracorporeal circulation

AIM

The precise understanding of myocardial metabolism is crucial for the optimization of cardiosurgical procedures. We attempted to gain a comprehensive insight into the purine metabolism of the porcine heart during reperfusion by measuring concentrations of nucleotides, nucleosides and oxypurines simultaneously in the myocardium and coronary sinus.

METHODS

Twenty-five pigs were subjected to sham cardiosurgery with extracorporeal circulation and cold cardioplegic arrest of 60 min. Myocardial biopsies, as well as coronary sinus and arterial blood samples were taken before aortic clamping and at 5, 20, 60 and 120 min of reperfusion. HPLC was used to measure concentrations of 17 purines in the bioptates and of 5 in plasma.

RESULTS

Reperfusion rapidly normalized the ischaemic decrease in the adenylate energy charge of the myocardium, but during 120 min failed to restore the reduced adenylate pool, because of irreversible loss of nucleosides by cardiomyocytes. Low adenylate energy charge and depletion of the adenylate pool were accompanied by analogous changes in the guanylates and growing deficit of NAD and NADP. Reperfusion was marked by significant release of inosine and guanosine from the heart, without any noticeable effect on hypoxanthine and xanthine.

CONCLUSIONS

Coronary sinus concentrations of purines provide only a limited insight into the metabolism of the porcine heart. Repeated biopsies of the heart muscle and HPLC determinations of purine profiles represent a comprehensive and unique method for the study of purine metabolism during ischaemia and reperfusion. Future research on myocardial metabolism in disease and during cardiosurgical procedures should additionally be oriented to deficits in guanine and pyridine nucleotides.

The Triiodothyronine for Infants and Children Undergoing Cardiopulmonary Bypass (TRICC) study: design and rationale

BACKGROUND

Cardiopulmonary bypass induces marked and persistent depression of circulating thyroid hormones in infants and children, possibly contributing to postoperative morbidity. Clinical studies have evaluated parenteral triiodothyronine supplementation after cardiopulmonary bypass in children. However, these investigations had relatively small subject numbers as well as age and diagnosis heterogeneity, thereby limiting ability to determine clinical effect. A double-blind, randomized, placebo-controlled trial is needed to define clinical safety and efficacy of triiodothyronine supplementation in infants.

METHODS AND RESULTS

The Triiodothyronine for Infants and Children Undergoing Cardiopulmonary Bypass (TRICC) study is a multicenter, randomized, clinical trial designed to determine safety and efficacy of triiodothyronine supplementation in children <2 years of age undergoing surgical procedures for congenital heart disease. Duration of mechanical ventilation after completion of cardiopulmonary bypass is the primary clinical outcome parameter with multiple secondary clinical and hemodynamic parameters. Nearly 200 patients will be randomly assigned to receive either triiodothyronine or placebo. Patient assignment will be performed using a stratified block randomization according to specific preoperative diagnosis.

CONCLUSIONS

The TRICC study will provide important data regarding the efficacy and safety of triiodothyronine in this age-specific population undergoing surgery for congenital heart disease.

Effects of intravenous triiodothyronine during coronary artery bypass surgery

A prospective randomized and double-blind study was performed to evaluate whether perioperative triiodothyronine administration has any effect on cardiovascular performance after coronary artery bypass surgery. Sixty patients were assigned to 2 groups of 30 each. When crossclamping ended, group A received an intravenous bolus of triiodothyronine, followed by infusion for 6 hours. Group B received a placebo. Serum triiodothyronine levels and hemo-dynamic parameters were serially measured. Mean postoperative cardiac index was slightly, but not significantly, higher in group A, whereas systemic vascular resistance was significantly lower in group A. Compared with preoperative values, serum triiodothyronine levels dropped significantly in group B at the end of cardiopulmonary bypass and remained low 12 hours postoperatively, while levels rose significantly in group A. No significant differences were detected between the groups in the incidence of arrhythmia, the need for inotropic support, intensive care unit stay, mortality, and morbidity. Perioperative administration of triiodothyronine increased cardiac output slightly and decreased systemic vascular resistance, but it had no effect on operative outcome. Routine use after coronary surgery is thus not recommended.

Thyroid hormone and cardiac surgery

Thyroid hormone has important effects on the heart and peripheral vascular system. The relationship between thyroid disease states and cardiovascular hemodynamics is well recognized. Diverse clinical situations are associated with low serum triiodothyronine (T3) levels including a number of cardiovascular illnesses. In particular, cardiopulmonary bypass and open heart operations result in a low T3 state and are often complicated by significant cardiovascular dysfunction similar to that observed in clinical hypothyroidism. Multiple lines of evidence have suggested that T3 can act acutely as a positive inotrope and vasodilator agent. This recognition has prompted a number of investigators to study the effects of T3 administration to patients in the perioperative period. This paper reviews the experimental background that supported such clinical trials as well as outlines the results that have been documented in both adult and pediatric patients undergoing cardiac surgery. Low serum T3 levels resulting from cardiopulmonary bypass can be safely reversed with pharmacologic T3 supplementation. Data have suggested that T3 repletion may improve postoperative hemodynamic performance and lower the incidence of arrythmias. However, beneficial effects on major clinical outcome variables have not yet been conclusively demonstrated, and require future large-scale clinical trials.

Triiodothyronine supplementation in patients undergoing cardiopulmonary bypass

Patients undergoing cardiopulmonary bypass may develop clinically significant physiologic alterations in the perioperative period, including alteration of thyroid hormone concentrations. Alterations in the concentration of thyroid hormones are of concern due to the effects of these hormones on cardiac function. Hypothyroidism is associated with a decrease in cardiac performance; therefore, supplementation with the active thyroid hormone triiodothyronine (T3) in patients undergoing cardiopulmonary bypass has been investigated to improve outcomes. In addition, T3 has been studied as an agent to reduce the frequency of atrial fibrillation after cardiopulmonary bypass.

Thyroid Hormone and Myocardial Metabolism after Heart Surgery in Dogs

Recent studies have demonstrated that thyroid hormone improves hemodynamics following open-heart surgery, through unknown mechanisms. The effect of triiodothyronine on myocardial metabolism was studied in dogs undergoing normothermic crystalloid cardioplegic arrest. Seven animals in group 0 served as controls, 8 in group 1 received 0.1μg·kg−1·min−1 triiodothyronine intravenously after aortic cross-clamping, and 3 dogs in group 2 received triiodothyronine 150 μg per day orally for 7 days preoperatively and intravenously (0.1 μg·kg−1·min−1) after aortic cross-clamping. Myocardial carbon dioxide production and the uptake of oxygen, lactate, glucose, and free fatty acids were determined before aortic cross-clamping and at 10, 30, 60, and 120 minutes after declamping. After aortic cross-clamping, increased myocardial uptake of oxygen, lactate, and glucose were observed in group 1 compared with group 0. Myocardial free fatty acid uptake decreased in all groups. Carbon dioxide production correlated with myocardial oxygen uptake. These findings suggest that intraoperative triiodothyronine supplementation improves myocardial metabolism but preoperative administration is ineffective.

The direct vasomotor effect of thyroid hormones on rat skeletal muscle resistance arteries

The present study examines the hypothesis that the hormones have direct vasodilatory effects and attempts to determine whether the effects are endothelium-dependent. Rat skeletal muscle resistance arteries of approximately 100 microns were dissected, and vessel diameter changes were monitored using a videodetection system. After equilibration at 37 degrees C, each vessel was preconstricted with the thromboxane analog U46619 1 microM, and the percentage of dilation was measured after exposure to increasing concentrations of triiodothyronine (T3) or levothyroxine (T4) (10(-10) to 10(-7) M). Dilation in response to T3 was also measured after endothelial denudation and pretreatment with the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA) 10 microM, the cyclooxygenase inhibitor indomethacin 10 microM, the adenosine triphosphate-sensitive K+ channel blocker glibenclamide 1 microM, or the beta-adrenergic antagonist propranolol 1 microM. Both T3 and T4 demonstrated concentration-dependent dilation of the U46619-preconstricted vessels (P < 0.001 each), with T3 having a greater effect than T4 (P < 0.05) (36% +/- 9% [mean +/- SD] dilation at 10(-7) M T3 vs 24% +/- 6% dilation at 10(-7) M T4). In comparison, isoproterenol 10(-7) M produced 56% +/- 6% dilation. T3-mediated vasodilation was attenuated but not abolished by endothelial denudation (18% +/- 3% dilation at 10(-7) M T3) (P < 0.01), L-NNA (15% +/- 7% dilation at 10(-7) M T3) (P < 0.01), indomethacin (20% +/- 9% dilation at 10(-7) M T3) (P < 0.05), and glibenclamide (22% +/- 7% dilation at 10(-7) M T3) (P < 0.01), but it was not affected by propranolol (37% +/- 20% dilation at 10(-7) M T3) (P = 0.99). We conclude that thyroid hormones possess direct vasodilatory effects with both endothelium-independent and endothelium-dependent components.

IMPLICATIONS

Thyroid hormones may have modest direct vasodilatory effects. This may partially account for the cardiovascular actions of the hormones in hyperthyroidism or when administered pharmacologically in cardiac surgery.

Triiodothyronine in cardiac surgery

Thyroid hormones have profound cardiovascular effects. Chronic hypothyroidism is associated with cardiovascular abnormalities that include diminished cardiac output and increased systemic vascular resistance. Acute hypothyroidism, frequently referred to as the "euthyroid sick syndrome," is present in diverse clinical situations such as brain death, sepsis, congestive heart failure, and cardiopulmonary bypass. Significant cardiovascular dysfunction often complicates each of these clinical situations. This article reviews the laboratory experiments and clinical trials that have evaluated triiodothyronine (T3) repletion in cardiac surgery. Animal experiments have shown that T3 repletion ameliorates postischemic cardiovascular dysfunction. While anecdotal clinical experience suggests that T3 repletion should be of clinical benefit, rigorous clinical trials have failed to support routine repletion of T3 in cardiac surgery. Based on the results of these clinical trials, we do not recommend routine administration of T3 to patients undergoing cardiac surgery. However, anecdotal experience suggests that T3 may help in weaning patients from cardiopulmonary bypass who are unable to be weaned from bypass despite maximal inotropic support. In use as a "rescue" agent, we administer the 0.8 microgram/kg dose that has been demonstrated to safely improve cardiac output and decrease systemic vascular resistance in the postischemic cardiopulmonary bypass patient.

Triiodothyronine therapy lowers the incidence of atrial fibrillation after cardiac operations

BACKGROUND

Cardiopulmonary bypass results in a euthyroid sick state, and recent evidence suggests that perioperative triiodothyronine (T3) supplementation may have hemodynamic benefits. In light of the known effects of thyroid hormone on atrial electrophysiology, we investigated the effects of perioperative T3 supplementation on the incidence of postoperative arrhythmias.

METHODS

One hundred forty-two patients with depressed left ventricular function (ejection fraction < 0.40) undergoing coronary artery bypass grafting were randomized to either T3 or placebo treatment groups in a prospective, double-blind fashion. Triiodothyronine was administered as a 0.8 micrograms/kg intravenous bolus at the time of aortic cross-clamp removal followed by an infusion of 0.113 micrograms.kg-1.h-1 for 6 hours. Patients were monitored for the development of arrhythmias during the first 5 postoperative days.

RESULTS

The incidence of sinus tachycardia and ventricular arrhythmias were similar between groups. Triiodothyronine-treated patients had a lower incidence of atrial fibrillation (24% versus 46%; p = 0.009), and fewer required cardioversion (0 versus 6; p = 0.012) or anticoagulation (2 versus 10; p = 0.013) during hospitalization. Six patients in the T3 group versus 16 in the placebo group required antiarrhythmic therapy at discharge (p = 0.019).

CONCLUSIONS

Perioperative T3 administration decreased the incidence and need for treatment of postoperative atrial fibrillation.

The direct effects of 3,5,3'-triiodo-L-thyronine (T3) on myocyte contractile processes. Insights into mechanisms of action

Administration of 3,5,3'-triiodo-L-thyronine (T3) has recently been suggested to acutely improve left ventricular performance. However, the cellular and molecular mechanisms responsible for this improvement in left ventricular function with T3 remained unknown. Accordingly, the present study examined the direct effects of T3 administration on myocyte contractile function and the sarcolemmal systems that might potentially contribute to these effects. In isolated porcine left ventricular myocytes (n = 81), velocity of shortening increased in the presence of 80 pmol/L T3 compared with that in untreated myocytes (117.0 +/- 5.0 versus 77.3 +/- 3.3 microns/sec, p < 0.05). In a separate series of experiments (n = 29), myocyte velocity of shortening increased in the presence of both T3 and beta-adrenergic receptor stimulation (25 nmol/L isoproterenol) to greater than that with beta-adrenergic receptor stimulation alone (274.3 +/- 16.9 versus 203.7 +/- 16.2 microns/sec, p < 0.05). Cyclic adenosine monophosphate generation was next examined in isolated myocyte preparations (n = 9). In the presence of T3, no significant increase in cyclic-adenosine monophosphate generation was observed compared with that in untreated myocytes (39.1 +/- 8.3 versus 24.7 +/- 5.8 fmols/myocyte, p = 0.17). However, in the presence of both T3 and beta-adrenergic receptor stimulation, cyclic-adenosine monophosphate generation increased significantly to greater than that with beta-adrenergic receptor stimulation alone (224.4 +/- 61.1 versus 120.1 +/- 35.5 fmoles/myocyte, p < 0.05). Because cyclic-adenosine monophosphate modulates intracellular Ca2+ processes, L-type Ca+2 channel current (patch clamp methods; -picoamp/picofarad, n = 15) and peak intracellular Ca+2 levels (fura 2 ionic measurement, n = 47) were next measured. In the presence of T3, a shift in the activation voltage at peak L-type Ca+2 channel current was observed from baseline (5.5 +/- 1.4 versus 9.0 +/- 1.0 mV, p < 0.05). Furthermore, in the presence of both T3 and beta-adrenergic receptor stimulation, peak L-type Ca+2 channel current (8.9 +/- 0.7 versus 6.3 +/- 1.0 mV, p < 0.05) and peak intracellular Ca+2 levels (189.9 +/- 8.4 versus 171.7 +/- 8.3 nmol/L, p < 0.05) increased compared with values obtained with beta-adrenergic receptor stimulation alone. Important findings from the present study were twofold: (1) T3 improved myocyte contractile processes through a cyclic-adenosine monophosphate-independent mechanism and (2) T3 potentiated the effects of beta-adrenergic receptor stimulation transduction by increasing cyclic-adenosine monophosphate production, L-type Ca+2 channel current, and Ca+2 availability to the myocyte contractile apparatus.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of triiodothyronine administration in experimental myocardial injury

Twelve healthy pigs were subjected to a 20-min, period of regional myocardial ischemia by snaring the left anterior descending coronary artery (LAD) between its first and second diagonal branches. The resulting myocardial injury caused significant acute hemodynamic impairments. Cardiac index declined significantly during reperfusion interval and returned to preischemic level by postoperative day 7. Plasma total triiodothyronine (TT3), free triiodothyronine (FT3) and free fatty acid (FFA) decreased gradually and reached the nadir at 6 h after LAD occlusion. In contrast, plasma reverse triiodothyronine (rT3) increased progressively after LAD occlusion and reperfusion. To investigate the effect of T3 on ischemic myocardium, T3 (0.2 microgram/kg/dose; n = 5) or saline (placebo; n = 6) was administered immediately, 30 min, 60 min, 90 min, and 120 min after reperfusion. Plasma TT3 and FT3 increased dramatically after triiodothyronine supplement but declined to presichemic level at six h after LAD occlusion. The pigs treated with T3 demonstrated a rapid improvement in cardiac index over the reperfusion interval, whereas cardiac index in the placebo group remained depressed. Myocardial oxygen consumption estimated by rate pressure product showed no difference between placebo and T3-treated groups. Oxygen extraction as O2 saturation difference between aorta and coronary sinus was less in T3-treated group. Nine pigs (four in the T3-treated group and five in the placebo group) were subjected to euthanasia with hypertonic KCl solution on postoperative day 7. Myocardial infarct size determined by triphenyltetrazolium chloride (TTC) tissue enzyme staining technique was not significantly different between T3-treated and placebo groups. We concluded that this animal model is a useful model of myocardial injury simulating "euthyroid sick syndrome" as seen in patients with cardiopulmonary bypass, and T3 supplementation after reperfusion significantly enhanced postischemic left ventricular functional recovery but did not affect myocardial oxygen consumption and myocardial infarct size.

Triiodothyronine improves left ventricular function without oxygen wasting effects after global hypothermic ischemia

Cardiopulmonary bypass results in a "euthyroid sick" state. Recently, interest has focused on the relationship between low serum triiodothyronine levels and postoperative cardiovascular hemodynamics. The present study was undertaken to more clearly define the acute effects of triiodothyronine on myocardial mechanics and energetics after hypothermic global ischemia using an ex-vivo canine heart preparation to model the clinical condition. Experiments were performed on isolated hearts subjected to hyperkalemic arrest with 90 minutes of hypothermic (10 degrees C) ischemia. Isolated hearts were cross-perfused by euthyroid support dogs in which triiodothyronine levels spontaneously decreased by 65% to 75% (p < 0.01) after the initiation of cross-perfusion. In nine heart preparations, triiodothyronine (Triostat) was given as a bolus dose (0.2 micrograms/kg) after 1 hour of baseline data collection with a subsequent measurable rise in serum triiodothyronine levels (p < 0.01). In six postischemic hearts, reverse triiodothyronine was given as a 0.2 micrograms/kg bolus. Triiodothyronine was also administered to a group of eight nonischemic, continuously perfused isolated hearts. Intrinsic myocardial contractility was assessed by analysis of the preload recruitable stroke work area, energetic efficiency from the myocardial oxygen consumption-pressure-volume area relationship, and coronary vascular resistance from analysis of coronary flow and perfusion pressure. Acute administration of triiodothyronine to postischemic hearts improved the preload recruitable stroke work area from 9.5 +/- 1.42 to 14.9 +/- 2.03 x 10(7) erg/ml, a 56% increase from baseline (p < 0.001), but had no effect on the preload recruitable stroke work area of the nonischemic hearts. The inotropic response resulting from triiodothyronine treatment did not alter the myocardial oxygen consumption-pressure-volume area relationship. Triiodothyronine treatment was associated with significantly decreased coronary resistance and increased coronary flow through a range of diastolic loading conditions in the postischemic hearts. The biologically inactive thyroid hormone metabolite reverse triiodothyronine was without effect on any of the measured parameters. On the basis of these results, we conclude that the low triiodothyronine state of cardiopulmonary bypass can be reproduced in this isolated heart model and that acute triiodothyronine treatment results in a unique inotropic action manifest only in the postischemic reperfused myocardium and is accomplished without oxygen wasting effects.