Increased sensitivity of the denervated transplanted human heart to isoprenaline both before and after beta-adrenergic blockade

Isoproterenol improves hemodynamics and right ventricle-pulmonary artery coupling after heart transplantation

Right ventricular failure (RVF) is a major cause of early mortality after heart transplantation (HT). Isoproterenol (Iso) has chronotropic, inotropic, and vasodilatory properties, which might improve right ventricle function in this setting. We aimed to investigate the hemodynamic effects of isoproterenol on patients with post-HT RVF. We conducted a 1-yr retrospective observational study including patients receiving isoproterenol (Iso) and dobutamine for early RVF after HT. A comprehensive multiparametric hemodynamic evaluation was performed successively three times: no isoproterenol, low doses: 0.025 µg/kg/min, and high doses: 0.05 µg/kg/min (henceforth, respectively, called no Iso, low Iso, and high Iso). From June 2022 to June 2023, 25 patients, median [interquartile range (IQR) 25-75] age 54 [38-61] yr, were included. Before isoproterenol was introduced, all patients received dobutamine, and 15 (60%) were on venoarterial extracorporeal membrane oxygenation (VA-ECMO). Isoproterenol significantly increased heart rate from 84 [77-99] (no Iso) to 91 [88-106] (low Iso) and 102 [90-122] beats/min (high Iso, P < 0.001). Similarly, cardiac index rose from 2.3 [1.4-3.1] to 2.7 [1.8-3.4] and 3 [1.9-3.7] L/min/m2 (P < 0.001) with a concomitant increase in indexed stroke volume (28 [17-34] to 31 [20-34] and 33 [23-35] mL/m2, P < 0.05). Effective pulmonary arterial elastance and pressures were not modified by isoproterenol. Pulmonary vascular resistance (PVR) tended to decrease from 2.9 [1.4-3.6] to 2.3 [1.3-3.5] wood units (WU), P = 0.06. Right ventricular ejection fraction/systolic pulmonary artery pressure (sPAP) evaluating right ventricle-pulmonary artery (RV-PA) coupling increased after isoproterenol from 0.8 to 0.9 and 1%·mmHg-1 (P = 0.001). In conclusion, in post-HT RVF, isoproterenol exhibits chronotropic and inotropic effects, thereby improving RV-PA coupling and resulting in a clinically relevant increase in the cardiac index.NEW & NOTEWORTHY This study offers a detailed and comprehensive hemodynamic investigation at the bedside, illustrating the favorable impact of isoproterenol on right ventricular-pulmonary arterial coupling and global hemodynamics. It elucidates the physiological effects of an underused inotropic strategy in a critical clinical scenario. By enhancing cardiac hemodynamics, isoproterenol has the potential to expedite right ventricular recovery and mitigate primary graft dysfunction, thereby reducing the duration of mechanical support and intensive care unit stay posttransplantation.

Acute myocardial infarction in heart transplant recipients: An 18-year national study

Among 11,622,528 acute myocardial infarction (AMI) hospitalizations, 892 had a history of heart transplantation (HT). In comparison to AMI admissions without HT, those with prior HT were more frequently complicated with cardiac arrest (8.3 % vs 5.0 %, p < 0.001), acute non-cardiac organ failure (17.4 % vs 9.4 %) (p < 0.001), lower rates of coronary angiography (55.4 % vs 63.6 %, p < 0.001), comparable rates of percutaneous coronary intervention (38.8 % vs 41.5 %, p = 0.10), higher rates of pulmonary artery catheterization (2.7 % vs 1.1 %, p < 0.001), invasive mechanical ventilation and acute hemodialysis compared to AMI admissions without HT. Compared to AMI admissions without HT, prior HT recipients had higher in-hospital mortality (11.8 % vs 6.2 %, adjusted odds ratio 2.87 [95 % CI 2.23-3.70]; p < 0.001).

Peritransplant Cardiometabolic and Mitochondrial Function: The Missing Piece in Donor Heart Dysfunction and Graft Failure

Primary graft dysfunction is an important cause of morbidity and mortality after cardiac transplantation. Donor brain stem death (BSD) is a significant contributor to donor heart dysfunction and primary graft dysfunction. There remain substantial gaps in the mechanistic understanding of peritransplant cardiac dysfunction. One of these gaps is cardiac metabolism and metabolic function. The healthy heart is an "omnivore," capable of utilizing multiple sources of nutrients to fuel its enormous energetic demand. When this fails, metabolic inflexibility leads to myocardial dysfunction. Data have hinted at metabolic disturbance in the BSD donor and subsequent heart transplantation; however, there is limited evidence demonstrating specific metabolic or mitochondrial dysfunction. This review will examine the literature surrounding cardiometabolic and mitochondrial function in the BSD donor, organ preservation, and subsequent cardiac transplantation. A more comprehensive understanding of this subject may then help to identify important cardioprotective strategies to improve the number and quality of donor hearts.

Beta-blocker therapy in heart transplant recipients: A review

Beta-blockers are essential drugs for the treatment of many cardiovascular diseases, such as heart failure, acute and chronic ischemic heart disease, tachyarrhythmias, and hypertension. However, these drugs have not been used in cardiac transplant patients for many years owing to the fear that they could reduce cardiac output and functional capacity. In recent years, however, some evidence has shown that even in cardiac transplanted patients, β-blockers are useful and effective in the treatment of sinus tachycardia, supraventricular and ventricular tachyarrhythmias, left ventricular systolic dysfunction, and arterial hypertension. Furthermore, some data have shown that the use of β-blockers is associated with reduced mortality in heart transplant recipients. In this review, we summarize this evidence with particular emphasis on the practical aspects of the use of β-blockers in post-transplantation patients to promote the use of this important class of drugs in clinical practice.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

Device Management in Heart Failure

PURPOSE OF REVIEW

Medical devices have become an integral part of comprehensive heart failure management. Not all heart failure patients, however, accrue benefit from every new device, and even with extensive practice guidelines, this remains an evolving field.

RECENT FINDINGS

The addition of implantable devices, like internal cardioverter defibrillators (ICDs), and novel pacing technologies, including cardiac resynchronization therapy (CRT), have helped to compliment goal-directed medical therapy and positively impact prognosis in multiple high-quality clinical trials. This review attempts to summarize the rapidly evolving literature with respect to existing device guidelines for routine implantable devices as well as some available and future technologies that are not yet a part of routine guidelines. ICD, CRT, and other implantable devices continue to save lives, decrease hospitalizations, and evolve the management of patients with heart failure beyond the capabilities of optimal guideline-directed medical therapy alone.

Systemic Sympathoexcitation Was Associated with Paraventricular Hypothalamic Phosphorylation of Synaptic CaMKIIα and MAPK/ErK

Systemic administration of adrenergic agonist (Isoproterenol; ISOP) is known to facilitate cardiovascular changes associated with heart failure through an upregulation of cardiac toll-like receptor 4 (TLR4). Furthermore, previous studies have shown that cardiac tissue-specific deletion of TLR4 protects the heart against such damage. Since the autonomic regulation of systemic cardiovascular function originates from pre-autonomic sympathetic centers in the brain, it is unclear how a systemically driven sympathetic change may affect the pre-autonomic paraventricular hypothalamic nuclei (PVN) TLR4 expression. Here, we examined how change in PVN TLR4 was associated with alterations in the neurochemical cytoarchitecture of the PVN in systemic adrenergic activation. After 48 h of intraperitoneal 150 mg/kg ISOP treatment, there was a change in PVN CaMKIIα and MAPK/ErK expression, and an increase in TLR4 in expression. This was seen as an increase in p-MAPK/ErK, and a decrease in synaptic CaMKIIα expression in the PVN (p < 0.01) of ISOP treated mice. Furthermore, there was an upregulation of vesicular glutamate transporter (VGLUT 2; p < 0.01) and a decreased expression of GABA in the PVN of Isoproterenol (ISOP) treated WT mice (p < 0.01). However, after a PVN-specific knockdown of TLR4, the effect of systemic administration of ISOP was attenuated, as indicated by a decrease in p-MAPK/ErK (p < 0.01) and upregulation of CaMKIIα (p < 0.05). Additionally, loss of inhibitory function was averted while VGLUT2 expression decreased when compared with the ISOP treated wild type mice and the control. Taken together, the outcome of this study showed that systemic adrenergic activation may alter the expression, and phosphorylation of preautonomic MAPK/ErK and CaMKIIα downstream of TLR4. As such, by outlining the roles of these kinases in synaptic function, we have identified the significance of neural TLR4 in the progression, and attenuation of synaptic changes in the pre-autonomic sympathetic centers.

Arrhythmias in the Heart Transplant Patient

Orthotopic heart transplantation (OHT) is currently the most effective long-term therapy for patients with end-stage cardiac disease, even as left ventricular devices show markedly improved outcomes. As surgical techniques and immunosuppressive regimens have been refined, short-term mortality caused by sepsis has decreased, while morbidity caused by repeated rejection episodes and vasculopathy has increased, and is often manifested by arrhythmias. These chronic transplant complications require early and aggressive multidisciplinary treatment. Understanding the relationship between arrhythmias and these complications in the acute and chronic stages following OHT is critical in improving patient prognosis, as arrhythmias may be the earliest or sole presentation. Finally, decentralised/ denervated hearts represent a unique opportunity to investigate the underlying mechanisms of arrhythmias.

Postoperative arrhythmias after cardiac surgery: incidence, risk factors, and therapeutic management

Arrhythmias are a known complication after cardiac surgery and represent a major cause of morbidity, increased length of hospital stay, and economic costs. However, little is known about incidence, risk factors, and treatment of early postoperative arrhythmias. Both tachyarrhythmias and bradyarrhythmias can present in the postoperative period. In this setting, atrial fibrillation is the most common heart rhythm disorder. Postoperative atrial fibrillation is often self-limiting, but it may require anticoagulation therapy and either a rate or rhythm control strategy. However, ventricular arrhythmias and conduction disturbances can also occur. Sustained ventricular arrhythmias in the recovery period after cardiac surgery may warrant acute treatment and long-term preventive strategy in the absence of reversible causes. Transient bradyarrhythmias may be managed with temporary pacing wires placed at surgery, but significant and persistent atrioventricular block or sinus node dysfunction can occur with the need for permanent pacing. We provide a complete and updated review about mechanisms, risk factors, and treatment strategies for the main postoperative arrhythmias.

Atrial Tachyarrhythmias After Cardiac Transplantation

Cardiac transplant recipients demonstrate a unique substrate for atrial tachyarrhythmias owing to the surgical techniques involved. Surgical modification of the atria during transplant surgery has both proarrhythmic and antiarrhythmic effects detailed in this paper. Cavotricuspid isthmus-dependent right atrial flutter is the most common arrhythmia identified. Atrial fibrillation is uncommon owing to obligatory surgical pulmonary vein isolation. Donor hearts can also contain pre-existing accessory pathways or dual AV nodal physiology causing supraventricular tachycardia for which adenosine treatment is not recommended, but catheter ablation is curable.

Safety and efficacy of ibutilide in heart transplant recipients

In this report we describe our experience with ibutilide, a relatively new Class III anti-arrhythmic agent, in 8 heart transplant patients with supraventricular tachycardia in various settings (3 patients with rejection, 2 after endomyocardial biopsy). Ibutilide treatment was successful in all patients, with the arrhythmia recurring early in 1 patient. There were no complications.

Adverse drug reactions in patients with cardiovascular disease

Adverse drug reactions (ADRs) occur frequently in modern medical practice, increasing morbidity and mortality and inflating the cost of care. Patients with cardiovascular disease are particularly vulnerable to ADRs due to their advanced age, polypharmacy, and the influence of heart disease on drug metabolism. The ADR potential for a particular cardiovascular drug varies with the individual, the disease being treated, and the extent of exposure to other drugs. Knowledge of this complex interplay between patient, drug, and disease is a critical component of safe and effective cardiovascular disease management. The majority of significant ADRs involving cardiovascular drugs are predictable and therefore preventable. Better patient education, avoidance of polypharmacy, and clear communication between physicians, pharmacists, and patients, particularly during the transition between the inpatient to outpatient settings, can substantially reduce ADR risk.

Left ventricular contractility in response to upright isometric exercise in heart transplant recipients and healthy men

PURPOSE

We evaluated left ventricular contractility during upright isometric exercise, in heart transplant recipients (HTRs) and in healthy controls, using ejection fraction and end-systolic pressure/volume ratio indexes.

METHODS

Fifteen healthy men (40 +/- 13 years) and 10 HTRs (42 +/- 12 years) underwent dead lift (DL) test at 30% of maximal effort for 3 minutes. Echocardiographic variables were measured during the final 45 seconds.

RESULTS

During DL test, HTRs were significantly different (P < .01) from controls in all parameters except end-diastolic volume. DL test had lower mean values of ejection fraction (49.9% +/- 8.3% vs 67.0% +/- 4.3%, respectively) and left ventricular end-systolic pressure/volume ratio (3.5 +/- 0.7 vs 5.5 +/- 1.2, respectively) whereas higher values of end-systolic volume (51.0 +/- 9.4 mL vs 34.1 +/- 5.3 mL, respectively). Importantly, an intergroup effect was found in end-systolic pressure/volume ratio, further signifying differential response of HTRs. End-systolic pressure/volume ratio increased consistently (P < .001) in both groups, whereas the overall main effect of ejection fraction response was not significant.

CONCLUSIONS

Left ventricular function during upright isometric exercise displays differential pattern of response in HTRs in comparison with healthy controls. However, cardiac contractility in HTRs remained stable at peak systolic blood pressure produced by the isometric DL exercise. Results suggest that both ejection fraction and end-systolic pressure/volume ratio indexes can be used for assessment of ventricular function in patients after heart transplantation.

Effects of physical training on cardiovascular control after heart transplantation

BACKGROUND

Exercise performance in heart-transplanted patients increases with respect to pre-transplantation but remains subnormal, and it does not improve with time after surgery. Possible causes include persisting denervation, and sympathetic vasoconstriction inducing functional vascular abnormalities that prevent adequate increase in blood flow to the exercising limbs. We tested the effects of physical training on baroreceptors-mediated control of heart rate and blood pressure in recently heart-transplanted subjects.

METHODS

Patients were randomly allocated to physical training (n=13, 30 min cycling at 60-70% of peak oxygen consumption for 5 days/week for 6 months) or to control (n=11). Upright exercise test to exhaustion was performed at the beginning of the study after 3 and 6 months. Reflex changes in RR interval and blood pressure in response to sinusoidal neck suction (6 and 12 cycles/min 0 to -30 mm Hg swing) were considered as evidence of reinnervation and baroreflex control of blood pressure, respectively.

RESULTS

After 6 months peak oxygen consumption (p<0.001), exercise time (p<0.01) and workload (p<0.01) increased in trained patients. Before training RR interval and blood pressure were not modified by neck suction. After physical training systolic (p<0.01) and diastolic blood pressure decreased, RR interval and blood pressure could be modulated (p<0.05) by slow (6 cycles/min) neck suction, indicating initial cardiac sympathetic reinnervation and restored sensitivity to autonomic modulation on the arteries. No changes were observed in controls.

CONCLUSIONS

Physical training improved exercise performance and the control exerted by the autonomic nervous system through the sympathetic nerves at both cardiac and vascular level.

Vasomotor responses to decreased venous return: effects of cardiac deafferentation in humans

We compared haemodynamic and peripheral vasomotor responses to lower body negative pressure (LBNP) in cardiac transplant recipients who had undergone bicaval anastomoses, involving right atrial deafferentation (-RA), and the conventional procedure in which some atrial baroreceptor afferents remain intact (+RA). We measured mean forearm blood flow (FBF) responses using Doppler/ultrasound during three randomised trials involving 0 (baseline), -20 and -40 mmHg LBNP in 15 transplant recipients (9 -RA, 6 +RA) and in eight healthy matched controls. A significant effect of LBNP on FBF existed between control and transplant groups (P < 0.05; two-way ANOVA). Mild LBNP (-20 mmHg), significantly decreased FBF by 29.7 +/- 10.0% relative to baseline in +RA subjects (P < 0.05), whereas the 17.7 +/- 10.3% decrease in -RA subjects was not significant. In response to -40 mmHg LBNP, FBF significantly decreased in control (42.4 +/- 4.6%, P < 0.05) and +RA subjects (33.3 +/- 11.4%, P < 0.05) with no significant change in the -RA group. The response of systolic blood pressure (SBP) to -40 mmHg significantly differed between groups (P < 0.05): -RA subjects decreased significantly (P < 0.05) whilst the decrease in SBP in +RA subjects did not achieve significance and control subjects exhibited an increase. The heart rate increase from baseline to -40 mmHg was significantly attenuated in -RA relative to controls and the +RA group (P < 0.05). The present study demonstrates that atrial deafferentation impairs reflex vasomotor control of the circulation in response to low- and high-level LBNP, indicating that atrial deafferentation may contribute to abnormal arterial pressure regulation.

[Perioperative implications of heart transplant]

Over the past 30 years, heart transplantation has evolved into a definitive therapy for patients with end-stage cardiomyopathy. However, perioperative management of patients undergoing heart transplantation remains a challenge for anesthesiologists. The presence of biventricular failure, arrhythmias and associated multisystem organ dysfunction may contribute to significant intraoperative hemodynamic instability prior to the initiation of cardiopulmonary bypass (CPB). Even after an uneventful transplantation, weaning from CPB may be difficult. Acute right ventricular failure can develop in the recipient secondary to pre-existing pulmonary hypertension. Treatment options frequently focus on therapeutic interventions directed towards decreasing pulmonary vascular resistance and improving right ventricular contractility. Intraoperative use of transesophageal echocardiography (TEE) enables the anesthesiologist to diagnose acute right ventricular failure early on and guide therapy. Concurrent pathology including kinking of the pulmonary artery anastomosis or valvular insufficiency in the transplanted heart can also be recognized and addressed. The number of patients undergoing cardiac transplantation is continually increasing. In addition, the use of more effective immunosuppressive agents has curtailed transplant rejection and permitted longer survival. Consequently, heart transplant recipients are more frequently presenting for non-cardiac surgical procedures. Thus, an understanding of physiological and pharmacological implications associated with heart transplantation is crucial for managing these patients in the perioperative period.

Acute cardiovascular responses to leg-press resistance exercise in heart transplant recipients

BACKGROUND

Reduced skeletal muscle strength is characteristic of individuals following heart transplantation. Weight lifting exercise has been demonstrated as an effective means by which to increase muscular strength in other cardiac patients but the appropriateness of this form of exercise in heart transplant patients has not been investigated. The purpose of this study was to describe the cardiovascular responses of heart transplant patients to a single, prolonged bout of weight lifting training.

METHODS

Twenty-three heart transplant recipients were stratified into early (Early; 3 months; n=6), intermediate (Intermediate; 1-3 years; n=7) and late (Late; 5-14 years; n=10) post transplant groups and studied in four experimental conditions: supine rest, upright rest, single leg-press exercise (28 repetitions over 2 min 20 s at 50% 1 repetition maximum) and recovery. Swan-Ganz catheterization allowed measurement of right heart pressures and cardiac output by thermodilution. Systemic arterial pressures and heart rate were measured continuously using a non-invasive finger cuff.

RESULTS

Cardiac output increased by 30, 40 and 54% during exercise in Early, Intermediate and Late, respectively. Heart rate increased by 4.5% in Early compared to 11 and 16% increases in Intermediate and Late. At peak exercise, systolic blood pressures reached average values of 179+/-9, 180+/-14 and 176+/-8 mmHg in Early, Intermediate and Late, respectively. Average mean pulmonary artery pressure did not exceed 30 mmHg and average pulmonary wedge pressure did not exceed 15 mmHg in any group during the exercise.

CONCLUSIONS

These observations indicate that a lengthened set of single leg-press exercise at a moderate lifting intensity can be performed within safe and acceptable physiological limits in patients following heart transplantation. To better address the specific rehabilitation needs of heart transplant recipients, future research should focus on developing training programs which include weight lifting exercise.

Exaggerated chronotropic and energetic response to dobutamine after orthotopic cardiac transplantation

BACKGROUND

After heart transplantation, the transplanted denervated heart displays both an exaggerated chronotropic and an exaggerated inotropic response to circulating catecholamines. This study assessed whether denervated transplanted hearts also display an exaggerated energetic response when challenged with dobutamine.

METHODS AND RESULTS

A total of 18 heart transplant recipients and 14 normal volunteers underwent measurements of myocardial oxygen consumption (MVO2), external work (EW), and pressure-volume area (PVA), at rest and during infusion of dobutamine. At rest, calculated myocardial (PVA/MVO2) and mechanical (EW/MVO2) efficiencies were similar among transplant recipients and normal volunteers. During low-dose dobutamine infusion (8 microg/kg/min), transplant recipients exhibited a larger increase in heart rate (to 126 +/- 14 vs 87 +/- 26 beats/min, p < 0.001) and MVO2 (to 269 +/- 43 vs 233 +/- 19 J/min/100g, p < 0.05) and a smaller increase in EW (64 +/- 18 vs 72 +/- 13 J/min/100g, p < 0.05) and PVA (70 +/- 16 vs 81 +/- 13 J/min/100g, p < 0.05) than did normal volunteers. As a result, both myocardial (26 +/- 4 vs 35 +/- 4%, p < 0.05) and mechanical (23 +/- 4 vs 30 +/- 4%, p < 0.001) efficiencies were lower during dobutamine infusion in transplant recipients than in normal volunteers. During the infusion of a higher dose of dobutamine (19 microg/kg/min), the chronotropic and inotropic responses of heart transplant recipients were even more exaggerated. The fall in myocardial efficiency induced by dobutamine correlated with the increase in heart rate (r = -0.58) and could be reproduced in normal volunteers by coadministration of atropine.

CONCLUSIONS

Transplant recipients exhibit a larger fall in contractile efficiency and a larger oxygen-wasting effect during dobutamine infusion than do normal volunteers. Because normal volunteers pre-medicated with atropine presented with a similar increase in heart rate and a similar fall in efficiency, the exaggerated energetic response of transplanted hearts to dobutamine likely resulted from the same mechanisms as their chronotropic supersensitivity, i.e., the loss of inhibitory parasympathetic innervation.

Rate-responsive pacing improves exercise tolerance in heart transplant recipients: a pilot study

BACKGROUND

Chronotropic incompetence is one cause of diminished exercise capacity in heart transplant recipients. If reinnervation occurs, it often is late after transplantation and is not always accompanied by functional improvements in peak heart rate and appropriate tachycardia during exercise. To determine the efficacy of rate-responsive pacing on peak heart rate and exercise capacity, the authors studied eight male heart transplant recipients (age 57 +/- 12 years; 23 +/- 9 months after transplantation) that had either atrial or dual-chambered pacemakers.

METHODS

All subjects completed two maximal graded exercise tests (GXT) using the Naughton treadmill protocol. During the first GXT, pacemakers were programmed for bradycardia support only and without rate responsiveness (unpaced). After a 14-day regimen of beta blockade with metoprolol to nullify the influence of circulating catecholamines on heart rate, subjects performed the second GXT with pacemakers programmed to respond optimally in the rate-responsive mode (paced).

RESULTS

Peak heart rate (149 versus 129 bpm), peak oxygen uptake (18.9 versus 15.4 mL/kg/min), treadmill time to exhaustion (14.6 versus 12.4 min), and minute ventilation (76.7 versus 66.2 L/min) were significantly increased (P < or = 0.05) during the paced versus unpaced GXT.

CONCLUSIONS

The results of this study demonstrate that chronotropic support of the transplanted heart using a rate-responsive pacemaker, with activity-based sensors programmed for maximal sensitivity, improves both peak heart rate and exercise capacity in heart transplant recipients significantly more than circulating catecholamines alone.

Hemodynamic monitoring by double-indicator dilution technique in patients after orthotopic heart transplantation

STUDY OBJECTIVES

A transpulmonary thermal-dye dilution (TDD) technique using cold indocyanine green dye was utilized to monitor cardiac index (CI) and preload in patients after heart transplantation. Preload, determined by intrathoracic blood volume index (ITBVI) and global end-diastolic volume index (GEDVI), was compared to central venous pressure (CVP) and pulmonary artery occlusion pressure (PAOP) and was correlated with stroke volume index (SVI).

DESIGN

Prospective study.

SETTING

Cardiac surgery ICU at a university hospital.

PATIENTS

Forty patients (34 men, 6 women) with a mean (+/- SD) age of 54.4+/-8.5 years after orthotopic heart transplantation.

MEASUREMENTS AND RESULTS

CI and preload measurements were performed with TDD and pulmonary artery catheters in the ICU at 3, 6, 12, 24, 36, 48, and 72 h postoperatively. The femoral artery CI was compared with the pulmonary artery CI. Changes in the ITBVI, GEDVI, CVP, and PAOP were correlated with changes in the SVI. No difference was found between the femoral and pulmonary arterial CIs (r = 0.98 [bias, 0.35 L/min/m(2)]; p<0.01). There was no statistically significant correlation between changes in the SVI and changes in CVP (r = -0.23,) and PAOP (r = -0.06). However, the ITBVI (r = 0.65; p<0.01) and the GEDVI (r = 0.73; p<0.01) were significantly correlated to changes in the SVI. Changes in the same direction occurred between the SVI and the GEDVI as well as between the SVI and the ITBVI in 76.3% and 71.9% of patients, respectively, while CVP and PAOP also changed in the same direction as SVI in only 35.1% and 36.9% of patients, respectively.

CONCLUSION

ITBVI and GEDVI are more reliable preload parameters than CVP and PAOP. Even in denervated hearts, ITBVI and GEDVI show significant correlations with SVI. The transpulmonary indicator dilution technique is promising and should be investigated further.

Safety profile and hemodynamic responses to beta-adrenergic stimulation by dobutamine in heart transplant patients

STUDY OBJECTIVE

Dobutamine stress echocardiography (DSE) has been used as a screening tool for coronary artery disease after heart transplantation and in the identification of patients at risk for development of cardiac events. However, the safety profile of high-dose dobutamine in heart transplant patients has not been systematically examined. Accordingly, we studied the safety profile and hemodynamic responses to escalating doses of dobutamine to determine the influence of denervation.

DESIGN

We assessed the hemodynamic responses, heart rate (HR), and arterial BP indexes (mean arterial pressure, systolic BP [SBP], diastolic BP [DBP], and pulse pressure) to dobutamine in 87 heart transplant patients ([mean +/- SD] age, 51 +/- 1 years) and compared the results with 97 nontransplant patients (age, 63.0 +/- 1 years) who served as innervated control subjects.

MEASUREMENTS AND RESULTS

The baseline HR (84 +/- 2 vs 69 +/- 1 beats/minute, respectively; p < 0.001) and peak HR response (144 +/- 2 vs 117 +/- 2 beats/minute, respectively; p < 0.001) were significantly higher in heart transplant patients than in the nontransplant patients. SBP was lower in heart transplant patients than in nontransplant patients at baseline (131 +/- 2 vs 138 +/- 2 mm Hg, respectively; p < 0.02) and at peak (150 +/- 3 vs 158 +/- 3 mm Hg, respectively; p < 0.03). However, baseline DBP was higher in transplant patients than in nontransplant patients (86 +/- 1 vs 77 +/- 1 mm Hg, respectively; p < 0.001). The decrease in DBP was similar in both groups (15 mm Hg). The dose-response curve for HR was shifted leftward in heart transplant patients. Heart transplant patients attained a higher absolute HR at each infusion stage and higher rates of increase, but the decrease in DBP was not significantly different in the two groups.

CONCLUSIONS

These results show that there is augmented chronotropic response and expected decline in DBP in response to dobutamine infusion in heart transplant patients. This increase in myocardial oxygen demand and a decrease in coronary perfusion pressure may be important mechanisms in the development of ischemic abnormalities that are detectable as regional dysynergy on echocardiography.

The Cox maze iii procedure: parallel normalization of sinus node dysfunction, improvement of atrial function, and recovery of the cardiac autonomic nervous system

OBJECTIVE

The Cox maze III procedure includes isolation of the pulmonary veins and multiple incisions in both atria in what corresponds to partial autotransplantation and partial denervation of the heart. The aim of this prospective longitudinal study was to identify physiologic effects of reinnervation on changes in heart rate at rest and in response to various stimulations and on atrial function after the Cox maze III procedure.

PATIENTS AND METHODS

Power spectral analysis of heart rate variability, exercise testing, 24-hour Holter monitoring, electrocardiography, and transthoracic and transesophageal echocardiography were performed in 30 adult patients after the combined Cox maze III procedure and mitral valve surgery (maze group). They were prospectively followed up at 1, 3, 6, and 12 months after the operation. The results were compared with those of 15 heart transplant recipients (transplant group) and normal probands (healthy adults, n = 12).

RESULTS

The physiologic effects of denervation with no differences in cardiac autonomic activity between the groups were seen early after the operation. Later, evidence of autonomic reinnervation was observed only in the maze group but not in the transplant group. Inappropriate heart rate responses during physical exercise were clearly evident in both groups after 1 and 3 months, with progressive improvement seen between 6 and 12 months only in the maze group. Left atrial function after the Cox maze procedure improved parallel to the recovery of sinus node function.

CONCLUSION

Progressive improvement of sinus node function and atrial contractions with significant functional normalization 1 year after the Cox maze procedure corresponded to functional reinnervation and recovery of the autonomic nervous system.

Vasovagal syncope in heart transplant patients during dental surgery

The pathogenesis of vasovagal syncope during emotional stress is controversial. Several authors have postulated that the vasodepressor response in humans may be initiated by C-fiber mechanoreceptors situated in the heart and connected via cardiac vagal afferents to the medullary center for cardiovascular control. It has been argued that heart transplant patients cannot show any vasovagal reaction because the donor heart is transplanted completely deprived of any vagal or sympathetic innervation. In this report, however, 3 episodes of vasovagal syncope are documented in 3 heart transplant patients undergoing periodontal surgery. During vasovagal syncope in each of these patients, a dramatic fall in systolic blood pressure (from 137 +/- 5 mmHg to 76 +/- 3.6 mmHg) was detected, but, in contrast to what is observable in normal subjects, the heart rate did not show any relevant change (from 96.7 +/- 4.5 beats per minute to 102.6 +/- 7.6 beats per minute). These unexpected findings emphasize the marginal role of the heart on the pathogenesis of the vasovagal syncope and underline the fact that a vasovagal reaction can develop even in the absence of the bradycardia that is the primary symptom usually reported in the literature.

Nonpharmacologic validation of the intrinsic heart rate in cardiac transplant recipients

BACKGROUND

The maximum sinus rate during exertion in humans is inversely related to age. However, the sinus rate at rest is quite variable. The intrinsic heart (IHR) following pharmacologic blockade of autonomic tone with propranolol and atropine has been proposed as a test of sinus node function and is related to age by the linear regression equation: IHR = 118.1 - (0.57 x age). Whether this relationship exists for transplanted hearts for which the donor sinus node is denervated has not been determined.

METHODS

The relationship between the resting heart rate and the age of the donor heart was examined in 103 patients 1 year following orthotopic cardiac transplantation in the absence of rejection or intercurrent illness. Patients receiving beta-blockers, calcium blockers, antiarrhythmic drugs, digitalis, theophylline, or with biopsy evidence of rejection or abnormal coronary arteriograms were excluded from analysis.

RESULTS

The recipient age, left ventricular ejection fraction, pulmonary capillary pressure, cardiac index, donor heart ischemic time and cardiopulmonary bypass time did not correlate with the rate of the resting donor sinus node. The resting heart rate was inversely related to age of the donor heart by the linear regression equation: HR = 112.0 - (046 x age).

CONCLUSION

The resting rate of the denervated sinus node is related to donor age with a regression equation that is similar, though slightly slower, than that predicted after pharmacologic autonomic blockade.

Exercise and organ transplantation

Life-saving treatment of disease by organ transplantation has become increasingly important. Annually over 35,000 transplantations of vital organs are carried out world-wide and the demand for knowledge regarding exercise in daily life for transplant recipients is growing. The present review describes whole-body and organ reactions to both acute exercise and regular physical training in persons who have undergone heart, lung, liver, kidney, pancreas or bone marrow transplantation. In response to acute exercise, the majority of cardiovascular, hormonal and metabolic changes are maintained after transplantation. However, in heart transplant recipients organ denervation reduces the speed of heart rate increase in response to exercise. Furthermore, lack of sympathetic nerves to transplanted organs impairs the normal insulin and renin responses to exercise in pancreas and kidney transplant recipients, respectively. In contrast, surgical removal of sympathetic liver nerves does not inhibit hepatic glucose production during exercise, and denervation of the lungs does not impair the ability to increase ventilation during physical exertion. Most studies show that physical training results in an improved endurance and strength capacity in almost all groups of transplant recipients, which is of importance for their daily life. With a little precaution, organ transplant recipients can perform exercise and physical training and obtain effects comparable with those achieved in the healthy population of similar age.

Comparison of in vitro cardiovascular function with in vivo echocardiographic assessment after long-term administration of cyclosporine to rats

Clinical reports indicate that cyclosporine is able to induce heart failure without rejection after heart transplantation. This supposition is supported by ex vivo animal studies, yet ex vivo studies do not account for the potential of counter-regulatory mechanisms, and the clinical observations seem rare in comparison with the number of patients treated with cyclosporine. We hypothesized that cyclosporine administration to rats would fail to exhibit any effect on myocardial contractility in vivo notwithstanding a negative influence ex vivo. Transthoracic echocardiographic examinations (two-dimensional targeted M-mode tracings) were done in a blinded fashion before and after 1-week treatment of rats (10 or 20 mg/kg/day cyclosporine i.p. vs. vehicle). After excision of the hearts, contractility and changes in coronary tone were determined ex vivo during flow-constant perfusion. Neither cyclosporine nor vehicle treatment resulted in changes of echocardiographic parameters (left ventricular diameter, fractional shortening). The heart rate was significantly increased in the high-dose cyclosporine group. This group showed a significant 38% reduction of contractility during the subsequent perfusion ex vivo, whereas low-dose cyclosporine or vehicle had no effect on myocardial performance. Vasoconstriction did not account for this impairment, because coronary tone was unaltered. Cyclosporine, given in doses used in animal studies, impairs myocardial contractility ex vivo but fails to exhibit any effect on myocardial performance in vivo, possibly because of an increase in sympathetic tone. Considering that the denervated transplanted heart in humans is even sensitized to adrenergic stimuli, our finding makes unlikely a clinical contribution of cyclosporine to failure after orthotopic heart transplantation.

Cardiac output responses during exercise in volume-expanded heart transplant recipients

The mechanisms responsible for immediate adjustments in cardiac output at onset of exercise, in the absence of neural drive, are not well defined in heart transplant (HT) recipients. Seven male HT recipients (mean +/- SD 57 +/- 6 years) and 7 age-matched sedentary normal control subjects (mean age 57 +/- 5 years) performed constant load cycle exercise at 40% of peak power output (Watts). Cardiac output and plasma norepinephrine were determined at rest and every 30 seconds during the first 5 minutes of exercise and at minutes 6, 8, and 10. All subjects were admitted to the General Clinical Research Center for determination of plasma volume. After 3 days of equilibration to a controlled and standardized diet, plasma volume was measured using a modified Evans Blue Dye (T-1824) dilution technique. Heart rate at rest was higher in the HT group (105 +/- 12 vs 74 +/- 6 beats/min), but during submaximum exercise, heart rates in the control group increased more rapidly (p < or = 0.05) and to a greater magnitude (54 +/- 7% vs 17 +/- 4% above rest). Stroke volume at rest was lower in HT recipients (45 +/- 4 vs 68 +/- 9 ml) but was significantly augmented immediately after onset of exercise (30 seconds) and the relative increase was greater than controls at peak exercise (61% vs 38% greater than baseline). Cardiac output at rest was within the normal range in both groups (4.58 +/- 0.27 vs 4.94 +/- 0.40 L/min). Relative increases in cardiac output were similar (p > or = 0.05) for the HT (106 +/- 12%) and control groups (97 +/- 10%). Plasma norepinephrine did not become significantly greater than resting values until approximately 4 minutes after onset of exercise in both groups. Blood volume, normalized for body weight, was 12% greater in the HT group. Thus, HT recipients with expanded blood volume (12%) augment stroke volume immediately after the onset of exercise. Plasma norepinephrine levels contribute negligibly to the rapid adjustment in cardiac output. Rather, we speculate that abrupt on-transit increases in stroke volume are due to augmented venous return, secondary to expanded blood volume.

Function of the transplanted heart: unique physiology and therapeutic implications

Orthotopic heart transplantation has become an established treatment for selected patients with refractory heart failure. Long-term survival rates are superior to those resulting from other forms of therapy for that patient population. In addition, an improved quality of life has been reported by many patients. However, despite these encouraging results, the transplanted heart does not provide the recipient with normal cardiac function. Cardiac physiology after heart transplantation is unique. Resting hemodynamics differ significantly, acutely and chronically, from those seen in healthy subjects. In addition, neural mechanisms undergo changes as a result of surgical denervation. Afferent control mechanisms and efferent responses both are altered, leading to important clinical abnormalities. Examples include altered cardiovascular responses to exercise, altered cardiac electrophysiology, and altered responses to cardiac pharmacologic agents. An improved understanding of the changes in cardiac physiology, which occur after heart transplant, may allow the care of these patients to be optimized.

Management of the cardiac transplant recipient: roles of the transplant cardiologist and primary care physician

Cardiac transplantation has become an accepted treatment for selected patients with end-stage heart failure. Despite a successful transplant, denervated transplanted hearts respond differently to cardiac drugs than nontransplanted hearts. The treatments for bradycardia, tachycardia, and hypotension are different than for nontransplanted hearts. Despite the improvement in long-term survival, a number of complications may occur posttransplantation. These complications include, allograft rejection, infection, allograft coronary artery disease, and malignancy. Additionally, posttransplant patients may have complications from the immunosuppressive agents cyclosporine, prednisione, and azathioprine. Such complications include drug interactions with commonly prescribed medications, hypertension, hyperlipidemia, osteoporosis, and gastrointestinal complications. The purpose of this article is to discuss the management of the cardiac transplant recipient as it relates to the aforementioned complications. Management of the cardiac transplantation patient by the primary care physician will also be discussed, including indications for consultation by the primary care physician with the transplant center.

Enhanced myocardial 18F-2-fluoro-2-deoxyglucose uptake after orthotopic heart transplantation assessed by positron emission tomography

OBJECTIVES

We sought to assess the relation between glucose metabolism, myocardial perfusion and cardiac work after orthotopic heart transplantation.

BACKGROUND

The metabolic profile of the transplanted cardiac muscle is affected by the lack of sympathetic innervation, impaired inotropic function, chronic vasculopathy, allograft rejection and immunosuppressive therapy. In relation to myocardial perfusion and cardiac work, glucose metabolism has not previously been studied in heart transplant recipients.

METHODS

Regional myocardial blood flow (ml.min-1.g-1) and 18F-2-fluoro-2-deoxyglucose (18FDG) uptake rate (ml.s-1.g-1) were measured after an overnight fast in 9 healthy male volunteers (mean age +/- SD 32 +/- 7 years) and in 10 male patients (mean age 50 +/- 10 years) who had a nonrejecting heart transplant, normal left ventricular function and no angiographic evidence of epicardial coronary sclerosis. Measurements were made by using dynamic positron emission tomography (PET) with 15O-labeled water and 18FDG, respectively. Heart rate and blood pressure were also measured for calculation of rate-pressure product.

RESULTS

18FDG uptake was similar in all heart regions in the patients and volunteers (intrasubject regional variably 12 +/- 8% and 16 +/- 12%, respectively, p = 0.51). Regional myocardial blood flow was similarly evenly distributed (intrasubject regional variability 14 +/- 10% and 12 +/- 8%, respectively, p = 0.67). Mean 18FDG uptake and myocardial blood flow values for the whole heart are given because no regional differences were identified. 18FDG uptake was on average 196% higher in the patients than in the volunteers (2.90 +/- 1.79 x 10(-4) vs. 0.98 +/- 0.38 x 10(-4) ml.s-1.g-1, p = 0.006). Regional myocardial blood flow and rate-pressure product were similarly increased in the patient group, but by only 41% (1.14 +/- 0.3 vs. 0.81 +/- 0.13 ml.min-1.g-1, p = 0.008) and 53% (11,740 +/- 2,830 vs. 7,689 +/- 1,488, p = 0.001), respectively.

CONCLUSIONS

18FDG uptake is homogeneously increased in normally functioning nonrejecting heart transplants. This finding suggests that glucose may be a preferred substrate in the transplanted heart. The magnitude of this observed increase is significantly greater than that observed for myocardial blood flow or cardiac work. In the patient group, the latter two variables were increased to a similar degree over values in control hearts, indicating a coupling between cardiac work load and myocardial blood flow. The disproportionate rise in 18FDG uptake may be accounted for by inefficient metabolic utilization of glucose by the transplanted myocardium or by the influence of circulating catecholamines, which may stimulate glucose uptake independently of changes in cardiac work load.

Effects of chemical denervation with 6-hydroxydopamine on myocardial responsiveness to isoproterenol in rabbits

This study examined the hypothesis that chemical denervation with 6-hydroxydopamine (6-OHDA) would increase myocardial responsiveness to isoproterenol. Five days previously, 15 New Zealand white rabbits were given 60 mg/kg 6-OHDA intravenously. Fifteen control rabbits received vehicle. Hemodynamic, coronary blood flow (CBF), and cardiac output measurements were obtained before and during isoproterenol infusion (0.5 microgram/kg/min for 15 min). Norepinephrine tissue content, beta-adrenoceptor number (Bmax) and affinity (Kd), cyclic AMP content and cyclic AMP-phosphodiesterase (PDE) activity were measured in the subepicardium (EPI) and subendocardium (ENDO). Myocardial norepinephrine content was significantly decreased from 1263 +/- 292 (EPI) and 874 +/- 221 ng/g tissue (ENDO) in the control to 148 +/- 33 (EPI) and 90 +/- 45 ng/g tissue (ENDO) in the denervated group. There were no significant changes in cyclic AMP-PDE activity or Bmax and Kd of beta-adrenoceptors. Cyclic AMP content was similar at baseline, but controls had a significantly larger increase (123-155%) during isoproterenol infusion when compared to the denervated group (27-37%). The denervated animals showed a smaller increase in cardiac output during isoproterenol infusion (from 203 +/- 30 to 235 +/- 26 ml/min), when compared to the control animals (from 135 +/- 18 to 216 +/- 42 ml/min). Baseline CBF was significantly higher in the EPI but not ENDO of the denervated group (185 +/- 20 ml/100 g/min in EPI and 150 +/- 8 in ENDO) compared to the control group (108 +/- 13 in EPI and 133 +/- 17 in ENDO). The relative increase in CBF during isoproterenol infusion was smaller in the denervated group (44-45%) than the control group (107-109%). Isoproterenol infusions of 0.1 and 2.5 micrograms/kg/min showed similarly depressed coronary blood flow responses in denervated animals. Thus, the chemically denervated animals did not have beta-adrenoceptor upregulation, exhibited a lesser increase in cyclic AMP with isoproterenol, and had a reduced functional and coronary blood flow response to isoproterenol. This occurred without any significant change in beta-adrenoceptor number or affinity, or in cyclic AMP-phosphodiesterase activity, indicating there may be receptor uncoupling or other changes in the signal transduction pathway.

Prevalence and prognostic significance of atrial arrhythmias after orthotopic cardiac transplantation

OBJECTIVES

We studied the duration and prognostic significance of atrial arrhythmias in the denervated transplanted heart, specifically the occurrence of atrial fibrillation in the absence of vagal modulation.

BACKGROUND

Substantial animal data indicate that vagally induced dispersion of atrial refractoriness plays a central role in the induction and maintenance of atrial fibrillation.

METHODS

We studied the occurrence of atrial arrhythmias in the denervated hearts of 88 consecutive orthotopic transplantations in 85 patients by means of continuous telemetry and all available electrocardiographic tracings.

RESULTS

Fifty percent of recipients (44 of 88) developed at least one atrial arrhythmia. Atrial fibrillation occurred 23 times (21 recipients), atrial flutter 39 times (26 recipients), ectopic atrial tachycardia 3 times (3 recipients) and supraventricular tachycardia 18 times (11 recipients). The number of atrial fibrillation and atrial flutter episodes did not differ (23 vs. 39, p = 0.072), but the mean duration of atrial flutter was longer than that of atrial fibrillation (37.0 +/- 10 vs. 6.6 +/- 3.6 h, p = 0.014). Atrial fibrillation was associated with an increased risk of subsequent death (10 of 21 recipients with vs. 15 of 67 without atrial fibrillation, risk ratio 3.15 +/- 0.18, p = 0.005 by Cox proportional hazards model). All 5 recipients who developed "late" atrial fibrillation (> 2 weeks after transplantation) died versus 5 of 16 who developed atrial fibrillation within the first 2 weeks (p = 0.007). Causes of death included rejection (three recipients), allograft failure (two recipients), infection (three recipients) and multiorgan failure (two recipients). Atrial fibrillation was not associated with age, gender, ischemic time, reason for transplantation, echocardiographic variables, invasive hemodynamic variables or biopsy grade. Mean time from atrial arrhythmia to echocardiography was 2.7 +/- 3.3 days; that to biopsy was 4.8 +/- 6.3 days. Atrial flutter was not associated with subsequent death. Only 7 (15.9%) of 44 recipients demonstrated moderate or severe allograft rejection at the time of the arrhythmia.

CONCLUSIONS

Atrial arrhythmias occur frequently in the denervated transplanted heart, often in the absence of significant rejection. Late atrial fibrillation may be associated with an increased all-cause mortality.

Anaesthesia for non-cardiac surgery in the post-cardiac transplant patient

As survival and quality of life continue to improve for cardiac transplant recipients, the number of patients with functioning heart transplants who present for surgery continues to increase. The conditions for which surgery may be required, the specific problems relating to anaesthesia and the necessary measures which should be taken to ensure an uncomplicated clinical course are discussed. A clear understanding of the physiology and pharmacology of the denervated heart is essential for these patients to undergo safely anaesthesia and surgery.

Training effects on the hydromineral endocrine responses of cardiac transplant patients

Cardiac transplant patients manifest several haemodynamic changes as well as altered peripheral responses to exercise which may disrupt body fluid regulation. This study examined the effect on an endurance training programme on the exercise-induced hydromineral endocrine responses of heart transplant patients. Seven patients underwent a square-wave exercise test before and after a 6-week training programme. The tests were performed at the same absolute intensity but, during training, the workload was increased to maintain the same relative exercise intensity. Pretraining results were compared to those obtained from age-matched controls. Training improved physical capacity, producing a significant increase in maximal tolerated power and workload between the first and last training session (P < 0.05, P < 0.001, respectively). Haematocrit and osmolality were increased in both groups at the end of exercise (P < 0.01) but changes observed post-training did not differ from pretraining values. Apart from atrial natriuretic peptide (ANP), which showed significantly higher concentrations at rest and during exercise (P < 0.01), the changes in hydromineral hormones of the patients resembled those of the controls. Basal plasma renin activity (PRA) was slightly raised prior to training (P < 0.07) compared to the controls and post-training. For both PRA and aldosterone, a significant training effect was revealed when both the exercise-stimulated increase and postexercise decline were considered (P < 0.05), possibly reflecting lower noradrenaline concentrations. Training had no effect on either basal or exercise stimulated ANP levels, which is compatible with the theory that ANP regulation is largely under mechanical rather than sympathetic nervous system control.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiographic and electrophysiologic properties of cardiac allografts

The increasing number of heart transplant patients requires that physicians be able to recognize the electrocardiographic (ECG) and electrophysiologic properties of cardiac allografts. Cardiac allografts are characterized by modifications of resting ECGs and frequent arrhythmias in the postoperative period, and the loss of autonomic nervous control illustrated by permanent tachycardia and loss of heart rate variability during 24-hour ambulatory ECG recording. Some clinical and experimental observations suggest a mid-term reinnervation of the cardiac allograft, but this requires histologic confirmation. The electrophysiologic characteristics of the denervated myocardium are similar to those of the innervated myocardium at rest. However, supersensitivity to circulating catecholamines has been observed in cardiac allografts as in experimentally denervated hearts, which is responsible for a progressive increase in heart rate during exercise and a slow decrease during recovery. Supersensitivity of the denervated heart to acetylcholine may explain the high prevalence of donor sinus dysfunction due to impairment of its automaticity. More often, the sinus node dysfunction is transient and can be treated with an adenosine antagonist, such as theophylline, before permanent implantation of a pacemaker. In the case of pacemaker implantation, synchronization of the donor atria with the recipient atria is desirable, and an endocardial lead implantation is preferred. Several electrophysiologic changes have been observed during acute cardiac allograft rejection. From experimental studies, the most important of these are the disturbance of conduction in the atria and the atrioventricular node and a decrease in the amplitude of the ventricular potential. Initial studies on isolated myocytes show profound changes in membrane conductance during experimental cardiac rejection. The development of new noninvasive detection methods of cardiac allograft rejection, such as intramyocardial voltage electrogram monitoring and high-resolution ECG, could help early diagnosis.

In vivo quantification of myocardial muscarinic receptors in heart transplant patients

BACKGROUND

Decreased myocardial adenylate cyclase activity in response to guanine nucleotide stimulation has been recently demonstrated in denervated myocardium of transplant patients, suggesting that changes in left ventricular muscarinic receptors may occur.

METHODS AND RESULTS

The concentration and affinity constants of myocardial muscarinic receptors were determined by positron emission tomography with 11C-labeled methylquinuclidinyl benzilate (MQNB), a specific hydrophilic antagonist, in six transplant patients 4.7 +/- 2.3 months after surgery and in six normal subjects. Patients had no sign of cardiac rejection at endomyocardial biopsy. After intravenous injections of MQNB, time-activity curves were obtained over different regions of interest and were fitted to a nonlinear mathematical model. No difference in the concentration of muscarinic receptors was found in transplant patients compared with control subjects: 24 +/- 4 versus 26 +/- 7 pmol/mL tissue, respectively (P = NS). The association rate constant k+1, the dissociation rate constant k-1, and thus the equilibrium-dissociation constant Kd were the same in transplant patients compared with control subjects.

CONCLUSIONS

Despite known decreased GTP-stimulated adenylate cyclase activity in transplant patients, the density and affinity constants of myocardial muscarinic receptors are not altered. This suggests abnormalities of the signal-transduction function, such as a change in the guanine nucleotide binding proteins.

Effect of beta blockade on the neurohumoral and cardiopulmonary response to dynamic exercise in cardiac transplant recipients

OBJECTIVE

To determine the effects of a small dose of beta blocker on neurohumoral and cardiopulmonary responses after cardiac transplantation.

BACKGROUND

Cardiac transplant recipients have a reduced exercise capacity and abnormal cardiovascular responses to exercise. The sympathoadrenal response to exercise has been shown to be abnormal with high venous noradrenaline. The effect of beta blockade on these neurohumoral mechanisms has not been defined.

METHODS

10 non-rejecting cardiac transplant recipients were studied. Patients carried out graded exercise to a symptom limited maximum. Blood samples were taken during exercise. Concentrations of noradrenaline, adrenaline, and atrial natriuretic peptide and plasma renin activity were measured. The next day, the exercise and sampling procedure were repeated after an oral dose of propranolol (40 mg).

RESULTS

Patients tolerated exercise poorly after beta blockade, which was reflected in the maximum workload reached. Heart rate and blood pressure were significantly higher at rest and during exercise before beta blockade. Although there was no significant difference when resting, mean (SEM) noradrenaline concentrations during peak exercise were higher after beta blockade (16.2 (2) v 23.6 (2.9) nmol/l, p = 0.001). Adrenaline concentrations at peak exercise were also greater after beta blockade (0.89 (0.31) v 1.18 (0.38) nmol/l, p = 0.055). Atrial natriuretic peptide concentrations tended to be higher after beta blockade (118.75 (50.2) v 169.79 (39.3) pmol/l, p = 0.36). There was no significant change in plasma renin activity.

CONCLUSIONS

A small oral dose of a competitive beta blocker such as propranolol has an adverse effect on exercise tolerance and cardiovascular response to exercise in cardiac transplant recipients. There are also increased concentrations of circulating noradrenaline and therefore, sympathetic activity during exercise. beta blockers should be used with caution in cardiac transplant recipients.

Changes in cAMP formation in mononuclear leukocytes of heart and renal transplant recipients

In mononuclear leukocytes (MNL) of renal transplant recipients treated with cyclosporine A and prednisone, an increase of basal cAMP generation has been observed. In order to characterize the mechanisms underlying changes of cAMP generation in patients who were treated with immunosuppressives following heart transplantation, we investigated the beta-adrenoceptor--G protein--adenylate cyclase signal transduction cascade in heart transplant recipients and for comparison in renal transplant recipients as well as controls. Basal cAMP formation in MNL was elevated in heart transplant recipients by 272% and in renal transplant recipients by 148% compared to controls. Following beta-adrenoceptor stimulation with isoprenaline, cAMP formation in MNL of heart transplant recipients was similar to the controls, but was enhanced in renal transplant recipients to 138%. Investigation of beta-adrenoceptor density on MNL as a possible cause for increased cAMP formation revealed similar receptor numbers in controls and in cardiac or renal transplant recipients. Furthermore, the increase of the beta-adrenoceptor density on MNL, which is observed following infusion of isoprenaline, was similar in controls and heart transplant recipients. The amount of pertussis- and cholera toxin substrates was the same in heart transplant recipients as in controls. In contrast, MNL of renal transplant recipients showed a marked increase of Gs alpha by 45% and a smaller albeit significant increase of Gi alpha by 15%, as judged by cholera toxin and pertussis toxin labeling, respectively. Investigation of inotropic parameters by echocardiography under control conditions and during the infusion of increasing concentrations of isoprenaline revealed no difference in the basal contractility and the inotropic response to beta-adrenergic stimulation in controls and heart transplant recipients. It is concluded that changes of G-protein expression are involved in the increase of the cAMP-generation in MNL of heart transplant recipients. These alterations in MNL cannot be taken as a model of cellular function in the transplanted heart, but it is reasonable to suggest that elevations of cAMP formation in MNL may contribute to the immunosuppressive effects of the treatment with cyclosporine A or corticosteroids, the mechanism of which could be an alteration of Gs alpha or the catalyst in renal transplant recipients and the catalyst in heart transplant recipients which occurs without any changes of beta-adrenoceptors.