Preoperative Amiodarone and Primary Graft Dysfunction in Heart Transplantation

BACKGROUND

Preoperative amiodarone effects on postorthotopic heart transplant (OHT) outcomes remain controversial.

OBJECTIVE

The purpose of this study was to determine the effect of cumulative pre-OHT amiodarone exposure on severe primary graft dysfunction (PGD).

METHODS

We retrospectively reviewed adult OHT recipients between August 2012 and June 2018. Primary outcome was severe PGD in patients receiving amiodarone at 3, 6, and 12 months prior to OHT compared with those not receiving amiodarone. Secondary outcomes included intensive care unit (ICU) and hospital length of stay, duration of mechanical ventilation, early graft failure (EGF), mortality at 3, 6, and 12 months post-OHT, and 30-day incidence of postoperative tachyarrhythmias, bradycardia, permanent pacemaker implantation, and rejection.

RESULTS

Incidence of severe PGD was 12.5% in those who received amiodarone compared to 6.8% in those who did not (14 vs 6, P = 0.18). Cumulative preoperative amiodarone significantly increased the odds of severe PGD at 3 months (odds ratio [OR]: 1.03; 95% confidence interval [CI]: 1.001-1.06; P = 0.044) and 6 months (OR: 1.02, 95% CI: 1.003-1.044; P = 0.024) in a multivariate logistic regression. Patients on amiodarone had significantly higher rates of postoperative bradycardia (13.4% vs 4.5%, P = 0.03).

CONCLUSION AND RELEVANCE

A trend toward increased PGD was present in patients receiving preoperative amiodarone. This finding combined with the regression showing significantly increased odds of PGD with increasing 3 and 6 month cumulative amiodarone dose is clinically concerning. Escalation of care with pacemaker implantation was required more frequently in patients on pre-OHT amiodarone.

Rare Variant Genetics and Dilated Cardiomyopathy Severity: The DCM Precision Medicine Study

BACKGROUND

Dilated cardiomyopathy (DCM) can lead to advanced disease, defined herein as necessitating a durable left ventricular assist device or a heart transplant (LVAD/HT). DCM is known to have a genetic basis, but the association of rare variant genetics with advanced DCM has not been studied.

METHODS

We analyzed clinical and genetic sequence data from patients enrolled between 2016 and 2021 in the US multisite DCM Precision Medicine Study, which was a geographically diverse, multiracial, multiethnic cohort. Clinical evaluation included standardized patient interview and medical record query forms. DCM severity was classified into 3 groups: patients with advanced disease with LVAD/HT; patients with an implantable cardioverter defibrillator (ICD) only; or patients with no ICD or LVAD/HT. Rare variants in 36 DCM genes were classified as pathogenic or likely pathogenic or variants of uncertain significance. Confounding factors we considered included demographic characteristics, lifestyle factors, access to care, DCM duration, and comorbidities. Crude and adjusted associations between DCM severity and rare variant genetic findings were assessed using multinomial models with generalized logit link.

RESULTS

Patients' mean (SD) age was 51.9 (13.6) years; 42% were of African ancestry, 56% were of European ancestry, and 44% were female. Of 1198 patients, 347 had LVAD/HT, 511 had an ICD, and 340 had no LVAD/HT or ICD. The percentage of patients with pathogenic or likely pathogenic variants was 26.2%, 15.9%, and 15.0% for those with LVAD/HT, ICD only, or neither, respectively. After controlling for sociodemographic characteristics and comorbidities, patients with DCM with LVAD/HT were more likely than those without LVAD/HT or ICD to have DCM-related pathogenic or likely pathogenic rare variants (odds ratio, 2.3 [95% CI, 1.5-3.6]). The association did not differ by ancestry. Rare variant genetic findings were similar between patients with DCM with an ICD and those without LVAD/HT or ICD.

CONCLUSIONS

Advanced DCM was associated with higher odds of rare variants in DCM genes adjudicated as pathogenic or likely pathogenic, compared with individuals with less severe DCM. This finding may help assess the risk of outcomes in management of patients with DCM and their at-risk family members.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT03037632.

Genetic Architecture of Dilated Cardiomyopathy in Individuals of African and European Ancestry

Importance

Black patients with dilated cardiomyopathy (DCM) have increased familial risk and worse outcomes than White patients, but most DCM genetic data are from White patients.

Objective

To compare the rare variant genetic architecture of DCM by genomic ancestry within a diverse population of patients with DCM.

Design

Cross-sectional study enrolling patients with DCM who self-identified as non-Hispanic Black, Hispanic, or non-Hispanic White from June 7, 2016, to March 15, 2020, at 25 US advanced heart failure programs. Variants in 36 DCM genes were adjudicated as pathogenic, likely pathogenic, or of uncertain significance.

Exposure

Presence of DCM.

Main Outcomes and Measures

Variants in DCM genes classified as pathogenic/likely pathogenic/uncertain significance and clinically actionable (pathogenic/likely pathogenic).

Results

A total of 505, 667, and 26 patients with DCM of predominantly African, European, or Native American genomic ancestry, respectively, were included. Compared with patients of European ancestry, a lower percentage of patients of African ancestry had clinically actionable variants (8.2% [95% CI, 5.2%-11.1%] vs 25.5% [95% CI, 21.3%-29.6%]), reflecting the lower odds of a clinically actionable variant for those with any pathogenic variant/likely pathogenic variant/variant of uncertain significance (odds ratio, 0.25 [95% CI, 0.17-0.37]). On average, patients of African ancestry had fewer clinically actionable variants in TTN (difference, -0.09 [95% CI, -0.14 to -0.05]) and other genes with predicted loss of function as a disease-causing mechanism (difference, -0.06 [95% CI, -0.11 to -0.02]). However, the number of pathogenic variants/likely pathogenic variants/variants of uncertain significance was more comparable between ancestry groups (difference, -0.07 [95% CI, -0.22 to 0.09]) due to a larger number of non-TTN non-predicted loss of function variants of uncertain significance, mostly missense, in patients of African ancestry (difference, 0.15 [95% CI, 0.00-0.30]). Published clinical case-based evidence supporting pathogenicity was less available for variants found only in patients of African ancestry (P < .001).

Conclusion and Relevance

Patients of African ancestry with DCM were less likely to have clinically actionable variants in DCM genes than those of European ancestry due to differences in genetic architecture and a lack of representation of African ancestry in clinical data sets.

Screening for Dilated Cardiomyopathy in At-Risk First-Degree Relatives

BACKGROUND

Cardiovascular screening is recommended for first-degree relatives (FDRs) of patients with dilated cardiomyopathy (DCM), but the yield of FDR screening is uncertain for DCM patients without known familial DCM, for non-White FDRs, or for DCM partial phenotypes of left ventricular enlargement (LVE) or left ventricular systolic dysfunction (LVSD).

OBJECTIVES

This study examined the yield of clinical screening among reportedly unaffected FDRs of DCM patients.

METHODS

Adult FDRs of DCM patients at 25 sites completed screening echocardiograms and ECGs. Mixed models accounting for site heterogeneity and intrafamilial correlation were used to compare screen-based percentages of DCM, LVSD, or LVE by FDR demographics, cardiovascular risk factors, and proband genetics results.

RESULTS

A total of 1,365 FDRs were included, with a mean age of 44.8 ± 16.9 years, 27.5% non-Hispanic Black, 9.8% Hispanic, and 61.7% women. Among screened FDRs, 14.1% had new diagnoses of DCM (2.1%), LVSD (3.6%), or LVE (8.4%). The percentage of FDRs with new diagnoses was higher for those aged 45 to 64 years than 18 to 44 years. The age-adjusted percentage of any finding was higher among FDRs with hypertension and obesity but did not differ statistically by race and ethnicity (16.2% for Hispanic, 15.2% for non-Hispanic Black, and 13.1% for non-Hispanic White) or sex (14.6% for women and 12.8% for men). FDRs whose probands carried clinically reportable variants were more likely to be identified with DCM.

CONCLUSIONS

Cardiovascular screening identified new DCM-related findings among 1 in 7 reportedly unaffected FDRs regardless of race and ethnicity, underscoring the value of clinical screening in all FDRs.

Effectiveness of the Family Heart Talk Communication Tool in Improving Family Member Screening for Dilated Cardiomyopathy: Results of a Randomized Trial

BACKGROUND

Managing disease risk among first-degree relatives of probands diagnosed with a heritable disease is central to precision medicine. A critical component is often clinical screening, which is particularly important for conditions like dilated cardiomyopathy (DCM) that remain asymptomatic until severe disease develops. Nonetheless, probands are frequently ill-equipped to disseminate genetic risk information that motivates at-risk relatives to complete recommended clinical screening. An easily implemented remedy for this key issue has been elusive.

METHODS

The DCM Precision Medicine Study developed Family Heart Talk, a booklet designed to help probands with DCM communicate genetic risk and the need for cardiovascular screening to their relatives. The effectiveness of the Family Heart Talk booklet in increasing cardiovascular clinical screening uptake among first-degree relatives was assessed in a multicenter, open-label, cluster-randomized, controlled trial. The primary outcome measured in eligible first-degree relatives was completion of screening initiated within 12 months after proband enrollment. Because probands randomized to the intervention received the booklet at the enrollment visit, eligible first-degree relatives were limited to those who were alive the day after proband enrollment and not enrolled on the same day as the proband.

RESULTS

Between June 2016 and March 2020, 1241 probands were randomized (1:1) to receive Family Heart Talk (n=621) or not (n=620) within strata defined by site and self-identified race/ethnicity (non-Hispanic Black, non-Hispanic White, or Hispanic). Final analyses included 550 families (n=2230 eligible first-degree relatives) in the Family Heart Talk arm and 561 (n=2416) in the control arm. A higher percentage of eligible first-degree relatives completed screening in the Family Heart Talk arm (19.5% versus 16.0%), and the odds of screening completion among these first-degree relatives were higher in the Family Heart Talk arm after adjustment for proband randomization stratum, sex, and age quartile (odds ratio, 1.30 [1-sided 95% CI, 1.08-∞]). A prespecified subgroup analysis did not find evidence of heterogeneity in the adjusted intervention odds ratio across race/ethnicity strata (P=0.90).

CONCLUSIONS

Family Heart Talk, a booklet that can be provided to patients with DCM by clinicians with minimal additional time investment, was effective in increasing cardiovascular clinical screening among first-degree relatives of these patients.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT03037632.

Prevalence and Cumulative Risk of Familial Idiopathic Dilated Cardiomyopathy

Importance

Idiopathic dilated cardiomyopathy (DCM) aggregates in families, and early detection in at-risk family members can provide opportunity to initiate treatment prior to late-phase disease. Most studies have included only White patients, yet Black patients with DCM have higher risk of heart failure-related hospitalization and death.

Objective

To estimate the prevalence of familial DCM among DCM probands and the age-specific cumulative risk of DCM in first-degree relatives across race and ethnicity groups.

Design, Setting, and Participants

A family-based, cross-sectional study conducted by a multisite consortium of 25 US heart failure programs. Participants included patients with DCM (probands), defined as left ventricular systolic dysfunction and left ventricular enlargement after excluding usual clinical causes, and their first-degree relatives. Enrollment commenced June 7, 2016; proband and family member enrollment concluded March 15, 2020, and April 1, 2021, respectively.

Exposures

The presence of DCM in a proband.

Main Outcomes and Measures

Familial DCM defined by DCM in at least 1 first-degree relative; expanded familial DCM defined by the presence of DCM or either left ventricular enlargement or left ventricular systolic dysfunction without known cause in at least 1 first-degree relative.

Results

The study enrolled 1220 probands (median age, 52.8 years [IQR, 42.4-61.8]; 43.8% female; 43.1% Black and 8.3% Hispanic) and screened 1693 first-degree relatives for DCM. A median of 28% (IQR, 0%-60%) of living first-degree relatives were screened per family. The crude prevalence of familial DCM among probands was 11.6% overall. The model-based estimate of the prevalence of familial DCM among probands at a typical US advanced heart failure program if all living first-degree relatives were screened was 29.7% (95% CI, 23.5% to 36.0%) overall. The estimated prevalence of familial DCM was higher in Black probands than in White probands (difference, 11.3% [95% CI, 1.9% to 20.8%]) but did not differ significantly between Hispanic probands and non-Hispanic probands (difference, -1.4% [95% CI, -15.9% to 13.1%]). The estimated prevalence of expanded familial DCM was 56.9% (95% CI, 50.8% to 63.0%) overall. Based on age-specific disease status at enrollment, estimated cumulative risks in first-degree relatives at a typical US advanced heart failure program reached 19% (95% CI, 13% to 24%) by age 80 years for DCM and 33% (95% CI, 27% to 40%) for expanded DCM inclusive of partial phenotypes. The DCM hazard was higher in first-degree relatives of non-Hispanic Black probands than non-Hispanic White probands (hazard ratio, 1.89 [95% CI, 1.26 to 2.83]).

Conclusions and Relevance

In a US cross-sectional study, there was substantial estimated prevalence of familial DCM among probands and modeled cumulative risk of DCM among their first-degree relatives.

Trial Registration

ClinicalTrials.gov Identifier: NCT03037632.

Noninvasive Assessment of Cardiac Output: Accuracy and Precision of the Closed-Circuit Acetylene Rebreathing Technique for Cardiac Output Measurement

Background

Accurate assessment of cardiac output is critical to the diagnosis and management of various cardiac disease states; however, clinical standards of direct Fick and thermodilution are invasive. Noninvasive alternatives, such as closed‐circuit acetylene (C₂H₂) rebreathing, warrant validation.

Methods and Results

We analyzed 10 clinical studies and all available cardiopulmonary stress tests performed in our laboratory that included a rebreathing method and direct Fick or thermodilution. Studies included healthy individuals and patients with clinical disease. Simultaneous cardiac output measurements were obtained under normovolemic, hypovolemic, and hypervolemic conditions, along with submaximal and maximal exercise. A total of 3198 measurements in 519 patients were analyzed (mean age, 59 years; 48% women). The C₂H₂ method was more precise than thermodilution in healthy individuals with half the typical error (TE; 0.34 L/min [r=0.92] and coefficient of variation, 7.2%) versus thermodilution (TE=0.67 [r=0.70] and coefficient of variation, 13.2%). In healthy individuals during supine rest and upright exercise, C₂H₂ correlated well with thermodilution (supine: r=0.84, TE=1.02; exercise: r=0.82, TE=2.36). In patients with clinical disease during supine rest, C₂H₂ correlated with thermodilution (r=0.85, TE=1.43). C₂H₂ was similar to thermodilution and nitrous oxide (N₂O) rebreathing technique compared with Fick in healthy adults (C₂H₂ rest: r=0.85, TE=0.84; C₂H₂ exercise: r=0.87, TE=2.39; thermodilution rest: r=0.72, TE=1.11; thermodilution exercise: r=0.73, TE=2.87; N₂O rest: r=0.82, TE=0.94; N₂O exercise: r=0.84, TE=2.18). The accuracy of the C₂H₂ and N₂O methods was excellent (r=0.99, TE=0.58).

Conclusions

The C₂H₂ rebreathing method is more precise than, and as accurate as, the thermodilution method in a variety of patients, with accuracy similar to an N₂O rebreathing method approved by the US Food and Drug Administration.

Mechanisms of Chronotropic Incompetence in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Chronotropic incompetence is common in heart failure with preserved ejection fraction (HFpEF) and is associated with impaired aerobic capacity. We investigated the integrity of cardiac β-receptor responsiveness, an important mechanism involved in exertional increases in HR, in HFpEF and control subjects.

METHODS

Thirteen carefully screened patients with HFpEF and 13 senior controls underwent exercise testing and graded isoproterenol infusion to quantify cardiac β-receptor-mediated HR responses. To limit autonomic neural influences on heart rate (HR) during isoproterenol, dexmedetomidine and glycopyrrolate were given. Isoproterenol doses were increased incrementally until HR increased by 30 beats per minute. Plasma levels of isoproterenol at each increment were measured by liquid chromatography with electrochemical detection and plotted against HR.

RESULTS

Peak VO₂ and HR (117±15 versus 156±15 beats per minute; P<0.001) were lower in HFpEF than senior controls. Cardiac β-receptor sensitivity was lower in HFpEF compared to controls (0.156±0.133 versus 0.254±0.166 beats per minute/[isoproterenol ng/mL]; P<0.001). Seven of 13 HFpEF subjects had β-receptor sensitivity similar to senior controls but still had lower peak HRs (122±14 versus 156±15 beats per minute; P<0.001).

CONCLUSIONS

Contrary to our hypothesis, patients with HFpEF displayed impaired cardiac β-receptor sensitivity compared with senior controls. In the 7 out of 13 patients with HFpEF with age-appropriate β-receptor sensitivity, peak HR remained low, suggesting impaired sinus node β-receptor function may not fully account for low exercise HR response. Rather in some patients with HFpEF, chronotropic incompetence might reflect premature cessation of exercise before maximal sinus node activation. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02524145.

Recurrent pump thrombosis is common after axial continuous-flow left ventricular assist device exchange

In selected patients with left ventricular assist device-associated infection or malfunction, pump exchange may become necessary after conservative treatment options fail and heart transplantation is not readily available. We examined the survival and complication rate in patients (⩾19 years of age) who underwent HeartMate II to HeartMate II exchange at our institution from 1 January 2010 to 28 February 2018. Clinical outcomes were analyzed and compared for patients who underwent exchange for pump thrombosis (14 patients), breach of driveline integrity (5 patients), and device-associated infection (2 patients). There were no differences in 30-day mortality (p = 0.58), need for temporary renal replacement therapy (p = 0.58), right ventricular mechanical support (p = 0.11), and postoperative stroke (p = 0.80) among groups. Survival at 1 year was 90% ± 7% for the whole cohort and 85% ± 10% for those who underwent exchange for pump thrombosis. In patients exchanged for device thrombosis, freedom from re-thrombosis and survival free from pump re-thrombosis at 1 year were 49% ± 16% and 42% ± 15%, respectively. No association of demographic and clinical variables with the risk of recurrent pump thrombosis after the first exchange was identified. Survival after left ventricular assist device exchange compares well with published results after primary left ventricular assist device implantation. However, recurrence of thrombosis was common among patients who required a left ventricular assist device exchange due to pump thrombosis. In this sub-group, consideration should be given to alternative strategies to improve the outcomes.

Reversing the Cardiac Effects of Sedentary Aging in Middle Age-A Randomized Controlled Trial: Implications For Heart Failure Prevention

BACKGROUND

Poor fitness in middle age is a risk factor for heart failure, particularly heart failure with a preserved ejection fraction. The development of heart failure with a preserved ejection fraction is likely mediated through increased left ventricular (LV) stiffness, a consequence of sedentary aging. In a prospective, parallel group, randomized controlled trial, we examined the effect of 2 years of supervised high-intensity exercise training on LV stiffness.

METHODS

Sixty-one (48% male) healthy, sedentary, middle-aged participants (53±5 years) were randomly assigned to either 2 years of exercise training (n=34) or attention control (control; n=27). Right heart catheterization and 3-dimensional echocardiography were performed with preload manipulations to define LV end-diastolic pressure-volume relationships and Frank-Starling curves. LV stiffness was calculated by curve fit of the diastolic pressure-volume curve. Maximal oxygen uptake (Vo₂max) was measured to quantify changes in fitness.

RESULTS

Fifty-three participants completed the study. Adherence to prescribed exercise sessions was 88±11%. Vo₂max increased by 18% (exercise training: pre 29.0±4.8 to post 34.4±6.4; control: pre 29.5±5.3 to post 28.7±5.4, group×time P<0.001) and LV stiffness was reduced (right/downward shift in the end-diastolic pressure-volume relationships; preexercise training stiffness constant 0.072±0.037 to postexercise training 0.051±0.0268, P=0.0018), whereas there was no change in controls (group×time P<0.001; pre stiffness constant 0.0635±0.026 to post 0.062±0.031, P=0.83). Exercise increased LV end-diastolic volume (group×time P<0.001), whereas pulmonary capillary wedge pressure was unchanged, providing greater stroke volume for any given filling pressure (loading×group×time P=0.007).

CONCLUSIONS

In previously sedentary healthy middle-aged adults, 2 years of exercise training improved maximal oxygen uptake and decreased cardiac stiffness. Regular exercise training may provide protection against the future risk of heart failure with a preserved ejection fraction by preventing the increase in cardiac stiffness attributable to sedentary aging.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT02039154.

Volume loading augments cutaneous vasodilatation and cardiac output of heat stressed older adults

KEY POINTS

Age-related changes in cutaneous microvascular and cardiac functions limit the extent of cutaneous vasodilatation and the increase in cardiac output that healthy older adults can achieve during passive heat stress. However, it is unclear if these age-related changes in microvascular and cardiac functions maximally restrain the levels of cutaneous vasodilatation and cardiac output that healthy older adults can achieve during heat stress. We observed that rapid volume loading, performed during passive heat stress, augments both cutaneous vasodilatation and cardiac output in healthy older humans. These findings demonstrate that the microcirculation of healthy aged skin can further dilate during passive heat exposure, despite peripheral limitations to vasodilatation. Furthermore, healthy older humans can augment cardiac output when cardiac pre-load is increased during heat stress.

ABSTRACT

Primary ageing markedly attenuates cutaneous vasodilatation and the increase in cardiac output during passive heating. However, it remains unclear if these responses are maximally restrained by age-related changes in cutaneous microvascular and cardiac functions. We hypothesized that rapid volume loading performed during heat stress would increase cardiac output in older adults without parallel increases in cutaneous vasodilatation. Twelve young (Y: 26 ± 5 years) and ten older (O: 69 ± 3 years) healthy adults were passively heated until core temperature increased by 1.5°C. Cardiac output (thermodilution), forearm vascular conductance (FVC, venous occlusion plethysmography) and cutaneous vascular conductance (CVC, laser-Doppler) were measured before and after rapid infusion of warmed saline (15 mL kg^-1 , ∼7 min). While heat stressed, but prior to saline infusion, cardiac output (O: 6.8 ± 0.4 vs. Y: 9.4 ± 0.6 L min^-1 ), FVC (O: 0.08 ± 0.01 vs. Y: 0.17 ± 0.02 mL (100 mL min^-1  mmHg^-1 )^-1 ), and CVC (O: 1.29 ± 0.34 vs. Y: 1.93 ± 0.30 units mmHg^-1 ) were lower in older adults (all P < 0.01). Rapid saline infusion increased cardiac output (O: +1.9 ± 0.3, Y: +1.8 ± 0.7 L min^-1 ), FVC (O: +0.015 ± 0.007, Y: +0.048 ± 0.013 mL (100 mL min^-1  mmHg^-1 )^-1 ), and CVC (O: +0.28 ± 0.10, Y: +0.29 ± 0.16 units mmHg^-1 ) in both groups (all P < 0.01). The absolute increase in cardiac output and CVC were similar between groups, whereas FVC increased to a greater extent in young adults (P < 0.01). These results demonstrate that healthy older adults can achieve greater levels of cutaneous vasodilatation and cardiac output during passive heating.

Implantation of a left ventricular assist device to provide long-term support for end-stage Duchenne muscular dystrophy-associated cardiomyopathy

A young man with Duchenne muscular dystrophy presented to the UT Southwestern Neuromuscular Cardiomyopathy Clinic with advanced heart failure. Despite maximal medical therapy, his cardiac function continued to decline requiring initiation of inotrope therapy. Given the patient's clinical deterioration, a left ventricular assist device (LVAD) was implanted as destination therapy after undergoing a multidisciplinary assessment. The patient tolerated the surgical implantation of the LVAD without any significant complications, and he has had a relatively unremarkable course 38 months post‐LVAD implantation. A critical factor contributing to the long‐term success of this patient was the decision to select an LVAD that would not disrupt the diaphragm and thus preserve the respiratory muscle strength. This case demonstrates that permanent mechanical LVADs should be considered for appropriately selected Duchenne muscular dystrophy patients with medically refractory end‐stage cardiomyopathy.

Healthy aging does not compromise the augmentation of cardiac function during heat stress

During heat stress, stroke volume is maintained in young adults despite reductions in cardiac filling pressures. This is achieved by a general augmentation of cardiac function, highlighted by a left and upward shift of the Frank-Starling relation. In contrast, healthy aged adults are unable to maintain stroke volume during heat stress. We hypothesized that this would be associated with a lack of shift in the Frank-Starling relation. Frank-Starling relations were examined in 11 aged [69 ± 4 (SD) yr, 4 men/7 women] and 12 young (26 ± 5 yr, 6 men/6 women) adults during normothermic and heat stress (1.5°C increase in core temperature) conditions. During heat stress, increases in cardiac output were attenuated in aged adults (+2.5 ± 0.3 (95% CI) vs. young: +4.5 ± 0.5 l/min, P < 0.01) because of an attenuated chronotropic response (+30 ± 4 vs. young: +42 ± 5 beats/min, P < 0.01). In contrast to our hypothesis, a leftward shift of the Frank-Starling relation maintained stroke volume during heat stress in aged adults (76 ± 8 vs. normothermic: 74 ± 8 ml, P = 0.38) despite reductions in cardiac filling pressure (6.6 ± 1.0 vs. normothermic: 8.9 ± 1.1 mmHg, P < 0.01). In a subset of participants, volume loading was used to return cardiac filling pressure during heat stress to normothermic values, which resulted in a greater stroke volume for a given cardiac filling pressure in both groups. These results demonstrate that the Frank-Starling relation shifts during heat stress in healthy young and aged adults, thereby preserving stroke volume despite reductions in cardiac filling pressures.

Abcc9 is required for the transition to oxidative metabolism in the newborn heart

The newborn heart adapts to postnatal life by shifting from a fetal glycolytic metabolism to a mitochondrial oxidative metabolism. Abcc9, an ATP-binding cassette family member, increases expression concomitant with this metabolic shift. Abcc9 encodes a membrane-associated receptor that partners with a potassium channel to become the major potassium-sensitive ATP channel in the heart. Abcc9 also encodes a smaller protein enriched in the mitochondria. We now deleted exon 5 of Abcc9 to ablate expression of both plasma membrane and mitochondria-associated Abcc9-encoded proteins, and found that the myocardium failed to acquire normal mature metabolism, resulting in neonatal cardiomyopathy. Unlike wild-type neonatal cardiomyocytes, mitochondria from Ex5 cardiomyocytes were unresponsive to the KATP agonist diazoxide, consistent with loss of KATP activity. When exposed to hydrogen peroxide to induce cell stress, Ex5 neonatal cardiomyocytes displayed a rapid collapse of mitochondria membrane potential, distinct from wild-type cardiomyocytes. Ex5 cardiomyocytes had reduced fatty acid oxidation, reduced oxygen consumption and reserve. Morphologically, Ex5 cardiac mitochondria exhibited an immature pattern with reduced cross-sectional area and intermitochondrial contacts. In the absence of Abcc9, the newborn heart fails to transition normally from fetal to mature myocardial metabolism.-Fahrenbach, J. P., Stoller, D., Kim, G., Aggarwal, N., Yerokun, B., Earley, J. U., Hadhazy, M., Shi, N.-Q., Makielski, J. C., McNally, E. M. Abcc9 is required for the transition to oxidative metabolism in the newborn heart.

Impaired exercise tolerance and skeletal muscle myopathy in sulfonylurea receptor-2 mutant mice

By sensing intracellular energy levels, ATP-sensitive potassium (K(ATP)) channels help regulate vascular tone, glucose metabolism, and cardioprotection. SUR2 mutant mice lack full-length K(ATP) channels in striated and smooth muscle and display a complex phenotype of hypertension and coronary vasospasm. SUR2 mutant mice also display baseline cardioprotection and can withstand acute sympathetic stress better than normal mice. We now studied response to a form of chronic stress, namely that induced by 4 wk of daily exercise on SUR2 mutant mice. Control mice increased exercise capacity by 400% over the training period, while SUR2 mutant mice showed little increase in exercise capacity. Unexercised SUR2 mutant showed necrotic and regenerating fibers in multiple muscle skeletal muscles, including quadriceps, tibialis anterior, and diaphragm muscles. Unlike exercised control animals, SUR2 mutant mice did not lose weight, presumably due to less overall exertion. Unexercised SUR2 mutant mice showed a trend of mildly reduced cardiac function, measured by fractional shortening, (46 +/- 4% vs. 57 +/- 7% for SUR2 mutant and control, respectively), and this decrease was not exacerbated by chronic exercise exposure. Despite an improved response to acute sympathetic stress and baseline cardioprotection, exercise intolerance results from lack of SUR2 K(ATP) channels in mice.

Mice lacking sulfonylurea receptor 2 (SUR2) ATP-sensitive potassium channels are resistant to acute cardiovascular stress

Adenosine triphosphate-sensitive potassium (K(ATP)) channels are thought to mediate the stress response by sensing intracellular ATP concentration. Cardiomyocyte K(ATP) channels are composed of the pore-forming Kir6.2 subunit and the regulatory sulfonylurea receptor 2 (SUR2). We studied the response to acute isoproterenol in SUR2 null mice as a model of acute adrenergic stress and found that the episodic coronary vasospasm observed at baseline in SUR2 null mice was alleviated. Similar results were observed following administration of a nitric oxide donor consistent with a vasodilatory role. Langendorff-perfused hearts were subjected to global ischemia, and hearts from SUR2 null mice exhibited significantly reduced infarct size (54+/-4 versus 30+/-3%) and improved cardiac function compared to control mice. SUR2 null mice have hypertension and develop cardiac hypertrophy. However, despite longstanding hypertension, fibrosis was absent in SUR2 null mice. SUR2 null mice were administered nifedipine to block baseline coronary vasospasm, and hearts from nifedipine-treated SUR2 null mice exhibited increased infarct size compared to untreated SUR2 null mice (42+/-3% versus 54+/-3%). We conclude that conventional sarcolemmal cardiomyocyte K(ATP) channels containing full-length SUR2 are not required for mediating the response to acute cardiovascular stress.

The frequency of Baker's cysts associated with meniscal tears

We reviewed the films of 1760 patients who had magnetic resonance image scanning of the knee joint to assess the most common pathologic changes associated with an incidental finding of a Baker's cyst. Of the 1760 knees scanned, Baker's cysts were noted in 238. The cysts were classified as small (55%), medium (30%), or large (15%) and were primarily found on the medial side of the knee (94%). The menisci were evaluated and changes were classified as complete tears, where signal contacts the surface, or degenerative intrasubstance tears. One hundred eleven (47%) complete meniscal tears were found, and 88 (37%) degenerative tears. The majority of tears were found in the posterior horn of the medial meniscus (65 complete tears and 45 degenerative tears). Thus, 199 tears were found in 170 knees, and 106 of the 170 knees (62%) had tears of the posterior horn of the medial meniscus. Baker's cysts are frequent findings on physical examinations and on magnetic resonance imaging scans of the knee. They are thought to be due to intraarticular pathologic changes, usually posterior meniscal tears. This study documents the association between Baker's cysts and meniscal tears and notes that a complete tear is not necessary for the cyst to be present.

Screening adolescents for metallic foreign bodies before MR procedures

The report describes a case in which routine prescreening procedures were found to be inadequate for an adolescent patient referred for MR imaging. Recommendations are provided to correct this potential problem.

[Possibilities of MR tomography of diseases of the hand and wrist]

MRI studies of 63 patients with various abnormalities of the hand and wrist were analyzed. Studies were performed on scanners with a field strength of 0.35, 0.5, or 1.5 T. Imaging parameters included T1- and T2-weighted sequences in the coronal and transverse planes and contiguous slices 3-5 mm thick. In 37 patients with post-traumatic disorders, MRI revealed carpal avascular necrosis, tendon abnormalities and, in some cases, abnormalities of interosseous ligaments and the triangular fibrocartilage. In 15 patients with such inflammatory diseases as arthritis, tenosynovitis and carpal tunnel syndrome and in 11 patients with tumors, MRI provided clear delineation of osseous and soft tissue abnormalities. The current role of MRI in the diagnosis of hand and wrist abnormalities is discussed on the basis of these results.

[Magnetic resonance tomography in the determination of the functional stability of posterolateral lumbar spondylodeses]

MR tomography was used to assess functional lumbar stability in 30 patients with posterolateral fusions. The vertebral bodies of 9 of the 12 patients with unstable lumbar fusions presented with areas of decreased signal intensity on T1- and intermediately weighted images, which increased on T2-weighting. The vertebrae of 15 of the 18 patients with stable fusions demonstrated zones of increased signal intensity on T1- and intermediately weighted images, which were less intense or invisible on T2-weighing. Surgical correlation was available in 11 of the 30 patients studied. Hyperemia and inflammation appear to be responsible for the abnormal signal intensities in the patients with stable fusions, whereas an increase in adipose marrow due to decreased biomechanical stress is thought to account for the atypical signal intensities in the vertebral bodies of the patients with stable fusions. MR tomography seems to be a potential method for evaluating functional lumbar fusion stability. MR tomography may be particularly helpful in those patients with multiple back surgeries and possible instability, recurrent disc herniation, or postoperative fibrosis. MR is recommended in the patient, who appears clinically unstable, whose radiographs and CT, however, do not demonstrate fusion failure.

[Three-dimensional computerized tomography of diseases of the bones and joints]

Three-dimensional CT (3-DCT) surface reconstructions were generated in 157 patients with various disorders of the musculoskeletal system. Whereas generating the 3-D display of ligaments, tendons, intervertebral discs and nerve roots was difficult and time-consuming, the comprehension of complex abnormalities of bony structures was easier than with two-dimensional CT. 3-DCT was particularly useful in the preoperative planning of hip and spine surgeries while it also simplified the intraoperative orientation. 3-DCT proved to be a useful diagnostic method supplementing axial computed tomography.