Histopathologic and ultrastructural observations of acute and convalescent myocarditis: a serial endomyocardial biopsy study

Transient myocardial thickening after routine ovariohysterectomy in a 15-month-old Ragdoll cat

A 15-month-old female Ragdoll cat was evaluated for progressive lethargy, tachypnoea and increased respiratory effort for 1 week after routine ovariohysterectomy. Thoracic radiographs and an echocardiogram showed evidence of congestive heart failure and a hypertrophic cardiomyopathy phenotype, respectively. The maximum left ventricular wall thickness in end diastole was 6.2 mm. The serum cardiac troponin I concentration was 20.86 ng/mL. The cat was treated with furosemide and clopidogrel and discharged after 3 days. A repeat echocardiogram 2 weeks later showed complete resolution of the hypertrophic cardiomyopathy phenotype (maximum left ventricular wall thickness: 5.0 mm). A repeat cardiac troponin I concentration was 0.041 ng/mL. All cardiac medications were discontinued. A final recheck 4 weeks later revealed stable normal echocardiogram and further reduction in cardiac troponin I concentration to 0.004 ng/mL. This case report demonstrates that resolution of transient myocardial thickening can take 2 weeks after the echocardiographic diagnosis of left ventricular thickening.

Beyond Acute COVID-19: A Review of Long-term Cardiovascular Outcomes

Statistics Canada estimated that approximately 1.4 million Canadians suffer from long COVID. Although cardiovascular changes during acute SARS-CoV-2 infection are well documented, long-term cardiovascular sequelae are less understood. In this review, we sought to characterize adult cardiovascular outcomes in the months after acute COVID-19 illness. In our search we identified reports of outcomes including cardiac dysautonomia, myocarditis, ischemic injuries, and ventricular dysfunction. Even in patients without overt cardiac outcomes, subclinical changes have been observed. Cardiovascular sequelae after SARS-CoV-2 infection can stem from exacerbation of preexisting conditions, ongoing inflammation, or as a result of damage that occurred during acute infection. For example, myocardial fibrosis has been reported months after hospital admission for COVID-19 illness, and might be a consequence of myocarditis and myocardial injury during acute disease. In turn, myocardial fibrosis can contribute to further outcomes including dysrhythmias and heart failure. Severity of acute infection might be a risk factor for long-term cardiovascular consequences, however, cardiovascular changes have also been reported in young, healthy individuals who had asymptomatic or mild acute disease. Although evolving evidence suggests that previous SARS-CoV-2 infection might be a risk factor for cardiovascular disease, there is heterogeneity in existing evidence, and some studies are marred by measured and unmeasured confounders. Many investigations have also been limited by relatively short follow-up. Future studies should focus on longer term outcomes (beyond 1 year) and identifying the prevalence of outcomes in different populations on the basis of acute and long COVID disease severity.

Electrocardiographic changes are strongly correlated with the extent of cardiac inflammation in mice with Coxsackievirus B3-induced viral myocarditis

OBJECTIVE

Viral myocarditis (VM) can induce changes in myocardial electrical conduction and arrhythmia. However, their relationship with myocarditis-associated arrhythmic substrates in the heart such as inflammation and fibrosis is relatively unknown. This we have analyzed in the present study.

METHODS

C3H mice were infected with 1×10⁵ plaque-forming units Coxsackievirus B3 (CVB3, n=68) and were compared with uninfected control mice (n=10). Electrocardiograms (ECGs) were recorded in all conscious mice shortly before sacrifice and included heart rate; P-R interval; QRS duration; QTc interval and R-peak amplitude of lead II and aVF. Mice were sacrificed at 4, 7, 10, 21, 35 or 49 days post-infection. Cardiac lesion size, calcification, fibrosis and cellular infiltration of CD45+ lymphocytes, MAC3+ macrophages, Ly6G+ neutrophils and mast cells were quantitatively determined in cross-sections of the ventricles. Putative relations between ECG changes and lesion size and/or cardiac inflammation were then analyzed.

RESULTS

Significant transient reductions in QRS duration and R-peak amplitude occurred between 4 and 14 days post-infection and returned to baseline values thereafter. The magnitude of these ECG changes strongly correlated to the extent of lymphocyte (days 7 and 14), macrophage (days 7 and 10) and neutrophil (days 7) infiltration. The ECG changes did not significantly correlate with lesion size and fibrosis.

CONCLUSION

VM induces transient changes in myocardial electrical conduction that are strongly related to cellular inflammation of the heart. These data show that even in mild VM, with relatively little cardiac damage, the inflammatory infiltrate can form an important arrhythmogenic substrate.

[Reversible left ventricular hypertrophy and congestive heart failure due to suspected myocarditis in a cat in the course of FLUTD]

A 2.5-year-old castrated male domestic shorthair cat with a past pertinent history of FLUTD treatment 8 days earlier was presented during the night due to apathy and anorexia. Radiographs, ECG, blood pressure measurement and echocardiography revealed left-sided congestive heart failure, left ventricular concentric hypertrophy, left atrial dilation, severe diastolic dysfunction, hypotension, and vagotonus-associated sinus bradycardia with a first degree AV-block as well as a right bundle brunch block. NT-ProBNP and troponin I concentrations were elevated (NT-ProBNP > 1500 pmol/l, Troponin I 32.87 ng/ml). Presumptive diagnosis was acute myocarditis. Bartonella henselae PCR and Toxoplasma gondii IgM titer were negative. Initial IgG titer amounted to 1:32 (reference range: < 1:32) and on later testing this was negative. FeLV and FIV tests exhibited negative results. Coronavirus testing was not performed because the cat was vaccinated accordingly. A metastatic infection with Proteus mirabilis, which had been isolated from the urine, appeared possible. Alternatively, a hypersensivity reaction to drugs or a stress-induced myocarditis was taken into consideration. The hospitalized cat was treated with furosemide (initialy and in the course of further treatment), theophyllin (initially), continuous infusion with lactated Ringer's solution, pimobendan, and the addition of enrofloxacin to the ongoing amoxicillin/clavulanic acid administration. After 4 days, the cat's general condition improved satisfactorily and blood pressure returned to normal range. Left ventricular hypertrophy resolved, however, diastolic dysfunction as well as left atrial dilation persisted. Within the next 8 weeks, echocardiographic findings and cardiac biomarkers returned to near normal values. All medication was tapered and finally discontinued. During the last recheck examination 7 months following initial presentation, no cardiac changes were apparent.

A case report on transient global ventricular wall thickening secondary to acute myocarditis: Focus on the unique role of cardiac MRI

INTRODUCTION

Transient left ventricular wall thickening is known to develop in the acute phase of myocarditis, with several reports documenting this unusual mode of myocarditis. Diagnosing myocarditis can be challenging because symptoms, clinical exam findings, electrocardiogram results, biomarkers, and echocardiogram results are often non-specific. Therefore, cardiac magnetic resonance imaging has become the primary non-invasive imaging tool in patients with suspected myocarditis.

PATIENT CONCERNS AND DIAGNOSIS

A 51-year-old male was referred to our hospital with a 20-day history of fever. Initial echocardiogram demonstrated diffuse concentric left ventricular hypertrophy with depressed left ventricular diastolic function, previously misdiagnosed as restrictive cardiomyopathy. Cardiac magnetic resonance imaging (MRI) showed global ventricular wall thickening, and the negative delayed enhancement made hypertrophic cardiomyopathy and myocardial amyloidosis less likely. This information, along with laboratory analyses, led to a diagnosis of acute myocarditis.

INTERVENTIONS AND OUTCOMES

The patient underwent a treatment regimen, including a prescription of levofloxacin and other supporting treatments. During the period following, the patient experienced a few minor episodes of atypical chest pain with spontaneous remission. The patient was discharged after 8 days of hospitalization. A cardiac MRI evaluation was repeated after 17 months, this time showing that the wall thickness had returned to normal; the myocarditis resolved without sequela.

CONCLUSIONS

In summary, we report on a case of transient global ventricular wall thickening secondary to acute myocarditis, which rarely has been described previously. Our study demonstrates that transient ventricular wall thickening related to myocardial interstitial edema also can involve the right ventricular wall, a fact that is important in diagnosis and differential diagnosis. Cardiovascular magnetic resonance currently is considered the most comprehensive and accurate diagnostic tool in patients with suspected myocarditis.

Moving Towards Therapy in SCA1: Insights from Molecular Mechanisms, Identification of Novel Targets, and Planning for Human Trials

The spinocerebellar ataxias (SCAs) are a group of neurodegenerative disorders inherited in an autosomal dominant fashion. The SCAs result in progressive gait imbalance, incoordination of the limbs, speech changes, and oculomotor dysfunction, among other symptoms. Over the past few decades, significant strides have been made in understanding the pathogenic mechanisms underlying these diseases. Although multiple efforts using a combination of genetics and pharmacology with small molecules have been made towards developing new therapeutics, no FDA approved treatment currently exists. In this review, we focus on SCA1, a common SCA subtype, in which some of the greatest advances have been made in understanding disease biology, and consequently potential therapeutic targets. Understanding of the underlying basic biology and targets of therapy in SCA1 is likely to give insight into treatment strategies in other SCAs. The diversity of the biology in the SCAs, and insight from SCA1 suggests, however, that both shared treatment strategies and specific approaches tailored to treat distinct genetic causes of SCA are likely needed for this group of devastating neurological disorders.

Transient Myocardial Thickening in Cats Associated with Heart Failure

Background

Cats with hypertrophic cardiomyopathy (HCM) and congestive heart failure (CHF) can have resolution of both left ventricular hypertrophy and CHF.

Objectives

To describe the clinical characteristics of cats with transient myocardial thickening (TMT) and CHF compared with a control population of cats without resolution of HCM.

Animals

A total of 21 cats with TMT, 21 cats with HCM.

Methods

Retrospective study. Clinical records at 4 veterinary centers were searched for TMT cases and a control group of cats with HCM and CHF. TMT was defined as initial maximal left ventricular wall thickness (LVWT) ≥6 mm with left‐sided CHF, with subsequent resolution of CHF, reduction in left atrium/aorta (LA/Ao), and LVWT<5.5 mm. HCM was defined as persistent LVWT ≥6 mm.

Results

Cats with TMT were younger (2 [0.4–11.4] years) than cats with HCM (8 [1.6–14] years) (P < 0.0001), and antecedent events were more common (15/21 versus 6/21, respectively) (P = 0.01). In cats with TMT, LVWT normalized from 6.8 [6.0–9.7] mm to 4.8 [2.8–5.3] mm and LA/Ao decreased from 1.8 [1.6–2.3] to 1.45 [1.2–1.7] after a mean interval of 3.3 (95% CI: 1.8–4.7) months. CHF recurred in 1 of 21 TMT and 15 of 21 cats with HCM. Cardiac treatment was discontinued in 20 of 21 cats with TMT and 0 of 21 HCM cats. All cats with TMT survived, whereas 8 of 19 cats with HCM died during the study period.

Conclusions and Clinical Importance

TMT occurs in younger cats, and antecedent events are common. The prognosis is better in cats with CHF associated with TMT than HCM.

Dilated cardiomyopathy in a 32-year-old woman with Russell-Silver syndrome

INTRODUCTION

Russell-Silver Syndrome (RSS) is a genetically determined condition characterized by severe intrauterine and postnatal growth retardation; relative macrocephaly; a small, triangular face; and fifth-finger clinodactyly. The etiology of RSS involves epigenetic regulation through either uniparental disomy or genomic imprinting via DNA methylation. There has been no documented association between RSS and cardiomyopathy.

METHODS

We present an original case of a 32-year-old woman with RSS with dilated a cardiomyopathy who on cardiac biopsy showed occasional hypertrophic and atrophic myocytes with no evidence of inflammation, abnormal sarcomeres and disintegration of the Z bands on ultrastructural analysis, abnormal desmin, and normal C9 immunoreactivity.

CONCLUSION

This case represents the first reported association between RSS and cardiomyopathy. Given the complex mechanisms of disease etiology in RSS, this novel case provides insights into the mechanism of progressive dilated cardiomyopathy in an older individual with RSS.

Breathhold multiecho fast spin-echo pulse sequence for accurate R2 measurement in the heart and liver

Measurement of proton transverse relaxation rates (R(2)) is a generally useful means for quantitative characterization of pathological changes in tissue with a variety of clinical applications. The most widely used R(2) measurement method is the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence but its relatively long scan time requires respiratory gating for chest or body MRI, rendering this approach impractical for comprehensive assessment within a clinically-acceptable examination time. The purpose of our study was to develop a breathhold multiecho fast spin-echo (FSE) sequence for accurate measurement of R(2) in the liver and heart. Phantom experiments and studies of subjects in vivo were performed to compare the FSE data with the corresponding even-echo CPMG data. For pooled data, the R(2) measurements were strongly correlated (Pearson correlation coefficient = 0.99) and in excellent agreement (mean difference [CPMG - FSE] = 0.10 s(-1); 95% limits of agreement were 1.98 and -1.78 s(-1)) between the two pulse sequences.

Acute myopericarditis with focal ECG findings mimicking acute myocardial infarction

BACKGROUND

Although history, physical examination, laboratory data points, and electrocardiogram (ECG) are helpful, distinguishing among pericarditis, myopericarditis, and myocardial infarction can be difficult.

OBJECTIVES

This case, which presents as pericarditis with concomitant myocarditis (myopericarditis), illustrates the four evolving ECG stages of pericarditis and highlights some of the potential difficulties in differentiating between myopericarditis and acute myocardial infarction.

CASE REPORT

We present the case of a previously healthy 15-year-old boy who presented to the Emergency Department (ED) from his family physician's office for chest pain and presumed pericarditis. The patient's initial ECG showed infero-lateral ST-segment elevation, and his troponin T was elevated at 1.54 ng/mL (ref. < 0.03). Several hours after presentation to the ED, the patient experienced "10/10" chest pain, and a repeat ECG showed ST elevation increased from the prior ECG. After an emergent echocardiogram revealed no regional wall abnormalities, he was transferred to a pediatric cardiac intensive care unit, where a heart catheterization revealed no coronary irregularities. He was discharged 4 days later with the diagnosis of myopericarditis.

CONCLUSION

This case report illustrates some of the difficulties in differentiating among myopericarditis and myocardial infarction in a 15-year-old patient presenting with chest pain.

Relation between myocardial edema and myocardial mass during the acute and convalescent phase of myocarditis--a CMR study

BACKGROUND

Myocardial edema is a substantial feature of the inflammatory response in human myocarditis. The relation between myocardial edema and myocardial mass in the course of healing myocarditis has not been systematically investigated. We hypothesised that the resolution of myocardial edema as visualised by T2-weighted cardiovascular magnetic resonance (CMR) is associated with a decrease of myocardial mass in steady state free precession (SSFP)-cine imaging.

METHODS

21 patients with acute myocarditis underwent CMR shortly after onset of symptoms and 1 year later. For visualization of edema, a T2-weighted breath-hold black-blood triple-inversion fast spin echo technique was applied and the ratio of signal intensity of myocardium/skeletal muscle was assessed. Left ventricular (LV) mass, volumes and function were quantified from biplane cine steady state free precession images. 11 healthy volunteers served as a control group for interstudy reproducibility of LV mass.

RESULTS

In patients with myocarditis, a significant decrease in LV mass was observed during follow-up compared to the acute phase (156.7 +/- 30.6 g vs. 140.3 +/- 28.3 g, p < 0.0001). The reduction of LV mass paralleled the normalization of initially increased myocardial signal intensity on T2-weighted images (2.4 +/- 0.4 vs. 1.68 +/- 0.3, p < 0.0001). In controls, the interstudy difference of LV mass was lower than in patients (5.1 +/- 2.9 g vs. 16.3 +/- 14.2 g, p = 0.02) resulting in a lower coefficient of variability (2.1 vs 8.9%, p = 0.04).

CONCLUSION

Reversible abnormalities in T2-weighted CMR are paralleled by a transient increase in left ventricular mass during the course of myocarditis. Myocardial edema may be a common pathway explaining these findings.

T2-weighted cardiovascular magnetic resonance imaging

Technical advances in T2-weighted cardiovascular MR (CMR) imaging allow for accurate identification and quantification of tissue injuries that alter myocardial T2 relaxation. Of these, myocardial edema is of special relevance. Increased myocardial water content is an important feature of ischemic as well as nonischemic cardiomyopathies, which are often associated with acute myocardial inflammation. In this article, we review technical considerations and discuss clinical indications of myocardial T2-weighted imaging.

Diagnostic performance of cardiovascular magnetic resonance in patients with suspected acute myocarditis: comparison of different approaches

OBJECTIVES

The aim of this research was to identify the diagnostic performance of gadolinium-enhanced and T2-weighted cardiovascular magnetic resonance (CMR) in suspected acute myocarditis.

BACKGROUND

Acute myocarditis is difficult to diagnose; CMR provides various means to visualize myocardial inflammatory changes. A CMR approach with clear-cut diagnostic criteria would be desirable.

METHODS

We investigated 25 patients with suspected acute myocarditis (18 males, 44 +/- 17 years) and 23 healthy controls (13 males, 29 +/- 10 years). Cardiovascular magnetic resonance studies included the following sequences: 1) T2-weighted triple inversion recovery; 2) T1-weighted spin echo before and over 4 min after gadolinium injection; and 3) inversion recovery-gradient echo 10 min after gadolinium injection. Qualitative and quantitative image analysis was performed for: 1) focal and global T2 signal intensity (SI); 2) myocardial global relative enhancement (gRE); and 3) areas of late gadolinium enhancement (LGE).

RESULTS

Both global T2 SI and gRE were higher in patients than in controls (T2: 2.3 +/- 0.4 vs. 1.7 +/- 0.4; p < 0.0001, gRE: 6.8 +/- 4.0 vs. 3.7 +/- 2.3; p < 0.001). The sensitivity, specificity, and diagnostic accuracy for T2 (cutoff value of 1.9) were 84%, 74%, and 79%, respectively; gRE: (cutoff value of 4.0) 80%, 68%, and 74.5% respectively; LGE: 44%, 100%, and 71%, respectively. The best diagnostic performance was obtained when "any-two" of the three sequences were positive in the same patient yielding a 76% sensitivity, 95.5% specificity, and 85% diagnostic accuracy.

CONCLUSIONS

A combined CMR approach using T2-weighted imaging, early and late gadolinium enhancement, provides a high diagnostic accuracy and is a useful tool in the diagnosis and assessment of patients with suspected acute myocarditis.

Narrowing of the left ventricular cavity associated with transient ventricular wall thickening reduces stroke volume in patients with acute myocarditis

It has been reported that some patients with acute myocarditis have transient ventricular thickening associated with narrowing of the left ventricular cavity caused by interstitial edema. The present study investigated this phenomenon in 20 patients with acute myocarditis. Based on the sum of the interventricular septal wall thickness and left ventricular posterior wall thickness (IVST + PWT), measured by M-mode echocardiography, patients were divided into group A (IVST + PWT >/=25 mm, n=12) and group B (IVST + PWT <25 mm, n=8). The IVST + PWT was 31.8 +/-3.5 mm in group A and 21.9+/-2.7 mm in group B (p<0.0001). The left ventricular end-diastolic dimension (LVDd) was 42.3+/-6.0 mm in group A and 49.4+/-6.7 mm in group B (p<0.05). The stroke volume (SV) was 41.1+/-20.5 ml and 73.0+/-32.3 ml in groups A and B, respectively (p<0.05). The left ventricular ejection fraction (LVEF) was similar in group A (47.9+/-13.0%) and group B (56.9+/-9.0%). The SV correlated inversely with IVST + PWT (r=-0.62, p<0.01), and directly with both the LVDd (r=0.95, p<0.0001) and LVEF (r=0.64, p<0.01). The LVDd correlated inversely with IVST + PWT (r=-0.62, p<0.01). In conclusion, the reduction in SV that occurs during the acute phase of myocarditis is not only the result of systolic dysfunction, but also of the concentric left ventricular wall thickening associated with myocardial interstitial edema, which results in narrowing of the left ventricular cavity at end diastole.

Innovative drug treatments for viral and autoimmune myocarditis

Myocarditis is a common cause of cardiomyopathy and is thought to account for 25% of all cases in humans. Unfortunately, the disease is difficult to detect clinically before a myopathic process ensues. Management of myocarditis-induced heart failure includes the standard regimen of diuretics, digoxin, angiotensin-converting enzyme inhibitors, angiotensin-II receptor blockers, and beta-adrenergic blockers. The management of myocarditis itself is dependent on the etiology of the illness. Treatments that are currently under investigation include immunosuppressants, nonsteroidal antiinflammatory agents, immunoglobulins, immunomodulation, antiadrenergics, calcium-channel blockers, angiotensin-converting enzyme inhibitors, nitric oxide inhibitors (e.g., aminoguanidine), and antivirals. Despite advances in treatment, more work needs to be done in the early detection of myocarditis. Additionally, better means need to be established for distinguishing between viral and noninfectious autoimmune forms of the disease, so that appropriate treatment can be instituted.

The tachycardia-induced dog model of atrial fibrillation. clinical relevance and comparison with other models

In the past, investigators have relied extensively on acute in vivo models of atrial fibrillation (AF), in which AF was induced either pharmacologicly or by vagal stimulation. More recently, there is a need and desire for more clinically relevant models that can only be achieved with the use of chronically instrumented animals. One of these models is the atrial tachycardia-induced AF dog model, which is the main focus of this review. The model produces a persistent AF in 80% of animals paced at 400 beats/min for 6 weeks. Atrial tachycardia also induces various pathophysiologic and ultrastructural changes that often resemble electrical remodeling of atria in patients that have a high susceptibility to AF. This model can also be used to evaluate drug efficacy with respect to attenuation of AF duration or conversion of AF to sinus rhythm. The model may therefore be used to provide further insights into the discovery of new therapeutic approaches to modifying this atrial arrhythmic disorder in man.

[Therapy of dilated cardiomyopathies with and without inflammation]

Diagnosis of inflammatory dilated cardiomyopathy relies on the histological and immunohistological examination of endomyocardial biopsies. Only with the demonstration of the etiological agents in the myocardium specific therapy can be attempted. Whereas the spontaneous course of endemic myocarditis with little hemodynamic impairment is fair, the prognosis of symptomatic myocarditis and dilated cardiomyopathy is poor, with complete restitution in 35% and a 10-year survival rate of 30%. Restriction of physical activity is a validated form of therapy with normalization of the heart size in 40 to 60%. Symptomatic medical therapy consists of digitalis, diuretics, ACE-inhibitors and vasodilators and betablocker therapy, where a reduction of mortality was demonstrated in clinical (sub)studies up to 60%. Specific forms of therapy in inflammatory cardiomyopathy rely on the demonstration or lack of viral persistence or signs of autoreactivity in the myocardial tissue. Immunosuppressive therapy in autoimmune forms improved cardiac function in up to 60% of the patients in controlled trials, when compared to controls (40%). The double-blind randomized myocarditis treatment trial, which unfortunately did not distinguish viral from autoimmune myocarditis could not demonstrate such a benefit, however. Depending on the etiology of the disease, immunomodulation with immunoglobulins or interferon or antiviral therapy with hyperimmunoglobulins are presently tested in clinical treatment trials (ESETCID) in patients with enterovirus-positive or cytomegalovirus-positive and adenovirus-positive chronic myocarditis. Specific therapies are aimed to avoid the progression of the disease which may ultimately lead to heart failure with a cardiac assist device or heart transplantation as ultimate therapeutic option.

Innovative drug treatments for viral and autoimmune myocarditis

Myocarditis has been shown to be a common cause of cardiomyopathy and is believed to account for 25% of all cases in human beings. Unfortunately, the disease is difficult to detect before a myopathic process ensues. Treatment of myocarditis-induced heart failure includes the standard regimen of diuretics, digoxin, angiotensin-converting enzyme inhibitors, and currently, beta-adrenergic blockers. Treatment of myocarditis itself is dependent on the etiology of the illness. Treatments under investigation include immunosuppressants, nonsteroidal antiinflammatory agents, immunoglobulins, immunomodulation, antiadrenergics, calcium-channel blockers, angiotensin-converting enzyme inhibitors, nitric oxide inhibition (e.g., aminoguanidine), and antiviral agents. Despite advances in treatment, more work needs to be done in the early detection of myocarditis. Additionally, better means need to be established for distinguishing between viral and autoimmune forms of the disease, so that appropriate treatment can be instituted.

Ultrastructural findings in cardiac transplant recipients

Ultrastructural findings in 350 endomyocardial biopsy specimens and 59 autopsy or explanted hearts from cardiac transplant recipients are reviewed. Myocyte degeneration can be readily distinguished from necrosis by the technique described. Vascular changes of endothelial activation, endothelial cell damage, and basement membrane reduplication can be readily identified. In addition, the myofilament composition of ischemic hearts in patients with allograft coronary artery disease is distinctive: There is a disproportionate loss of actin over myosin, giving a coarse appearance to the myofilaments. These changes are useful in further defining the morphologic features associated with rejection and ischemia in cardiac transplant recipients.