The heart in hypothyroidism

CARDIAC STRUCTURAL AND FUNCTIONAL ABNORMALITIES IN FEMALES WITH UNTREATED HYPOPITUITARISM DUE TO SHEEHAN SYNDROME: RESPONSE TO HORMONE REPLACEMENT THERAPY

OBJECTIVE

Data on cardiac abnormalities in females with untreated hypopituitarism are limited. We investigated echocardiographic abnormalities in females with untreated hypopituitarism and their response to treatment.

METHODS

Twenty-three females with treatment-naïve hypopituitarism and 30 matched healthy controls were evaluated for cardiac structure and function. Echocardiographic evaluation was done at presentation and after achieving a euthyroid and eucortisol state.

RESULTS

Fourteen (61%) patients had mitral regurgitation, and 11 (48%) had pericardial effusion as against none among controls. Indices of left ventricular (LV) size like LV end diastolic dimension (LVEDD; 44.5 ± 3.5 mm in cases vs. 47.6 ± 3.8 mm in controls, P = .004), and LV diastolic volume (LVEDV; 91.8 ± 18.0 mL versus 106.5 ± 20.4 mL, P = .009) were significantly lower in the SS group compared with controls. LV mass (LVM) was 70.8 ± 19.2 g in cases and 108.0 ± 33.2 g in controls (P = .02). Similarly, indices of LV systolic function like stroke volume (SV; 59.1 ± 12.0 mL in cases and 74.4 ± 15.8 mL in controls; P = .000), ejection fraction (EF; 64.3 ± 6.2 % in cases against 69.9 ± 9.2 % in controls; P = .03), and fractional shortening (FS; 34.9 ± 4.7% versus 40.1 ± 4.4%, P = .000) were significantly decreased in patients compared with controls. Cardiac abnormalities normalized with restoration of a euthyroid and eucortisol state.

CONCLUSION

Pericardial effusion, mitral regurgitation, and diminished LVM are common in females with untreated hypopituitarism.

ABBREVIATIONS

ACTH = adrenocorticotrophic hormone BMI = body mass index DT = deceleration time EDV = end-diastolic volume EF = ejection fraction FS = fractional shortening GH = growth hormone IGF-1 = insulin growth factor-1 ITT = insulin tolerance test IVSd = interventricular septal diameter LH = luteinizing hormone LV = left ventricular LVEDD = LV end diastolic dimension LVEDV = LV end diastolic volume LVM = LV mass MRI = magnetic resonance imaging MVP = mitral value prolapse PPH = postpartum hemorrhage PWd = posterior wall diameter SS = Sheehan syndrome SV = stroke volume T3 = triiodothyronine T4 = thyroxine TSH = thyroid-stimulating hormone.

Cardiovascular risk and subclinical hypothyroidism: focus on lipids and new emerging risk factors. What is the evidence?

Controversy remains as to the risk of cardiovascular disease (CVD) associated with subclinical hypothyroidism (SCH), defined as an increased serum thyrotropin (TSH) concentration with normal free thyroxine and triiodothyronine levels. Substantial evidence indicates altered cholesterol and lipoprotein metabolism in SCH when serum TSH is above 10 mU/L. Observed abnormalities include elevated plasma levels of total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C); the altered TC/high-density lipoprotein-cholesterol (HDL-C) and LDL-C/HDL-C ratios suggest a potential accelerated risk for CVD. The influence of SCH on lipids is directly proportional to the degree of TSH elevation and becomes more significant with the progression from SCH to overt disease, thereby accelerating any propensity to atherosclerosis. Although many clinicians may tend to ignore SCH with TSH levels <10, it is apparent that an enhanced CV risk could apply to these individuals, perhaps compounded by insulin resistance and amplified by the copresence of other risk factors such as endothelial dysfunction and elevated C-reactive protein.

Ultrasonic myocardial textural analysis in subclinical hypothyroidism

BACKGROUND

In subclinical hypothyroidism (sHT), a condition in which impaired hormone synthesis is compensated by thyroid-stimulating hormone (TSH) hypersecretion, previous studies have suggested the presence of disturbances in left ventricular (LV) function.

OBJECTIVES

Our goal was to investigate LV structure and function through the combined use of conventional Doppler echocardiography and ultrasonic videodensitometry.

METHODS

We studied 16 patients with sHT (aged 32+/-12 [mean +/- SD] years) who had raised TSH levels (> 3.6 mIU/L) but normal levels of free thyroid hormones (free thyroxine [FT(4)] and free triiodothyro-nine [FT(3)]), and 16 carefully age- and sex-matched euthyroid subjects. Transmitral flow Doppler analysis and quantitative analysis of the echocardiographic digitized images were performed in all study subjects. Textural parameters of the septum and posterior wall were obtained as mean gray levels, which were then used to calculate the cyclic variation index (CVI), that is, the percent change in mean gray levels between diastole and systole.

RESULTS

Patients with sHT had a significantly higher LV mass index (92 +/- 16 versus 76 +/- 16 g.m(2), P<.01) and isovolumic relaxation time corrected for heart rate (IVRTc) (2.9 +/- 0.6 versus 2.5 +/- 0.6, P<.04) than did controls. On videodensitometry, patients had lower CVIs both for the septum (-5% +/- 22% versus 33% +/- 9%, P<.0001) and the posterior wall (10% +/- 26% versus 49% +/- 18%, P<.0001). IVRTc discriminated only 25% of the patients from the controls, whereas CVI analysis correctly identified 85% of the patients with sHT (P<.002). Furthermore, CVI values were found to be significantly related to serum FT(4) and FT(3) concentrations in a direct fashion, and to serum TSH levels in an inverse fashion.

CONCLUSIONS

Subclinical hypothyroidism is associated with changes in videodensitometric myocardial structure. These changes, which are not accurately detected by conventional or Doppler echocardiography, are quantitatively related to loss of thyroid function and could represent an early sign of myocardial damage in hypothyroidism.

Covert hypothyroidism presenting as a cardiovascular event

Hypothyroidism presenting with classic signs and symptoms is generally easily recognized. Less often, patients with hypothyroidism may present with symptoms and laboratory abnormalities suggestive of cardiovascular disease. In this article, we describe six such patients. Hypothyroidism was suspected when creatine phosphokinase (CPK) levels were persistently elevated. The diagnosis was confirmed by thyroid function tests, and thyroid hormone therapy resulted in resolution of symptoms and CPK elevations. Persistently elevated CPK levels associated with cardiovascular symptoms but without demonstrable myocardial damage should prompt consideration of covert hypothyroidism.

The direct effect of the thyroid hormone on cardiac chronotropism

To establish whether thyroid hormone modifies the heart rate directly or through an action on other neuroendocrine modulators, the authors have examined several animals models differing in the plasma levels of such compounds. Induction of the hypothyroid state in rats produced a slow onset of bradycardia, which may be removed by a prolonged triiodothyronine treatment. The involvement of TSH was excluded as, by comparing thyroidectomized, hypophysectomized and cold exposed rats, the heart rate was found to vary according to the thyroid levels and not to the TSH levels. Moreover growth hormone, corticotropin and gonadotropins do not influence the heart rate, as the bradycardia induced by hypophysectomy was fully removed by triiodothyronine treatment. The lack of influence by ACTH and GnH was confirmed by treatment of thyroidectomized rats with corticosteroids or testosterone, respectively. Finally, thyroid hormone did not act on the heart rate by changing the norepinephrine output at the sympathetic nerve endings in the heart. In fact, thyroidectomy produced a more intense bradycardia than sympathectomy, and such bradycardia was equally removed by triiodothyronine treatment in thyroidectomized rats and in thyroidectomized and then sympathectomized ones. The authors suggest that the direct effect of the thyroid hormone on cardiac chronotropism is due to an early enhancement of beta-adrenoceptors, followed by a late modification of the electrophysiological properties of the myocardium.

Effects of thyroid status on atrial natriuretic peptide release from isolated rat atria

The effect of thyroid hormone on circulating levels of atrial natriuretic peptide (ANP) was studied in experimental hyperthyroid and hypothyroid rats. Plasma ANP was 102 +/- 5 pg/ml in euthyroid rats, 82 +/- 4 pg/ml in hypothyroid rats, and 138 +/- 11 pg/ml in hyperthyroid rats. We have also measured immunoreactive ANP in the atria of euthyroid, hypothyroid, and hyperthyroid rats. ANP content and concentration in the atria were lower (546 +/- 32 pg/mg tissue) in hyperthyroid rats than in hypothyroid rats (802 +/- 74 pg/mg tissue). Right atrium from euthyroid, hypothyroid, and hyperthyroid rats was superfused with a modified Langendorff preparation. Spontaneous release of ANP was significantly higher from the hyperthyroid rats (20 +/- 2 pg.min-1.mg-1) than from the hypothyroid rats (5.6 +/- 0.5 pg.min-1.mg-1). ANP release from the euthyroid rats was 9.3 +/- 1.2 pg.min-1.mg-1. These results indicate hyperthyroidism causes an increase in ANP secretion and a decreased release occurs during hypothyroidism.

Pericardial effusion in hypothyroidism

Thirty-nine patients with untreated hypothyroidism have been examined using echocardiography for the presence of a pericardial effusion. Effusions were present in twelve patients who tended to be more severely hypothyroid. Plasma creatine phosphokinase and lactate dehydrogenase levels were higher in the presence of an effusion. Nine were reinvestigated during thyroxine replacement therapy and the effusions did not disappear until thyroid function tests had returned to normal. There were no specific electrocardiographic changes associated with the presence of an effusion which could be associated with a normal cardiac silhouette on a standard P.A. chest X-ray.

Echocardiographic characterization of the reversible cardiomyopathy of hypothyroidism

Nineteen patients with untreated hypothyroidism were evaluated by M-mode echocardiography. Asymmetric septal hypertrophy (ASH), defined as a ratio of interventricular septal thickness to left ventricular posterior wall thickness (IVS/LVPW) equal to or greater than 1.3, was identified in 17 cases. Additional abnormalities recognized by echocardiography included reduced amplitude of systolic septal excursion (SSex) [13 patients], reduced per cent of systolic septal thickening (%SST)[19 patients], reduced left ventricular outflow tract dimension (LVOT)[five patients] and systolic anterior motion of the mitral valve (SAM)[five patients]. These findings are similar to some of the echocardiographic features of idiopathic hypertrophic subaortic stenosis (IHSS). In 10 patients who returned to euthyroid state with L-thyroxine therapy, these abnormalities resolved. We conclude that long-standing hypothyroidism leads to a reversible cardiomyopathy, manifested by asymmetric septal hypertrophy with or without other echocardiographic features of a hypertrophic obstructive cardiomyopathy. This previously unrecognized features of hypothyroidism has important diagnostic and therapeutic implications.

Basement membrane changes in myocardial and skeletal muscle capillaries in myxedema

Nineteen dogs were given 131 I and later administered appropriate amounts of methimazole or propylthiouracil daily. Over a period of 4-7 years several developed severe clinical features of myxedema. The myocardium and skeletal muscle of these severely myxedematous dogs displayed an array of morphologic changes on an ultrastructural level. Particularly interesting was the two- to threefold increase in the thickness of the myxedematous capillary basement membranes over those of normals. Increased tortuosity, lamination, and perivascular fibrosis were also observed as part of the myxedematous changes. These studies also demonstrated severe microcellular modifications, such as mitochondrial disruption, loss of cristae, lipid inclusions, and the presence of myelin figures, all a part of the diffuse systemic cardiovascular connective tissue pathology in myxedema.