Fasting insulin, calcium metabolism and the electrocardiogram in hypertensive subjects

Parathyroid Hormone and Cardiac Electrophysiology: A Review

Calcium has long been known to be essential to cardiac electrical activity. Parathyroid hormone (PTH) is the main regulator of serum calcium and is central to calcium homeostasis. Although there are significant data linking parathyroid disease states with changes in cardiac electrophysiology, most data have focused on how PTH modulates serum calcium to produce these effects. Close scrutiny of early literature demonstrates that the relationship between PTH and electrocardiographic changes is not straightforward, and numerous studies have linked PTH to arrhythmia. Basic science research has demonstrated that there is a basis for a direct role of PTH on cardiac electrophysiology outside of its effect on serum calcium. Later studies in secondary hyperparathyroidism indicate that PTH disturbances could have important implications for broad categories of patients with cardiovascular disease. The current review summarizes the existing literature on PTH and electrophysiology based on clinical and basic science studies of various parathyroid states, providing directions for future study.

Systemic hemodynamics in young adults with the metabolic syndrome: the Cardiovascular Risk in Young Finns Study

OBJECTIVE

We conducted the present study to examine associations of three different metabolic syndrome (MetS) definitions and their components to arterial stiffness, systemic vascular resistance, and left ventricular function at population level. In addition, the objective of the study was to examine associations of spontaneous recovery from MetS over 6 years' follow-up to systemic hemodynamics.

METHODS

The study population consisted of 1,741 Finnish young adults (aged 30-45 years) who had complete MetS risk factor and hemodynamic data available at 2007. Associations of spontaneous recovery from MetS to systemic hemodynamics was studied on a subpopulation of 1,391 subjects who had also complete MetS risk factor data available at 2001. Hemodynamic measurements were performed using a whole-body impedance cardiography device.

RESULTS

MetS and increasing number of MetS components were associated with lower stroke index (P < 0.001) and higher systemic vascular resistance index (P < 0.005) and arterial pulse wave velocity (P < 0.005). In MetS persistent group, stroke index was lower (P = 0.024), and pulse wave velocity was higher (P = 0.003) compared to MetS recovery group.

CONCLUSION

All current MetS definitions identify young adults with altered systemic hemodynamics, and recovery from MetS is associated with a favorable hemodynamic profile.

Insulin resistance and hyperinsulinemia: No independent relation to left ventricular mass in humans

BACKGROUND

Hyperinsulinemia and insulin resistance may contribute to the development of cardiac hypertrophy. In humans, however, the evidence is inconclusive.

METHODS AND RESULTS

We studied 50 nondiabetic subjects covering a wide range of age (20 to 65 years), body mass index (BMI, 19 to 40 kg x m(-2)), and mean blood pressure (72 to 132 mm Hg). Plasma insulin concentrations and secretory rates were measured at baseline and during an oral glucose tolerance test; insulin sensitivity was measured by the insulin clamp technique. Left ventricular mass (LVM) (by 2D M-mode echocardiography) was distributed normally and was higher in obese (BMI >/=27 kg x m(-2), n=16) or hypertensive patients (blood pressure >140/90 mm Hg, n=21) (50+/-8 and 55+/-10 g x m(-2.7), respectively) than in 13 nonobese, normotensive subjects (40+/-8 g x m(-2.7), P:=0.0004). In a multivariate model adjusting for sex, age, BMI, and blood pressure, neither insulin concentrations (fasting or postglucose) nor insulin sensitivity or secretory rates were significant correlates of LVM. Systolic blood pressure (P:=0.003) and BMI (P:=0.01) were the only independent correlates of LVM. From the regression, the impact of hypertension (as a systolic pressure of 180 versus 140 mm Hg=+20%) was twice as large as that of obesity (as a BMI of 35 versus 25 kg x m(-2)=+11%), the two factors being additive.

CONCLUSIONS

When adequate account is taken of body mass and blood pressure, insulin, as concentration, secretion, or action, is not an independent determinant of LVM in nondiabetic subjects.

The relationship of plasma glucose and electrocardiographic parameters in elderly women with different degrees of glucose tolerance

Plasma glucose has been regarded as a risk factor for macrovascular complications in diabetes, but less is known about its role in the development of cardiac impairment other than coronary heart disease (CHD). The aim of our study was to determine the relationship between basal and post-OGTT (Oral Glucose Tolerance Test) plasma glucose levels and some ECG parameters in a group of elderly women with normal or impaired glucose tolerance (IGT). One-hundred and one women with normal fasting glucose (<6.0 mmol/L) and no familial history or clinical signs of CHD and diabetes underwent an OGTT and a resting ECG. Based on the degree of glucose tolerance, we identified 24 women with a diagnostic OGTT for either IGT or diabetes; the 77 women (age range 52-88 years) with normal glucose tolerance were further divided into two groups according to their post-OGTT area under the curve (AUCG): below and above the median value (32 and 45 women, respectively). Basal plasma glucose and insulin levels, as well as lipid profile and percent of hypertensive patients were similar in the three groups. Mean corrected QT (QTc) was prolonged as a function of progressive worsening of glucose tolerance even after adjustment for possible confounding factors (p=0.03). A similar relationship was apparent when post-OGTT plasma glucose peak (GP) was considered. In a multiple regression analysis, AUCG and GP were the only factors independently related to both QTc and Sokolow index. Our observations suggest that, even in the presence of a normal glucose tolerance, plasma glucose concentrations during an OGTT are associated with peculiar ECG signs potentially combined with an increased risk of sudden death, arrhythmias, or cardiovascular mortality.

Insulin effects on the left ventricle in older hypertensive subjects

BACKGROUND

To evaluate the effects of hyperinsulinemia on left ventricular (LV) structure and function in older hypertensive subjects

METHODS

Thirty-seven hypertensive subjects (17 men/20 women) aged 50 to 80, were studied. LV mass were evaluated echocardiographically according to the Penn convention. A 75-g oral glucose tolerance test (OGTT) was performed after overnight fasting, and both blood glucose and insulin concentrations were assayed at 0, 30, 60, 90, 120, and 180 minutes. Comparison between groups was performed by analysis of variance. A P value of .05 was considered statistically significant.

RESULTS

When the hypertensive patients were divided into two groups according to the median value of 2-hour post-loading plasma insulin, there was no difference in blood pressure levels between the groups. However, hyperinsulinemic hypertensive subjects had an increased LV mass (P < .05), mean wall thickness, and interventricular septum thickness (P < .05 for both parameters) and had better systolic function-ejection and shortening fractions (P < .0001 for both indices).

CONCLUSIONS

Hyperinsulinemia may be associated with increased left ventricular mass and with a better systolic performance in older hypertensive subjects.

Dynamic assessment of the electrocardiographic QT interval during citrate infusion in healthy volunteers

OBJECTIVE

To investigate changes in the electrocardiographic QT interval during rapidly induced, sustained hypocalcaemia in healthy volunteers.

DESIGN

Serial rate corrected QT measurements were made during and after a variable rate trisodium citrate infusion designed to "clamp" the whole blood ionised calcium concentration 0.20 mmol/l below baseline for 120 min.

SUBJECTS

12 healthy teetotallers aged 19- 36 years who were not receiving medication known to influence calcium homoeostasis.

MAIN OUTCOME MEASURES

Whole blood ionised calcium concentration and QaTc intervals (onset of the Q wave to T wave apex divided by the square root of the RR interval).

RESULTS

Mean (SD) ionised calcium concentration decreased from 1.18 (0.03) mmol/l preinfusion to values close to target (0.98 mmol/l) between 10 and 120 min. The QaTc interval lengthened from a baseline of 0.309 (0.021) to a maximum 0.343 (0.024) s0.5 at 10 min before returning to a stable level from 15 to 120 min (0.334 (0.023) and 0.330 (0.023) s0.5 respectively). The change from baseline of both variables expressed as a ratio (delta QaTc/ delta [Ca2+]) was greater during rapid induction of hypocalcaemia (at 5 and 10 min) than at other times during and after the infusion (P < 0.02).

CONCLUSIONS

The disproportionate prolongation of QaTc interval during prompt induction of hypocalcaemia suggests rate dependency which can be represented by a hysteresis relation between (ionised calcium, QaTc) coordinates. This finding may have clinical implications.

Serum calcium and the ECG in patients with primary hyperparathyroidism

Primary hyperparathyroidism (HPT) is associated with cardiovascular disease, but there are no systematic studies on the electrocardiographic findings in HPT. Preoperative electrocardiograms from 139 patients with primary HPT and 97 control patients were therefore investigated. Serum calcium levels were found to be significantly correlated to the QRS amplitude (r = .26, P < .002), ST-segment duration (r = -.55, P < .0001), QT interval (r = -.64, P < .0001), and T wave duration (r = .19, P < .009). These relations were still significant when the influence of age, sex, and blood pressure level were taken into account in the multiple regression analysis. Thus, the electrocardiograms from HPT patients, compared to normocalcemic control patients, showed a shorter duration of the ST-segment, representing the systolic interval, and an increased amplitude of the QRS complex, representing ventricular muscle mass. Furthermore, the duration of the T wave was significantly prolonged in HPT patients. The hemodynamic effects of these findings have to be further evaluated.

Cytoplasmic calcium regulation and the electrocardiogram in patients with primary hyperparathyroidism

Primary hyperparathyroidism (HPT) is a disease caused by an abnormal cytosolic regulation of calcium concentration [Ca++]i leading to an increased secretion of parathyroid hormone and thereby increased levels of extracellular calcium. It is well known that the QT-interval measured at electrocardiography (ECG) is shortened in HPT subjects. Whether this is due to an abnormal intracellular handling of calcium also in the heart or to the raised extracellular calcium levels is not known. In order to study the extent to which the deranged extra- and intracellular levels of calcium in HPT patients were related to ECG characteristics, [Ca++]i was determined in vitro by microfluorometry in surgery-removed parathyroid cells at extracellular calcium concentrations of 0.5 mM and 30.0 mM and ECG was recorded preoperatively in 42 HPT patients and in 15 subjects operated on for atoxic goitre. Serum calcium and plasma-ionized calcium also were measured preoperatively. The QT-interval and ST-segment duration were both shortened in the HPT patients compared to controls (P < 0.001). [Ca++]i at 3.0 mM extracellular calcium divided by that at 0.5 mM was correlated to the QT-interval, when measured at the onset of the T-wave (QoT, r = 0.39, P < 0.03) and early diastolic phase (end of T-wave to onset of p-wave, r = -0.34, P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)