Early presentation of dilated cardiomyopathy as a part of seroconversion illness in human immunodeficiency virus infection

It has been debated whether dilated cardiomyopathy seen in patients with acquired immune deficiency syndrome is caused by the virus itself or by the combination of other factors such as presence of opportunistic pathogens and/or severe immunosuppression. This paper describes the first reported case of a patient with human immunodeficiency virus (HIV) infection presenting with dilated cardiomyopathy during his acute seroconversion illness. Presence of cardiac involvement at a very early stage of HIV infection with no evidence of opportunistic infections, or immunosuppression with high CD4 count indicates that HIV may itself be a cardiac pathogen. This case also illustrates the importance of testing for HIV infection as part of the assessment of any patient presenting with myocarditis or dilated cardiomyopathy.

Plasma insulin-like growth factor-1 elevated in mild-to-moderate but not severe heart failure

BACKGROUND

Insulin-like growth factor 1 (IGF-1) promotes favorable cardiac remodeling in heart failure. However, the relation of plasma IGF-1 in patients with various degrees of heart failure is not known.

METHODS

Venous plasma samples were collected from patients with clinically documented heart failure (n = 24) and from control subjects (n = 21) for measurements of IGF-1 levels. In the heart failure group, functional assessment of the physical capacity was determined by means of the New York Heart Association (NYHA) score. Objective determination of ventricular performance was made by transthoracic echocardiographic measurement of left ventricular fractional shortening (FS).

RESULTS

IGF-1 levels were higher in patients with heart failure (mean age, 67 +/- 2 years; 17 men) than in control subjects (age, 71 +/- 2 years; 9 men) (20.2 +/- 2 mU/L, 14.1 +/- 2 mU/L, respectively, P <.05). However, the elevated IGF-1 levels were demonstrated only in patients with mild-to-moderate symptoms (NYHA classes I and II) of heart failure (24.7 +/- 3.3 mU/L, n = 12, P =.005 vs control subjects) but not in patients with severe symptoms (NYHA classes III and IV) (15.7 +/- 2.3 mU/L, n = 12). There was a strong positive correlation between IGF-1 levels and left ventricular FS (%) (r = 0.58, P =.003, n = 24). Adjustments for other potential confounders including age, sex, treatment received, and underlying cause of heart failure did not alter the relation between IGF-1 and left ventricular FS (odds ratio, 2.01; 95% confidence interval, 1.26 to 6.24; P =.01).

CONCLUSIONS

Plasma levels of IGF-1 show distinct variations with the severity of heart failure and may play a vital role in compensated heart failure.

Thrombosis in one coronary artery causes generalized coronary vasoconstriction in a dog model of unstable angina

We investigated the effect of thrombosis in one coronary artery upon the vascular resistance of another coronary artery. In previous investigations, using an animal model of unstable angina, we have observed increased resistance downstream from thrombus within a left circumflex coronary artery (LCx) stenosis and vasoconstriction of collateral vessels from the left anterior descending artery (LAD) supplying the distal LCx vascular bed. In the present paper, we induced thrombosis within a stenosis of the LCx of 16 beagle dogs, and observed the changes in blood flow to the myocardium supplied by the LAD using the radioactive microsphere technique. This blood flow decreased with thrombosis (P = 0.005) in these animals, whereas it did not do so in three time-control experiments. The pressures across the coronary vascular bed, i.e. arterial pressure to coronary venous pressure (coronary sinus catheter), did not change. Thus the vascular resistance of the LAD bed increased significantly from 147 +/- ll.5 mmHg/ml/sec/g of tissue to 172 +/- 13.4 mmHg/ml/sec/g of tissue (P = 0.02). As the LAD territory is not perfused with blood from the artery containing thrombus, we conclude that the effect observed is caused either by release of vasoconstrictors from the thrombus into the general circulation, or by activation of a neural reflex vasoconstriction. The study suggests that unstable angina involving thrombosis in one coronary artery is a global coronary vascular disease.

Acute and convalescent changes in plasma homocysteine concentrations in acute coronary syndromes

BACKGROUND

Raised plasma homocysteine is a risk factor for coronary artery disease. Patients with myocardial infarction or unstable angina show greater activation of coagulation, greater troponin release, and a worse outcome.

OBJECTIVE

To examine variations in plasma homocysteine concentration in relation to C reactive protein (CRP) in patients presenting with acute coronary syndromes.

METHODS

Consecutive patients presenting with acute myocardial infarction (22) and unstable angina pectoris (12) were studied. Plasma samples were obtained on admission (before clinical intervention), on days 2, 7, and 28, and again six months after admission. Plasma homocysteine, assayed by high performance liquid chromatography, and CRP were both determined at the same time points. Changes were assessed by analysis of variance.

RESULTS

CRP concentrations showed a classical rise on day 2, followed by a gradual decline to normal values taken at six months from admission in both myocardial infarction (p < 0.0001) and unstable angina (p = 0.02). Homocysteine concentrations in myocardial infarction (median, 25th to 75th interquartile range) were: 11.9 (10.7 to 12.6), 11.5 (9.1 to 13.4), 12.1 (11.4 to 14.1), 12.4 (11.1 to 14.4), and 12.1 (11.2 to 14.0) micromol/l, for days 1, 2, 7, 28, and 180, respectively (p = 0.02). Significant differences were observed only between day 2 and day 7 (p < 0.05). The final homocysteine measurement was not different from the admission level. Homocysteine concentrations in unstable angina did not differ between admission and convalescence (12.5 (9.1 to 14.5) micromol/l and 12.3 (7.7 to 14.9) micromol/l, respectively).

CONCLUSIONS

Plasma homocysteine concentrations are minimally influenced by acute phase variations with reliable measurements obtained on admission in patients with myocardial infarction and unstable angina.

Chronic catecholamine depletion switches myocardium from carbohydrate to lipid utilisation

PURPOSE

Chronic cardiac transplantation denervation (i.e., global sympathetic denervation with myocardial catecholamine depletion, plus parasympathetic denervation) is known to inhibit myocardial oxidation of glucose. It is not known whether this is due to increased utilization of lactate, lipid or ketone bodies. The purpose of the present study was to test the hypothesis that the extraction and contribution of blood-borne fatty acids (FA) to overall oxidative energy conversion is increased.

METHODS

In anaesthetised dogs (control n = 6, cardiac denervated n = 6), we investigated fatty acid (FA) utilization. The studies were made at least four weeks after surgical cardiac denervation. Measurements were made of total FAs and with a radio-labelled tracer (U-14C palmitate).

RESULTS

The contribution of FA utilisation to overall substrate oxidation rose from 31% (control) to 48% (cardiac denervated). The increase in the ratio (%) of CO2 production from palmitate oxidation to total CO2 production increased from 4.0 +/- 1.8 (control) to 10.6 +/- 5.8 (denervated, p = 0.04). The time from uptake of FA to release of CO2 product was unaltered.

CONCLUSION

We conclude that the contribution of FA oxidation to overall energy conversion is increased in chronically denervated hearts, which is postulated to result from a decline in the active form of pyruvate dehydrogenase. This would appear to be a result of chronic catecholamine depletion.

Elevated homocysteine levels are associated with increased ischemic myocardial injury in acute coronary syndromes

OBJECTIVES

This study was conducted to determine whether the amount of myocardial damage during acute coronary syndromes (ACS) is related to the admission plasma homocysteine concentration.

BACKGROUND

Elevated homocysteine levels are associated with increased thrombosis in patients presenting with ACS. It is not known whether this association is reflected in the degree of myocardial injury in those patients.

METHODS

We studied consecutive patients presenting with acute myocardial infarction (MI) (n = 205) and unstable angina pectoris (UAP) (n = 185). Plasma samples were collected on admission and prior to clinical intervention and were assayed for homocysteine by high performance liquid chromatography (HPLC). Myocardial necrosis was assessed by measurements of cardiac troponin T (cTnT) on admission and 12 h after admission (peak cTnT). The patients were studied by quintiles of homocysteine concentration.

RESULTS

There was a significant increase in peak cTnT in the 5th homocysteine quintile in MI (analysis of variance [ANOVA], p = 0.005), the levels being 4.10, 3.86, 4.13, 6.20 and 7.85 microg/liter for quintiles 1 to 5, respectively (p < 0.0001, for top vs. bottom quintile). Similarly, there was a step-up in peak cTnT levels in the top homocysteine quintile in UAP (ANOVA, p < 0.0001), the levels being 0.03, 0.03, 0.02, 0.04 and 0.15 microg/liter, (p < 0.0001 for top vs. bottom quintile). In a multivariate regression model, the association between peak cTnT and the top homocysteine quintile remained strong after adjustment of other confounders including age, gender, final diagnosis and thrombolysis treatment (odds ratio [OR]: 2.92 (1.75-4.87) p < 0.0001). The patients with UAP were further examined according to peak cTnT levels below (cTnT negative) or above (cTnT positive) 0.1 microg/liter. Homocysteine levels were significantly higher in cTnT positive than cTnT negative patients; 13.8 (11.7-15.3) vs. 10.3 (9.4-11.3) micromol/liter, respectively, p = 0.002.

CONCLUSIONS

Elevated homocysteine levels are associated with a higher risk of ischemic myocardial injury in patients presenting with ACS.

Measurement of coronary collateral flow and resistance in the presence of an open critical stenosis, and the response to intra-arterial thrombosis

OBJECTIVE

(1) Can one measure coronary collateral flow around an open critical stenosis? (2) Does intracoronary platelet thrombosis affect native coronary collateral vessels?

METHODS

We measured regional myocardial blood flow by the radioactive microsphere technique in seven anaesthetised dogs with an ultrasonic flowmeter on the circumflex branch of the left coronary artery (LCx). Measurements were made (a) in a control period, (b) after induction of a tight stenosis on the LCx, and (c) after additional arterial damage at the stenosis to induce intraluminal thrombosis. Collateral flow was calculated from LCx tissue flow(in ml/min/g tissue) minus LCx flowmeter flow which is in ml/min. Therefore, it was necessary to use scaling by reference back to the control measurements and conversion to ml/min/g tissue equivalent.

RESULTS

LCx stenosis induced collateral flow from the other coronary arteries into the LCx area of supply, which decreased (mean+/-S.E.) from 0.23+/-0.03 to 0.15+/-0.05 ml/min/g tissue with thrombosis. Collateral resistance correspondingly increased with thrombosis from 187.6+/-18. 2 to 1069+/-544 mmHg/ml/min/g (P<0.02).

CONCLUSION

Coronary collateral flow around an open stenosis can be measured by reference back to control conditions. The coronary collaterals vasoconstrict in the presence of thrombosis even though they are in the stream of blood coming from normal coronary arteries.

Chronic cardiac denervation affects the speed of coronary vascular regulation

OBJECTIVE

We tested the hypothesis that the rate of adaptation of coronary metabolic vasodilatation and autoregulation is modulated by the cardiac nerves.

METHODS

Anaesthetised dogs (seven innervated (control) and seven with denervated hearts) were subjected to controlled pressure perfusion of the left main coronary artery. Heart rate was controlled by pacing.

RESULTS

The steady state autoregulation curves and metabolic regulation curves were similar in the two groups. A sudden increase or decrease in heart rate was associated with a faster response (22% shorter half-times) in the innervated than the denervated dogs (P < 0.001). A sudden increase or decrease in coronary arterial perfusion pressure was associated with a slower response (24% longer half-times) in the innervated than the denervated hearts (P < 0.005).

CONCLUSIONS

We conclude that the speed of response to metabolic and perfusion pressure changes is partly mediated by cardio-cardiac reflexes. Reflex coronary vasodilatation appears to reinforce the metabolic vasodilatation of a heart rate increase and oppose the vasoconstriction in response to increased perfusion pressure.

Significance of an index of insulin resistance on admission in non-diabetic patients with acute coronary syndromes

BACKGROUND

Insulin resistance is associated with ischaemic heart disease and has been proposed as a risk factor for subsequent myocardial infarction.

AIM

To investigate the potential use of a recently proposed insulin resistance index in identifying insulin resistance in patients admitted with an acute coronary syndrome.

METHODS

Single centre study of 441 non-diabetic patients admitted with chest pain to a coronary care unit and followed prospectively for a median of three years for outcome. Admission glucose and insulin concentrations were measured and from these values an admission index of insulin resistance (AIRI) calculated. Its association with other known factors in the insulin resistance syndrome, and subsequent outcome, was examined.

RESULTS

The AIRI was greater in patients with myocardial infarction than in a control group without myocardial infarction (p < 0.0001). A Cox regression model for subsequent cardiac death identified previous myocardial infarction (p < 0.0001), infarct size (p < 0.0001), and AIRI (p = 0. 0033) as positive risk predictors. Patients of Indian subcontinent ethnic origin had greater AIRI values than white patients: mean (SD) 7.5 (1.3) v 4.6 (0.2), p < 0.001.

CONCLUSIONS

A simple index of insulin resistance measured on patients admitted with myocardial infarction provides an important predictive measure of poor outcome and is superior to admission glucose measurement. It may be useful in identifying patients admitted with myocardial infarction who could benefit from alternative early management strategies.

Circulating stress hormone and insulin concentrations in acute coronary syndromes: identification of insulin resistance on admission

We re-examined, in the context of modern practice, plasma insulin and stress hormone concentrations in patients admitted to hospital with acute coronary syndromes. Venous blood sampling was carried out prior to anti-thrombotic therapy in 148 patients with myocardial infarction (MI); 76 patients with unstable angina (UA) pectoris were also studied, together with 27 patients with non-cardiac chest pain (NCP). There were significant progressive increases in the concentrations of catecholamines, cortisol, glucose and insulin from NCP to UA to MI patients. Hyperglycaemia (glucose >8 mmol/l) was present in over 50% of MI patients. The plasma cortisol and insulin levels were both significantly positively correlated with the glucose concentration on admission. Only the cortisol concentration was correlated with peak cardiac enzyme levels. The glucose and insulin concentrations on admission in 141 MI and UA patients were related to insulin resistance, as judged from subsequent insulin and glucose concentrations measured while fasting and during a glucose tolerance test. The product of admission insulinxglucose (divided by 25; the admission insulin-resistance index, or AIRI) was significantly correlated with indices of insulin resistance, and was significantly higher (approximately double) in the MI group (7. 81+/-0.76) and the UA group (6.88+/-1.19) than in the control NCP group (3.59+/-0.06; Kuskul-Wallis: P=0.0001), implying that the insulin levels in the first two groups were approximately twice as high as is appropriate for the glucose levels. The ethnic origin of 20% of the patients was the Indian subcontinent; admission insulin and glucose levels in this subgroup were higher than in the non-Asians across all the groups with chest pain. Cortisol was the only stress hormone that was raised in proportion to the size of the infarct, and is a likely partial cause of the elevation in blood glucose. The high insulin levels were related to the prevalence of insulin resistance, and this was particularly important in the Asian subgroup presenting with MI and UA. Thus it appears feasible to identify acute coronary syndrome patients who are insulin-resistant at a time (on admission) when alternative early therapeutic strategies can be instituted.

Downstream resistance effects of intracoronary thrombosis in the stenosed canine coronary artery

OBJECTIVE

The presence is well established in unstable angina of intracoronary thrombosis in a stenosed epicardial coronary artery. The effects of the thrombus formation on the distal microcirculation are however still unclear.

METHODS

We adapted the Folts canine model of left circumflex coronary arterial stenosis and intracoronary thrombosis by the insertion of a pressure catheter distal to the stenosis and by the use of 15 microns radioactive microspheres for measurement of regional myocardial blood flow. This permitted measurement during circumflex artery occlusion of collateral flow, downstream vascular resistance and collateral resistance.

RESULTS

Distal circumflex resistance, obtained by dividing the distal circumflex coronary pressure gradient by the collateral flow, significantly increased with thrombosis (94.47 +/- 35.72 to 120.06 +/- 34.47; p = 0.0018) mmHg/ml/min/g. Changes in collateral flow and resistance in the presence of thrombosis, during maximum ischaemic vasodilatation, were inconsistent.

CONCLUSION

Thrombosis causes increased vascular resistance in the microcirculation distal to the site of injury. This may be of clinical relevance in unstable angina, characterised by episodes of thrombus growth and embolization, in which ischaemic episodes may be worsened by generalised downstream vascular changes.

Myocardial contractility is not constant during spontaneous atrial fibrillation in patients

BACKGROUND

The variation in stroke volume and pulse pressure characteristic of atrial fibrillation is usually ascribed to time-dependent ventricular filling, implying a single positive relationship between end-systolic pressure and volume, which defines a single state of myocardial contractility. We tested the hypothesis that contractility also varies.

METHODS AND RESULTS

We measured the left ventricular pressure and volume continuously with a conductance catheter with catheter-tip micromanometer introduced retrogradely into the left ventricle. The end-systolic pressure-volume relationship was determined in 6 patients in atrial fibrillation undergoing cardiac catheterization for diagnostic purposes and 4 control patients in sinus rhythm undergoing coronary artery bypass graft surgery. The normal positive relationship between end-systolic pressure and volume was found in the control patients, but no such positive relationship was found in any patient in atrial fibrillation. In the latter, the slopes of the linear regressions were either not significantly different from zero or significantly negative (r values <0.08), both results indicating a change in contractility from beat to beat. Significantly negative relationships were found between end-systolic volume and preceding R-R interval (-0.82<r<-0.24), indicating the presence of mechanical restitution. Significantly positive relationships were found between end-systolic volume and the R-R interval before the preceding R-R interval (0.35<r<0.74), indicating the presence of postextrasystolic potentiation.

CONCLUSIONS

Myocardial contractility is constantly changing from beat to beat in atrial fibrillation because of the influence of the force-interval relationships.

Depletion of endogenous dopamine stores and shift in beta-adrenoceptor subtypes in cardiac tissue following five weeks of chronic denervation

Surgical ablation of extrinsic cardiac nerve fibers results in a chronically denervated state of the left ventricle of the heart. The present study was performed to elucidate the effect of a period of 5 weeks of chronic denervation on cardiac catecholamine levels in general and dopamine in particular. Moreover, the possible effect on cardiac beta-adrenoceptor subtypes was investigated. Experiments were performed on adult dogs. In addition to adrenaline and noradrenaline the tissue levels of dopamine were found to be severely depressed. A significant shift from beta1- to beta2-adrenoceptor subtype was observed, while the total beta-adrenoceptor density remained unaffected. The present findings indicate that catecholamine synthesis in chronically denervated hearts is impaired upstream of dopamine and that a shift in beta-adrenoceptor subtype occurs already within a relatively short period of five weeks of denervation, and suggest that the lack of endogenous catecholamines influence the relative expression levels of the two subtypes of beta-adrenoceptors present in cardiac tissue.

Evidence for an influence of mechanical restitution on beat-to-beat variations in haemodynamics during chronic atrial fibrillation in patients

OBJECTIVE

We tested the hypothesis that beat-to-beat changes in haemodynamics during atrial fibrillation include an effect of each preceding R-R interval through the interval-strength relationship (mechanical restitution).

BACKGROUND

The variation in stroke volume and pulse pressure characteristic of atrial fibrillation is usually ascribed to time dependent ventricular filling.

METHODS

We measured the maximum rate of rise of left ventricular pressure (LVdP/dtmax), and aortic blood velocity and its integral in patients with atrial fibrillation undergoing cardiac catheterisation. The contractile response of isometric human myocardial trabeculae to sequences of atrial fibrillation was also studied, using the recorded ECGs as stimuli. The trabeculae were obtained from the resected right ventricular outflow tracts of patients with Fallot's tetralogy undergoing operative correction.

RESULTS

Beat-to-beat variations in contractile function during atrial fibrillation in the patients were recorded as LVdP/dtmax and left ventricular ejection (ascending aortic) velocity integral (proportional to stroke volume). Both these indices correlated well with the response to the same ECG (R wave) sequences in the isometric model measured as the maximum rate of rise of force, dF/dtmax, r = 0.72 to 0.81, p, 0.0001. When short pre-preceding intervals were excluded (minimizing the effect of post-extrasystolic potentiation), these variables showed a positive curvilinear relationship to preceding interval typical of mechanical restitution.

CONCLUSIONS

Mechanical restitution, which causes beat-to-beat changes in inotropic state, accounts in part for the changes in stroke volume in atrial fibrillation.

Metabolic alterations in the chronically denervated dog heart

OBJECTIVE

Previous studies have shown that chronic cardiac denervation impairs myocardial glucose oxidation. To investigate this further we tested whether the tissue content of glucose transporters, activity of glycolytic enzymes or metabolic capacity of pyruvate dehydrogenase were altered. Moreover, we investigated whether the decline in glucose utilization was associated with an upregulation of proteins and enzymes involved in fatty acid handling. Chronic cardiac denervation results also in decreased left ventricular efficiency. We explored whether alterations in mitochondrial properties could be held responsible for this phenomenon.

METHODS

Twelve adult dogs were included in the study. In 6 of them chronic cardiac denervation was accomplished by surgical ablation of the extrinsic nerve fibers. The other 6 dogs were sham-operated. Biopsies were obtained from the left ventricle after 4-5 weeks of denervation. The content or enzymatic activity of proteins involved in fatty acid and glucose handling was assessed. Features of glutamate oxidation were measured in freshly isolated mitochondria.

RESULTS

The content or activity of a set of fatty acid handling proteins did not change during chronic cardiac denervation. In contrast GLUT1 content significantly increased in the chronically denervated left ventricle, while the active form of pyruvate dehydrogenase declined (p < 0.05). Glutamate oxidation characteristics in freshly isolated mitochondria were not affected by chronic denervation.

CONCLUSION

The impairment of glucose oxidation in the chronically denervated myocardium is most likely caused by a decline of pyruvate dehydrogenase in its active form. It is unlikely that the decrease in work efficiency is caused by alterations in mitochondrial properties.

Beneficial effect of the calcium-sensitizing drug EMD 57033 in a canine model of dilated heart failure

1. Pacing-induced heart failure was studied in eight dogs. Heart failure was induced by right ventricular pacing at 250-260 beats/min for 6 weeks. Evidence of heart failure was determined clinically and by measurement of left ventricular (LV) dimensions by transoesophageal echocardiography. 2. Haemodynamic measurements of LV pressure, maximum rate of rise of LV pressure (LVdP/dtmax), cardiac output, mean arterial pressure, heart rate, pulmonary artery and pulmonary wedge pressures were made during infusion of solvent (control) and the calcium sensitizer EMD 57033 (0.6 mg min-1 kg-1). 3. The degree of heart failure varied from mild to severe in different individuals, but in each case EMD 57033 exerted a positive inotropic effect on LV haemodynamics and dimension. 4. The positive inotropic effect of the calcium sensitizer was manifest by increased peak LVdP/dt with a subsequent increase in cardiac output at the same mean arterial pressure. 5. This study clearly demonstrates that there is the potential for improvement of contractility of the failing myocardium of the intact mammal by an agent with a mechanism of action which does not involve an increase in intracellular calcium.

Increased urinary albumin and retinol-binding protein in type I diabetes. A study of identical twins

OBJECTIVE

Indexes of early renal glomerular and tubular dysfunction have been demonstrated in type I diabetes, but it remains uncertain whether such changes are genetically determined or are secondary to the disease process. We therefore undertook to study whether early markers of renal dysfunction are a consequence of type I diabetes or inherited.

RESEARCH DESIGN AND METHODS

We estimated both urinary albumin excretion (UAE) and urinary retinol-binding protein (RBP) in 51 identical twin pairs discordant for type I diabetes and in 51 matched control subjects.

RESULTS

UAE and RBP were significantly higher in the diabetic twins than in their nondiabetic co-twins (P < 0.0001 and P < 0.0002, respectively). Seven diabetic twins had elevated UAE, but none of the nondiabetic co-twins did. In a subgroup of 44 twins with normal UAE (albumin excretion rate < 20 micrograms/min), diabetic twins had both a higher albumin excretion function (median [range]; 0.64 [0.18-2.74] mg/mmol creatinine) than their nondiabetic co-twins (0.48 [0.24-1.40], P < 0.01) and higher levels of RBP excretion (10.4 [4.0-167.0] micrograms/mmol creatinine) than their nondiabetic co-twins (7.5 [0.97-23.0], P < 0.05). Values between twins of a pair were significantly correlated for RBP (r = 0.36, P < 0.05) but not for UAE (r = 0.13).

CONCLUSIONS

These results suggest that in type I diabetes, an index of renal tubular function (RBP), but not glomerular function (UAE), is influenced by shared genetic and nongenetic factors. Type I diabetes can affect renal tubular function even when glomerular function is normal. We conclude that neither the increased UAE nor urinary RBP found in type I diabetes is inherited independently of the diabetes process.

Tachycardia-induced failure alters contractile properties of canine ventricular myocytes

OBJECTIVE

Rapid cardiac pacing has been used as a model for experimentally-induced cardiomyopathy. However, its relevance to human heart failure is not clear at present because little is known about changes in size and function of ventricular myocytes. We have therefore studied the responses to graded increases in frequency and calcium in canine ventricular myocytes from failing hearts. The aim of our study was to evaluate the resemblance between canine pacing-induced and human end-stage heart failure.

METHODS

Myocytes were isolated from the left ventricular wall of dogs that were in heart failure after 6 weeks of pacing at 250 beats/min. Cell shortening was measured by edge detection.

RESULTS

Clinical signs of failure included dyspnea, ascites, and heart dilatation; the hemodynamic parameters were: LVdP/dtmax 1613 +/- 149 vs. 4713 +/- 304 mmHg/s in 6 control dogs; LVEDP 17.2 +/- 4.4 vs 5.6 +/- 1.1 mmHg; LV volume 60.5 +/- 6.2 vs. 30-35 ml. Myocytes from failing hearts were longer and thinner than those from controls (from factor: 0.40 +/- 0.01 vs. 0.47 +/- 0.01, P < 0.001, > 30 cells/heart). With 6 mM Ca2+ and at 0.5 Hz, contraction amplitude was significantly attenuated in myocytes from failing hearts: 6.6 +/- 0.9% cell shortening vs. 10.0 +/- 0.8% in controls (P < 0.05). This deficit was exacerbated at higher stimulation rates. Time-to-peak contraction and time-to-50% relaxation were not altered. There was no difference in sensitivity to thapsigargin.

CONCLUSION

As with cells from human failing hearts, contraction amplitude showed rate-dependent depression in this animal model, whereas features like slowing of contraction and relaxation and reduced sensitivity to thapsigargin, were not reproduced.

Platelet 5-hydroxytryptamine is decreased in a preliminary group of depressed patients receiving the 5-hydroxytryptamine re-uptake inhibiting drug fluoxetine

1. In view of the importance of 5-hydroxytryptamine in coronary thrombosis, we wanted to know whether a potentially protective decrease in platelet 5-hydroxytryptamine could be achieved by treatment with an inhibitor of 5-hydroxytryptamine uptake, fluoxetine. 2. We studied 15 patients treated for psychiatric indications with fluoxetine, and compared the findings with those obtained with blood from 18 patients treated with amitriptyline and 13 controls previously treated for affective disorders. 3. Platelet-rich plasma 5-hydroxytryptamine levels were significantly decreased in the fluoxetine group (P < 0.005) but not in the amitriptyline group compared with the control group. 4. Collagen-induced aggregation in whole blood anticoagulated with hirudin was measured by sequential single platelet counting. The contribution of 5-hydroxytryptamine was assessed from the effect of adding the 5-hydroxytryptamine specific antagonist ICI 170809. This contribution was significantly decreased in the fluoxetine group but not in the amitriptyline group compared with the control group. 5. It is concluded that platelet 5-hydroxytryptamine is indeed decreased by fluoxetine, and we would predict a protective effect of fluoxetine against coronary thrombosis.

Failure of thrombin inhibition to prevent intracoronary thrombosis in the dog

1. Recurrent occlusion after thrombolysis may be caused by thrombin receptor-mediated platelet thrombosis occurring in a residual stenosis. To test the relative importance of the platelet thrombin receptor under conditions of high shear and endothelial damage (the Folts model of intracoronary thrombosis) we used the specific thrombin inhibitor recombinant hirudin. 2. A critical coronary artery stenosis overlying an area of crushed endothelium was used in a repeated measures study of eight open-chest anaesthetized dogs. In the control period, recurrent thrombosis occurred at an average rate (+/- SD) of 4.4 +/- 1.4 ml/min2. Infusion of recombinant hirudin at 1.6 mg h-1 kg-1 abolished recurrent thrombosis in three dogs, but the thrombosis rate averaged 4.7 +/- 2.9 ml/min2 in the remaining five animals. 3. Haematological measurements demonstrated the activity of recombinant hirudin: thrombin time rose from 13 +/- 3 s to > 165 s universally (P < 0.01), partial thromboplastin time rose from 14 +/- 2 s to 29 +/- 10 s (P < 0.01). Bleeding time rose from 2.3 +/- 0.8 min to 4.7 +/- 1.8 min (P < 0.05). 4. It is concluded that specific thrombin inhibition, despite affecting coagulation, is relatively ineffective in preventing intracoronary thrombosis under conditions of high shear.

Natriuresis caused by blood volume expansion in dogs is not mediated by the renal nerves

The influence of renal denervation on the renal response to rapid blood volume expansion was investigated by measurement of urine volume, sodium and osmolar excretion rates, sodium p-aminohippurate and free water clearances, and systemic haemodynamic and plasma hormone (atrial natriuretic peptide, arginine vasopressin and plasma renin activity (PRA)) changes in ten control and ten renal-denervated chloralose-anaesthetized mongrel dogs. Following renal denervation, blood volume expansion caused a similar increase in sodium excretion to that in the control group. Renal denervation resulted in systemic vasodilatation and decreased PRA. During fluid loading the right atrial pressure and pulmonary capillary wedge pressure were significantly higher in the control group. In the control group, volume expansion caused a large fall in PRA, whereas in the renal-denervated dogs, PRA remained suppressed. We conclude, from the fact that natriuresis is preserved after renal denervation, that this response is not mediated by a reflex with efferent limb in the renal nerves.

Mechanical restitution and recirculation fraction in cardiac myocytes and left ventricular muscle of adult rats

Unloaded cell shortening was measured in electrically stimulated myocytes from adult rat hearts to compare the contractile response to stimulation with that in isometrically contracting left ventricular papillary muscles under similar experimental conditions, but preloaded to produce maximum twitch tension. Mechanical restitution in cells followed a biexponential function with time constants of 0.19 +/- 0.03 s and 36.4 +/- 10.2 s (7 cells from 5 hearts, n = 7/5). The time constants for papillary muscles were 0.58 +/- 0.05 s and 14.6 +/- 1.0 s (n = 6/6). In myocytes, maximum post-rest potentiation occurred after 30 to 60 s of rest. The potentiation after 60 s of rest was 2.48 +/- 0.31 times the steadystate in cells and 2.63 +/- 0.16 in papillary muscles. Recirculation fraction of C2+ as calculated from the decay of post-rest potentiation was 0.84 +/- 0.04 in single cells and 0.59 +/- 0.02 in papillary muscles (p < 0.005). Caffeine (3mM) abolished post-rest potentiation in both types of preparations. The numerical values for the time constants of mechanical restitution, potentiation factor and recirculation fraction in papillary muscles did not depend on preload. It is concluded that interval-dependent changes of contractility are preserved in single cardiac cells but the kinetics of decay of potentiation appear to have changed quantitatively.

The pressure-flow relation in the canine coronary artery: combined effects of critical stenosis and intracoronary thrombosis

OBJECTIVE

To characterise the effect of coronary intra-arterial thrombosis upon the downstream vascular bed.

BACKGROUND

The vascular response downstream from a coronary intra-arterial thrombus has not previously been characterised. We postulated that downstream vasoconstriction might result from the presence of endothelial damage with consequent growth of platelet-rich thrombus.

METHODS

We measured the pressure gradient and flow across, and the pressure/flow ratio distal to, a canine left circumflex artery stenosis with and without endothelial damage causing intracoronary thrombosis. We also observed the effects of transient complete conclusions.

RESULTS

At occlusion, the pressure gradient was maximal; relief of occlusion caused a rapid increase flow and distal pressure with a rapid decrease in stenosis pressure gradient and resistance. Subsequently there was a period of stable stenosis resistance with pressure gradient and flow declining; distal pressure therefore increased at this time. Finally in the thrombus group only, stenosis resistance increased again towards re-occlusion. During occlusion, distal pressure averaged 49 +/- 18 mmHg in the presence of thrombus vs. 22 +/- 4 mmHg in its absence (P < 0.001). Following release of occlusion, the flow increased faster than distal pressure, so that the ratio (distal pressure/flow) fell rapidly. Subsequently, distal pressure continued to increase after flow had reached a peak and begun to decline, suggesting vasoconstriction. In the presence of thrombus, the distal pressure/flow ratio was higher than in the absence of thrombus, both at maximal vasodilation (P < 0.005) and at maximum vasoconstriction (P < 0.025).

CONCLUSIONS

During cyclic flow variations the stenosis resistance changes are exactly as expected from thrombus growth and embolisation. The distal pressure/flow ratio showed a time-dependent increase which appeared greater when conditions favoured intracoronary thrombosis.

Limitation of infarct size by trimetazidine in the rabbit

The influence of trimetazidine on infarct size was studied with a 45-minute period of coronary occlusion followed by 24 hours of blood reperfusion in the rabbit heart. The groups studied were 7 control rabbits and 7 rabbits pretreated with 3 mg/kg of trimetazidine. Twenty-four hours after coronary artery ligation for 45 minutes, infarct size was measured in myocardial slices using trinitrophenyl tetrazolium staining, and the area at risk was determined by injection of zinc/cadmium particles and delineated at the same time by imaging, under fluorescent light, the areas of tissue that fluoresced. The range of area at risk was similar in both of the groups. There was a significant reduction in the size of infarct that developed in the trimetazidine-treated group when compared with the control rabbits. It is concluded that pretreatment with trimetazidine in the blood-perfused rabbit heart is effective in reducing myocardial infarct size.

Doppler determined aortic acceleration after dipyridamole in the prediction of coronary artery disease

Change in the acceleration of aortic blood flow with stress testing is reported to reflect the presence of myocardial ischaemia. We studied its clinical usefulness when compared with dipyridamole thallium scintigraphy in 101 patients, of whom 64 had coronary angiography. Maximum aortic acceleration increased after dipyridamole (P < 0.0001), although no correlation existed between the aortic acceleration and evidence of thallium perfusion abnormalities. For the patients who had angiography, the increase in aortic acceleration was similar for those with no significant coronary stenoses, single vessel or multi-vessel disease. Compared with coronary angiography, Doppler measurement of maximum aortic acceleration had a sensitivity of 92% and a specificity of 37% for the detection of coronary artery disease. When patients with previous myocardial infarction or left ventricular dysfunction were excluded, there was still no relationship between the maximum aortic acceleration and the presence of coronary artery disease. We conclude that changes in the acceleration of aortic blood flow after dipyridamole stressing do not predict the presence or severity of coronary artery disease as measured from perfusion defects at thallium scintigraphy or by coronary angiography. We have observed a wide variability of aortic maximum acceleration in the evaluation of myocardial ischaemia, which we feel introduces serious limitations to its use in routine clinical practice.

Impaired platelet aggregation after cardiopulmonary bypass in man: enhancement of collagen-induced aggregation in whole blood and plasma by adrenaline ex vivo

1. We tested the effect of intravenous adrenaline at 0.55-1.10 nmol min-1 kg-1 (for 3-8 min, at 7-10 min post bypass; n = 7) on both microaggregation in hirudinized whole blood, using platelet counting, and macroaggregation in platelet-rich plasma, using optical aggregometry. Control (n = 12) blood samples were taken before and at 10 and 20 min after bypass. 2. Post-bypass plasma adrenaline levels (nmol/l) increased slightly in controls (1.0 versus 0.7 at 10 min, medians; P = 0.05) and markedly with adrenaline infusion (36 versus 0.5 before infusion, P = 0.02). Microaggregation (percentage decrease in single platelets) in stirred blood, reflecting largely ADP-dependent 'spontaneous' aggregation, was not influenced by adrenaline infusion. In contrast, collagen (0.2 microgram/ml)-induced microaggregation in blood was enhanced by adrenaline (92% versus 41%, P = 0.02), with no change in controls (60% versus 53%, P = 0.61). 3. In controls, collagen (0.6 microgram/ml)-induced macroaggregation in platelet-rich plasma (extent of increase in light transmission, cm) was impaired at 10 min post bypass (5.3 versus 12.1 before bypass, P = 0.01), but was enhanced by adrenaline (7.0 versus 3.6 before infusion, P = 0.02). Platelet counts (x 10(9)/l) were decreased postbypass (155 versus 220, P = 0.02) and were not influenced by adrenaline infusion (167, P = 0.93).(ABSTRACT TRUNCATED AT 250 WORDS)

Post-rest potentiation and its decay after inotropic interventions in isolated rat heart muscle

The effects of various inotropic interventions on post-rest potentiation and its decay were investigated in isolated cardiac muscle. The inotropic interventions studied were: reduced extracellular Na+ and elevated extracellular Ca2+ concentration; exposure to ouabain, monensin, isoprenaline, phenylephrine and cirazoline. Force of contraction (stimulation frequency 2 Hz) was measured isometrically in left atria and right ventricular strips of rat hearts. Maximum post-rest potentiation was reached after 10 sec. of rest and amounted to 245 +/- 26% of pre-rest control in ventricle and 192 +/- 15% in atria. Ca(2+)-recirculation fraction was calculated from the decay of post-rest potentiation after resumption of regular stimulation, it was 0.77 +/- 0.01 in 11 control ventricular strips. High concentrations of caffeine (3 mmol/l) completely abolished post-rest potentiation in both tissues. The development of post-rest potentiation was accelerated in the presence of most of the inotropic agents. However, with the exception of ouabain and only in atrial muscle, none of the inotropic interventions produced higher post-rest contraction amplitudes than during controls. In rat heart muscle, the inotropic interventions studied are not any more effective in augmenting force of contraction than prolonged stimulation intervals. This suggests that (1) the distribution of Ca2+ into the sarcoplasmic reticulum is at a maximum during post-rest potentiation; (2) modifications of signal transduction pathways cannot further increase post-rest potentiation; and therefore that (3) shifts in Ca2+ distribution act as a limiting factor.

Lack of importance in humans of the slow component of the response of force to an increase in cardiac muscle length

1. An increase in length in isolated animal muscles causes an immediate increase in contractile force, which is followed by a slower further progressive increase: the slow component. However, the pressure-volume concept, used in characterizing left ventricular function, is dependent on a constant relationship between pressure and volume. 2. We therefore examined the possible occurrence of the slow inotropic component of the response to cardiac muscle stretch in man at cardiac catheterization. 3. Human subjects undergoing left heart catheterization for clinical indications were studied. The development of the slow component was studied by measurement of rate of rise in left ventricular developed pressure and the time course after an increase in end-diastolic volume. 4. No evidence for any slow component was elicited. 5. It is concluded that the slow component of force (or pressure) increase after an increase in cardiac muscle length (or volume) does not have a role in the human heart in situ.

Macroaggregation of platelets in plasma, as distinct from microaggregation in whole blood (and plasma), as determined using optical aggregometry and platelet counting respectively, is specifically impaired following cardiopulmonary bypass in man

We determined changes in platelet aggregability following cardiopulmonary bypass, using optical aggregometry to assess macroaggregation in platelet-rich plasma (PRP), and platelet counting to assess microaggregation both in whole blood and PRP. Hirudin was used as the anticoagulant to maintain normocalcaemia. Microaggregation (%, median and interquartile range) in blood stirred with collagen (0.6 micrograms/ml) was only marginally impaired following bypass (91 [88, 93] at 10 min postbypass v 95 (92, 96] prebypass; n = 22), whereas macroaggregation (amplitude of response; cm) in PRP stirred with collagen (1.0 micrograms/ml) was markedly impaired (9.5 [8.0, 10.8], n = 41 v 13.4 [12.7, 14.3], n = 10; p < 0.0001). However, in PRP, despite impairment of macroaggregation (9.1 [8.5, 10.1], n = 12), microaggregation was near-maximal (93 [91, 94]), as in whole blood stirred with collagen. In contrast, in aspirin-treated patients (n = 14), both collagen-induced microaggregation in whole blood (49 [47, 52]) and macroaggregation in PRP (5.1 [3.8, 6.6]) were more markedly impaired, compared with control (both p < 0.001). Similarly, in PRP, macroaggregation with ristocetin (1.5 mg/ml) was also impaired following bypass (9.4 [7.2, 10.7], n = 38 v 12.4 [10.0, 13.4]; p < 0.0002, n = 20), but as found with collagen, despite impairment of macroaggregation (7.2 [3.5, 10.9], n = 12), microaggregation was again near-maximal (96 [93, 97]). The response to ristocetin was more markedly impared after bypass in succinylated gelatin (Gelofusine) treated patients (5.6 [2.8, 8.6], n = 17; p < 0.005 v control), whereas the response to collagen was little different (9.3 v 9.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of left ventricular contractile behaviour during atrial fibrillation

OBJECTIVES

The purpose of this study was to explore the physiology underlying the beat-to-beat variations of ventricular function during atrial fibrillation (AF).

METHODS

Left ventricular pressure, and its first derivative (LVdP/dtmax, an index of contractility, and aortic blood velocity (and its integral AVI, an ejection index), were recorded using cathetermounted transducers in 15 patients with AF during cardiac catheterisation. Transfer function modelling was used to examine the influence of preceding intervals on LVdP/dtmax, and of LVdP/dtmax on AVI. The technique also allowed simulation of the behaviour of LVdP/dtmax in response to specific manipulations of interval.

RESULTS

The variations in LVdP/dtmax recorded from the AF patients were shown to be dependent on up to six preceding intervals; a maximum of 91% of the variation was explicable in this way. The influences of mechanical restitution (MR, the relationship between preceding interval and contractility), postextrasystolic potentiation (PESP, the inverse relationship between pre-preceding interval and contractility) and the decay of that potentiation were all demonstrated. These influences collectively appeared to be powerful determinants of AVI. Simulations of LVdP/dtmax, following single interval perturbations, were entirely consistent with these interval force effects.

CONCLUSIONS

The cardiac interval force relationship in man is an important determinant of the beat-to-beat variations of contractile and ejection function during AF: the beat-to-beat variations in contractile (or inotropic) function are independent of changes in ventricular filling or fibre-length.

The inotropic and hemodynamic effects of intravenous milrinone when reflex adrenergic stimulation is suppressed by beta-adrenergic blockade

Milrinone is an inotropic and vasodilator agent proven to be effective in the treatment of heart failure. This study evaluated whether milrinone produces inotropic and hemodynamic effects independent of reflex adrenergic stimulation. Eleven stable heart failure patients (New York Heart Association class II to III) undergoing cardiac catheterization received intravenous (i.v.) milrinone (50 micrograms/kg for 10 minutes followed by 0.5 micrograms/kg/min for 50 minutes) during beta-adrenergic blockade. After beta-blockade with a 50-mg oral dose of metoprolol, heart rate decreased by a mean of 16.6%. The peak inotropic response to i.v. milrinone measured using the maximum rate of rise of left ventricular pressure (LV dP/dt) was fully developed at 20 minutes. Mean absolute inotropic response of LV dP/dt from baseline was statistically significant at 10, 20, 30, and 40 minutes (P < 0.05). Mean percentage increase in cardiac index from baseline was statistically significant at 20 and 30 minutes, and mean absolute decline from baseline for pulmonary capillary wedge pressure was statistically significant at 20 and 40 minutes (P < 0.05). The inotropic and hemodynamic effects of i.v. milrinone were thus preserved during beta-adrenergic blockade. This finding is consistent with a mechanism of action of i.v. milrinone--myocardial phosphodiesterase inhibition--that is independent of reflex adrenergic stimulation.

Risk factors for cardiovascular disease in IDDM. A study of identical twins

Patients with insulin-dependent diabetes mellitus (IDDM) have an excess mortality, predominantly attributable to cardiovascular disease. To determine the effect of IDDM on potential risk factors for cardiovascular mortality, we studied subjects from the British Diabetic Twin Study Group. Forty-five identical twin pairs discordant for IDDM were recruited in addition to 45 matched nondiabetic singleton control subjects. All were selected to be normotensive and to have normal albumin excretion rates. Four variables differed significantly between the diabetic twins and their nondiabetic identical co-twins: diabetic twins had higher systolic blood pressure (sBP) ([mean +/- SD] 127 +/- 17 vs. 123 +/- 18 mmHg, P < 0.05), high-density lipoprotein (HDL) cholesterol (1.36 +/- 0.31 vs. 1.25 +/- 0.29 mM, P < 0.05) and fibrinogen (3.23 +/- 0.81 vs. 2.98 +/- 0.71 mg/ml, P < 0.05) but lower factor VII (114 +/- 34 vs. 122 +/- 31%, P < 0.05). All four of these risk factors were significantly correlated (P < 0.001) within the identical twin pairs, as were the other risk factors. These significant correlations within twins for the risk factors studied reflects the impact of shared genetic and environmental influences. IDDM affects sBP, HDL cholesterol, fibrinogen, and factor VII, but only sBP and fibrinogen are affected adversely.

Exercise electrocardiography and aortic Doppler velocimetry in asymptomatic identical twins discordant for type 1 (insulin dependent) diabetes

OBJECTIVE

To determine the influence of insulin dependent diabetes on the prevalence of myocardial ischaemia and on global left ventricular systolic performance.

DESIGN

Stress treadmill electrocardiograms and simultaneous Doppler measurement of aortic maximum acceleration were obtained during exercise on symptom free subjects. The electrocardiograms were scored blindly according to the Minnesota code.

PARTICIPANTS

39 identical twin pairs (22 male) discordant for insulin dependent diabetes and 39 non-diabetic controls of similar age and sex were examined. The twins and controls had a mean age of 37 (range 25-69) with a mean (SD) duration of diabetes in the diabetic twin of 17 (7) years. Those selected were normotensive and had no renal impairment.

RESULTS

Systolic blood pressure was significantly higher in the diabetic twins than in their non-diabetic cotwins both at rest (p < 0.05) and at peak exercise (p < 0.01). Electrocardiographic evidence of ischaemia was not correlated within twin pairs and was found in similar numbers of diabetic twins, their non-diabetic cotwins, and control subjects. Abnormal electrocardiograms were found in a similar number of diabetic twins (23%), non-diabetic cotwins (18%), and controls (15%). There was a significant correlation in Doppler measurements of global left ventricular systolic function within the identical twins; no significant difference was found for these Doppler measurements in the diabetic twins, non-diabetic cotwins, or controls.

CONCLUSION

Exercise characteristics and cardiac function seem to be subject to shared genetic or shared environmental influences or both, whereas electrocardiographic features of ischaemia seem to be environmentally determined. In a selected cohort of diabetic identical twins without evidence of nephropathy there was no evidence that diabetes influenced the prevalence of myocardial ischaemia or global left ventricular systolic function.

Enoximone in chronic stable angina: a double-blind placebo-controlled cross-over trial

Enoximone, a phosphodiesterase inhibitor (PDEI), has both positive inotropic and vasodilatory properties. We examined the effect of a single oral dose of enoximone as compared with placebo on myocardial ischaemia and global left ventricular (LV) function using both exercise ECG and Doppler measurements of aortic blood flow, respectively. Twenty patients (16 men, 4 women) with a mean age of 59 years and stable angina were studied. Total exercise duration was significantly longer after enoximone as compared with placebo treatment, with a mean difference of 22.8 s (p = 0.003). Times (mean +/- SD) to onset of angina and development of significant ST-segment decrease were similar after placebo (454 +/- 101 and 352 +/- 155 s, respectively) or enoximone (500 +/- 155 and 413 +/- 192 s, respectively), although both showed trends in favour of enoximone. As compared with placebo, significantly higher heart rate (HR) was measured for enoximone both at rest (75 +/- 18 vs. 90 +/- 22 beats/min, p < 0.01) and on recovery from exercise (81 +/- 18 vs. 89 +/- 19 beats/min, p < 0.05). Enoximone had no significant effect on systolic or diastolic blood pressure (SBP, DBP) or rate-pressure product (RPP) generated at rest or during exercise. Changes in both acceleration and velocity of aortic blood flow during exercise were similar after administration of enoximone or placebo. We showed that a single oral dose of enoximone is well tolerated in patients with ischaemic heart disease, improving both exercise capacity and favourably influencing ST-segment changes with no increase in adverse events or significant haemodynamic disturbances.

Serum lipids and thyrotropin in women with coronary artery disease

Abnormalities of thyroid function are associated with changes in lipid concentrations and in the incidence of ischaemic heart disease. Whether lipid concentration and thyroid function are related when thyroid function is normal in ischaemic heart disease is uncertain. This study was undertaken to investigate the relationship between thyroid function, serum lipids and ischaemic heart disease in euthyroid women. Forty-six euthyroid patients were studied. Patients with diseases known to affect lipid levels or receiving drugs known to alter lipid or thyroid metabolism were excluded. Twenty-three had ischaemic heart disease (IHD) and were matched with 23 controls. Correlations were found between thyrotropin (TSH) and cholesterol (P = 0.05) low density lipoprotein (LDL) (P = 0.09) and triglyceride (P = 0.009) in the IHD group but not between any serum lipids and TSH in the control group. Analysis of covariance showed a statistically significant difference between groups of the association between cholesterol and TSH (P < 0.05 (slope) P < 0.001 (means)), LDL and TSH (P < 0.005 (means)) and between triglyceride and TSH (P < 0.05 (means)). This study suggests that TSH within the normal range is having a statistically significant effect on lipid levels in women with ischaemic heart disease.

Emerging patterns of heart disease in HIV infected homosexual subjects with and without opportunistic infections; a prospective colour flow Doppler echocardiographic study

We studied 124 homosexual men aged 36.7 +/- 7.6 years (range 23-57) using Doppler echocardiography. One hundred and one patients (Group A) had had acquired immunodeficiency syndrome for 1.6 +/- 1.0 years and 23 patients (Group B) had had HIV infection without opportunistic infections for 3.2 +/- 2.3 years. Doppler echocardiography was normal in 31% of Group A patients and in 61% of Group B. Pericardial effusion was found in 44 Group A patients (44%) and two Group B patients (9%). In Group A, left ventricular dilatation and/or dysfunction were found in 20 patients (20%), aortic root dilatation and regurgitation in eight patients (8%) and an intracardiac echogenic mass in seven patients (7%); in Group B one patient (4%) had an intracardiac mass. Forty-four (44%) Group A patients had cardiac presentations, and of these 22 had cardiomegaly with clinical signs of heart failure; 10 patients had tachyarrhythmias compared to only two in Group B. Although the CD4 lymphocyte count (%) was significantly lower in Group A than in Group B (5.4 +/- 6.1 vs 13.3 +/- 7.3, P < 0.001), the presence of pericardial effusion, left ventricular dysfunction, right-sided cardiac enlargement or the duration of HIV infection, did not relate to the CD4 level in either group. Although often not diagnosed clinically, cardiac involvement in patients with AIDS is a clinical reality, with pericardial effusion, cardiomyopathy and left ventricular dysfunction appearing to have a high prevalence in male homosexual patients with AIDS. These clinical and echocardiographic findings are associated with clinically apparent intercurrent opportunistic infections, rather than the HIV virus per se, or the severity of infection as reflected by the CD4 count.

Influences of stimulation frequency and temperature on interval-force relationships in guinea-pig papillary muscles

Relationships between contractile force and the preceding and pre-preceding stimulation intervals were studied in papillary muscles by interposing variable test intervals during steady-state pacing. The strength of test contractions increased exponentially to a maximum as the preceding (test) interval was lengthened. Contractility decreased as an exponential function of pre-preceding interval. At 37 degrees C, the half times for these processes were unaffected by increasing the steady-state frequency from 1 to 3 Hz. At 27 degrees C, the force increase with preceding interval was accelerated and the decay with pre-preceding interval was retarded as the stimulation frequency was increased from 0.33 to 2 Hz. The time-courses of force increase and decay were similar to each other during stimulation at an optimum frequency characteristic for the temperature. Cooling from 37 to 27 degrees C prolonged the half times for force increase and decay by factors of 4.5 and 3 respectively. The slope of the linear relationship between the force of the contraction pre-preceded by the test interval and the immediately subsequent contraction (recirculation fraction) was also halved. These results suggest that high stimulation frequency and low temperature uncouples cellular processes underlying the interval dependence of cardiac contractility. The temperature sensitivities are consistent with these processes being enzymatic. The reduced recirculation fraction provides a mechanism for the lowered threshold frequency for sustained mechanical alternans at 27 degrees C.

Antagonism of the platelet 5HT2 receptor in the presence of thrombolysis

Thrombolysis of coronary arterial thrombi is often accompanied by occlusion due to continued platelet thrombosis. We modified the Folts' model of intracoronary thrombosis (critical stenosis with endothelial damage) to produce up to 35-min occlusions of the circumflex coronary artery in seven open-chest anaesthetised dogs. Administration of recombinant plasminogen activator (rtPA 200 micrograms.kg-1 bolus plus 1 mg.kg-1.h-1 infusion), without heparin or aspirin, always produced effective thrombolysis. Fibrinogen decreased (P < 0.05), thrombin time increased (P < 0.025), bleeding time trebled (P < 0.025) and initial arterial patency was achieved. Addition of a selective 5HT2 antagonist, increased coronary blood flow (P < 0.01) and reduced rethrombosis rate (P < 0.025), but did not affect coagulation or bleeding. The time the vessel spent occluded was significantly decreased (P < 0.01) and correlated with the fibrinogen level (r = 0.97, P < 0.01), thereby implying the presence of fibrin within the thrombus. After rt-PA was withdrawn, bleeding time and fibrinogen level normalised within 30 and 60 min, respectively, but full coronary patency was maintained. Thus, when rt-PA alone had produced full thrombolysis, 5HT2 antagonism prevented intracoronary thrombosis without additional bleeding complications.

Mechanisms of excitation-contraction coupling studied using the principle of transient perturbation

We have studied the responses to a brief interruption of a train of steady state beats, namely: (1) a single prolonged depolarisation within the train; (2) a single short interval within the train; (3) a single long interval within the train. These responses are predicted by a two compartment model of intracellular calcium handling. They are characterised by the following phenomena. (1) Prolongation of one depolarisation/action potential in the steady state train causes potentiation of the following beat. We postulate on the basis of the published evidence that this may be due to "reversed" sodium/calcium exchange during late systole leading to extra calcium entry during the prolonged depolarisation. (2) Postextrasystole potentiation is postulated to share this mechanism when a depolarisation (extrasystole) is introduced immediately after one of the steady state depolarisations (single short interval). The postextrasystolic beat is then potentiated. (3) A single short interval during the steady state train also leads to attenuation of contractile force on the beat immediately after the short interval, that is, the extrasystole. Mechanical restitution is the term applied to the recovery of this force with increasing interval. This consists of two phases. The initial rapid phase is ryanodine and caffeine insensitive, indicating possible independence of sarcoplasmic reticular function. We postulate that a "membrane compartment" of internal calcium may be responsible. The second, slower, phase of mechanical restitution is ryanodine and caffeine sensitive, indicating that it is likely to be a property of the sarcoplasmic reticulum.(ABSTRACT TRUNCATED AT 250 WORDS)

Obliterative bronchiolitis with atypical features: CT scan and necropsy findings

We describe the natural history of cryptogenic bronchiolitis obliterans in a patient followed for 24 yrs with serial pulmonary function tests and radiology. Severe, progressive airway obstruction developed, with overinflation but preservation of KCO. There was progressive hypoxaemia, which worsened on exertion; hypercapnoea was modest until late in the illness. Neither bronchodilators nor steroids were effective. The chest radiograph remained normal; CT showed irregular areas of low attenuation peripherally throughout the lungs, with Hounsfield numbers typical of emphysema, but no bullae. Postmortem studies included histology and quantitative studies of a corrosion cast of one lung. They showed marked airway narrowing at all levels, with pruning of peripheral branches, mucus plugging, and some emphysema. The case illustrates that cryptogenic bronchiolitis obliterans may be chronic and difficult to distinguish clinically or by investigation from other forms of chronic obstructive airways disease, particularly emphysema.