The effects of enalapril and spironolactone on terbutaline-induced hypokalemia

Prolongation of QT interval by terbutaline in healthy subjects

In a double-blind, randomized placebo-controlled crossover study, we characterized how terbutaline prolonged cardiac corrected QT interval (QTc). The study was carried out in six young and healthy male subjects in supine position. Escalating terbutaline doses were administered intravenously at infusion rates of 6 mL/h (10 microg terbutaline/min), 12 mL/h (20 microg terbutaline/min), and 18 mL/h (30 microg terbutaline/min). Terbutaline maximally prolonged QTc intervals on average by 60%, from 358 milliseconds (SD 28) to 456 milliseconds (SD 19). The effect was closely associated with a simultaneous decrease in plasma potassium concentration from 4.0 mmol/L (SD 0.1) to 2.5 mmol/L (SD 0.1). The final phase of slow ventricular repolarization, the interval between the apex and the end of T wave, was proven to be highly sensitive to the hypokalemic terbutaline actions, whereas the earlier repolarization phases were not strongly affected by terbutaline. Estimated by using the classic Nernst equation for membrane potentials, terbutaline-induced hypokalemia hyperpolarized ventricular myocardium from the resting level of -90 mV to -110 mV. The prolongation of QTc interval was related to ventricular hyperpolarization with a Pearson correlation coefficient of 0.91. Terbutaline-induced prolongation of QTc interval in healthy volunteers is in conformity with repolarization studies carried out in isolated canine heart ventricular preparations in which the cardiac ventricular cell membrane potential determines the duration of the final phase of slow ventricular repolarization.

Use of Angiotensin-Converting Enzyme Inhibitors in Elderly People With Heart Failure: Prevalence and Outcomes

BACKGROUND

There is a lack of information on the effects of angiotensin-converting enzyme (ACE) inhibitors in very old people with heart failure (HF). The objective of this study is to estimate the prevalence of prescriptions of ACE inhibitors in elderly people with HF discharged from acute care hospitals, and to evaluate the effect of these drugs on 1-year mortality rates.

METHODS

We used data from the Gruppo Italiano di Farmacovigilanza nell'Anziano (GIFA). In 1998, we undertook a 1-year longitudinal study on elderly people (aged 65+ years) discharged with a diagnosis of HF. We compared the demographic and clinical characteristics associated with a prescription at discharge of ACE inhibitors, and used a Cox proportional hazard regression model to calculate the relative hazard of dying associated with the use of ACE inhibitors.

RESULTS

We enrolled 818 patients in the study with a mean age of 79 years (range: 65-101 years). One fourth of the participants were aged 85 years or older. ACE inhibitors were prescribed to 550 patients (67.2%) at discharge. Older age and physical disability were negatively correlated with the use of ACE inhibitors. People using ACE inhibitors had a 40% reduction of mortality (HR [hazard ratio]: 0.60; 95% CI [confidence intervals]: 0.42-0.88). The reduction in mortality was much stronger among disabled people (HR: 0.35; 95% CI: 0.19-0.64).

CONCLUSION

ACE inhibitors are still underprescribed among elderly people with HF discharged from acute care hospitals. Even in this frail, elderly population, we found a beneficial effect of ACE inhibitors. There is room to further improve the quality of care for elderly people with HF.

Cardiopulmonary interactions of salbutamol and hypoxaemia in healthy young volunteers

1. Nebulised salbutamol is frequently used in the treatment of asthma and chronic obstructive pulmonary disease. Its effects on the cardiovascular system have been extensively investigated although as yet little is known concerning its effects on the pulmonary circulation, particularly during hypoxaemia. We have therefore examined the effects of nebulised salbutamol on pulmonary haemodynamics to see if it modifies hypoxic pulmonary vasoconstriction. 2. Eight healthy normal volunteers were studied on two separate occasions. After resting to achieve baseline haemodynamics patients were randomised to receive 5 mg salbutamol or placebo via a nebuliser. They were restudied after 30 min and then rendered hypoxaemic by breathing an N2/O2 mixture to achieve an SaO2 of 75-80%. Doppler echocardiography was used to measure mean pulmonary artery pressure (MPAP), cardiac output (CO) and hence pulmonary vascular resistance (PVR). 3. Treatment with salbutamol significantly increased MPAP during normoxaemia and hypoxaemia compared with placebo at 12.0 +/- 1.2 vs 8.0 +/- 0.7 mm Hg and 28.6 +/- 0.9 vs 25.2 +/- 1.0 mm Hg, respectively (P < 0.05). Salbutamol caused a significant increase in heart rate compared with placebo and effects were additive to those of hypoxia at 74 +/- 2 vs 67 +/- 3 beats min-1 during normoxaemia and 84 +/- 3 vs 77 +/- 4 beats min-1 during hypoxaemia, respectively (P < 0.05). Whilst systemic vascular resistance fell in response to salbutamol, PVR was unchanged by salbutamol during either normoxaemia or hypoxaemia. Cardiac output was increased by salbutamol and by hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)