Heart failure, where the heart is unable to maintain a sufficient blood flow to supply the body’s needs, is a leading cause of death, especially among the over 65’s. Half of all chronic heart failure patients die within four years of diagnosis. It can have a number of causes, for example damage to heart tissue after a heart attack, and leads to a variety of problems in patients. Fatigue and muscle weakness are common as the muscles receive insufficient oxygen, and because waste products cannot be removed from tissues quickly enough fluid can build up in the lungs and other parts of the body, often the legs and abdomen. The extra strain placed on the heart as it tries to maintain adequate blood pressure can lead to further damage to the heart and ultimately cardiac arrest.
In heart failure the rate at which the heart beats is often increased, and group of scientists led by Karl Svedberg and Michael Komajda set up the SHIfT study, to evaluate whether a drug called Ivabradine, which lowers the heart rate, could reduce risk of death or hospitalization in a group of patients who had heart failure accompanied by an elevated resting heart rate. Significantly fewer patients taking Ivabradine in addition to their existing treatments required hospital admission during the course of the study, compared to a control group who were given a placebo in addition to their existing treatment. The most striking outcome was that Ivabradine cut the risk of death by 26%.
So what is Ivabradine, and where does it come from?
Ivabradine slows the heart rate by inhibiting an electrical current known as the If current* which is a major regulator of the activity of the sinoatrial node – better known as the pacemaker. Inhibiting the If current slows the generation of the electrical impulses by the sinoatrial node that trigger heart contraction, and therefore slows the heart rate itself. Ivabradine, then known as S16257, was first developed in the early 1990’s when it was found to be able to block the If current in-vitro in sinoatrial node tissue from rabbits and guinea pigs, and slowed the generation of electrical impulses in a manner that was safer than other bradycardic drugs (1). Ivabradine was then evaluated in live rats and dogs, where it safely reduced the heart rate, and moreover did so without reducing the blood pressure (2,3). While beta-blockers such as Propranolol can reduce the heart rate they also lower the blood pressure – indeed they are used to treat hypertension – and hence are not suitable for many patients, so the development of a drug that could reduce heart rate without affecting blood pressure was very welcome.
Following the successful animal studies Ivabradine entered human clinical trials and in 2005 was approved for the treatment of angina pectoris. In angina pectoris the heart muscle receives too little oxygen, a problem exacerbated by a fast heart beat that increases the need for oxygen, so lowering of the heart rate by Ivabradine reduced oxygen demand and prevents angina attacks. The success of Ivabradine in the treatment of angina pectoris in turn led to its evaluation in heart failure.
The successful outcome of SHIfT study is a major boost to the development of better treatment regimes for heart failure, and if it is confirmed by further clinical trials will improve and prolong the lives of many heart failure patients.
* Hence the name of the SHIfT study – Systolic Heart failure treatment with the If inhibitor ivabradine Trial
1) Thollon C. et al. “Electrophysiological effects of S 16257, a novel sino-atrial node modulator, on rabbit and guinea-pig cardiac preparations: comparison with UL-FS 49.” Br J Pharmacol. Volume 112(1), Pages 37-42 (1994) PubMedCentral:PMC1910295
2) Gardiner S.M. et al. “Acute and chronic cardiac and regional haemodynamic effects of the novel bradycardic agent, S16257, in conscious rats.” Br J Pharmacol. Volume 115(4):579-586 (1995) PubMedCentral:PMC1908496
3) Simon L. et al. “Coronary and hemodynamic effects of S 16257, a new bradycardic agent, in resting and exercising conscious dogs.” J Pharmacol Exp Ther. Volume 275(2), Pages 659-666 (1995) PubMed:7473152