Fundamental Information on Inotropes that You Need to Know

In 2015, heart disease remained the No. 1 cause of death in the US. While engaging in healthy lifestyle promotes the good cardiovascular system, there are other risk factors that are beyond people’s control such as genetics and environmental pollution. When heart problems occur, infusion therapy for inotropes is commonly prescribed to help fix heart problems or at least manage the condition.

Specifically, last year’s data revealed that around 633,842 deaths in the country are caused by diseases of the heart. That’s approximately 1 out of 4 deaths. It is also a 0.9% increase in the age-adjusted death rates caused by heart diseases from 2014.1

What are inotropes

Inotropes are medicines that can help change the strength of a patient’s muscular contractions. Also known as inotropic agents, they are commonly dispensed for the management of a variety of cardiovascular conditions especially due to heart failure. These agents influence the cardiac muscle to help ensure that the heart can pump at an effective rate.

To effectively circulate blood within the body, there are two important and related requirements: (1) the volume of fluid to be circulated, and (2) the heart’s capability to pump this fluid to meet the oxygen demands of the entire body. In essence, having sufficient volume can be useless if the cardiac muscle contractions (myocardial contractility) are not strong enough. Similarly, an effective contractility can be useless if there’s not enough fluid.

Two Kinds of Inotropes

Positive inotropes strengthen the force of the heartbeat so that more blood is circulated and that the body is well-oxygenated even with a slow heart rate. Calcium is necessary for the heart to contract, and thus, positive inotropes work by boosting the levels of calcium on the muscle cell’s cytoplasm and by enhancing the receptor proteins’ sensitivity to calcium. The calcium buildup within the cells will create a stronger force of contraction.

Negative inotropes, on the other hand, weakens myocardial contractility. They are also used to slow down heart rate, and thus, are used to for patients with chronic heart failure, high blood pressure, and other cardiac overload conditions. They can be classified into several types with different functions.

  • Calcium-channel blockers (CCB) are negative inotropes that help lower blood pressure by slowing the rate at which calcium goes into the vessel walls through the heart muscle. Also called as calcium channel antagonists or simply calcium antagonists, these inotropes help in relaxing the vessels, allowing for a smoother blood flow.
  • Beta-blockers (β-blocker) are negative inotropes that obstruct the body’s beta receptors for adrenaline, and thus, reducing hormonal influences to the heart. A heart failure typically causes a variety of abnormal effects such as activation of inflammatory mediators, higher oxygen demand and other conditions that overwork the heart. Beta-blockers can slow down the nerve impulses through the heart and thereby avoid the organ from working too hard.
  • Antiarrhythmic medicines are negative inotropes that help normalize the rhythm of the heart when its electrical activity goes erratic. Specifically, they slow down the heart’s electrical system by blocking the channels for sodium (Na+), potassium (K+) or calcium (Ca2+), all of which are electrolytes in the blood.

As you can see, there is a wide range of inotropic agents and each drug differs in how they work within the body. Moreover, inotropes have a potent effect on the patients’ cardiovascular system. To make things more complicated, the choice of inotropes for a patient is largely dependent on the chosen agents’ pharmacodynamics with the condition. It is for these reasons that the administering medical professional should have thorough knowledge in giving the drugs in a ‘safe, effective and patient-centered manner.’

It is also necessary to inform the doctor of other medicines that the patient is taking before any inotropic therapy, as they can weaken or boost the effectiveness of the inotropes. These medicines include but not limited to the following:

  • Anti-diarrhea medicines,
  • Laxatives,
  • Diet pills,
  • Cholesterol-related medications, and
  • Over-the-counter drugs for flu, cough, cold, sinusitis or hay fever.

Many inotropic agents are also vasopressors, which provide a risk of injury if the drugs enter the local tissue. Therefore, it is often recommended that these kinds of inotropes should be administered through the central line. Moreover, research on published case studies revealed that local tissue injury is less likely to occur if the vasopressor infusion is administered through well-established peripheral IV for less than 2 hours.

What conditions require infusion therapy for inotropes?

Infusion therapy for inotropes is generally provided to patients to improve their cardiovascular system that has been compromised by heart failure, which is caused by various conditions including heart attack, diabetes, high blood pressure and abnormal cardiac valves, among others.

Conditions requiring positive inotropes

Congestive heart failure happens when the heart’s pumping action is weakened and can’t simply perform its main function, which is to pump and circulate oxygen-rich and nutrients-laden blood throughout the body despite having sufficient supply of the fluid. Treatment options for patients with CHF include surgery, oral medications, and heart pump medication, also referred as inotropic therapy. Infusion therapy through IV can also be done at home for some carefully selected CHF patients awaiting heart donor or transplantation even for those in advanced or end-stage condition.

Heart attack, technically called myocardial infarction or acute myocardial infarction, happens when blood stops flowing to a part of the cardiac organ resulting to heart muscle damages. This condition requires medical attention immediately with the goal to avoid complications and to save as much heart muscle as possible. To boost the blood supply to the heart, nitroglycerin can be administered whether orally or intravenously, If that medicine is not effective, morphine may also be provided.

Other conditions in need of positive inotropes include:

  • Cardiogenic shock, or insufficient blood circulation as a result of the heart ventricles’ failure to effectively function;
  • Cardiomyopathy, the cause of which is often unknown; and
  • Septic shock, which happens when the body has low blood pressure and abnormal cellular metabolism brought about by organ damage or injury as a response to infection.

Conditions requiring negative inotropes

Prevention of Secondary Heart Attack. Patients who had their first attack can be administered with beta blockers to prevent another cardiac arrest. In fact, there’s firm evidence that these negative Inotropes are effective in long-term prevention of a secondary heart attack.12

Arrhythmia or irregular heart rhythm can be treated with antiarrhythmics which are meant to disrupt the electrical conduction or impulses in the cardiovascular system. These negative inotropic agents are also used to help manage the symptoms associated with arrhythmias such as heart palpitations, chest pain, lightheadedness, shortness of breath, fast and irregular heartbeats and fainting.

Angina or Angina pectoris is a chest pain caused by heart disease. The beta blockers, as well as calcium-channel blockers, are prescribed to lower the workload of the heart and its oxygen requirement.

Other conditions that can be managed or improved with negative inotropes include chronic heart failure and hypertension or high blood pressure.