Chronotropic Incompetence

An article written by Dr Edward Leatham, Consultant Cardiologist

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Introduction

Pulse rate or heart rate is a fundamental metric of heart health. It’s easily accessible—whether through feeling the pulse on your wrist or neck or using devices like a smartwatch or Fitbit. This convenience means that many people closely monitor their pulse rate, often leading to unnecessary anxiety over variations. One diagnosis that often gets overlooked  is chronotropic incompetence, a condition where the heart fails to adjust its rate appropriately during exercise or activity.

Stroke Volume

The cardiac output of the heart is the stroke volume (volume of blood ejected in each heart beat in L)   multiplied by the heart rate.

The stroke volume is the amount of blood ejected during a normal heartbeat from the human heart, typically varying between 50 and 100 ml per heartbeat. There is not only considerable variation in stroke volume across the population, partly due to the size of the individual, but also significant variation beat to beat within a person depending on physical activity and the condition of their heart muscle.

A young and healthy heart can double its stroke volume in a heartbeat, explaining why, in the early days before the invention of pacemakers, patients born with a very low heart rate due to congenital heart block could manage normal activities with a fixed and low heart rate by increasing their stroke volume. In the 60s and 70s, all artificial pacemakers had fixed heart rates; however, patients equipped with these devices maintained relatively normal exercise capacity because they could increase their cardiac output by altering their stroke volume. However, this capability diminishes with an ageing heart, especially one that has been subjected to high blood pressure and/or poor glucose control over many years. These factors cause the left ventricle to stiffen in many people as they age, limiting their left ventricle’s  ability to change its stroke volume. Consequently, any change in cardiac output in older individuals or those with a stiff heart becomes dependent on increasing the heart rate.

Chronotropic incompetence (CI) is diagnosed when the heart rate cannot increase adequately, leading to relatively fixed cardiac output which results  in breathlessness and general exhaustion during activity. Many patients with CI are not properly recognised or diagnosed, and thus do not receive treatments that could significantly improve their symptoms.

Modern pacemakers are equipped with sensors for detecting chest wall impedance and movement which sense when an increase in heart rate is necessary due to increased metabolic demands. These pacemakers, known for their rate responsiveness can be transformative for individuals with chronotropic incompetence.

Pacemaker  devices can be programmed post-implantation, allowing adjustments to be made, for instance, as the patient exercises on a treadmill to ensure a smooth increase in heart rate corresponding to their workload.

Signs and Symptoms of Chronotropic Incompetence

Individuals with chronotropic incompetence often experience symptoms like shortness of breath, fatigue, or dizziness during physical activities. These symptoms occur because the heart rate does not rise sufficiently to meet the demands of exercise, leading to inadequate blood flow and oxygen supply to muscles. For those affected, even everyday activities like walking or climbing stairs can become challenging.

This condition can be easily detected by the patient equipped with a simple pulse oximeter, which measures pulse rate during rest and activity. If your pulse fails to increase appropriately during exercise, this could be an indicator of chronotropic incompetence. Doctors can confirm the diagnosis with stress ECG testing and or ambulatory ECG testing.

Chronotropic Incompetence and Other Heart Conditions

Chronotropic incompetence is particularly significant in people with atrial fibrillation (AF), a common heart rhythm disorder affecting over 8% of men in their 70s. In AF, the atrium (upper chamber of the heart) beats irregularly and rapidly, rendering the sinoatrial node (the natural pacemaker of the heart) ineffective. The heart rate in AF patients is instead determined by the action of the atrioventricular (AV) node, which filters the chaotic impulses from the atrium. This can lead to variable heart rates, with some experiencing abnormally low rates and others excessively high rates during rest or activity.

Patients with “tachy-brady syndrome” experience both fast and slow heart rates, making management more complex. Treating the fast rates with medications like beta-blockers can further suppress heart rate response during exercise, aggravating symptoms of chronotropic incompetence. Such patients often require a pacemaker to regulate their heart rate effectively.

Treatment Options for Chronotropic Incompetence

In many cases, low heart rates—especially those above 40 bpm—may not require intervention unless symptoms are present. However, if the heart rate fails to rise appropriately with exercise, cardiologists may recommend treatment to alleviate symptoms and improve quality of life. One of the most common solutions is the implantation of a pacemaker. A pacemaker can be programmed to ensure a minimum heart rate is maintained during rest and increase appropriately with physical activity.

Pacemakers are particularly beneficial for those with sinoatrial node dysfunction or significant AV node involvement, as they can provide a stable heart rhythm and prevent the sudden drops in heart rate that cause symptoms like dizziness or blackouts. For patients with conditions like tachy-brady syndrome, a pacemaker allows for the use of medications to control fast heart rates without causing dangerously slow rates.

Conclusion

• Chronotropic Incompetence is often overlooked as an important cause for breathlessness in older people.
• It is easy to screen for it using a simple pulse oximeter.
• Treatments include stopping medications that may be making it worse and fitting a rate adaptive pacemaker.

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Other related articles

1. Chronotropic Incompetence: Causes, Consequences, and Management
2. Bradycardia: When a Slow Heart Rate Becomes a Health Concern?

The Naked Heart is an educational project owned and operated by Dr Edward Leatham. It comprises a series of blog articles, videos and reels distributed on Tiktok, Youtube and Instagram  aimed to help educate both patients and healthcare professionals about cardiology related issues.

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