Do children need treadmill test?

Do children need treadmill test?

Unlike in adults treadmill exercise test or any other type of exercise test is done only very rarely in children. Exercise testing in children is mainly for evaluation of heart rhythm disorders than for disorders of blood circulation of the heart as in adults.

In a child with suspected disease of the sinus node, exercise testing can be done to assess the response of the heart rate to exercise. Sinus node is the natural pacemaker of the heart which gives regular electrical pulses to cause heart beats. If sinus node is defective, the normal increase in heart rate with exercise will be deficient. This is known as chronotropic incompetence.

In a condition known as congenital complete heart block, exercise testing can be done to assess the response of heart rate, which is important while making treatment decisions. Congenital complete heart block is a birth defect in the electrical system of the heart. Signals from the sinus node are blocked lower down so that they do not reach the ventricles, the lower chambers of the heart.

A subsidiary pacemaker, usually in the lower part of AV node situated at the lower part of right atrium, takes over function in such cases. Increase in heart rate will be lesser when AV node is controlling the heart than when the sinus node is controlling the heart.

This ECG shows congenital complete heart block with a rate of 47/min in the lower chambers and 63/min in the upper chambers.

In stage I of the exercise test using Bruce protocol, rate in the upper chamber (atrial rate) has increased to 100/min, but the rate in the lower chamber (ventricles) is only 60/min.

ECG at peak exercise shows atrial rate 150/min and ventricular rate of 83/min. Increase in movement artefacts is visible on comparing the raw rhythm at the bottom of the image. Other recordings are computer averaged processed beats which do not show the movement artefacts much.

Another situation in which exercise test is useful in children is when they have accessory conduction pathways in a condition known as WPW syndrome (Wolff-Parkinson-White syndrome). This produces early activation of the lower chambers as they act as bypass tracts, bypassing the normal delay of signals in the AV node. Accessory pathway conduction can get blocked during exercise. The heart rate at which the block of conduction occurs is important while making treatment decisions.

If the early activation of the ventricles disappears in response to exercise, they are thought to have lower risk of very fast rates if a condition known as atrial fibrillation occurs. Atrial fibrillation is a fast irregular rhythm from the upper chambers. In normal persons, most of the signals from upper chambers get blocked at the AV node so that ventricular rate does not go very high. But in WPW syndrome, they can get conducted down the accessory pathway and cause dangerously high rates in the ventricles.

Congenital long QT syndrome is another condition in which exercise testing is useful. Congenital long QT syndrome is a disease with high risk of dangerous heart rhythm abnormalities arising from the ventricles. They have a prolonged QT interval on the ECG. Normally QT interval shortens with exercise. But it may not do so in some of types of congenital long QT syndrome.

Those with some types of congenital long QT syndrome and another condition known as catecholaminergic polymorphic ventricular tachycardia (CPVT), may develop dangerous fast rhythms from the ventricles during exercise. This ECG shows fast rhythm from the ventricles, known as ventricular tachycardia, occurring during exercise.

This ECG during recovery from exercise shows that the ventricular tachycardia has subsided, but irregular beats are being fired from the ventricles, showing persisting irritability of the ventricles.

Though treadmill exercise produces higher peak heart rates, better quality ECG can be recorded with bicycle exercise because of lesser body motion which could produce baseline shifts and other artifacts. Maximal oxygen uptake is about 10% higher with treadmill exercise than a bicycle ergometer. Bicycle ergometer is an equipment using a static bicycle for exercise testing.

An advantage of treadmill is that most people are familiar with walking or running, including young children. But exercise on a treadmill is not a natural form of walking or running for a person not familiar with exercise on a moving surface. Hence time for practice on the treadmill should be provided before testing.