Final answer:
Children with a resting HR above 100 bpm typically do not display tachycardia symptoms of instability, as this can be normal for them. In adults, tachycardia is defined as a HR over 100 bpm and treatments vary based on the cause. Symptoms may not always present but can include dizziness and shortness of breath.
Step-by-step explanation:
Tachycardia symptoms of instability usually do not become a primary concern when children have a resting heart rate above 100 beats per minute, as this can be normal for their age group. In adults, tachycardia is defined as a resting heart rate (HR) over 100 bpm and may be linked to a variety of factors including stress, fever, anemia, hypoxia, hyperthyroidism, and certain cardiac conditions. Symptoms can include dizziness, shortness of breath, and fainting (syncope). Treatment for tachycardia depends on the underlying cause but could involve medications, implantable cardioverter defibrillators, ablation, or surgery. Resting heart rate in an adult should ideally be measured after recovery from exercise to distinguish it from exercise-induced heart rate elevations, which are normal and expected.