Hello -- What you describe sounds like a pretty common (and relatively normal) problem, exercise-induced premature heartbeats, most likely premature ventricular beats (PVCs) although they could be atrial (PACs) or a combination. This is a fairly common finding and is almost never dangerous. That being said, and given you may have experienced panic attacks in conjunction with these palpitations, it might be reassuring to have a cardiological workup and perhaps wear a Holter monitor or event monitor briefly to determine whether or not what's happening is, in fact, just clusters of premature beats. Oh, and before I forget, since this tends to happen when you're hiking, do you by any chance consume anything containing caffeine? Or for that matter, any so-called energy drinks (which also contain caffeine)? This can provoke more palpitations than might otherwise take place, and can also trigger, in the vulnerable, panic attacks. This latter is something often seen along with palpitations, either as a cause or as a side-effect (and this can work in either direction, with palpitations as trigger for panic or caused by panics). Again, it is extremely unusual for these to have any diagnostic significance whatsoever, and we all have these at various times, but some of us are more or less aware of them than others, and while most of us have them during quiet (at rest) times (in which case exercise usually makes them go away), some also have the paradoxical type that are brought on by exercise. They are extremely common in persons with mitral valve prolapse syndrome (MVPS) and while this also is almost never dangerous, it is also commonly seen in conjunction with anxiety and panic disorder. These people tolerate exercise well in general, but can be interrupted by what seems momentarily erratic heart behavior.
On the off-chance this may not be premature beats but some other arrhythmia (such as supraventricular tachycardia or atrial fibrillation or flutter), while these are also not in themselves life-threatening, they can be disruptive at least, and also are eminently treatable (whereas premature beats are rarely treated, and almost always only to ease the emotional stress they cause).
I'd ask for a one-time cardio workup including resting and exercise EKG, blood work, a good listen to heart sounds, and perhaps a Holter monitor and even, if it seems reasonable, an echocardiogram. All of this is non-invasive and should rule out any extremely unlikely dangerous conditions. It is an especially good idea for the anxious patient with palpitations, as it can be very reassuring and if heart problems can be emperically eliminated, sometimes the anxiety/panic disorder can be isolated and effectively treated, and sometimes the reassurance alone is enough to ease this.
I hope this is helpful to you. Please follow up with us as needed and best of luck to you.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist