Welcome to the forum. I'm the administrator and host, as well as a retired neurologist.

It's very important to understand that we need not see the palpitation events at all to determine whether your heart health is at risk or if there is an underlying pathology. The reason is that pathological arrhythmias are manifested due to underlying pathology that we can see even in their absence. The focus for patients is what they can feel in the way of symptoms, therefore they only associate the presence of difficulty when the symptoms arise. This is quite natural, but to make the point, it would be impossible for a patient to determine the kind of data that an ECG provides merely by what they sense. Do you see my point here? In other words, it's what we don't see that counts more than the documentation of the benign palpitation events that really provides us with satisfactory evaluation of the complaint.  

Thus, many patients are quite frustrated when palpitation of the type you are experiencing often fail to appear when under the scrutiny of diagnostic evaluation and with good reason; these palpitations are benign because they are extra-cardiac in nature, meaning that they originate from outside the heart. They are induced by the vagus nerve as a parasympathetic nervous system response. While they can technically be characterized as a paroxysmal contraction, it's important to realize that they can either be PACs or PVCs depending upon precisely when the evoked potential from the vagus nerve enters the conduction cycle of the heart. For instance, if the signal arrives during ventricular depolarization, then it would be characterized as a PVC and if it arrived during atrial depolarization, it might be characterized as a PAC or paroxysmal atrial contraction. If the signal arrives during ventricular repolarization, then while it may be characterized as a PVC, the patient might sense what feels like the absence of a heartbeat or a prolonged period between the start of the cardiac cycle. This can be frightening to many patients because they feel as though their heart has stopped. Actually, the vagus-induced signal merely diminishes or otherwise masks the normal sino-atrial node potential and reduces the normal cardiac force and rhythm.

The incidental finding of mild mitral valve prolapse is of no concern, since it appears in a good number of patients and does nothing to impair the performance of the heart. Since your ejection fraction was most likely within normal parameters, the finding constitutes a mere normal variant. While significant MVP has been associated with palpitations and panic threshold, particularly more prominent in young women than men, the presence of mild valvular prolapse in your instance would not be contributory to the palpitation events in any regard.

Realize that a resurfacing of the events or increase in their frequency otherwise is most often associated with increased stressful life events of some type. Understand that vagus-induced palpitation events are actually a natural physiological event occurring at an inappropriate interval. I'm sure that you've heard people who have been suddenly startled or frightened exclaim "That made my heart skip a beat!" Well that is precisely the same event which occurs in persons with palpitations in the absence of a direct stimulus. The reason is that stress alters the nervous system and changes between the sympathetic and parasympathetic nervous system can produce physiological manifestations that virtually all people experiencing the phenomenon misinterpret as symptoms of an underlying problem, most often heart disease.

The second most common reason for palpitation events to occur is the presence of GI tract disturbances, which often coincide with stress. The vagus nerve innervates the GI tract as the pneumogastric nerve and when excess air becomes trapped in the lumen of the intestines, or alternatively when GI motility is disturbed for other reasons, it can produce an evoked potential, or signal, which travels upward along the vagus nerve to its other terminal points, ie the spleen, the lungs, the heart and the larnyx among others. Although these other points respond to the signal, the heart is especially affected because it is such a dynamic organ and muscle. In fact, people indeed can experience the sensation of vagus stimulation at other terminal points such as the larnyx, which causes some patients to coincidentally cough within the same timeframe as the palpitation occurs. Some patients may also describe a sensation of something stuck in their throat or difficulty in swallowing. This too is a parasympathetic response by the vagus nerve and is known as Globus Hystericus. Some patients might also describe what seems to be erratic respiration, wherein they become vigilent to tidal respiration often complaining that they either can't obtain a deep inspirational breath or alternatively that they feel it necessary to voluntarily establish a respiration pattern as though the autonomic function is somehow depressed. This too is a sensation produced by the vagus nerve.

You can relax in knowing that the palpitation events have nothing to do with your heart with regard to anything pathological. It is not straining under the demand of exercise and the palpitation events are entirely incapable of inducing any type of cardiac event.

You'll be fine.

Best regards and Good Health