I have a long history of SVT's probably dating back to my early adulthood, but until I reached my early 50's the episodes only lasted a couple minutes and occurred so infrequently (once every few years) I paid little attention to them and would forget about them after the episodes. The episodes became more frequent when I hit the 50's, and the first one that took me to the ER was an episode that didn't stop on its own after several hours, and was hovering around 210-220 beats/minute when I got there. They slowed it down with an adenosine IV, followed by a digoxin drip overnight and it was back to normal the next morning. They did ultrasounds to see if I'd thrown any clots ( none seen), and started me on 100 mg metoprolol succinate ( extended release)

With subsequent visits to a cardiologist and my primary care doc, I was reminded that I had high blood pressure ( I knew it but had been mostly ignoring it for too many years, assuming that diet and exercise would control it) and started taking Diovan HCZT ( valsartan combined with a diuretic) for blood pressure.
At first this combination of medications made me light-headed and sort of "loopy", but these side effects disappeared after a couple weeks.

The metoprolol did an excellent job of controlling the SVT, and it continued doing so for quite a few years. The cardiologist wanted me to have an SVT ablation, but I refused it, thinking the metoprolol was doing so well in keeping the SVT at bay, I didn't need the ablation. The cardiologist said without the ablation I'd have to take the metoprolol for life, and that SVTs/arrhythmias tend to worsen as we get older, and the medication becomes less effective in controlling them. I said "so be it", and refused the ablation.

The metoprolol continued to do a good job at controlling the SVT over the next 10-12 years or so, even when the amount was cut down to 50 mg/day ( at my request), and the PCP added 180 mg/day of diltiazem ER for added blood pressure and SVT control. And I didn't have side effects I was aware of during these times. I took my meds, lived a full busy life and didn't think much at all about the SVT- or my blood pressure, for that matter.

Fast forward to my mid-60's ( about 15 years after that first trip to the ER for SVT), I woke up with the same SVT symptoms ( for me, that was a fluttering in my chest, some chest discomfort- like an overworked muscle is the best way I can describe it, light-headedness and slight shortness of breath) in the wee hours of the morning, got up, sat in the lounger, took my meds and waited, and waited, and waited for the episode to stop. When it didn't about 4 hours later we headed to the ER, where they hooked me up for an EKG and informed me I had atrial flutter- not the same SVT I'd had in earlier episodes. This episode stopped, finally, right after I got into an ER bay, but the doc insisted on admitting me overnight and referred me to a cardiologist.

So, I met the cardiologist the next day, who took me on as a patient, and I still see him to this day. He changed the metoprolol succinate I'd been taking to the shorter acting version ( metoprolol tartrate), changed one of the blood pressure meds, and ordered a 3 week cardiac monitor to see if I had subsequent episodes of A-flutter or fib ( they worry more about these than the garden variety SVT due to the stroke risk associated with these arrhythmias). Over the years I took the metoprolol, diltiazem and blood pressure drugs and we were on the lookout for any of those arrhythmias. My SVT increased several years later after the doc stopped the diltiazem, and this was frequent and bothersome enough to cause quality of life issues, so he increased the metoprolol to 150 mg/day, and this helped to keep them under control.

Fortunately this doesn't happen to everyone, but over the years I developed bradycardia in addition to the SVT- so I had both. I don't know how much of this might have been due to the metoprolol ( bradycardia is a side effect) or whether the metoprolol just made an underlying condition I had worse, or surface, but the bradycardia got worse over a couple years as it became symptomatic and it definitely effected my quality of life. I had three cardiologists ( two EPs and this guy) inform me that the bradycardia was due to an underlying problem I had- sinus node dysfunction- though it was probably aggrevated by the metoprolol- and I had a dual chamber pacemaker implanted in June 2019.
The pacemaker was a game changer in that it made me feel much better, and to this day I continue to take the metoprolol at 150 mg/day, now to control the SVT ( identified as atrial tachycardia by the EP that put in the pacemaker), atrial flutter and atrial fibrillation that I've developed over the years. This drug still does a respectible job at keeping the arrhythmias/tachycardia at bay most of the time. I have some breakthoughs, but these episodes are for the most part brief ( less than 2 minutes, mostly), and don't happen every day. My quality of life is still good, I think I have the pacemaker to thank for that, as it keeps my heart rate where it should be, and also allows me to take enough medication to control the SVTs and company without my heart rate tanking.