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The holter may not catch the abnormality if the heart rate doesn't increase during those 24 hours. Heart rate of 150 could be due to anxiety or due to some electrical circuit abnormalities causing supraventricular tachycardia. Beta blockers would have been a great solution for both of them. But you are not tolerating them. There is another drug called ivabradine which will only lower your heart rate to 55 or 60 and prevent sinus tachycardia as in conditions like anxiety. You could ask your doctor for a prescription of ivabradine. If after ivabradine you continue to get tachycardia you may undergo electrophysiological testing of the heart circuit and if some abnormality is found you could undergo treatment called radio frequency ablation. But that is if ivabradine fails.
Dr Vivek Mahajan