A "galloping heartbeat" is actually a "gallop rhythm." It usually indicates that the two heart ventricles are not beating at precisely the same time. It is not necessarily cause for alarm in and of itself, but it is important to determine the underlying cause. If a cat has never had a gallop rhythm and suddenly develops one while on intravenous fluid therapy, it could mean impending fluid overload. Gallop rhythms are usually associated with some degree of heart "stiffness," such as a thickened muscle, dilated chamber, or some scar tissue or other fibrous tissue. The first thing usually recommended is that a cat's blood pressure be checked, since elevated blood pressure can sometimes precipitate a gallop rhythm. Common causes for increased blood pressure in cats are hyperthyroidism and/or kidney disease. A complete cardiac evaluation, with a chest X-ray and echocardiogram (cardiac ultrasound), is recommended, because the cardiologist will be able to evaluate the thickness and contractility of the heart chambers and recommend medication, if needed. An echocardiogram will also help to distinguish a gallop with something that sounds very similar, called a "systolic click," which is not nearly as serious.
I hope that answers your question. If not, let me know.
Yes. What you said about the feedings is good. Vomiting once is not too bad. If her heart is OK and the only thing you need to worry about is the fatty liver, then getting the feeding tube will greatly increase her chances of pulling through. The nasal tube can work--it's just harder to maintain. It sounds as if your vet hospital is doing all the right things. I need to go off-line now and will be unavailable until tomorrow night. I promise I will check in again to see how everything went. Take care. I'll be thinking of you (and her).