Firstly, do not ever let the doctor that prescribe fluoxetine and venlafaxine together anywhere near you again, Emma.
As for escitalopram, yes it may potentially cause long QT in doses higher than the recommended maximum, but this is true of many drugs including some for cardiovascular disease. You can find the full list of medications linked to long QT at the CredibleMeds
website (they maintain it for the U.S. FDA), however, free registration is required to access it. But you can use the site's search engine to check on individual meds without registering.
The case against citalopram and escitalopram in long QT has been challenged by cardiovascular specialists. To quote from
van Haelst IMM, 2013 (escitalopram doses are half that of citalopram):
In a thorough QT/QTc study of citalopram, a mean change in QTc interval of 8.5 milliseconds was found for 20 mg per day and 18.5 milliseconds for 60 mg per day. On the basis of these findings, the FDA stated that citalopram should no longer be prescribed at doses of greater than 40 mg per day and that the maximum citalopram dose is 20 mg per day in elderly patients.12 However, there is still no consensus whether an increase in QTc of this magnitude (< 20 milliseconds) for a dosage of 60 mg is clinically relevant.4, 28 The guidelines of the Committee for Proprietary Medicinal Products (CMPC) suggest that individual changes of QTc interval length need to be at least between 30 and 60 milliseconds from baseline to raise concern for potential risk of drug-induced arrhythmias.23-PDF Another commonly accepted threshold for a clinically significant drug-induced change in QTc length is even higher, with an increase = 60 milliseconds.28, 30.
I don't know what you read, but there is a lot of evidence that serotonergic ADs do the opposite, reducing the risk of heart attacks and ischaemic strokes, though slightly increasing it for the much less common haemorrhagic stroke.
Serotonin isn't only a brain neurotransmitter. It has many roles in the body including in the regulation of blood vessel tone, constriction and dilation and in wound repair. Serotonergic ADs can affect these function usually by slightly dilating arteries and reducing the amount of serotonin held in blood platelets which results in a reduction in blood coagulation, i.e. they 'thin' the blood.
SSRIs are commonly prescribed to heart attack/stroke survivors who often develop anxiety disorders and/or depression. They may be the largest SSRI/SNRI taking patient cohort.
BTW-if worry about heart disease is a significant driver of anxiety disorder consider taking Omega-3/fish and N-Acetyl-L-Cysteine (NAC) supplements. Fish oil you probably already know about, NAC is an amino acid analogue mostly used medically to protect the liver in cases of paracetamol, aka acetaminophen, overdose and has other
medical uses. It is a potent antithrombic (
blood clot reducer) and helps clear arteries. It is often given during and
following cardiovascular surgery. As an added bonus it may increase the effectiveness of ADs, especially in OCD and there is also growing evidence that it may significantly lower the risk of dying from the COVID-19 virus (these two
Youtube - 26:45m;
Youtube - 13:32m; clips explore the science).
CAUTION: do not take either fish oil, or NAC without discussing it with your GP first. And don't go mad on dose as both are also mild anticoagulants - up to 2,000mg fish oil and 1,200mg NAC daily should be okay, but watch out for increased bruising and/or nose and/or gum bleeding.
SSRIs rarely do harm, much less kill, Emma. It would be bad for business.
I can't say whether escitalopram will be the right med for you, but there is a good chance it could be. The only way to know is by taking it. Hopefully, you've only been prescribed a starting dose of 5mg for the first week, or two to reduce the severity of any initial side-effects and not the usual 10mg maintenance dose.