You should be evaluated for the following which are the commonest cause for fainting or syncope;
1) bradyarrhythmias; this is sudden slowing of the heart. it is mainly due to sinus and atrial node dysfunctions. Sick sinus syndrome is a prototype of these arrhythmias and is a major cause for syncope / fainting. Your second cardiologist is likely to consider this diagnosis.
2) neurocardiogenic mechanisms; this is fall of the blood pressure suddenly due to a sudden sympathetic failure (failure of the autonomic nervous system). It can be accompanied by shortness of breath.
3) carotid hypersensitivity syndrome is an exaggerated response to carotid sinus stimulation. In some studies almost 50% cognitively normal people who had experienced fainting were diagnosed with carotid hypersensitivity.
4) orthostatic hypotension is due to failure of autonomic nervous system and related heart regulatory mechanisms.
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.
Thank you for your answer, it was helpful. I wanted to mention though that I had a stress echo done and the cardiologist thought it was normal...at one point he thought he saw something but then played it in slow motion and said it was ok.
So, according to your reply, I could have a normal ecg and still suffer from fainting due to my blood pressure which is one thing I wanted to know. I did look up about sick sinus node earlier but surely this would have shown up on the echocardiogram wouldn't it? Are there certain things that don't show up because they are intermittent? I thought there would still show some damage there.
Thank you but this is still not quite answering all of my questions.
If you could just help me with the following then I think I'm done;
I understand the bradycardia/sick sinus syndrome but I thought the echcardiogram would have shown that up. Is that not always the case? And just to point out, you answered earlier saying that low blood pressure can cause shortness of breath. I have high blood pressure. I get profuse sweating, headaches and fainting-can the dizziness/fainting be attributed to high or is it only low blood pressure? I have just measured it three times in a row and it was 138-148/85-95 which is quite good for me, it is usually higher, and heart rate was 90-95 (and been at rest) and I have palpitations but pulse is only slightly high. Can the rapid heartrate, ie, when it goes up to 135 as shown on the 24 hr ambulatory - heart rate 34-135, cause symptoms like lightheadedness and weakness and stumbling, I feel like my legs go weak and I fall a lot and I don't know why.