"So my question is, with all of these abnormal results, how reliable are these tests, really?"
Unfortunately, no diagnostic test/imaging modality is 100% perfect, as they all have their inherent strengths and weaknesses.
There is a medical term known as the cardiothoracic ratio (CTR), which is a measurement on a chest X-ray (CXR) of the width of the heart divided by the width of the chest.
Typically, a CTR greater than 50% is suggestive of an enlarged or dilated heart. Noteworthy though, in some cases, a heart may/can be greater than 50% of the cardiothoracic ratio and still be considered a normal heart.
It is important to remember that EKGs are not 100% accurate. Normal recordings can be obtained in patients with significant heart disease , or some "abnormalities" may exist in the presence of a normal heart.
Echocardiography is prone to a certain margin of error due to the nature of soundwaves, and noteworthy, sometimes, the results can be misread or misinterpreted as well as the results can be technically difficult or limited (image quality suffers), inconclusive or wrong due to an individual's body habitus (build, construction), anatomical abnormalites, obesity, operator technique or error as well as faulty equipment or not being adjusted/working correctly.
While the treadmill-only stress test has some accuracy limitations, adding nuclear imaging, gated-SPECT (synced to an electrocardiogram/ECG), with technetium-based radioisotopes Cardiolite or Myoview, improves the diagnostic accuracy substantially by aiding in differentiating attenuation artifacts, if/when that occurs.
An artifact is a false image (as reported from breast attenuation, diaphragmatic attenuation, and other sources of artifacts), which causes a false-positive (F-P) result'finding, indicating a problem when there actually isn't one.
"My cardiologist states my heart is 100% perfect"
Well, if for any reason you are skeptical of this, do feel free to seek a second professional medical opinion, of course, bringing ALL your test results with you.
Best of luck down the road of life.
WebMD member (since 8/99)
Learn about the HEART
The Heart: (Human Anatomy) Pictures, Definition, Location in the Body and Heart Problems
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