Over the years, the doctor’s stethoscope has been replaced by whiz-bang gadgetry to assess the functioning of the heart. Although these diagnostic tools are better than a doctor’s ear at picking up abnormalities in the heartbeat, they can be insensitive when detecting heart disease in women, children and babies in utero.
The electrocardiogram, or ECG, which monitors electrical signals from the heart, is one such diagnostic tool. There are two types for detecting heart disease: the resting ECG and the exercise stress test. Both are relatively safe. However, the ECG does have its fair share of shortcomings.
A study of 2000 heart patients in the US and Canada found that women are often misdiagnosed and less likely to be referred on for further tests when results are positive (N Engl J Med, 1991; 325: 226-30). According to Dr Michael Miller, director of preventive cardiology at the University of Maryland, one reason for misdiagnosis is that non-invasive tests are not sensitive enough for women.
Doctors are slow to detect heart problems in women because the usual patterns of chest pain and ECG changes are often not present. Some believe that studies don’t take into account the inherent differences between men and women so that tests are geared for men only.
Some critics revealed that many exercise tests come back with false-positive results, creating unnecessary stress in healthy patients. This is because most women, especially older ones, perform less well on exercise tests than men do (Arq Bras Cardiol, 2001; 76: 540-4).
Another shortcoming of the ECG test is its inability to detect left ventricular hypertrophy (LVH; enlargement of the pumping chamber) in children, a condition that is linked with coronary heart disease (Am Heart J, 2003; 145: 716-23).
In addition, ECGs cannot diagnose heart problems in babies in the womb. They are reported to have problems in fetal heart monitoring. Transabdominal fetal ECG - monitoring a baby’s heart in utero - can only be carried out between 18-28 weeks of gestation because the electrical signals are otherwise too weak to be recorded.
Also, ECGs are unable to distinguish between sinus bradycardia - a heart rate of less than 60 beats per minute, common in healthy young adults and in athletes - and a complete heart block, where the electrical impulses that make the heart beat are impaired (Children’s Hospital Heart Matters, 2001; vol 4, issue 4).
Stress echocardiograms - otherwise known as ‘echo’ - also have been known to have limitations (an accuracy rate of only 80 per cent; J Am Coll Cardiol, 1999; 33: 1462-8), but they may be better for diagnosing congenital valvular and ischaemic diseases, and as a screening tool for LVH in children. But if your risk is low, both tests are likely to give false results (N Engl J Med, 1996; 334: 1311-5).