Fetal Ultrasound Small
13 April 2016

Cardiology Advances Promise Earlier Heart Defect Diagnosis

Operating on a fetus prenatally, while the child is still in the womb, remains largely a dream of science fiction.

Intervening Before Birth

Small successes, however, have been reported, according to Medscape. In 1975, Israeli surgeons were able to stop a child’s arrhythmia during labor, by administering the mother a beta blocker. While promising, the intervention was also indirect, relying for its outcome on the transmission of chemicals across the placental barrier.

More radical was the successful, albeit not entirely successful, placement of a pacemaker, achieved in 1985 by a team of obstetricians in Houston. Led by Dr. Robert Carpenter Jr., doctors were able to implant a small electrical device into the heart of a 24-week-old fetus, using a catheter inserted through the mother’s abdomen. While the child ultimately died 4 hours after the pacemaker’s placement, the pacemaker itself appeared to have no adverse effect, either to mother or child.

Catheters have also been successfully used to widen overly-narrow heart valves, in cases of aortic valve stenosis, pulmonic valve atresia and hypoplastic left heart syndrome. Beyond the obvious positive of treating a child’s potentially-fatal condition, prenatal interventions are desirable because they “set the stage” for proper heart development. There’s also evidence to suggest that the fetal environment is particularly favorable for wound healing, which means, in so many words, that patients may heal faster, and more effectively, after prenatal surgeries than ones performed after birth.

Obvious risks, however, have prevented these techniques from being used more widely. In fact, prenatal interventions are so experimental, that depending on location, surgeons may be required to classify the procedures as research, rather than clinical care.

How Doctors Diagnose Heart Defects Prenatally

None of these breakthroughs would be possible, though, without the ability to diagnose congenital heart defects prenatally, and physicians use two techniques to do so. Ultrasound, which uses high-frequency sound waves to create an image of a child inside the womb, is likely the most familiar, but it’s far from the most accurate.

Ultrasound

Taking congenital heart defects (CHD) associated with genetic syndromes out of the picture, prenatal ultrasounds are only able to detect around 16% of heart defects, according to Danish researchers, who compared the rate of diagnostic success across the birth registries of 20 European countries.

Of course, ultrasound is certainly better than nothing, especially when the technique is being used to identify children with heart defects prior to birth. That became eminently clear when lead author Ester Garne, a pediatric cardiologist at the University of Southern Denmark, discovered vast disparities between diagnoses in countries like Denmark and the Netherlands, where no prenatal ultrasound programs exist, and countries with strong prenatal ultrasound programs, like France, Spain and Germany.

In Western European countries that have established national screening programs, nearly 1 out of every 3 CHD cases was caught by ultrasound prior to delivery, allowing cardiologists more time to develop targeted treatment plans and, in rare cases, intervene surgically before the mother had gone into labor. In Croatia, Lithuania and Ukraine, on the other hand, Garne found that only between 3% and 9% of congenital heart defects were noticed prenatally.

Reading The Blood

Some CHD, however, are easily missed by traditional detection methods like ultrasound. But researchers in New Zealand think they may have found an answer, and it’s a lot like a Band-Aid. While their diagnostic is still in early trial phases, scientists at Auckland University have developed a small patch that, when pasted to a newborn’s heel and exposed to a special sensor, can measure the amount of oxygen in a baby’s blood.

The new “plaster,” a term for the device used by Brad Clark, executive at New Zealand’s Starship National Children’s Hospital, may be most effective in catching minor congenital heart defects, which can have a wide range of adverse effects over the long-term, but are likely to be overlooked at delivery.

Pulse Oximetry

The invention could also overcome one of the limitations of pulse oximetry, a similar diagnostic method that uses a clamp-like device to measure the blood’s oxygen content. Pulse oximetry is fairly good at catching very serious congenital heart defects, abnormalities that have a drastic effect on oxygen saturation. But in the presence of smaller defects, the device can throw out erroneous results, leading to overall detection rates of between 17% and 21%, according to Pekka Valmari, a pediatric cardiologist in Finland.

Pulse Oximeter

A pulse oximeter.

In 2007, Valmari reviewed 10 studies on the diagnostic possibilities of pulse oximetry for a paper published in the British Medical Journal’s ADC Fetal & Neonatal edition. For children with severe heart defects, he found that pulse oximetry worked more often than clinical examination, identifying 72% of the anomalies compared to only 58% caught during a cardiologist’s physical exam.

Far Less Effective, Clinical Exam Still Necessary

But clinical examination still has its place in our endeavors to spot heart defects early. In fact, one of the studies Valmari looked at, which included more than 5,200 diagnostic exams, found that every heart defect identified through pulse oximetry was missed by clinical examination, but pulse oximetry missed every CHD that was noticed by clinical examination. As you might expect, putting both techniques together for every newborn was nearly twice as effective as either method on its own.

Pulse oximetry is most effective in finding heart defects that necessarily cause cyanosis, a range of symptoms, most of which can be readily identified through physical inspection, that result from poor blood oxygenation. In his review, Valmari found that “reading” a baby’s blood for oxygen levels was able to identify a vast majority of children born with:

The technique proved even more beneficial for children born with atrioventricular septal defect and total anomalous pulmonary venous return, two acutely severe conditions that rarely produce murmurs, characteristic sounds that doctors often rely on to check for heart defects. Pulse oximetry was able to detect 6 out of 8 babies born with AVSD, while pediatric cardiologists, even given routine follow-up appointments, could only catch 3 out of 19 AVSD cases using physical examination alone.

1 In 10 Heart Defects Missed In Childhood

Congenital heart defects are probably more common than you think, and certainly closer-to-home than many people with CHD know. While nearly 1% of all children born in the United States have a heart defect, around 10% of them will survive well into adulthood without their condition being discovered, according to Stanford cardiologist Euan Ashley, who wrote in his 2004 textbook Cardiology Explained, about a wide range of heart conditions that could easily go unnoticed.

To complicate the issue, Ashley says that the world’s most common congenital heart defects, ventricular and atrial septal defects, are also those most likely to be asymptomatic at birth. Both conditions involve holes in cardiac tissue, which remain open between the heart’s chambers, but those holes can be very small. In fact, some are so small that they close of their own accord. But even moderately-sized defects may not register as abnormal on an electrodiagram, a machine that charts the organ’s electrical activity, or with a chest x-ray.

Even more problematic is that, when a patient eventually begins to present symptoms, those symptoms can be extremely nonspecific. Breathlessness and fatigue are the most frequent clues, but of course, numerous conditions can cause both simultaneously. WebMD’s symptom checker tool returns 99 possible diagnoses, although, to its credit, considers “heart rhythm disorder” the most likely.

Notwithstanding the questionable accuracy of a computer algorithm, if the National Heart, Lung, and Blood Institute‘s statistics are correct, around 3,500 of the 4 million children born every year in the US will grow into adulthood with undiagnosed congenital heart defects.

Signs Of CHD In Older Children

While their conditions are almost necessarily symptomless until middle age, presenting few obvious adverse effects doesn’t mean these heart defects are harmless. Far from it, according to Joel Brenner, MD, chief of pediatric cardiology at Johns Hopkins, who says “even a symptomless heart defect can still cause progressive, insidious damage.”

Brenner cites pulse oximetry as a major breakthrough in the early diagnosis of congenital heart defects, but notes that a “subset” of children will still slip through. That’s what makes parental vigilance, and a qualified pediatrician, so important. So what can you look out for now in your own child? Brenner outlines a number of “classic” CHD symptoms that may present themselves in older children and adolescents:

  • heart palpitations
  • dizziness
  • being easily fatigued after physical activity

Often, it’s still not obvious, but Brenner says that if you notice your child having difficulty keeping up with their playmates, it may be time to visit a pediatrician.