April 7, 2009
School of Medicine, Kochi
A large number of patients with a common form of congenital heart defect, namely atrial septal defect (ASD) regularly come to Amrita to seek treatment. Some of them may have also developed pulmonary hypertension. A clinical research study undertaken at the School of Medicine points to a new method, surprisingly simple, that can help predict whether or not a particular patient will respond well if surgery if undertaken. “The method is so easy that it can be done in the outpatient department also,” said Dr. L. Srinivas, who led the study. “Unlike other methods, this one offers a high degree of specificity and accuracy.”
The patient is asked to perform some exercises on a symptom limited treadmill. If there is arterial de-saturation after the exercise, that is, if the level of oxygen in the blood drops, then the risk of heart failure and sudden death following heart surgery is high. Otherwise, there are good chances that the patient will respond well to surgery and recover. “A very thorough and meticulous study was undertaken by Dr. Srinivas to arrive at this result,” stated Dr. Krishna Kumar, HoD of the Department of Pediatric Cardiology. “This is a difficult problem that we encounter regularly; this study now provides some guidelines to operate on this challenging set of patients,” he added.
Dr. Srinivas is a second year fellow in the department. He topped a national level selection exam, the FNB (Fellow National Board of Examinations) and chose Amrita for his studies. Currently working on many funded research projects, Dr. Srinivas had won the Young Investigator Award for a research paper presented at the 10th Annual Conference of the Pediatric Cardiology Society of India last year. For this study, Dr. Srinivas won the AV Gandhi Award for Excellence in Cardiology. The award carries a citation, a gold medal and a cash award of Rs 1 lakh for the candidate and Rs 50,000 for the department. We congratulate the Amrita team for this research work in cardiovascular exercise physiology.
L Srinivas, Decline in arterial pO2 after exercise helps to stratify patients with atrial septal defect and severe pulmonary hypertension
Objective: To examine the utility of decline in arterial partial pressure of oxygen (paO2) after exercise as a marker of pulmonary vascular obstructive disease (PVOD) in patients with atrial septal defect (ASD) and pulmonary arterial hypertension (PAH).
Methods: A symptom limited treadmill exercise was performed in three groups of patients. Healthy volunteers (n = 6), large ASD with no PAH (n = 5) and 15 patients with ASD and PAH. Patients with advanced PVOD (sats < 90%) were excluded. Arterial blood gas samples were obtained before and immediately after the peak exercise. A decline in paO2 ≥ 10 mmHg after exercise was considered significant. Those with ASD and PAH underwent cardiac catheterization and hemodynamic datasets were obtained on room air, oxygen and a mixture of oxygen and nitric oxide (30-40 ppm).
Results: None of the controls (healthy / ASD, no PAH) had a drop in paO2 except one healthy volunteer (9mmHg decline). In the study group, all the patients who had ≥10mmHg drop in paO2 after exercise (n=9) had a basal pulmonary vascular resistance index (PVRI) of ≥ 7WU.m2. Five of 6 patients who had <10mmHg drop in paO2 after exercise had a basal PVRi of < 7WU.m2 (p=0.001). A decline in paO2 of ≥10mmHg predicted a basal PVRi of ≥7WU.m2 with a specificity of 100% and a sensitivity of 90%.
Conclusions: A decline in paO2 following exercise appears to predict a high PVRI (basal, post O2 and post NO) in patients with ASD and PAH. This test appears promising for assessment of operability in borderline situations.
Keywords: Atrial septal defect, pulmonary hypertension, pulmonary vascular obstructive disease, exercise, arterial paO2