The effects of exercise induced tachycardia on the maternal electrocardiogram

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Abstract
To determine whether pregnancy has an effect on the maternal electrocardiographic response to stress. Eight maternal ECG parameters were screened before, during and after exercise induced tachycardia at 29 and 37 weeks gestation and at 6 weeks post partum for each participant. General Hospital in Safed, Israel. Fifteen healthy, pregnant women aged 22 to 34 years with singleton pregnancies volunteered from the peripheral antenatal clinics. Exercise stress tests were performed on a Quinton 3000 treadmill stress test system according to a Modified Bruce Protocol, producing a heart rate of 85% of age predicted maximum. The ST-segment, T-wave, QRS complex, axis, rhythm, disorders of impulse conduction, the P-Q and Q-T intervals were screened before, during and after the exercise test. The study results suggest an increase in the ST-segment changes induced by stress at 37 weeks of pregnancy compared to 29 weeks (ST-depression in 6 women out of 15 versus 2, P = 0.125, McNemar's Test for Correlated Proportions-Exact Test, two tailed; 95% CI, 0.042-0.492, 0.01 < P < 0.05) and to the post partum test (ST-depression in 6 women out of 15 versus 1, P = 0.125; 0.029-0.637, 0.01 < P < 0.05). No significant alteration of the other ECG parameters. No significant correlation between blood haemoglobin level, serum levels of sodium, potassium, calcium, glucose and 17 beta-oestradiol with the appearance of the ECG change. The increase in the exercise induced ST-segment abnormalities at 37 weeks of pregnancy may be another physiological effect of late pregnancy which has not been demonstrated previously.