Changes in heart rate variability and QT variability during the first trimester of pregnancy

Abstract

The risk of new-onset arrhythmia during pregnancy is high, presumably relating to changes in both haemodynamic and cardiac autonomic function. The ability to non-invasively assess an individual's risk of developing arrhythmia during pregnancy would therefore be clinically significant. We aimed to quantify electrocardiographic temporal characteristics during the first trimester of pregnancy and to compare these with non-pregnant controls. Ninety-nine pregnant women and sixty-three non-pregnant women underwent non-invasive cardiovascular and haemodynamic assessment during a protocol consisting of various physiological states (postural manoeurvres, light exercise and metronomic breathing). Variables measured included stroke volume, cardiac output, heart rate, heart rate variability, QT and QT variability and QTVI (a measure of the variability of QT relative to that of RR). Heart rate (p < 0.0005, p < 0.0005, p < 0.0005) and cardiac output (p = 0.043, p < 0.0005, p < 0.0005) were greater in pregnant women in all physiological states (respectively for the supine position, light exercise and metronomic breathing state), whilst stroke volume was lower in pregnancy only during the supine position (p < 0.0005). QTe (Q wave onset to T wave end) and QTa (T wave apex) were significantly shortened (p < 0.05) and QTeVI and QTaVI were increased in pregnancy in all physiological states (p < 0.0005). QT variability (p < 0.002) was greater in pregnant women during the supine position, whilst heart rate variability was reduced in pregnancy in all states (p < 0.0005). Early pregnancy is associated with substantial changes in heart rate variability, reflecting a reduction in parasympathetic tone and an increase in sympathetic activity. QTVI shifted to a less favourable value, reflecting a greater than normal amount of QT variability. QTVI appears to be a useful method for quantifying changes in QT variability relative to RR (or heart rate) variability, being sensitive not only to physiological state but also to gestational age. We support the use of non-invasive markers of cardiac electrical variability to evaluate the risk of arrhythmic events in pregnancy, and we recommend the use of multiple physiological states during the assessment protocol.

Maternal cardioautonomic responses during and following exercise throughout pregnancy

“…Our observations of diminished resting HRV (SDNN and RMSSD) with gestation, indicating parasympathetic control blunting, are consistent with previous research (Carpenter et al 2015;Chamchad et al 2007;Lucini et al 1999;Speranza et al 1998). This was matched with a marked reduction in total power, indicating sympathetic dominance (Task Force of the European Society of Cardiology and North American Society of Pacing and Electrophysiology 1996).…”

“…The observed reduction in QT interval, the duration of ventricular depolarization and repolarization, with advancing gestation supports previous findings. (Carpenter et al 2015;Carpenter et al 2017a), although the previous studies showed that QT interval was altered as early as the first trimester, these studies agree that ratecorrected QT (QTc) is not altered during pregnancy (Baumert et al 2010). Changes in cardiac time interval in response to exercise were as expected.…”

“…Interestingly, whether these differences persist into exercise appears to be unclear. Findings byCarpenter et al (2015) showed that Total Power, High Frequency Power, Low Frequency Power, Standard Deviation of N-N Intervals and RMSSD remained lower during exercise in pregnancy. In contrast, findings byAvery et al (2001) agreed that Low Frequency Power remained lower during sub-threshold exercise in pregnancy but showed that Total Power and High Frequency Power were similar between pregnant and non-pregnant women during exercise.…”

“…This includes increased normalized high-frequency power and both decreased Root Mean Squared of Successive Differences (RMSSD) and Standard Deviation of N-N Intervals (SDNN) (Carpenter et al 2017a;Chamchad et al 2007;Kuo et al 2000;Speranza et al 1998). Concurrently, the duration of ventricular depolarization and repolarization, electrocardiographically measured with the QT interval, declines (Carpenter et al 2015). Other cardiac time intervals are not well explored in pregnancy.…”

“…Carpenter et al 2015;Avery et al 2001). Interestingly, whether these differences persist into exercise appears to be unclear.…”