Pregnancy Related Inappropriate Sinus Tachycardia

This is a non-interventional, physiological study which will explore the feasibility of examining autonomic function and related haemodynamic variables in pregnant women with and without inappropriate sinus tachycardia, with the aim of providing scope for future research.

Sinus tachycardia (normal heart rhythm but fast heart rate) is common and usually related to an obvious cause (e.g. exercise such a running or cycling) and doesn't cause any untoward symptoms. In rare cases however, sinus tachycardia can occur without an obvious cause (i.e. it is inappropriate to the situation) and can cause distressing symptoms such as palpitations, dizziness and breathlessness at rest or with minimal exertion. This syndrome of inappropriate sinus tachycardia is poorly understood and can be difficult to manage; especially when the affected individual is pregnant. In order to understand the condition better and improve care pathways we aim to measure various features of the cardiovascular system in pregnant women with and without IST.

• ECG (Diagnostic test): 12-lead electrocardiogram
• heart rate monitor (Diagnostic test): 24-hour heart rate monitor used to calculate mean heart rate and heart rate variability
• Autonomic Nervous System (ANS) Activity (Diagnostic test): Heart Rate Variability (HRV) and Baroreflex sensitivity (BRS): Resting and exercise HRV and BRS calculated from ECG, Dundee Step test and blood pressure measurements.
• Haemodynamic variables (Diagnostic test): Cardiac output (CO), stroke volume (SV) and systematic vascular resistance (SVR) will be assessed and calculated using a non-invasive, inert gas re-breathing technique whereby expired gases will be sampled and analysed alongside and blood pressure measurements.
• Echocardiogram (Other): optional (for non-IST participants only)

Primary outcomes

• Feasibility of examining autonomic function and related haemodynamic variables in pregnant women with and without inappropriate sinus tachycardia [Up to 3 years]: Number of women in each group who agree to participate in the study
• Assessment of autonomic function and related haemodynamic variables in pregnant women with and without inappropriate sinus tachycardia [Up to 3 years]: Heart rate variability (HRV) at rest using time and frequency domain (e.g. SDNN ms and LF and HF), combined to give absolute power in ms².
• Assessment of autonomic function and related haemodynamic variables in pregnant women with and without inappropriate sinus tachycardia [Up to 3 years]: Baroreflex sensitivity (BRS) at rest calculated from the change in systolic pressure and change in R-R interval to give change in pressure per change in RR interval, measured in milliseconds (mmHg/ms)

Secondary outcomes

• Assessment of ANS function in pregnant women with and without IST, at rest and during mild exercise [Up to 3 years]: Stroke volume in ml
• Assessment of ANS function in pregnant women with and without IST, at rest and during mild exercise [Up to 3 years]: Heart Rate Variability during mild exercise (3 minute step test) using time and frequency domain (e.g. SDNN ms and LF and HF), combined to give absolute power in ms².
• Assessment of ANS function in pregnant women with and without IST, at rest and during mild exercise [Up to 3 years]: Cardiac Output in litres/minute
• Assessment of ANS function in pregnant women with and without IST, at rest and during mild exercise [Up to 3 years]: Blood Pressure in mm/Hg

Sex: Female, ages: 18 Years to 45 Years, accepts healthy volunteers

Inclusion Criteria:

* Aged 18-45 years of age
* Able to give written informed consent and willing to participate
* The participant falls into one of the below categories:

  i. Pregnant women with IST ii. Pregnant women without IST

Exclusion Criteria:

* Obesity (BMI > 29.9)
* Current or recent (within last 3 months) smoker
* Known medical condition likely to affect HRV (other than IST in relevant groups)
* Previous history of hypertensive disorders in pregnancy
* Lack of written informed consent

• Mark Belham, Principal investigator, Cambridge University Hospitals NHS Foundation Trust