Left Atrial Strain Values as an Early Predictor of Atrial Fibrillation

Atrial fibrillation (AF) is the most common type of abnormal heart rhythm. This occurs as the chambers of the heart pump irregularly, often resulting in a fast heart rate and symptoms of irregular pounding and fluttering. There are many risk factors predisposing to AF, however, the cause cannot always be easily determined. Additionally, not all AF patients experience symptoms and consequently, this abnormal rhythm may go undetected and may be discovered accidentally. This is detrimental to patients, as untreated AF patients are at an increased risk of stroke.

Patients that are suspected of having AF are referred for an ultrasound scan of the heart (echocardiogram). It is expected to see structural changes to the heart's chambers. However, structural and electrical changes of the heart may be the cause of AF but may also be a result of AF, resulting in a chicken and egg situation. It may be possible that a different type of measurement can be used during an echocardiogram to detect subtle changes in heart muscle patterns. This measurement may then serve to be an early predictor of AF. This would be determined by comparing the patterns in patients with a normal, regular rhythm to those with AF.

Potential candidates are initially screened based on their echocardiogram referral. If deemed suitable for this study, the study process is explained to the patient and written informed consent is invited and received. The echocardiogram will be performed as normal with a focus on the area and volume measurements taken of one of the top chambers of the heart. An additional measurement will be taken to observe any subtle changes in the arrangement of heart cells within this same heart chamber. These measurements can be compared to each other to establish any relationship as well as compared to patients with and without AF.

Atrial fibrillation (AF) is the most prevalent type of arrhythmia within an adult population and is characterised by disorganised, chaotic, electrical activity and thus, ineffective atrial contraction causing irregular ventricular contraction. AF can be categorised into three different groups: paroxysmal, persistent and permanent. The prevalence of AF increases with age and is associated with a range of risk factors including: hypertension, obesity and alcohol consumption. There is a plethora of both cardiac and non-cardiac causes of AF and the cause is not always clear for each patient. Furthermore, causes of AF can also present as the by-product of AF, this increases the difficulty in determining the individual patient's cause of onset. A diagnosis of AF can be incidental as not all patients are symptomatic. If AF goes undetected, this puts the patient at an increased risk of blood clot formation and stroke.

Patients suspected of having AF are routinely referred for a transthoracic echocardiogram (TTE). It is common for AF patients to have a dilated left atrium (LA). This can be visually confirmed, and the LA area and volume can be measured during a TTE. LA strain measurements are not routinely measured during TTEs but may be able to detect subtle changes in longitudinal strain patterns of the myocardium. By comparing the strain patterns in patients with normal sinus rhythm (control) to those with AF, a scale can be created to suggest and predict whether a patient is likely to develop AF in the future based on these subtle changes before any changes in LA size occur. Furthermore, this can then be further developed to determine whether there are any significant differences in strain patterns between the three AF groups.

Objectives:

To determine whether there is a significant difference in atrial strain values between patients that are in normal sinus rhythm (NSR, control group) to patients that are known to have atrial fibrillation (disease group). A disease-control group of controlled hypertensive patients in NSR will also be utilised as hypertension is a known risk factor for atrial fibrillation.

Providing that there is a significant difference in the values between NSR and AF patients, a further comparison will be conducted on patients in different type of AF: paroxysmal AF, persistent AF and permanent AF to determine if there is a deterioration in atrial strain values within AF patients.

Left atrial area and volume size will also be measured in all patients and this can then be compared to atrial strain values.

Eligibility Criteria:
Inclusion Criteria:

* Criterion 1: subjects will be included in the study if they are within one of the following groups:

  * Known to be in normal sinus rhythm, are normotensive and have no underlying health problems.
  * Known to be in normal sinus rhythm and have controlled hypertension. This must have been diagnosed by a healthcare professional and the patient should be taking appropriate antihypertensive medication.
  * Known to have chronic atrial fibrillation (persistent or permanent AF). This must have been diagnosed by a healthcare professional and the patient should be appropriately anticoagulated.
* Criterion 2: subjects should ideally be ≥ 50 years, but subjects will be age matched across all three groups.
* Criterion 3: patients should have an EF ≥ 50%.
* Criterion 4: good quality TTE images.
* Criterion 5: No valvular pathologies. o Patients with AF that have \< moderate valvular pathologies may be considered (as per the British Society of Echocardiography Guidelines).

Exclusion Criteria:

* Criterion 1: subjects with any valvular pathologies in the control and disease- control groups.
* Criterion 2: subjects with AF that have ≥ moderate valvular pathologies (as per the British Society of Echocardiography Guidelines).
* Criterion 3: subjects with an EF \< 50%.
* Criterion 4: subjects \< 50 years old.
* Criterion 5: poor quality TTE images.
* Criterion 6: inability to provide informed consent.
* Criterion 7: permanent atrial / ventricular pacing.
* Criterion 8: previous cardiac surgery.
* Criterion 9: unsatisfactory tracking of the LA endocardial border.
* Criterion 10: patients unwilling to have their results potentially published.