The diagnostics advisory committee considered evidence on KardiaMobile 6L for measuring QT interval from several sources, including an early value assessment report, cost and resource use report and an overview of the reports. Full details are in the project documents for this guidance.
Having access to less intrusive QT interval measurement with flexibility around the time and place of the appointment is important
3.1 Psychiatric service user experts explained that it is important for people to have their QT interval measured and to understand that this is done to make sure the antipsychotic medication that is offered is suitable for them. This is important both in the acute phase of their condition and for ongoing monitoring. The service user experts noted that because antipsychotic medication has side effects, having flexibility around the time and place of the electrocardiogram (ECG) appointment is important. In a recent NHS pilot in community and inpatient wards, service users found having an ECG with KardiaMobile 6L more comfortable than with a 12‑lead device, said KardiaMobile 6L was easier to use, preferred it for dignity and privacy, and considered 12‑lead ECG to be more intrusive than KardiaMobile 6L. The committee recognised that it is important to offer QT interval measurement to people at a place and time they can attend and in a way that they feel comfortable. It acknowledged that offering information about why QT interval is measured is important.
There is an unmet clinical need for an easily accessible and available QT interval measurement in the psychiatric service setting
3.2 Clinical experts explained that QT interval is not always measured before people start having antipsychotic medication. ECG recording or interpretation may not be available during the appointment so service users may need to travel to another place or the recording may need to be sent elsewhere for interpretation. The ECG appointment and results may not be readily available. This could delay starting antipsychotic medication, an alternative medication that is potentially less effective but has less cardiac risk may need to be offered, or the decision to offer the most suitable antipsychotic medication may need to be made without the information about the cardiac risk related to the QT interval length. The clinical experts noted that to offer QT interval measurement in psychiatric services, staff training to record and interpret ECGs is essential.
There is limited evidence on using KardiaMobile 6L for measuring QT interval in adults having antipsychotic medication
3.3 The committee considered the available evidence for using KardiaMobile 6L for measuring QT interval in adults having antipsychotic medication. It noted that the external assessment group's (EAG's) review found no published evidence in this population. The only evidence available in this population was unpublished reports of survey data from 2 recent NHS pilot projects.
Concordance data does not provide enough information to determine how well using KardiaMobile 6L works for measuring QT interval
3.4 The EAG's review found 8 published studies that evaluated the technical performance of KardiaMobile 6L compared with a 12‑lead device. Instead of diagnostic accuracy to detect prolonged QT interval, these studies reported on concordance (how closely the QT interval measurements from the 2 devices matched each other). The mean difference in corrected QT interval (QTc) between the 12‑lead device and KardiaMobile 6L was generally small. But in 1 study (Azram et al. 2021), the QTc results from the 2 devices for some people differed by over 50 milliseconds. A further study (Kleiman et al. 2021) reported that the absolute difference in QTc was 40 milliseconds or more in 5% of the people. Across all the studies, the apparent direction of the difference in results suggested that on average, KardiaMobile 6L slightly underestimated the QT interval length. But the committee further noted that the Bland–Altman plots from the Kleiman et al. study showed that the KardiaMobile 6L results were biased both ways. This error could be related to the ECG trace and largest in people at highest risk from medication that can prolong the QT interval. The committee concluded that the concordance data did not provide enough information to determine how well using KardiaMobile 6L to measure QT interval worked compared with using the 12‑lead device.
Data from KardiaMobile 6L technical validation studies in other settings may not be generalisable to the psychiatric service setting
3.5 None of the 8 technical validation studies included people having antipsychotic medication. The committee noted that because of risk factors for prolonged QT such as advanced age, sex, heart disease and using certain medications, the prevalence and levels of normal and prolonged QT may differ in different populations. Also, there may be differences between people having antipsychotic medication and other populations for example in the ability to sit still, having tremors and flexibility of fingers, which could result in lower quality ECG readings from the KardiaMobile 6L device. The committee further noted that how accurate the QT interval measurement depends on the accuracy of ECG interpretation (measuring QT length, calculating QTc, and deciding whether QT is prolonged), which may differ between professionals. The clinical experts explained that in many 12-lead devices, this is automated but in KardiaMobile 6L it is currently done manually which can affect the accuracy. The committee noted that in the 8 technical validation studies, ECGs were interpreted by 1 or more cardiologists rather than a psychiatric nurse or a psychiatrist who is likely interpret an ECG in a psychiatric service setting. The committee concluded that data from KardiaMobile 6L technical validation studies in other settings may not be generalisable to the psychiatric service setting.
Differences in the time to do the test, who interprets the ECG, and the number of repeat QT interval measurements may affect costs
3.7 Several resource use and cost parameters were identified as relevant for future economic modelling. The committee noted that the parameter values were informed by very limited data sources so they are uncertain. The committee considered that differences in 3 resource parameters between KardiaMobile 6L and a 12‑lead device could particularly affect the costs associated with their use:
Data sources suggested that it was faster to use KardiaMobile 6L than the 12-lead device. But the times and how they were estimated varied greatly, so it was not certain whether using KardiaMobile 6L would save time.
The costs of measuring QT interval varied depending on who interpreted the ECG. It was not clear how often ECGs were interpreted by different healthcare professionals and services, and if this differed between KardiaMobile 6L and the 12‑lead device.
It was uncertain how often the QT interval measurement from Kardiamobile 6L would need repeating using a 12‑lead device, and why this may be needed.
The committee noted that differences in these parameters may also affect how long it takes before antipsychotic medication is started. It concluded that more data on these parameters is needed.