Cardiovascular magnetic resonance (CMR) has evolved from a pure imaging method to a powerful tool in the diagnostic management of congenital heart disease (CHD) . This evolution is in a large part due to the capability of CMR to measure flow by phase-velocity CMR . To measure flow by phase-velocity CMR, synchronisation of the images to the heart phase is needed. This synchronisation is realised by ECG triggering. ECG triggering is based on real-time R-wave detection and ensures that each portion of an image is allocated to a specific phase of the cardiac cycle. Accordingly, an imprecise detection leads to an incorrect allocation of the images to the cardiac cycle and ultimately to false diagnostic results [2, 3]. Therefore, optimal ECG triggering is of paramount importance for correct blood flow quantification during CMR.
Reasons for imprecise triggering are known and efficient algorithms have been developed and used for several years. An important reason beside the general noise in normal ECG is the MR-specific environment, especially the magnetohydrodynamic effect. This effect leads to a deformation in the ST segment and may exhibit a T-wave with a larger amplitude than the QRS complex and finally to a wrong triggering.
In normal ECGs these problems seem to have been solved satisfactorily .
However, optimal ECG triggering and therefore blood flow quantification are impaired in many patients with CHD due to complex QRS patterns.
For example patients with CHD such as Tetralogy of Fallot or Ebstein anomaly partially show complex ECGs [4, 5]. Accordingly, in our routine clinical experience incorrect ECG triggering leading to unsatisfactory flow measurements using the old ECG-trigger algorithm occurs frequently. However, the exact extent of incorrect flow measurements is unknown. In a previous study 2 of 347 assessments even failed totally due to unreliable triggering .
Therefore, a new ECG-trigger algorithm was developed to address triggering problems and achieve better performance in patients with complex ECGs.
The new trigger is mainly based on a matched filter . The matched filter is able to detect the R-waves on the rising edge of the R-wave after an initial learning phase.
The old trigger algorithm works with threshold values, which are derived from the ECG.
The aim of this study was to test this new ECG-trigger algorithm in routine clinical patients with CHD and to measure its impact on blood flow quantification.