Algorithm for cavo-tricuspid isthmus flutter on surface ECGs: the ACTIONS study

Abstract

Objective: Cavo-tricuspid isthmus atrial flutter (CTI-AFL) is an important arrhythmia to recognise because there is a highly effective and relatively low-risk ablation strategy. However, clinical experience has demonstrated that providers often have difficulty distinguishing AFL from atrial fibrillation.

Methods: We developed a novel ECG-based three-step algorithm to identify CTI-AFL based on established CTI flutter characteristics and verified on consecutive ablation cases of typical flutter, atypical flutter and atrial fibrillation. The algorithm assesses V1/inferior lead F-wave concordance, consistency of P-wave morphology and the presence of isoelectric intervals in the inferior leads. In this observation study, the algorithm was validated on a cohort of 50 second-year medical students. Students were paired in a control and experimental group, and each pair received 10 randomly selected ECGs (from a pool of 50 intracardiac electrogram-proven CTI-AFL and 50 AF or atypical AFL cases). The experimental group received a cover sheet with the CTI algorithm, and the control group received no additional guidance.

Results: There was a statistically significant difference in the mean number of correctly identified ECGs among the students in the experimental and control groups (8.12 vs 5.68, p<0.001). Students who used the algorithm correctly identified 2.44 more ECGs as being CTI-AFL or not CTI-AFL. Using the electrophysiology study as the gold standard, the algorithm had an accuracy of 81%, sensitivity of 81%, specificity of 82%, positive predictive value of 78% and negative predictive value of 84% in identifying CTI-AFL.

Conclusion: We developed a three-step ECG algorithm that provides a simple, sensitive, specific and accurate tool to identify CTI-AFL.

Keywords: arrhythmias; atrial flutter; cardiac; electrocardiography.

Figure 1

Types of AFL including typical AFL and atypical AFL, along with their occurrence rates. AFL, atrial flutter; CTI, cavo-tricuspid isthmus.

Figure 2

The CTI algorithm as it appeared when distributed to the medical students in the experimental group. BPM, beats per minute; CTI, cavo-tricuspid isthmus.

Figure 3

Parts of the algorithm demonstrated on ECGs. CTI-AFL, cavo-tricuspid isthmus atrial flutter. The left panel shows non-uniform morphology of the P wave and thereby all three criteria are not met thus, this is not CTI-AFL. The middle panel shows an isoelectric interval in the inferior leads and thereby all three criteria are not met thus this is not CTI-AFI. The right panel shows that all three criteria are met thereby, identifying the EGG as CTI-AFL.