Clinical Characteristics and Outcomes in Patients With Atrial Fibrillation and Pathogenic TTN Variants

Background: TTN encodes a sarcomeric protein called titin. Pathogenic rare variants in TTN are the most common finding in patients with atrial fibrillation (AF) and positive genetic testing.

Objectives: This study sought to define the characteristics and outcomes in patients with AF and pathogenic TTN variants compared with genotype-negative patients with AF.

Methods: Patients who presented initially with AF were enrolled in an AF registry. Retrospectively they underwent research sequencing for cardiomyopathy and arrhythmia genes. TTN(+) AF cases were defined as participants with pathogenic or likely pathogenic (P/LP) rare variants located in exons with high cardiac expression. They were matched 1:2 with control subjects with no P/LP variants. Phenotyping used retrospective manual chart review.

Results: Among 2794 participants; 57 (2.0%) TTN(+) AF cases were identified and matched with 114 control subjects. Low QRS complex voltage was present more often in TTN(+) AF cases (18% vs 5%; P < 0.01), with no difference in PR, QRS interval, or QTc. More TTN(+) AF cases had persistent AF at enrollment (44% vs 30%; P = 0.028) and had undergone multiple cardioversions (61% vs. 37%; P < 0.01). By end of follow-up (median 8.3 years; Q1, Q3: 4.5, 13.7 years), 11% of TTN(+) AF cases developed sustained ventricular tachycardia/ventricular fibrillation, 44% left ventricular (LV) systolic dysfunction (LV ejection fraction <50%), and 47% met a combined endpoint of sustained ventricular tachycardia/ventricular fibrillation or LV systolic dysfunction.

Conclusions: TTN(+) AF patients undergo more cardioversions and have more persistent forms of AF. Approximately 50% develop LV systolic dysfunction and/or malignant ventricular arrhythmias. These results highlight the need for diagnostic evaluation and management in TTN(+) patients beyond the usual care for AF.