Postoperative AF in mitral valve repair: risk increases from 11 mm septum thickness

Predicting postoperative atrial fibrillation: the contribution of preoperative echocardiography

Mitral valve repair is the gold standard for treating degenerative mitral regurgitation (DMR), offering superior survival compared to valve replacement. However, acute postoperative atrial fibrillation (POAF), documented in the literature in nearly 46.7% of patients after mitral surgery, significantly burdens postoperative outcomes by increasing morbidity, mortality, and length of hospital stay. While age and hypertension are classic risk factors, the preoperative determinants specific to the DMR population undergoing reparative surgery remain insufficiently characterized.

This retrospective study, including 1127 patients operated on between 2017 and 2022, aims to identify preoperative risk factors for acute PO-AF occurring within 30 days following mitral valve repair for DMR. The authors tested the hypothesis that a rigorous evaluation of clinical comorbidity combined with precise echocardiographic parameters — with a specific focus on interventricular septum (IVS) thickness — would allow for better risk stratification in these patients.

Protocol and patient selection

This retrospective cohort study included 1,127 patients (from an initial screening of 1,318 individuals) who underwent surgical repair for degenerative mitral regurgitation (DMR) between 2017 and 2022. Inclusion criteria targeted adults with primary DMR confirmed by transthoracic echocardiography. Patients with a history of atrial fibrillation (AF), concomitant aortic pathology, mitral stenosis, or prior valvular surgery were excluded.

Echocardiographic parameters and intervention

The preoperative evaluation systematically collected the following data:

• Left atrial size and left ventricular ejection fraction (LVEF).
• Interventricular septum (IVS) and posterior wall thickness.
• Left ventricular end-diastolic diameter (LVEDD) and left ventricular end-diastolic volume (LVEDV).
• Calculation of the Left Ventricular Mass Index (LVMI).

Les interventions, réalisées sous sternotomie médiane, incluaient diverses techniques de réparation (annuloplastie, cordages artificiels, transfert de cordages) sélectionnées selon les lésions individuelles.

Evaluation of results and statistical analyses

The primary endpoint was the occurrence of acute postoperative AF (POAF), defined as any episode of AF lasting more than 30 seconds documented by continuous telemetry or 12-lead ECG within 30 days following surgery. Statistical analysis was based on univariate and multivariate logistic regression models to identify independent predictors. A ROC (Receiver Operating Characteristic) curve was specifically used to determine the optimal predictive threshold (cut-off) for interventricular septum thickness.

Incidence and clinical profile of patients

Of the 1,127 included patients who underwent mitral valve repair for DMR, the incidence of acute postoperative atrial fibrillation (POAF) within 30 days was 13.5% (n=152). Comparative analysis shows that patients who developed POAF were significantly older (56.6 ± 10.8 years versus 49.7 ± 13.0 years, p < 0.001) and presented a higher prevalence of arterial hypertension.

Preoperative echocardiographic parameters

The study highlights marked cardiac structural differences in patients developing POAF. The latter presented a wider ascending aorta (33.8 ± 4.8 mm vs 31.9 ± 4.3 mm, p < 0.001), a more dilated left atrium (46.7 ± 7.6 mm vs 44.8 ± 7.6 mm, p = 0.003) and a slightly but significantly lower left ventricular ejection fraction (LVEF) (63.7 ± 4.8 % vs 65.0 ± 5.0 %, p = 0.002).

Independent predictors and critical SIV threshold

Multivariate analysis identified several independent risk factors for acute PO-AF:

• Age: OR 1.05 (95% CI: 1.03–1.07, p < 0.001).
• Hypertension: OR 1.50 (95% CI: 1.03–2.21, p = 0.037).
• LVEF: OR 0.95 (95% CI: 0.92–0.98, p = 0.004).
• Left atrial enlargement: OR 1.03 (95% CI: 1.00–1.06, p = 0.019).
• Interventricular septum (IVS) thickness: OR 1.21 (95% CI: 1.06–1.38, p = 0.005).

IVS thickness proved to be a robust predictor. ROC curve analysis determined an optimal cutoff value of 11.0 mm. An IVS > 11 mm is associated with an increased risk of POAF with an adjusted OR of 1.73 (95% CI: 1.03–2.89, p = 0.037). This association remained consistent across subgroup analyses.

Clinical analysis of risk factors for POAF

This retrospective study, conducted on a cohort of 1127 patients, demonstrates that postoperative atrial fibrillation (POAF) affects 13.5% of subjects following degenerative mitral regurgitation (DMR) repair. The results highlight that preoperative cardiac structural remodeling is the primary driver of this arrhythmia. Beyond classic factors such as age (OR 1.05) and hypertension (OR 1.50), the study sheds light on the importance of interventricular septum (IVS) thickness. An IVS greater than 11 mm is identified as a robust independent predictor, increasing the risk of POAF by 73% (OR 1.73).

The correlation between a thick IVS and POAF suggests that ventricular hypertrophy, even moderate, reflects changes in pressure and myocardial stress that impact atrial electrical stability. Furthermore, the reduction in left ventricular ejection fraction (LVEF) and left atrial (LA) enlargement confirm that the underlying condition is as decisive as the surgical procedure itself.

Study limitations and framework

The interpretation of these data must take into account the retrospective nature of the study. Furthermore, POAF detection was performed exclusively during the hospitalisation period using telemetry and standard ECG. In the absence of ambulatory monitoring or implantable devices after discharge, the actual 30-day incidence could be underestimated. The study also focuses on a single centre, which limits the generalisability of the exact thresholds to other populations.

Implications for surgical practice

These results offer an opportunity for precise preoperative stratification. Transthoracic echocardiography should no longer only serve for valve assessment, but for a true rhythmic risk score. Identifying a patient with an IVS > 11 mm allows for proactive management, whether through therapeutic optimization or prolonged telemetric monitoring in the immediate postoperative period.

Conclusion

Preoperative evaluation of echocardiographic parameters, particularly IVS thickness, is essential for identifying patients at high risk of POAF after mitral surgery.

Summary of results

This retrospective study conducted on 1,127 patients reveals a postoperative atrial fibrillation (PO-AF) incidence of 13.5% following degenerative mitral repair. In addition to age and hypertension (OR 1.50), interventricular septum (IVS) thickness emerges as the new warning signal: beyond 11 mm, the risk of PO-AF jumps by 73% (OR 1.73; p=0.037). A lower ejection fraction (LVEF) (OR 0.95; p=0.004) and left atrial enlargement are also confirmed as independent predictors.

In concrete terms, for the practitioner:

• Refine your stratification: a patient with an SVI > 11 mm on preoperative ultrasound must be classified as high rhythmic risk, regardless of other comorbidities.
• Individualise prophylaxis: this "thick septum / low LVEF" profile justifies stricter telemetric monitoring and, depending on your protocol, more aggressive optimisation of anti-arrhythmics or beta-blockers from the perioperative phase.

Study lexicon

DMR (Degenerative Mitral Regurgitation): Primary mitral regurgitation caused by degeneration of the leaflets or chordae, resulting in excessive systolic valve movement (prolapse ≥ 2 mm into the left atrium).

POAF (Postoperative Atrial Fibrillation): Atrial fibrillation occurring postoperatively, defined in this study as any arrhythmia episode lasting more than 30 seconds within 30 days following mitral repair.

Interventricular septum thickness (IVS): Echocardiographic parameter measuring the septal wall; a preoperative thickness > 11.0 mm has been identified as a major independent predictor of acute POAF.

LVEF (Left Ventricular Ejection Fraction): Measure of ventricular systolic function; the study demonstrates that a lower ejection fraction is independently associated with an increased risk of postoperative AF.

LVMI (Left Ventricular Mass Index): Left ventricular mass index calculated from septal thickness, posterior wall, and end-diastolic diameter to assess cardiac hypertrophy.

Left atrial enlargement (LA enlargement): Dilation of the left atrial cavity, identified in multivariate analysis as a significant independent risk factor for the development of POAF.

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