Review Reevaluates Mitral Annular Disjunction as Potential Arrhythmia Trigger

A critical review published in Cardiovascular Ultrasound reevaluates the clinical significance of mitral annular disjunction, suggesting that the structural anomaly may often be an innocent anatomical bystander rather than the primary driver of fatal ventricular arrhythmias in patients with mitral valve prolapse. Mitral valve prolapse affects approximately 3 percent of the general population and generally follows a benign clinical course, with more than 90 percent of individuals remaining asymptomatic or reporting clinically insignificant complaints such as exertional dyspnoea, atypical chest pain, and palpitations. Nevertheless, a distinct minority comprising 5 to 10 percent of patients develop severe mitral regurgitation that requires surgical intervention. Of even greater concern to clinicians, ventricular arrhythmias and sudden cardiac death occur in 1 to 3 percent of younger individuals with the condition, even in the complete absence of left ventricular dysfunction or severe valvular regurgitation, defining a clinical subset known as arrhythmic or malignant mitral valve prolapse.

For decades following the introduction of M-mode echocardiography, cardiologists sought morphological stigmata that could reliably identify patients at risk of complex arrhythmias and sudden cardiac death. Historically, leaflet redundancy was the only morphological characteristic consistently linked to these adverse outcomes. In recent years, however, mitral annular disjunction, defined as a structural separation between the posterior mitral leaflet hinge line and the crest of the ventricular myocardium, emerged as a leading candidate marker for arrhythmic malignancy. First identified in a 1981 case report detailing a sudden cardiac death with an elongated posterior annulus moored on the atrial side, the anomaly was systematically investigated in 1986 by researchers who introduced the formal term and identified it in 23 of 25 patients with bi-leaflet prolapse. While early investigators hypothesized that disjunction might serve as the primary inciting anomaly leading to redundant and floppy leaflets, subsequent anatomical examinations showed disjunction in standard valves as well, raising long-standing questions regarding whether the separation represented a true pathology or an ordinary anatomical variation.

The traditional diagnostic framework for mitral annular disjunction established it as a dynamic systolic event. Under this widely accepted model, the posterior annulus appears appropriately positioned in diastole but paradoxically detaches and slides upward toward the left atrial roof during systole as the posterolateral myocardium contracts. Recent expert consensus statements described the phenomenon as a systolic separation between the ventricular myocardium and the mitral annulus supporting the posterior leaflet, quantifying disjunction length as the measured gap between the hinge line and the ventricular crest, which ranges from a few millimeters up to one centimeter. Examinations utilizing three-dimensional transesophageal echocardiography in patient cohorts demonstrated that disjunction predominantly involved the P1 and P2 scallops of the posterior leaflet and correlated with a functional decoupling from the left ventricular myocardium during mid-to-late systole, marked by paradoxical systolic expansion.

Despite widespread clinical adoption, the authors of the review emphasize that this dynamic sliding model presents significant anatomical contradictions. Cardiac surgeons performing mitral valve repairs consistently observe that the posterior leaflet and annulus remain firmly attached without the mobility or slackness implied by dynamic systolic displacement, suturing prosthetic rings directly onto the anatomical annulus. Using cardiac magnetic resonance imaging in patients previously diagnosed with bi-leaflet prolapse and disjunction by echocardiography, researchers demonstrated that many systolic observations represent an optical misinterpretation termed pseudo-MAD. During ventricular systole, the billowing belly of the posterior leaflet frequently presses directly against the left atrial wall, making it exceptionally difficult to differentiate leaflet tissue from adjacent atrial myocardium on standard long-axis transthoracic echocardiography due to limited spatial and temporal resolution. The hyperdynamic contraction of the basal myocardium further exaggerates this appearance, creating a false impression of a detached neo-migrated annulus whose systolic expansion merely reflects normal atrial wall movement.

True anatomical disjunction, wherein the hinge line of the posterior leaflet remains physically detached from the ventricular crest during both systole and diastole, appears to be far less prevalent than previously estimated. High-resolution imaging modalities, including modern echocardiographic systems, cardiac magnetic resonance, and computed tomography, allow clinicians to conduct frame-by-frame analyses across the cardiac cycle to distinguish true structural separation from dynamic juxtaposition. This distinction becomes particularly discernible during the mid-diastolic diastasis phase, a brief suspension period when the mitral leaflet is neither fully open nor fully closed, exposing the true annular insertion point. In an observational evaluation of 603 consecutive patients with mitral valve prolapse analyzed across these three imaging modalities, researchers discovered that 221 of 263 patients, or 84 percent of those previously categorized as having disjunction, actually exhibited pseudo-MAD, reducing the confirmed prevalence of true anatomical disjunction to just 7 percent.

Adding further complexity to its clinical evaluation, structural disjunction of the posterior annulus is frequently present in normal human hearts. Anatomical dissections conducted nearly fifty years ago identified a collar-shaped fibrous extension measuring 3 to 8 millimeters in height connecting the posterior leaflet hinge to the ventricular wall in standard heart specimens, while subsequent histological studies demonstrated that this subvalvular membrane is discontinuous along the posterior hinge line. Modern imaging investigations have confirmed these anatomical insights in healthy living cohorts. Cardiac magnetic resonance studies have identified disjunction scattered across regions of normal annular arrangement, while cardiac computed tomography evaluations detected disjunction in 96 percent of normal adult hearts, displaying a bimodal distribution across the P1 and P3 scallops. Similarly, an analysis of 2,607 participants within the United Kingdom Biobank revealed that 76 percent possessed at least one disjunction site when applying lower diagnostic thresholds of 1 to 2 millimeters, while post-mortem examinations of 224 normal hearts identified disjunction in 20 percent of specimens.

The proposed clinical link between mitral annular disjunction and malignant ventricular arrhythmias has produced conflicting results across observational studies. An initial investigation of 116 patients diagnosed with disjunction by clinical echocardiography documented ventricular arrhythmias in 34 percent of subjects, who were notably younger and presented with lower ejection fractions and higher rates of papillary muscle fibrosis; intriguingly, while 78 percent had prolapse, prolapse itself was not tied to arrhythmias, leading investigators to propose that disjunction was an independent arrhythmogenic entity. However, subsequent research did not replicate this finding. A larger cohort study evaluating 595 patients with bileaflet prolapse and leaflet redundancy found that while overall long-term survival did not differ between patients with and without disjunction, disjunction was associated with a significantly higher arrhythmic risk. Another evaluation of 610 prolapse patients found that individuals with ventricular arrhythmias exhibited greater disjunction height and a higher prevalence of combined prolapse and disjunction compared to non-arrhythmic controls.

A critical limitation of earlier clinical investigations was the failure to differentiate between true structural disjunction and pseudo-MAD. When investigators re-evaluated cohorts using advanced cardiac magnetic resonance and frame-by-frame analysis, they discovered that both true disjunction and pseudo-MAD conferred comparable risks of ventricular arrhythmias. Notably, patients in both categories demonstrated significantly higher levels of late gadolinium enhancement, reflecting localized myocardial fibrosis, compared to prolapse patients without disjunction. This observation reinforces longstanding physiological hypotheses proposing that mechanical traction and abnormal systolic tension on the papillary muscles and adjacent myocardium induce tissue injury and subsequent fibrotic scarring, predisposing the heart to electrical instability.

Cardiovascular evidence increasingly identifies myocardial fibrosis rather than anatomical disjunction as the primary substrate responsible for life-threatening arrhythmias. In a cohort study of 474 patients with mitral valve prolapse followed over an average of 3.3 years without significant regurgitation or ventricular dysfunction, the extent of late gadolinium enhancement proved to be a far stronger predictor of adverse cardiac events, including sustained ventricular tachycardia and sudden cardiac death, than the mere anatomical presence of disjunction, which showed no independent predictive value. From an electrophysiological perspective, fibrosis provides the vulnerable anatomical substrate required for malignant re-entry circuits, which can degenerate into lethal rhythms when triggered by premature ventricular complexes.

The review concludes that while mitral annular disjunction remains an intriguing morphological feature, the current balance of scientific evidence does not support its designation as the direct causal trigger of sudden cardiac death. True anatomical disjunction is present in only a small minority of prolapse cases and represents an ordinary anatomical variant throughout healthy populations, whereas the vast majority of prolapse patients previously labeled with the condition exhibit pseudo-MAD resulting from echocardiographic imaging limitations. Because myocardial fibrosis consistently serves as the primary determinant of arrhythmic risk, mitral annular disjunction appears increasingly likely to represent an innocent bystander in arrhythmogenesis, underscoring the critical necessity of advanced frame-by-frame multimodality imaging and myocardial tissue characterization when assessing cardiovascular risk.

Subject of Research: Evaluation of mitral annular disjunction and its clinical significance in mitral valve prolapse and arrhythmias

Article Title: MAD or MADness?

Article References: Faletra, F. F., Sgarito, G., Parisi, F., Franca, E. L., Mulè, M., Carvelli, A., Di Stefano, G., Borrello, R. L., Nuzzi, V., Manca, P., & Cipriani, M. (2025). MAD or MADness?. Cardiovascular Ultrasound, 23(1), Article 2. https://doi.org/10.1186/s12947-025-00337-3

Image Credits: AI Generated

DOI: 10.1186/s12947-025-00337-3

Keywords: mitral valve prolapse, mitral annular disjunction, cardiovascular ultrasound, ventricular arrhythmias, sudden cardiac death, cardiac magnetic resonance, pseudo-MAD, leaflet redundancy, myocardial fibrosis, late gadolinium enhancement, three-dimensional echocardiography, computed tomography, posterior mitral annulus, cardiac imaging, clinical cardiology, arrhythmogenic MVP