Benign Tumor, Malignant Rhythm: Sudden Cardiac Arrest from a Giant Interventricular Lipoma

Description of Clinical Presentation: A young male (31 y.o.) collapsed during a boxing match due to ventricular fibrillation. He was successfully resuscitated with cardiopulmonary resuscitation and defibrillation, followed by extracorporeal membrane oxygenation (ECMO) and intensive care management. After recovery and stabilization, further investigations were performed to clarify the underlying cause of this malignant arrhythmic event. Ambulatory electrocardiography (ECG) and 24-hours Holter monitoring revealed frequent multifocal premature ventricular complexes, including couplets, bigeminy, and trigeminy, as well as several short runs of non-sustained ventricular tachycardia (NSVT) (Table 1).

Diagnostic Techniques and Their Most Important Findings: Transthoracic echocardiography showed a large, lobulated, moderately echogenic mass measuring approximately 10×8 cm, occupying the apical left ventricular cavity and extending into the right ventricular apex. The lesion had ill-defined borders and no detectable vascular flow. Non-contrast computed tomography (CT) confirmed a well-circumscribed, low-attenuation lesion within the apical interventricular region, consistent with fat density (Figure 1).


Cardiac magnetic resonance (CMR) confirmed a multilobulated, fat-containing intramyocardial mass centered in the mid–apical septum protruded into both left and right ventricles (LV and RV) and measuring 8.6×8.1×8.0 cm. The mass showed high signal on T1- and T2-weighted sequences, complete suppression on fat-saturation sequences, and no contrast enhancement, nor diffusion restriction. These features are consistent with a lipoma (Figure 2). Despite mass effect, global biventricular systolic function remained preserved.


A biopsy has been scheduled to obtain histological confirmation. Given the occurrence of ventricular fibrillation, subcutaneous ICD was implanted for secondary prevention, while conservative management of the mass was chosen, pending histology. Despite benign imaging features, the mass showed malignant arrhythmogenic substrate, resulting in out‑of‑hospital ventricular fibrillation during exertion (an “arrhythmic paradox”). This case highlights that benign-appearing cardiac masses should not be underestimated in arrhythmic risk assessment, particularly in young athletes.

Learning Points from this Case: This case shows that a benign-appearing mass can act as an arrhythmogenic substrate. A multimodality pathway is essential, highlighting the crucial role of CMR in tissue characterization and the importance of integrating imaging with clinical data to guide management [1].

• Giant myocardial lipomas, although benign, can present with malignant arrhythmias and sudden cardiac arrest.


• Cardiac MRI is the gold standard for noninvasive diagnosis and comprehensive tissue characterization.


• Benign-appearing cardiac masses should not be underestimated in arrhythmic risk assessment, particularly in athletes.


• This case illustrates the essential role of multimodality imaging and arrhythmic risk stratification in guiding management of benign cardiac tumors, particularly in young athletes.

Summary of Arrhythmic Findings

 
 

Events	Findings	Clinical Relevance
Ambulatory ECG	Avarage HR 68 bpm; occasional PACs; frequent multifocal PVCs with couplets, bigeminy, trigeminy; 3 runs of NSVT (3 beats each)	Frequent ventricular ectopy with NSVT episodes
Holter (24h)	Avarage HR 60 bpm (range 45–120); 6,269 PVCs (PVC burden 7%); 6 runs of NSVT (max 6 beats at 163 bpm); 1 episode of AIVR (4 beats at 98 bpm)	High arrhythmic burden, consistent with risk of malignant ventricular arrhythmias
Clinical Event	Out-of-hospital ventricular fibrillation cardiac arrest during exertion (boxing)	Malignant arrhythmic manifestation requiring S-ICD

 
Abbreviations: AIVR = Accelerated Idioventricular Rhythm; ECG = Electrocardiogram; HR = Heart Rate; NSVT = Non-sustained Ventricular Tachycardia; PAC = Premature Atrial Complex; PVC = Premature Ventricular Complex; S-ICD = Subcutaneous Implantable Cardioverter-Defibrillator.  
Figure 1. Four-chamber transthoracic echocardiography (left) demonstrates a large, lobulated, echogenic mass occupying the apical region of LV and RV. Non-contrast enhanced computed tomography (right) confirms a well-circumscribed, low-attenuation lesion consistent with a fat-containing lesion, highly suggestive of a cardiac lipoma. Abbreviations: CT = Computed Tomography; LV = Left Ventricle; RV = Right Ventricle.
Figure 2. Multimodality CMR and tissue characteristics. (a) Four-chamber and short-axis cine sequences demonstrate a large multilobulated (septated) mass occupying the apical left ventricle and protruding into the right ventricular cavity. (b) Four-chamber STIR imaging shows homogeneous suppressed signal without edema. (c) Axial diffusion-weighted imaging (b = 800) and ADC map confirm absence of diffusion restriction. (d) Four-chamber post-contrast sequence shows no abnormal enhancement. (e) Four-chamber PSIR late gadolinium enhancement sequence confirms absence of contrast uptake, consistent with a benign lesion. (f) Short-axis T1 and T2 mapping demonstrate relaxation times compatible with fat-containing tissue (comparable with subcutaneous fat). Abbreviations: ADC = Apparent Diffusion Coefficient; CMR = Cardiac Magnetic Resonance; DWI = Diffusion-Weighted Imaging; PSIR = Phase-Sensitive Inversion Recovery; SAX = Short Axis; STIR = Short Tau Inversion Recovery.