Implantable Cardioverter-Defibrillator and Lipomas: A Case-Series

Abstract

Lipomas are hamartomas of adipose tissue that can be found in various anatomical locations. Herein we describe 3 cases of de-novo lipomata formation over implanted defibrillators, characterize their incidence and speculate on possible mechanisms for their development.

Introduction

The implantable cardioverter-defibrillator (ICD) improves survival in patients with a history of ventricular arrhythmias or in those at increased risk for their development. ¹

One of the most common complications after ICD implantation is infection; which is reported in approximately 1-5% of cases worldwide. However, complications involving lipomatous growth over implanted defibrillators remain undescribed.

Lipomas are benign tumors consisting primarily of adipocytes. ² They derive from mesenchymal preadipocytes and vary in size from several millimeters to a few centimeters in diameter. Lipomas greater that 10 cm in diameter are relatively uncommon but when present can contain malignant features including cellular dysplasia and localized invasive spread. ³ Malignant lipomas or liposarcomas are most often found in deep muscle or deep soft tissue compartments such as the retroperitoneum and are rarely found within the subcutaneous space. Genetic analysis reveals these subtypes of lipomata are due to aberrations in the MDM2/p53 axis. ⁴

Most often benign lipomas are encapsulated lobules of adipose tissue and are found most commonly in the upper extremities. ⁵ There are many different types of lipomas, including subcutaneous solitary lipomas and angiolipomas. Subcutaneous solitary lipomas usually present as soft, painless, thinly encapsulated well-circumscribed lobular masses and are most frequent in men aged 40-60. ⁶ Genetic analysis demonstrates that most solitary lipomas are associated with abnormalities on chromosome 12. ⁴

Angiolipomas however usually present as firm, painful subcutaneous nodules, with thin walled blood vessels and intravascular fibrin thrombi. ⁴ Angiolipomas typically have a normal karyotype, although chromosome 13 aberrations are present in some cases. ⁴ Approximately 5% of angiolipomas are familial, displaying an autosomal dominant inheritance pattern. ⁴ Angiolipomas most commonly appear on the upper extremities, and occasionally within perinephric fat planes. ⁴ Angiolipomas have highest incidence among young adults being rarely found in adults over 50 or children. ⁴

Herein, we describe 3 cases of patients who developed lipomas of the subcutaneous tissues overlying the ICD implant, usually within several years of its insertion. Although the direct etiology of their lipomata is unknown, we seek to review the literature and hypothesize on the probable etiology of this new clinical finding.

Case Reports

Three patients, a 63-year old female with lipoma excised 3.5 years after ICD insertion, a 39-year old male with lipoma excised 8 years after ICD insertion, and a 62-year old male with lipoma excised 8 years after ICD insertion were identified. Each patient had a different ICD implant with lipoma formation occurring between 3.5-8 years after implantation (Table 1). Lipoma size and type tended to vary, with 2 patients developing solitary lipomas and one developing an angiolipoma (Table 1). After removal, patients have not had lipomatous recurrence. Molecular and genetic analysis of the lipoma was performed in one patient though histological confirmation of lipomatous growth was conducted on all 3 specimens.

Table 1.

Patient demographics, pacemaker implant data, and histopathology. (N/A=not available, Dil. CM=dilated cardiomyopathy, HTN=hypertension, AF=atrial fibrillation, ARVC=arrhythmogenic right ventricular cardiomyopathy, CAD=coronary artery disease, T2DM=type 2 diabetes mellitus).

Patient	Age/gender	BMI	PMHx	ICD type	Time from insertion (years)	Mass size (cm)	Histopathology
1	63F	N/A	Dil. CM, HTN, AF	Biventricular ICD Boston Scientific Cognis 100D	3.5	11 X 5.2 X 2.9	Solitary lipoma
2	39M	26.3	ARVC	Medtronic Maximo 7278 Dual Chamber ICD	8	4.2 X 4.2 X 2.2	Angiolipoma
3	62M	31.6	CAD, HTN, T2DM	Boston Scientific Telogen E102 single chamber ICD	8	5.5 X 4.8 X 1.1	Solitary lipoma

Patient 1

A 63-year-old female with a history of dilated cardiomyopathy, hypertension and atrial fibrillation presented 3 and a half years after insertion of a biventricular ICD with a soft tissue mass over her defibrillator. An 11 x 5.2 x 2.9 cm lipomatous mass was completely removed. However, no cytogenetic analysis was performed. The patient had no recurrence after 8 years of follow-up.

Patient 2

A 39-year-old male patient with a history of biventricular heart failure presented with a lipoma 8 years following insertion of a dual chamber ICD. It had been inserted for the treatment of arrhythmogenic right ventricular cardiomyopathy. The soft tissue mass was found at the infero-medial aspect of the ICD pocket and it was noted at time of generator change. This was resected en-bloc at the time of ICD replacement and sent for histopathology. The mass measured 4.2 x 4.2 x 2.2 cm and pathologic analysis found it to be an angiolipoma with no cytogenetics tested. Patient had no recurrence at a 7-year follow-up.

Patient 3

A 62-year-old male with history of hypertension, coronary artery disease and diabetes mellitus developed a mass over his single chamber ICD 8 years following its insertion. The soft tissue mass was resected at the time of ICD removal for suspected infection. Clear fluid present in the pocket cultured Staphylococcus epidermidis. The excised mass measured 5.5 x 4.8 x 1.1 cm. This was found to be a lipoma with normal, non-malignant genetic studies (FSH (Follicle stimulating hormone) normal, 18: CG3033, MDM2 (mouse double minute 2) negative).

Discussion

Considering each patient had a different ICD implant, it is unlikely that the lipomatous growths resulted from a specific model of ICD.

In each of our reported cases, none had lipomatous growth prior to the ICD insertion and no studies to date suggest that the electrical currents induce lipomatous growth around the implanted device. Cases of lipoma formation atop or around surgically implanted devices remain rare, although they have been antecedently reported in the case of a total hip replacement. ⁷ For the cardiology team associated with this case report, their incidence of lipomata formation over 8 years of ICD placements and roughly 6,400 implants placed is 0.04%.

Previous studies have indicated that trauma may cause lipoma formation. ^8-10 Several theories have been proposed although 2 are most probable. One theory purports that the release of growth factors, inflammatory mediators, cytokines and fat necrosis following trauma induce the production of lipoma promoting factors and/or preadipocyte differentiation leading to lipoma formation. ^9,10 The second theorizes that trauma-induced prolapse of adipose tissue may be responsible for lipoma formation. ^8,10 Yet, exactly how long it takes for a lipoma to form after trauma and what traumatic forces are required to form lipomas remain unclear. It seems plausible that trauma from the surgical insertion of the ICD could lead to lipoma formation. However, most lipoma formation after trauma has been documented following blunt force, not surgical trauma. ^8-10 Although these theories adequately explain solitary lipoma formation, they do not explain how angiolipomas may form in response to physical injury.

Though potential theories explaining lipoma formation may exist, none seem to adequately explain how or why lipomas developed over the ICD pulse generator in the cases mentioned. Specific molecular and genetic markers that could or may have led to such unique lipoma formation in the patients studied have yet to be identified.

Clinically, plastic surgery intervention may help improve outcomes related to lipomata formation as the resection of such masses produces cosmetically favorable results, healing with linear scars and without recurrent lipoma formation, hence the dual team involvement in these rare cases at Hamilton Health Sciences (Hamilton, Ontario, Canada).

This study has reported a 3 patient case series describing lipomatous growth over ICD pulse generators. The probable origins of the patients’ lipoma formation remain unknown, and we offer a model predicated on soft tissue trauma to explain these findings. Perhaps in the future, as we endeavor to understand more about lipoma etiology, especially concerning those that form at or around ICDs, we may gain further insight into their formation and prevention.