Pocket-related adverse events following CIED implantation, conventionally divided into acute, sub-acute and late complications, range from more frequently encountered events, such as pocket hematoma, skin decubitus or superficial and deep infection, to less frequently observed events, including CIED dysfunction or material allergy, twisting of the pulse generator inside the pocket (i.e. Twiddler’s syndrome) or migration of the device to the ipsilateral axilla or breast tissue due to improper device fixation to the pectoralis muscle (1). Complications including injuries to the anterior chest wall structures, such as brachial plexus or sympathetic nerve fibers injury or bone lesions, such as fractures, are extremely rare, especially in the absence of direct trauma (2–4).
Non-traumatic or stress fractures, histologically defined as an as imbalance between osteoclast-mediated resorption and osteoblast-mediated repair (5) and pathophysiologically delineated as either insufficiency- or fatigue-generated fracture processes (6), are a relatively common entity across all patient demographics. While insufficiency fractures result from normal loading upon abnormal bone, as encountered in osteoporotic post-menopausal women, fatigue fractures result from an abnormal repetitive load upon normal bone occurring when osteoclast resorption surpasses osteoblast replacement during an abrupt increase in frequency, duration or intensity of activity, especially in young athletes or military recruits (6). Although stress fractures are predominantly identified as injuries of the weight-bearing bones of lumbar spine, pelvis, and lower extremities, several smaller case series and case reports have also described stress fractures of ribs, primarily in athletes practicing activities generating forceful tensile, compressive and rotational stress on the thorax, such as weight-bearers and lifters, overhead throwers, axial rotators and rowers, and secondarily in non-athlete individuals with endocrinological pathologies or after vigorous coughing or repetitive unphysiological outside pressure (7). We strongly believe that repetitive unphysiological pressure from the sub-muscularly implanted PM was the most likely pathophysiological mechanism for a stress fracture also in our patient. Namely, in our young, asthenic female patient with no history of intense physical activity, vigorous coughing, any endocrinological disease or direct trauma, a sub-muscularly implanted pulse generator, lying in a discrete subclavicular space directly on the upper ribs, has been persistently forced towards the thoracic wall by a normal day-to-day motion of the right shoulder, putting increased repetitive pressure force on the underlying bones and finally causing a fatigue stress fracture of the second rib 9 months after CIED implantation.
Since stress fractures to the bone are a continuum of mechanical failure ranging from simple bone marrow oedema to small micro-cracks with minor cortical disruption or complete fracture with or without fragments displacement, the most suitable diagnostic procedure is usually location-specific and patient-dependent. Evidence indicates that magnetic resonance imaging (MRI) has the highest combined sensitivity and specificity in the diagnostics of rib stress fractures, outperforming plain radiography, computed tomography (CT), positron emission tomography CT (PET-CT) and bone scintigraphy by delineating rib injury up to 14 days earlier when compared to other diagnostic modalities (8). However, in patients with CIEDs implanted in either subclavicular region, MRI faces significant interpretation-related disadvantages in readings for rib fractures due to artefacts produced by the metallic housing of the pulse generator, regardless of the implanted system’s MRI-compatibility status. Thus, in CIED patients presenting with unexplained symptoms of painful pocket, CT-based modalities should be regarded as first-line diagnostic tool to enable timely diagnosis and proper treatment. Unsurprisingly, plain radiography reading in our patient was negative and only a CT scan and a PET-CT performed later revealed a stress fracture.
As conservative therapy with partial or complete discontinuation of causative activities is generally advocated to patients with rib stress fracture without fragments dislocation (9), a conservative therapy with relative rest and nonsteroidal anti-inflammatory medications was initially recommended to our patient (10). Only after no improvement in her physical status with ongoing severe palpation- and arm adduction-generated pain in the right subclavicular region was observed, a surgical extraction of CIED with a de-novo implantation of a single-chamber device on the contralateral side was performed. Afterwards, all pain was alleviated and patient’s quality of life significantly improved. Moreover, bone healing was confirmed on the repeated CT scan 6 months following the surgical intervention. In CIED individuals with exhausted bilateral subclavicular implantation possibilities, an alternative implantation approaches including epicardial leads with sub-xyphoid access and epigastrial supra-muscular device position or leadless transcatheter device implantation directly in the right ventricle can be advised if applicable.