Pathophysiology
Cardiac herniation can occur when there is a significant defect within the pericardial sac. Pericardial tears may involve either the superior/left/right pleuropericardium or the diaphragmatic pericardium. The defect can allow cardiac luxation and, in the case of diaphragmatic pericardial tear, herniation of abdominal contents into the pericardial sac. Clarke et al, one of the largest reviews to date, included a review of 132 cases plus 10 further cases of their own [3]. They found the superior/left/right pleuropericardium were injured in 4%/50%/17% respectively, with the remaining 27% of injuries originating from the diaphragmatic pericardium [3, 7]. Of these cases, the rate of cardiac herniation was 28% [3]; however, in a more recent literature search (since 1987), a rate of 64% of the 55 patients with BTPR had cardiac herniation [7]. Defects of the pleuropericardium usually occur vertically along the phrenic nerve; as in our cases [8]. If the tear is large enough, approaching 8-12 cm, the heart can sublux through the defect [9]. The resulting torsion of the great vessels can lead to a form of obstructive cardiogenic shock and cardiovascular instability [8].
Clinical presentation
As seen with our own experience and those of others there is often a delay in diagnosis of BTPR and cardiac herniation, which is a real concern given that, once recognised, the treatment is simple and effective [10].
The most common mechanism for BTPR are those involved in road traffic collisions and sudden decelerations; particularly those involving a vector of injury from the left side of the chest [3]. The following pattern of associated injuries should also arouse suspicion of BTPR [3]:
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Cardiac - contusions and dysrrthmias (28%). The delayed penetrating cardiac injury as a result of rib fractures, as witnessed in the second case is one of the only reported cases of its kind.
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Chest - multiple rib fractures, haemopneumothoraces and pulmonary contusions almost universally seen.
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Neurological - particularly thoracic spine fractures and spinal cord injuries as well as traumatic brain injuries (32%).
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Abdominal injuries (27%).
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Pelvic and long bone fracture indicative of a high velocity/energy impact (49%).
Given the severity of associated injuries patients usually require invasive ventilation early on. However, if the patient is conscious, they may report symptoms of palpitations, shortness of breath and chest pain as well as angina type pains as a result of coronary obstruction following herniation [2, 11].
The main clinical signs, which may be subtle but should be sought, are:
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Signs similar to that of tamponade; in particular that of hypotension, pulsus paradoxus and raised jugular venous pressure (JVP) [2, 12]. This may occur early or late depending on the timing of herniation [13]. This haemodynamic compromise may manifest itself despite fluid administration and inotropic support [13].
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Fluctuating haemodynamic parameters, sometimes to the extent of sudden cardiac arrest (often as a result of change in patient's position) should evoke a high index of suspicion of BTPR [14].
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Tachycardia and dysrrthymias may also be seen [11], such as the atrial tachyarrythmias noted in our case.
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Displaced and heaving apex beat [2, 8, 12].
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A splashing murmur "bruit de Moulin" as a result of the heart moving in a haemopneumopericardium [5, 10, 12].
Investigations
Identifying these symptoms and signs in a noisy and stressful trauma environment may well prove difficult. However, there is a multitude of investigations available to most hospitals that can assist in the diagnosis:
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Electrocardiogram - may show a tachycardia as well as dysrrthymias particularly those of atrial origin. Also present could be an electrical axis deviation associated with the cardiac herniation and rotation [2, 8, 12] and a right bundle branch block [9, 10]. Ischaemic changes may be noted as a result of coronary artery occlusion by the pericardial band [8, 12]. In fact, Rippey et al [12] reported an elevated Troponin I of 9.20 μg/L in a patient later diagnosed with BTPR and cardiac herniation. This was thought to be multifactorial but predominantly as a result of a contusion and coronary insufficiency.
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Chest radiograph - as a readily available imaging modality, it is a useful screening tool for BTPR and cardiac herniation. Given the very real chance of the chest x-ray being completely normal, serial films may also be of use to identify any evolving pathology [13]. Findings may include: cardiac silhouette may be unusually prominent ("boot shaped") and demarcated from the diaphragm; pneumopericardium; pneumomediastinum; bowel gas/loops within pericardial sac; prominent pulmonary artery contour; herniation and rotation of the heart into either hemithorax with a possible pericardial sac contour visible distinct to the cardiac silhouette [2, 8, 10, 13]. Associated injuries include haemopneumothoraces, pulmonary contusions, lower lobe collapse/atelectasis/consolidation, surgical emphysema, rib/clavicle/sternal and thoracic spine fractures [13–15].
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Transthoracic/oesophageal echocardiography and Focused Assessment with Sonography for Trauma - TTE/TOE have been used with varying reports of success but the sensitivity for diagnosing even large pericardial defects is thought to be low [7, 15]. With the presence of surgical emphysema and pneumopericardium, the echographic windows will be poor and, along with operator variability, cannot be relied upon [15]. The importance of echocardiography lies in its ability to rule out other differential diagnoses (such a cardiac contusion or pericardial effusion and possible tamponade) non-invasively and quickly. This can be particularly useful in the patient who is haemodynamically shocked, with a raised JVP, ± reduced heart sounds, and is unresponsive to fluids and inotropic support.
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Computed Tomography (CT) - along with its increasing availability and use in the multiply injured trauma patients, CT is also more sensitive for identifying cardiac axis changes and pericardial discontinuity than plain radiographs [13, 15].
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▪ Characteristic changes for a pericardial rupture include [7, 14, 15]:
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▪ Characteristic changes for a cardiac herniation include [7, 15]:
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▪ "Empty pericardial sac" sign, air outlining the empty pleuropericardium as a result of cardiac luxution into the hemithorax.
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▪ "Collar" sign is the result of compression of the cardiac contour as a result of constriction by the pericardial band caused by the defect.
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▪ Associated signs include dilated inferior vena cava (IVC), reflux of contrast into IVC and deformed ventricular silhouette, as well as, secondary signs of tamponade periportal lymphoedema, pericholecystic fluid and ascites.
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Magnetic Resonance Imaging (MRI) - In haemodynamically stable patients with a suspected BTPR where other imaging modalities have been suggestive but inconclusive, cardiac MRI has been used to clarify its presence [7].
Management
Once BTPR and cardiac herniation has been diagnosed, treatment is simple and effective. It has even been suggested that, as it is such a rapidly reversible cause of sudden cardiac arrest, there may be a role for post-arrest emergency thoracotomy for select patient groups with blunt chest trauma and positional cardiovascular instability [14].
Video-assisted thoracoscopy has been suggested by some, for the assessment and management of stable patients where there is a lack of diagnostic clarity [8]. Small pericardial defects where cardiac herniation is unlikely, especially those on the left side can be left alone [3, 11]. The treatment of choice for tears of the diaphragmatic pericardium, right pleuropericardium, and moderate/large left pleuropericardium defects, is surgical closure [3, 10]. Closure of moderate-sized pericardial defects is best achieved by interrupted non-absorbable sutures and larger ones with a mesh prosthesis [3, 10, 11].