Cardiac injuries in blunt chest trauma

Blunt chest traumas are a clinical challenge, both for diagnosis and treatment. The use of Cardiovascular Magnetic Resonance can play a major role in this setting. We present two cases: a 12-year-old boy and 45-year-old man. Late gadolinium enhancement imaging enabled visualization of myocardial damage resulting from the trauma.


Background
Blunt chest traumas are a clinical challenge, both for diagnosis and treatment, since they are often associated with substantial cardiac injury [1]. If not recognized and treated promptly, it may have severe, or even fatal, complications for the patient due to myocardial herniation [2]. Myocardial contusion usually shows enzyme rises, electrocardiographic abnormalities and contractile dysfunction [1]. Since these symptoms can be similar for acute peri-traumatic myocardial infarction, a correct diagnosis may be difficult. The use of Cardiovascular Magnetic Resonance (CMR) can play a major role in diagnosing the etiology of the cardiac abnormalities in this setting.

Patient Description
We present two cases where the use of CMR is illustrated for the diagnosis and understanding of cardiac injury. The first patient was a 12-year-old boy referred to our center after a blunt thoracic-abdominal trauma by a rollover vehicle accident at the age of six. Although he was initially asymptomatic, a subsequent tachycardia was noted. An echocardiogram, acquired two years after the trauma, revealed a left midventricular aneurysm with loss of myocardium affecting the septal and posteriorlateral walls.
The second patient was a 45-year-old man who suffered from a blunt chest trauma after precipitating into a trench in which he was buried by construction material and lost consciousness. His echocardiogram showed a ventricularseptal defect with a left to right shunt. The CMR was performed the day after the trauma.

Examination
Both patients underwent an CMR examination to estimate the severity of myocardial damage using a 1.5 T scanner (Signa CVi-HDx, GE Medical Systems, Waukesha, WS) with a dedicated cardiac coil. The protocol included balanced steady-state free precession gradient-echo images (CINE) and late gadolinium enhancement (LGE) inversion recovery images (after IV administration of 0.2 mmol/kg of gadopentate dimeglumine contrast).
The main structural abnormality observed in both patients was the loss of myocardium. The first patient ( Figure 1) developed a posterolateral mid-wall aneurism without wall rupture ( Figure 1). The LGE images revealed a helical pattern of enhancement, starting at the lower midseptum, along the inferior wall up to the posterolateral wall above the insertion of the papillary muscle (Figure 1B-F). This contrast distribution does not correspond to any particular coronary territory. The second patient ( Figure 2) had a rupture of the interventricular septum and the inferior wall with a secondary haemopericardium. The location of septal thinning and the inferior wall rupture are possible points of increased wall stress, as depicted in Figure 3. The LGE images showed no marked contrast enhancement ( Figure 2F).

Discussion
The patterns of myocardial damage visible from these images are consistent with previously reported injury sites [3,4]. In Figure 3, a possible mechanism is presented for explaining the observed rupture. We hypothesize that the sudden increase in intrathoracic pressure during trauma [5] causes the right ventricular pressure to rise and the cavity to expand. This fastly displaces the right ventricular free wall outward, stretching the moderator band and generating a point of high wall stress around its septal insertion. Additionally, the induced increase in left ventricular pressure closes the mitral valve and stretches the tendinous chords and papillary muscles, creating a higher wall stress around the insertion of the papillary muscles. The increased stress from the right ventricular moderator band and the chordal apparatus puts the connecting (helical) endocardial muscle fibres, which run along the septal, inferior and lateral wall, from apex towards the base (Figure 3 right), under extreme wall stress, resulting in fibre damage, as observed in patient 1.
Finally, the lack of LGE in the second patient might be due to either: the acute state of the injury or the strong loss of myocardium resulting in no-reflow [6]. However, further investigation is required to establish the prevalence of this condition among patients.
CMR has the potential to distinguish acute infarction from myocardial contusion, since it allows for a threedimensional evaluation of the myocardial injury caused by blunt chest trauma. The use of CINE images can depict motion abnormalities and myocardial rupture, while the pattern observed in LGE images can describe the extent of injury (helical pattern vs. coronary territory).

Conclusion
In summary, CMR imaging enables to visualize the typical pattern of myocardial damage resulting from a blunt chest trauma, thus enabling to make an accurate evaluation of the induced injuries. It can be used to differentiate myocardial contusion from a peri-traumatic myocardial infarction.

Consent
Written informed consent was obtained from the patients for publication of this case report and any accompanying images. http://www.jcmr-online.com/content/11/1/35