Chapter 44 - myocardial contusion

Question 1

Arrhythmias associated with myocardial injury may be delayed how long?

Answer 1

48 hours

Question 2

In humans, myocardial injury is associated with poorer patient outcomes, increased expense associated with testing, monitoring and prolonged hospitalisation. T/F

Answer 2

F - no effect on patient outcome

Question 3

Gold standard for diagnosing myocardial injury?

Answer 3

Direct visualisation, histopathology

Question 4

Incidence of myocardial injury in humans and dogs?

Answer 4

8-95%; 10-96%

Question 5

Two proposed mechanisms of myocardial injury?

Answer 5

1. Elastic thoracic wall –> transmission of compressive & concussive forces from forceful contact with ribs, sternum, vertebrae w/ acceleration/ deceleration (most commonly due to lateral compression)
2. distortion of thoracic cage increases intrathoracic & intracardiac pressures –> shearing stress within myocardium resulting in contusions

Question 6

In vivo studies in dogs to mimic blunt chest trauma showed trauma to which cardiac anatomic locations with left and right sided trauma respectively?

Answer 6

Left: craniolateral wall of left ventricle
Right: septal & right ventricular wall

Question 7

Describe one proposed pro arrhythmic mechanism of myoctyte trauma.

Answer 7

1. lowering of the ratio of effective refractory period to action potential duration & increased resting membrane potential (less negative)
2. alterations in Na+ & Ca2+ currents across cell membranes, increased intracellular Ca2+ availability, increased sensitivity to depolarisation

Question 8

Other common pathophysiology of arrhythmias in trauma patients?

Answer 8

hypoxia, anemia, metaboic acidosis, electrolyte imbalances, intracranial injuries, catecholamine release (all lead to alterations in membrane transport and permeability to cations –> decreased resting membrane potential)

Question 9

Myocardial injury should be suspected in traumatized dogs with which 4 concurrent injuries?

Answer 9

1. orthopedic (fractured extremities, spine, pelvis)
2. external evidence of chest wall trauma
3. radiographic evidence of chest wall trauma (contusions, pneumothorax, hemothroax, diaphragmatic rupture, rib/scapular F#)
4. neurologic injury

Question 10

Echocardiographic features of myocardial injury in dogs?

Answer 10

1. increased end-diastolic wall thickness
2. impaired contractility, indicated by wall motion abnormalities and decreased fractional shortening
3. increased echogenicity
4. localised areas of echo lucency consistent with intramural hematomas

Question 11

Cardiac troponin T & I are detectable at increased levels within how long of injury? How long to they remain elevated?

Answer 11

4-6 hours, up to 7 days

Question 12

Most sensitive single indicator of injury?

Answer 12

cTnI

Question 13

negative predictive value of normal cTnI + normal ECG on arrival in human trauma patients?

Answer 13

100%

Question 14

Anti arrhythmic therapy should be considered when the which criteria have been met?

Answer 14

When properly stabilised patients develop multiform VPCs, sustained V tach (140-180bpm), R-on-T esp when clinical evidence of decreased CO (hypotension, weakness, pale MM, delayed CRT, syncope, collapse)

Question 15

Maximum suggested cumulative dose of lidocaine boluses? Associated side effects?

Answer 15

8mg/kg, vomiting, seizures

Question 16

Second line anti arrhythmic? Vaughan Williams classification? Side effects?

Answer 16

Procainamide? 1a, hypotension, AV block

Question 17

B-blockers should be considered under which circumstances?

Answer 17

1. ventricular ectopy persistent in spite of analgesia, treatment for shock
2. ventricular ectopy persistent in spite of treatment with class 1 anti arrhythmics
3. animals that are receiving positive inotropes
4. 1 + 2

Question 18

Anaesthetic agents with increased likelihood of inducing arrhythmias include:

Answer 18

halothane
atropine
thiobarbiturates