Clinical Review: Dextrocardia

   You are dispatched to a young patient in cardiac arrest. When you arrive, your training sets in and you get right down to business. You have good CPR in place and get an airway in no time at all. You have even gained some peripheral venous access with little difficulty. As you are applying the defibrillator pads to the patient, the scared mother yells, "He has dextrocardia." What do you do?

What Is Dextrocardia?

   Dextrocardia situs inversus is a congenital condition characterized by a heart that is horizontally inverse, or mirrored. It is thought to occur in a small portion of the population--about 1 in 12,000 people. With this rare condition, the main mass of the heart is on the right side of the sternum, as opposed to the left natural placement.

   There are multiple variations of this condition. Dextrocardia situs inversus totalis refers to the condition where all visceral organs are reversed.¹ Levocardia is characterized by normal heart placement with transposition of the great vessels. Isolated dextrocardia with situs solitus (normally placed thoracic and abdominal organs) is sometimes referred to as dextroversion.

   People with dextrocardia are generally unaware of their condition until they seek medical attention or treatment for an unrelated ailment and the treating physician becomes alarmed when certain findings within the assessment appear abnormal.

Assessment Findings

   There are a number of different assessment findings in a patient with situs inversus. If you are one of the few people who perform percussion, or organ palpation, you will recognize that the hollow and solid organs are located on the opposite side with totalis. Most prehospital clinicians will not recognize any abnormalities other than those found on the electrocardiogram. Not all findings are always present, but there are specific changes associated with a dextrocardia that will present with normal electrode placement. To recognize these differences, it is important that you have a clear understanding of the electrical axis and how ECG leads work.

   The electrical axis is the direction in which the heart's electrical activity flows. Consider the normal heart, with the right atrium as the place of impulse conception. The impulse generated in the right atrium first spreads across both atria, moves down to the base of the ventricular septum, spreads around the ventricular walls and heads back in a superior direction. To put it simply, it goes down and then back up.

   Each ECG lead has a different direction. Lead II is usually closest to the mean electrical axis, which is why it is the most common monitoring lead. Lead II has a positive electrode at the left leg and a negative at the right arm. When the impulse travels toward the positive electrode, it shows as a positive deflection on the ECG tracing and shows negative when it travels away from that electrode. So, in lead II with normal conduction you have a big positive R-wave as the impulse travels down and a negative S-wave when it travels back up. With lead I, the positive electrode is on the left arm. When the impulse travels down it is also directed slightly to the left, resulting in a positive R-wave in lead I as well.

ECG Findings for Dextrocardia

• Global negativity in lead I (a negative P-wave, QRS complex and T-wave)
• Positively deflected QRS complex in aVR
• Negative P-wave in lead II
• Reverse R-wave progression in precordial leads
• Right axis deviation.

   If you understand the way the heart's electrical vectors work, it is quite easy to understand why this structural abnormality could cause these ECG changes. With the mass of the heart on the right side, the mean electrical axis will follow. Rather than the initial impulse traveling down and slightly left, with the dextrocardic patient it travels down and to the right.