Clinical Review: Dextrocardia

Adam Thompson, EMT-P

Original Contribution

Clinical Review: Dextrocardia

November 2010

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.

Right axis deviation is normally due to a pathological cause such as left posterior fascicular block. Extreme right axis deviation, or ERAD, is normally only seen with ventricular rhythms, such as ventricular tachycardia or paced rhythms. ERAD may be a normal finding with a patient who has dextrocardia.⁴

Right axis deviation is easily identified by a predominantly negative QRS complex in lead I with positively deflected QRS complexes in leads II and III. If leads II and III are negative with the QRS of lead I, the patient has ERAD. In the absence of wide QRS complexes, as with ventricular rhythms, dextrocardia should be considered.

On a standard ECG with normal heart placement, lead I will almost always be positive and lead aVR negative with any supraventricular rhythm. This is because of the leads' direction of view.

The finding of a positively deflected QRS complex in aVR and a negative in lead I should cause concern for the treating paramedic. The most common cause for this finding is reversed electrode placement. If this situation presents and the clinician has assured correct limb lead placement, dextrocardia should be on the list of differentials. Once again, consider ventricular arrhythmias first.

R-wave progression is defined as the transition of a predominantly negative QRS complex in V1 to a predominantly positive QRS complex in V6 on the 12-lead ECG.

The change that is a normal variant with dextrocardia is a reversal of this normal pattern, which would present as a predominant R-wave in V1 and a predominant S-wave in V6.

Treatment Considerations

Considering that dextrocardia is rare, it is even less common to have a prehospital patient with this condition. Knowing this, it would be reasonable to assume that the average clinician, even if presented with a dextrocardic patient, would not likely experience a situation that would involve altered treatment.

Considerations for a patient with dextrocardia include reversing normal electrode placement for better ECG interpretation. To counteract the altered electrical axis of the dextrocardic heart, horizontally mirror the electrode placement. This goes for the chest leads of the 12-lead ECG as well. Similar to a right-sided ECG, use the same physiological landmarks to place the 12-lead electrodes on the right side of the chest.

Another consideration for treatment is the placement of pacer or defibrillator pads. Effectiveness of defibrillation would be limited if normal placement were utilized. To deliver the most beneficial amount of energy, use anterior/posterior placement just to the right of the patient's sternum. Traditional pad placement can be mirrored as well.⁵

Conclusion

While dextrocardia is one of those rare conditions the average clinician may never see in the field, it is still important to have a general knowledge of its physiology. It is impossible for EMS providers to know about every possible condition, although some may benefit from altered treatment strategies. It will not likely pose a problem if dextrocardia goes unrecognized, however. As with most congenital conditions, traditional treatments will not generally harm these individuals.

Causes of Dextrocardia

Marden-Walker syndrome: A rare genetic disorder characterized by blepharophimosis (small eyelids), joint contractures and fixed facial expression.²

Kartagener's syndrome: A rare genetic disorder characterized by enlarged bronchial tubes, sinusitis and cross positioning of body organs.³

Camptomelia Cumming type: A rare syndrome characterized by limb and multiple abdominal organ abnormalities. The disorder results in death before birth or soon after.

Patients with these congenital conditions commonly lead healthy lives. There is about a 5%-10% prevalence of congenital heart disease in people with dextrocardia situs inversus and a 95% occurrence in situs inversus with levocardia. This would significantly increase the risk of acute coronary syndrome in situs inversus patients with levocardia, meaning they are at a much higher risk for a life-threatening cardiac emergency.

REFERENCES

1. Durant AM. What is your diagnosis? Thoracic and abdominal situs inversus totalis. J Am Vet Med Assoc 232(2):197-198, Jan 15, 2008.

2. Soekarman D, Volcke P, Legius E, et al. Marden-Walker phenotype: A diagnostic dilemma. Genet Couns 7(1):31-39, 1996.

3. Shakya K. Kartagener syndrome: A rare genetic disorder. J Nepal Med Assoc 48(173):62-65, Jan-Mar 2009.

4. Jones MB, Glancy DL, Jain N. ECG of the month: Right-axis deviation of the QRS complex with precordial R-wave regression. Situs inversus with mirror-image dextrocardia, sinus rhythm, and a long P-R interval. J La State Med Soc 161(3):125-128, May-Jun 2009.

5. Gorenek B, Kuskus S, Kudaiberdieva G, et al. Electrical cardioversion of atrial fibrillation in a case of dextrocardia. Can J Cardiol 20(8):819-821, Jun 2004. Comment in Can J Cardiol 21(1):99, Jan 2005; author reply pp. 99-100.

Adam Thompson, EMT-P, is a paramedic with Lee County EMS in southwest Florida and an EMS educator with Edison State College. Contact him at Paramedicine101@gmail.com.