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Heart Rate Abnormalities

Cardiac symptoms in mitochondrial disease include rhythm abnormalities described in specific disorders (like heart block in Kearns-Sayre syndrome, Wolff-Parkinson-White syndrome in diseases associated with mtDNA abnormalities) (Towbin, 2006). Cardiomyopathy, a potential complication of many different energy disorders (Scaglia, 2004; Towbin, 2006), can be associated with tachycardia in association with ventricular dysfunction and/or heart failure.

Autonomic dysfunction is an important consideration in mitochondrial disease (Zelnik, 1996; Axelrod, 2006). The heart rate abnormalities associated with autonomic are probably much more common than primary rhythm abnormalities. The changes in heart rate can come on for no reason or because of certain triggers; inappropriately severe tachycardia can occur with activity or heat or infection (or any significant systemic stress). Bradycardia more commonly occurs during sleep. Associated symptoms include palpitations and sometimes shortness of breath.

Mitochondrial Differential Diagnosis

1. Mitochondrial cardiac disease

2. Autonomic dysregulation

Assessment and Recommendations

1. Mitochondrial cardiac disease:

a. Determine what symptoms are associated with the heart rate abnormalities and whether or not there are any trigger factors.

b. When symptoms are present, evaluate oxygen saturation.

c. Chest x-ray and EKG with rhythm strip. Consider Holter monitoring.

Recommendations:

1. If the symptoms are significant or recurrent, consider a cardiology referral. Regular follow-up with a cardiologist is indicated for any patient with confirmed mitochondrial disease.

2. Autonomic dysregulation:

a. Assess for autonomic dysfunction and those factors that can cause autonomic dysfunction: temperature dysregulation, abnormal (usually low) basal body temperature, heat and cold intolerance, abnormal sweating patterns, tachy- and bradycardia, dizziness, and bladder dysfunction.

Recommendations:

1. Evaluate for vascular dysautonomia, and look for orthostatic changes in heart rate and blood pressure which can cause fatigue and dizziness.

2. If fluid or calorie intake is low, encourage fluids and/or calories. A trial of IV fluids might improve symptoms and support an autonomic etiology.

3. If the patient demonstrates significant orthostasis resulting in dizziness and/or significant fatigue, increased fluids and/or salt supplementation should be considered. If these do not bring sufficient improvement, medications such as fludrocortisone or midodrine could be an option.

4. See AUTONOMIC DYSREGULATION.

References

Axelrod FB, Chelimsky G, Weese-Mayer DE. Pediatric autonomic disorders. Pediatrics 2006;118:309-21.

Scaglia F, Towbin JA, Craigen WJ, et al. Clinical spectrum, morbidity, and mortality in 113 pediatric patients with mitochondrial disease. Pediatrics 2004;114:925-31.

Towbin J. Mitochondrial cardiology. In Mitochondrial Medicine. DiMauro S, Hirano M, Schon EA, eds. Informa Healthcare, Abingdon, 2006. Pg 75-104.

Zelnik N, Axelrod FB, Leschinsky E, et al. Mitochondrial encephalomyopathies presenting with features of autonomic and visceral dysfunction. Pediatr Neurol 1996;14:251-4.

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