TACHYCARDIA

Tachycardia, like dyspnea, is usually a sign that the tissues are not getting enough oxygen to meet their demands. To recall a list of causes, pathophysiology is applied. If tachycardia results from anoxia then the causes can be developed on the basis of the causes for anoxia, which may result from a decreased intake of oxygen, a decreased absorption of oxygen, and inadequate transport of oxygen to the tissues. Tachycardia also results when the tissues’ demand for oxygen increases. Another cause is peripheral arteriovenous shunts. In addition, anything that stimulates the heart directly, such as drugs, electrolyte imbalances, or disturbances in the cardiac conduction system, will cause tachycardia. Let us review the conditions that may fall into each of these categories.

1. Decreased intake of oxygen. Anything that obstructs the airway and prevents oxygen from getting to the alveoli should be recalled in this category. Bronchial asthma, laryngotracheitis, chronic bronchitis, and emphysema are most important to recall. In addition, if the “respiratory” pump (thoracic cage, intercostal and diaphragmatic muscles, and respiratory centers in the brainstem) is affected by disease, especially acutely, there will be tachycardia. Poliomyelitis, myasthenia gravis, barbiturate intoxication, and intoxication by other central nervous system (CNS) depressants are examples of disorders in this category. Finally, the intake of oxygen may decrease if there is a low atmospheric oxygen tension. High altitude is an obvious cause, but hazardous working conditions must also be considered.
2. Decreased oxygen absorption. This may result from three mechanisms.
3. A. Alveolar–capillary block in sarcoidosis, pneu- moconiosis, pulmonary fibrosis, congestive heart failure (CHF), alveolar proteinosis, and shock lung.
4. B. Diminished perfusion of the pulmonary capillaries in pulmonary emboli and pulmonary and cardiovascular arteriovenous shunts.
5. C. Disturbed ventilation/perfusion ratio in which alveoli are perfused but not well ventilated, in alveoli that are not well ventilated, or in alveoli that are ventilated but not well perfused. This is typical of pulmonary emphysema, atelectasis, and many chronic pulmonary diseases.
6. Inadequate oxygen transport. Severe anemia, shock, and CHF (regardless of the cause) fall into this category, as do methemoglobinemia and sulfhemoglobinemia.
7. Increased tissue oxygen demands. Fever, hyperthyroidism, leukemia, metastatic malignancies, polycythemia, and certain physical or emotional demands fall into this category.
8. Peripheral arteriovenous shunts. These shunts may occur in the popliteal fossa following a gunshot wound, in the sellar area following the rupture of a carotid aneurysm into the cavernous sinus, and in Paget disease.
9. Disorders that directly affect the heart. Stimulants of the heart such as caffeine, adrenalin (pheochromocytomas), thyroid hormone (hyperthyroidism), amphetamines, theophylline, and other drugs fall into this category. Nervous tension and neurocirculatory asthenia may be the cause. Electrolyte disturbances such as hypocalcemia and hypokalemia may precipitate ventricular tachycardia. Excessive amounts of digitalis may also provoke atrial or ventricular tachycardia.

Tachycardia of various types may occur from disturbances in the conducting system of the heart. Digitalis has already been mentioned, but the Wolff–Parkinson–White syndrome, focal myocardial anoxia from emboli or infarction, and distention of various chambers of the heart (atria in mitral stenosis, ventricles in essential hypertension and cor pulmonale) are also etiologies of this mechanism. Anticholinergic drugs such as atropine block the ability of the vagus to slow the heart and may cause or contribute to tachycardia. All of the above categories are outlined in Table 56 where a few diseases that are more specific are mentioned.

Approach to the Diagnosis

The association of other clinical signs and symptoms will often help to pinpoint the diagnosis. Tachycardia with tremor and an enlarged thyroid suggests hyperthyroidism. Tachycardia with respiratory wheezes suggests bronchial asthma. Tachycardia with a black stool suggests a bleeding peptic ulcer. If the blood pressure is low, the workup will proceed as that of shock . In contrast, tachycardia with a normal blood pressure should prompt thyroid function studies, pulmonary function studies, arterial blood gases, and a venous pressure and circulation time. Electrolyte determinations, a drug screen, and 24-hour urine for catecholamine determinations may be indicated if there is hypertension as well.

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TACHYCARDIA

	V	I	N	D
	Vascular	Inflammatory	Neoplasm	Degenerative
Decreased Intake of Oxygen	Aortic aneurysm with compression of bronchi	Laryngitis Bronchitis	Carcinoma of the lung	Pulmonary emphysema
Increased Oxygen Absorption	Pulmonary embolism	Pneumonia	Hemangioma Carcinoma of the lung	Pulmonary emphysema Fibrosis
Inadequate Oxygen Transport	Shock from myocardial infarction Congestive heart failure	Septicemic shock		Aplastic anemia
Peripheral Arteriovenous Shunts				Paget disease
Increased Tissue Demands for Oxygen		Septicemia Fever of any infection	Leukemia Hodgkin lymphoma Polycythemia vera
Disorders Affecting the Heart Directly	Myocardial infarction Essential hypertension	Myocarditis Tuberculosis Pericarditis	Rhabdomyosarcoma	Muscular dystrophy

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TACHYCARDIA

I	C	A	T	E
Intoxication	Congenital	Allergic and	Trauma	Endocrine
		Autoimmune
Pneumoconiosis	α 1-trypsin deficiency Cystic fibrosis	Bronchial asthma	Pneumothorax
Nitrofurantoin Pneumoconiosis Shock lung Lipoid pneumonia	Congenital cyst	Scleroderma Wegener granulomatosis	Shock lung	Fat emboli
Drug-induced shock Methemoglobinemia	Sickle cell anemia Cooley anemia	Hemolytic anemia (autoimmune)	Hemorrhagic shock
	Carotic–cavernous shunt		Popliteal aneurysm
				Hyperthyroidism
Caffeine Amphetamines Alcohol Hyperkalemia Digitalis	Wolff–Parkinson–White syndrome Glycogen storage disease	Lupus erythematosus	Traumatic aneurysm	Hyperthyroidism Pheochromocytomas

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Other Useful Tests

1. Complete blood count (CBC) (anemia)
2. Sedimentation rate (infection)
3. Chemistry panel (liver disease, uremia)
4. Antinuclear antigen (ANA) (collagen)
5. Antistreptolysin O (ASO) titer (rheumatic fever)
6. Blood cultures (subacute bacterial endocarditis [SBE])
7. Febrile agglutinins (fever of unknown origin)
8. Serial electrocardiograms (ECGs) and cardiac enzymes (myocardial infarction)
9. Lung scan (pulmonary embolism)
10. Holter monitoring (cardiac arrhythmia)
11. Echocardiography (CHF, valvular heart disease)
12. 5-hour glucose tolerance test (insulinoma)
13. Temperature chart (fever of unknown origin)
14. Sleeping pulse rate (anxiety neurosis)
15. Psychiatric consult

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Book Source Details

• Book Title: Differential Diagnosis in Primary Care
• Author(s): R. Douglas Collins MD, FACP
• Year of Publication: 2007
• Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.

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