Diseases Of The The Myocardium And The Pericardium: Myocarditis And Pericarditis
Introduction And Causes
The myocardium may be the seat of damage in a wide variety of conditions such as infections, hypersensitivity reactions, connective tissues diseases, adverse reaction to drugs and chemicals and nutritional disorders. The cardiac muscle shows patchy or diffuse lesions with degeneration, cellular infiltration and destruction. Myocarditis may be acute or chronic.
- Infection: Rheumatic fever, pneumonia, septicemia, viral infections such as influenza, measles, mumps, rubella, hepatitis, Echo virus, adenovirus, poliomyelitis, Coxackie B infection, infectious mononucleosis, etc. Parasitic infections, eg, trichinellosis, south American trypanosomiasis (Chagas disease), toxoplasmosis, schistosomiasis, etc.
- Connective tissue disorders: Disseminated lupus erythematosus, polyarteritis nodosa, scleroderma and rheumatoid disease.
- Nutritional disorders: Deficiency of thiamine-beriberi
- Drugs and toxins: Emetine, adrenaline, digoxin, daunorubicin, poisons such as cerbera odollum, cerbera thevetia, viper bite, scorpion stings.
- Allergic disorders: Serum sickness, postvaccinal myocarditis
- Miscellaneous group: Irradiation, idiopathic pericarditis, Fiedler’s myocarditis, electric shock and lightening.
In many cases, no cause may be evident.
Referred Pain In Angina
Clinical Features And Management
Unexplained tachycardia, arrhythmias, hypertension, cardiomegaly and evidence of cardiac failure occurring in the presence of any of the etiological disorders should suggest the possibility of myocardial damage. The disease process affects the impulse producing and conducting tissues and produces arrhythmias and varying grades of conduction defects. The ECG shows nonspecific changes in ST and T-wave conduction defects and low voltage complexes. X-ray may reveal cardiomegaly.
This condition may follow the acute condition or arise denovo. The clinical picture resembles one of cardiomyopathy.
Myocarditis is a serious condition associated with mortality. Death occurs as a result of sudden cardiac failure, heart block or fatal arrhythmias. The prognosis depends upon the extent of cardiac involvement and the underlying cause.
The condition should be anticipated and early treatment instituted. The patient is put to absolute bed rest with cardiac monitoring. Complications such as cardiac failure, heart block and arrhythmias are managed as they arise.
An Overview Of The Pericardium
The pericardium is a serous membrane covering the heart and the root of the great vessels. The visceral layer is closely opposed to the heart and the parietal layer encloses the pericardial space which contains a thin film of fluid which lubricates the surfaces. Function of the pericardium is to keep the heart in position and allow smooth andcontrolled movements within the thorax.
Inflammation of the pericardium is pericarditis. Pericarditis starts as inflammation of both layers of the pericardium, but soon fluid accumulates in the pericardial cavity, giving rise to pericarditis with effusion. Pericardium may be affected primarily or it may be affected by diseases occurring in neighboring structures like the pleura, lungs or liver.
Disease Of The Pericardium
Causes And Pathology
- Viral infections e.g, Coxackie B
- Bacterial infections eg, tuberculosis, penumococci, staphylococci, streptococci, salmonellae.
- Protozoa leg, E. histolytica, Toxoplasma. In tropical countries amoebic liver abscess may give rise to pericarditis and effusion.
- Fungal e.g, histoplasmosis, actinomycosis, nocardiosis.
- Connective tissue disorders:
- Rheumatic fever
- Disseminated lupus erythematosus
- Rheumatoid disease
- Polyarteritis nodosa
- Myocardial infarction
- Immune-mediated disorders: Postmyocardial infarction and postcardiotomy syndromes.
- Traumatic: Blunt injury to chest. Penetrating injuries, following paracentesis of pericardium.
- Metabolic disorders: Uremia, myxedema.
- Malignancy: Leukemia, lymphomas, secondary deposits from the primary tumours.
- Other causes: Rupture of aortic aneurysm, dissecting aneurysm of the aorta, irradiation, cardiomyopathy.
Among the known causes, viral infections, tuberculosis, connective tissue diseases and myocardial infarction account for the majority of cases.
In acute pericarditis, the pericardium becomes thick and opaque and a fibrinous exudates accumulates between the two layers, giving rise to a “bread and butter” appearance. Effusion develops later. The nature of this fluid (serous, purulent or hemorrhagic) depends upon the aetiology. Up to 2 liters of fluid may collect in some cases. In tuberculous and viral inflammations. In malignant lesions, the fluid may show neoplastic cells. In the majority of cases, the inflammation and effusion subside with therapy, but some cases become chronic. Fibrosis develops and the two layers of the pericardium become adherent. Thickening of the pericardium restricts diastolic filling of the heart and this leads to hemodynamic abnormalities. Calcification of the pericardium may develop as a sequel.
In summary, Myocarditis and pericarditis are of huge clinical significance in medicine and public health.
© 2014 Funom Theophilus Makama