Sudden Cardiac death

Cardiac causes of sudden death accounts for more than 300k deaths every year in the U.S. out of which 80% are due to coronary arteriosclerosis. Ischemic heart disease is the commonest cause of sudden death in most parts of the world. Coronary atherosclerosis – degenerative disease of the coronary arteries – is the largest contributor to ischemic heart disease. Coronary artery disease is accepted as synonymous with coronary atherosclerosis, although this should be avoided, as there are other diseases of the coronary arteries.

Ischemic heart disease comprises

  • Hypertensive cardiovascular disease
  • Coronary atherosclerosis
  • Anomalies
  • Cardiomyopathies
  • Valvular diseases
  • Myocarditis

HYPERTENSIVE CARDIOVASCULAR DISEASE

Uncontrolled hypertension can result in marked left ventricular hypertrophy and cardiomegaly. In the past, the thickness of the ventricular wall was used as a reference for hypertrophy, with measurements of left ventricular wall exceeding 15 mm and right ventricular wall thickness exceeding 0.3-0.5 cm taken as the criteria for diagnosis. Recent studies have shown that the weight is a more reliable indicator of hypertrophy. The ‘normal’ heart varies between individuals but normally weighs around 400 grams. Heart weighing more than 500 grams are generally accepted to be hypertrophied.

Hypertensive cardiovascular disease is associated with concentric thickening of the arterial wall. In case of plaque formation, there is eccentric thickening of the wall. In case of elderly, the vessel wall are rigidly calcified. The most commonly involved arteries are left main coronary artery and proximal left anterior descending coronary artery. For diagnosis of death due to coronary arteriosclerosis, the circumstances of death should be taken into account. After ruling out other causes beyond reasonable doubt, the diagnosis may be give as death due to coronary arteriosclerosis.

CORONARY ATHEROSCLEROSIS

Coronary arteriosclerosis has been associated with a 9-fold increase in mortality. It shows increased incidence with increase in age and affects men more than women in all age groups. A positive stress test is associated with increased risk of myocardial infarction. Symptoms range from vague symptoms like tiredness and fatigue, generalized cardiac symptoms like to chest pain, palpitations and shortness of breath.

In one-fourth of patients, the first sign is death. About half of all sudden death victims present with history of atherosclerotic heart disease. The diktat for coronary arteriosclerosis is that it can result in death at any time and any place. Sudden death is the first and last symptom in 25% of individuals with cardiovascular disease. Half of individuals with coronary atherosclerosis die suddenly. Sudden dysarythmias occur in people with no distress previously. The mechanism of sudden death in an individual can be attributed to myocardial ischemia, which leads to an acute electrical event, most commonly a ventricular tachydysrhythmia, in the presence of a super-imposed transient risk factor.

Hypertension is the most important risk factor for sudden death in individuals with coronary arteriosclerosis. Hypertension and arteriosclerosis are risk factors for myocardial infarction and hence have a multi-fold increased risk of sudden death. Other risk factors include stimulation of vagal discharge, coronary artery spasm, thromboembolism and sympathomimetic drugs like caffeine, epinephrine.

The cause for this ischemia is occlusion of coronary arteries by atheromatous plaques. While the severity of stenosis before death occurs is debatable, most authors agree that at least 80 per cent of the lumen must be occluded for death to be attributable to coronary atherosclerosis. Myocardium may show evidence of fibrosis and even recent infarcts.

Hemorrhagic Myocardial Infarction

The difficulty in diagnosis of coronary atherosclerosis lies in quantifying the degree of stenosis. In addition, post-mortem examinations demonstrate empty vessels that are collapsed. The occlusion may be focal, of varying size and the rest of the artery may be normal. It is extremely easy to miss a focal lesion if the entire system is not examined with cuts no more than 3 mm apart. Opening the vessels lengthwise obviates this danger, but has the disadvantage of not being able to measure the degree of stenosis accurately.

CONGENITAL ANOMALIES

Congenital anomalies of the conducting system may be compatible or incompatible with life. Those that are compatible with life may cease to be so following external insult. Some common anomalies found in healthy individuals are

  • Persistent fetal dispersion of AV node
  • Ectopic connections between the node and ventricles
  • Ectopic His bundle, Ectopic AV tracts
  • Marked sclerosis of the artery to AV node.

Role of these anomalies in sudden cardiac death is debatable and undecided.

DEVELOPMENTAL ANOMALIES

Other anomalies include developmental anomalies of the coronary arteries. These are some common developmental anomalies

  • Left coronary artery arises from right sinus of Valsalva, and passing between aorta and pulmonary artery
  • Single coronary ostium in right sinus of Valsalva with left coronary artery arising from proximal right coronary artery
  • Origin of right coronary artery from left sinus of Valsalva
  • Origin of left coronary artery from right sinus of Valsalva and passing dorsal to aorta
  • Coronary artery hypoplasia – no diagnostic criteria has been set forth for this entity

Sudden death is more likely when the anomalous artery forms an acute angle with the sinus of Valsalva or produces a right angle in the artery itself.

Other congenital anomalies that are less compatible with life are bridging of the coronary arteries, Dissecting coronary aneurysm and coronary artery spasm.

Bridging of coronary arteries – This refers to the anomalous pathway of the epicardial arteries where the artery runs an intramural course. Therefore, on contraction of myocardium, the artery gets occluded; leading to ischemia and thereby may be a cause of sudden death.

Dissecting coronary aneurysm – may be primary or secondary to extension of the aortic root dissection. The extension of the aortic root dissection may be spontaneous or due to trauma. Seen more commonly in peri-partal females.

Atheromatous plaque can cause intimal defects and weakening of arterial wall media, allowing blood from the lumen to enter between the layers and dissect the weakened wall. The flow of blood being under pressure extends the dissection further along the aortic wall.

Massive Abdominal hemorrage following rupture of Aortic Dissection

The commonest origin is in the thoracic aorta with the dissection extending distally, sometimes reaching the iliac or even the femoral arteries. The aneurysm may rupture at any point, resulting in massive hemorrhage into the thorax or abdomen.

Rarely, the aneurysm may extend proximally, around the wall of the arch of aorta and into the pericardial sac, resulting in hemopericardium, cardiac tamponade and sudden death. Dissecting aneurysms are common in hypertensive individuals, and commonly seen in younger individuals with connective tissue defects, like Marfan syndrome.

Rupture of Aortic Dissection

In elderly, the commonest site of aneurysm is the abdominal aorta. The aneurysms may be saccular or fusiform. The wall of the aneurysm is frequently calcified and the lumen lined by old laminated thrombus.

Retro-peritoneal hematoma following rupture of Aortic Dissection

Many aneurysms remain intact throughout the lifetime and are found incidentally following autopsy for some other cause. Rupture of the aneurysm results in massive intra peritoneal hemorrhage, which may be repaired surgically if diagnosed in time. This typically affects older individuals that are hypertensive and of a poorer economic strata. As a result, many individuals die quickly before medical assistance can be availed. The bleeding is mostly in the retroperitoneal space. It may envelope an entire kidney in case of saccular aneurysms. Rarely, the aneurysm or hematoma may rupture into the peritoneum resulting in massive hemoperitoneum.

Coronary artery spasm – The coronary artery undergoes spasms, which cause significant constriction and decrease in blood supply leading to ischemia. Angina associated with acute MI-like symptoms are the primary complaints. However, on autopsy, infarct is not seen and neither is there any significant atherosclerosis. This is seen in Printzmetal’s angina and unstable angina.

CARDIOMYOPATHY

Cardiomyopathy is a group of diseases characterized by myocardial dysfunction. The cause may be known or unknown, and is not the result of arteriosclerotic, hypertensive, congenital or valvular diseases. It can be divided into 3 broad categories.

  • Dilated or congestive
  • Hypertrophic
  • Restrictive or obliterative

Dilated or congestive cardiomyopathy

Dilated or congestive cardiomyopathy is associated with enlargement of the heart with dilatation of all four chambers on gross examination. It usually presents with presence of endocardial thrombi. Microscopically, it presents as extensive interstitial and perivascular fibrosis. Most common causes being chronic alcoholism, peri-partum cardiomyopathy, chronic myocarditis and idiopathic.

In chronic alcoholism, the effects are due to direct toxicity of alcohol on the cardiac musculature, nutritional effects of alcohol on the body and toxic effect of additives like cobalt.

Heart failure with gross enlargement of the chambers in the last month of pregnancy or in the first six months post-partum is designated Peri-partum cardiomyopathy. In about half of the individuals, the enlarged heart returns to normal in 6-12 months post-partum. If however, the failure becomes incompatible with life and death occurs, the finding on gross examination would be presence of grossly dilated heart with flabby myocardium. Presence of mural thrombosis is a common finding in these cases. Microscopically, signs of degeneration and/or hypertrophy may be present. It may also present as focal or diffuse interstitial myocardial fibrosis. Microscopically, one can find scattered mononuclear infiltrates as well as occasional fatty infiltrates.

In chronic myocarditis, the common cause is the exposure to toxic substances like cobalt and Adriamycin. The mechanism in these cases is due to the direct toxicity of the substance to the cardiac musculature, due to atypical reaction to the toxin and due to excessive dosage of the drug. This is clinically associated with arrhythmias leading to sudden death.

Hypertrophic cardiomyopathy

Hypertrophied Heart

Hypertrophic cardiomyopathy is the single most common cause of sudden death in adolescent and young adults. It shows an autosomal dominant genetic inheritance. On gross, the left ventricle is hypertrophied without dilatation.

Transverse cut-sections of heart showing non concentric hypertrophy

The hypertrophy is disproportionate, asymmetrical in the septum as compared to the left ventricle. This causes obstruction to the outflow tract. Rarely, it may also present as concentric hypertrophy of the left ventricle similar to that seen in hypertensive patients. On microscopy, the myocardial fibers are in disarray with presence of hypertrophied bizarre myocardial cell. This is typically seen in the septal myocardium.

VALVULAR DISEASE
The commonest valvular diseases are mitral valve prolapse, aortic stenosis and acute bacterial valvulitis

Mitral valve prolapse also known as floppy mitral valve, myxomatous degeneration of the mitral valve or Barlow’s syndrome is one of the commonest cardiac conditions in the world. It is thought that 15% of the world’s population is inflicted with symptomatic or asymptomatic mitral valve prolapse. It is generally an asymptomatic condition that continues to remain undetected unless it becomes symptomatic due to some associated insult. Generalized cardiac symptoms are the primary indicators like angina, palpitation, shortness of breath etc.

Aortic stenosis has become more prevalent than mitral stenosis in today’s world. This is due to the decrease in mitral stenosis of rheumatic fever as well as advancement in the field of surgery for mitral stenosis. Congenital aortic stenosis is the commonest etiology followed by Rheumatic, secondary calcification of congenital bicuspid valves and Primary degenerative calcification of normal aortic valves.

Thrombo-embolic accident following acute bacterial valvulitis is another common cause of sudden death that might be missed. It most commonly involved the tricuspid valve and is seen commonly in IV drug abusers.

MYOCARDITIS
Clinical features of myocarditis could range from being asymptomatic to non-specific symptoms and could result in death. The causes could be infective, secondary to connective tissue disorders, due to physical agents, chemical poisons or drugs.

Etiology

  • Infective
    • Bacterial
    • Rickettsial
    • Viral
    • Protozoal
    • Fungal
  • Connective tissue disorders
    • Rheumatic Disease
    • Rheumatoid Arthritis
  • Physical agents
  • Chemical poisons or drugs
  • Idiopathi