Difference Between “Heart attack” and “Cardiac arrest”

“Heart attack” and “Cardiac arrest” are two clinical conditions which are often used synonymously in clinical settings. However, they differ on various clinical and pathophysiological aspects. The present article would portray the comparison between “Heart attack” and “Cardiac arrest”. Heart attack is actually the synonym for myocardial infarction (MI). Myocardial infarction refers to the damage in the myocardium (heart muscles). The damage to the myocardium is manifested as necrotic lesions. The necrotic lesions occur due to unavailability of oxygen and nutrients in the myocardium.  The myocardium receives of oxygen and nutrients through the coronary blood vessels. In conditions like atherosclerosis, LDL- cholesterol (low density lipoproteins-cholesterol) gets deposited in the endothelium (innermost layer of the blood vessels) of the coronary vasculature. The lumen of the coronary blood vessels gets narrowed, which impairs the flow of blood to the myocardium. This situation leads to the genesis of MI. Moreover, the narrowing of the blood vessels may occur due to atherosclerotic plaques. When coronary arteries are blocked by such plaques, it predisposes an individual to the risk of heart attack. The sudden blockage results from the rupturing of atherosclerotic plaques in the coronary arteries. The symptoms of heart attack include chest pain and sweating. The pain increases with mobility or with an increase in workload on the body (Demirovic &Myerburg 1994).

The blockage of the arterial lumen often manifests as unstable angina or heart attack. Unstable angina refers to the pain that result from lack of oxygen supply to the myocardium. Heart attack and unstable angina are grouped together as acute coronary syndrome (ACS).  ACS is managed by vasodilators, angioplasty and stent implantation. The objective of all these interventions is to prevent the narrowing of coronary arteries and for restoring the flow of blood in the myocardium. If blood flow is immediately after a heart attack, permanent damage to the myocardium is prevent in most occasions. If the attack involves a large area of the myocardium, the heart fails to contract. This situation may lead to cardiac arrest. The ECG shows typical elevation of the ST segment (Figure 1) (Demirovic &Myerburg 1994).

When the heart fails to contract effectively or stops contracting totally, the condition is referred as cardiac arrest or cardiopulmonary arrest. Under such situations, the cardiac output is insufficient to meet the oxygen requirements of different organs in our body. In most instances, the vital organs are primarily affected. A decreased perfusion in the brain leads to stroke or transient ischemic attack (TIA). This leads to damage and necrosis of the brain cells, which may further lead to paralysis. Cardiac arrest is caused to defects in the conduction system on the heart. The heart contracts under the influence of electrical impulses generated by the pacemakers on the myocardium. SA node and AV node generates electrical impulses, which is conducted over the atrial and ventricular musculature. When there are defects in the conduction systems (Bundle of His or Purkinje Fibers), the impulse fails to spread over the myocardium appropriately. The atria may beat faster than the ventricles, resulting in ventricular fibrillation. This situation is referred as arrhythmia. The symptoms of cardiac arrest include stroke, TIA, respiratory distress and sudden death. Cardiopulmonary resuscitation (CPR) is performed either manually or by the use of defibrillators (Figure 3). The objective of such intervention is to revive the conduction of electrical impulses over the myocardium. Cardiac arrest is often caused due to underlying disorders like left ventricular hypertrophy, heart attack or heart block. The ECG shows dissociation of the P wave and the QRS complex. Moreover, the QRS complex often remains inverted (Figure 2)( Rea, Pearce & Raghunathan 2004).

Fig 2: Inversion of QRS complex

Fig 3: CPR Approach (manual)

A brief comparison between Heart Attack & Cardiac Arrest is described below:

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