Pathophysiology of Other Heart Disorders

1. Dilated Cardiomyopathy

This is characterized by the enlargement and weakening of the ventricles. Because the muscle becomes stretched and thin, the heart suffers from a "weak squeeze," leading to systolic heart failure, where the ejection fraction (the percentage of blood pumped out with each beat) is decreased.

2. Hypertrophic Cardiomyopathy

In this type, the ventricular muscle becomes abnormally thickened. This massive muscle growth restricts the ability of the chambers to expand and fill with blood, often resulting in diastolic heart failure.

3. Restrictive Cardiomyopathy

This condition is defined by stiff, non-compliant ventricles. While the muscle thickness might not be as extreme as in hypertrophic types, the stiffness prevents normal filling, causing blood to back up into the atria.

Arrhythmias and Conduction Disturbances

The heart relies on a precise electrical conduction system—starting at the SA node and traveling through the AV node, Bundle of His, and Purkinje fibers—to coordinate contraction. Arrhythmias (or cardiac dysrhythmias) occur when there is a malfunction in this electrical system, often caused by hypoxia, electrolyte imbalances, or stress.

Classifications of Rhythm

Arrhythmias are often classified by their rate or their origin within the heart:

• Tachycardia: A heart rate exceeding 100 beats per minute.
• Bradycardia: A heart rate below 60 beats per minute.
• Supraventricular Arrhythmias: These originate above the ventricles. A common example is atrial fibrillation, where the atria quiver rather than contracting effectively. Atrial flutter is another supraventricular disturbance involving a rapid, regular rhythm.
• Ventricular Arrhythmias: These originate in the ventricles and are often more dangerous. Ventricular tachycardia involves rapid ventricular rates, while ventricular fibrillation is a chaotic state where the ventricles merely quiver, resulting in zero cardiac output and imminent cardiac arrest.

Conduction Blocks

Disturbances can also manifest as Heart Blocks, which represent delays or interruptions in the electrical signal:

• First-degree Heart Block: A partial delay in the signal passing through the AV node.
• Total Heart Block (Third-degree): The most severe form, where the atria and ventricles beat independently of one another. This causes a marked decrease in cardiac output and can lead to syncope (fainting).
• Bundle Branch Block: A delay or blockage in the electrical impulses traveling through the specialized conduction pathways in the ventricles.

Study Tip: If a patient presents with a regular heart rate of 45 bpm and an ECG showing no P waves, consider an AV-junction escape pacemaker (junctional rhythm) rather than the SA node.

Treatment Strategies

Management of arrhythmias typically focuses on restoring a normal sinus rhythm or managing the heart rate. Common interventions include:

1. Antiarrhythmic drugs: Such as $\beta$-adrenergic blockers or calcium channel blockers.
2. Pacemakers: Artificial devices used to regulate the heart rate, especially in cases of symptomatic bradycardia or total heart block.