Cardiac Arrhythmias

Cardiac arrhythmia refers to any variation in the normal heartbeat and includes disturbances in rhythm, rate, or the conduction pattern of the heart. Cardiac arrhythmias are present in a significant percentage of the population, many of whom will seek dental treatment. Most arrhythmias are of little clinical concern for either the patient or the dentist; however, some can produce symptoms, including anxiety and loss of consciousness, and a few may be life threatening.

Potentially fatal arrhythmias can be precipitated by strong emotion such as anxiety or anger and by various drugs, both of which are factors likely to be encountered in the dental setting. Therefore, patients with significant arrhythmias must be identified before undergoing dental treatment so appropriate modifications in dental management are administered. Dental practitioners also should be aware that patients with significant arrhythmias are at risk for fatal cardiac arrhythmias, which can be precipitated by strong emotion, various drugs, or the performance of dental procedures.

Epidemiology

Cardiac arrhythmias are relatively common in the general population, and their prevalence increases with age. They more frequently occur in older adults, people with a long history of smoking or alcohol use, patients with underlying ischemic heart disease, and those taking certain drugs or who have various systemic diseases. In the United States, arrhythmias occur in 15% to 17% of the population and are present in about 35% of people older than 65 years of age. In studies of patients treated in dental and other health care settings, about 4% of the detected arrhythmias have been serious, potentially life-threatening cardiac arrhythmias. Arrhythmias directly account for more than 36,000 deaths annually and constitute the underlying or contributing cause in almost 460,000 cases. The most common type of persistent arrhythmia is atrial fibrillation (AF). AF affects more than 2.7 million people, and the majority are older than 60 years of age. In a dental practice of 2000 adults, one can expect about 300 patients to have some type of cardiac arrhythmia.

Etiology

Cardiac contractions are controlled by a complex system of specialized excitatory and conductive neuronal circuitry ( Fig. 5.1 ). The normal pattern of sequential depolarization involves the structures of the heart in the following order: (1) sinoatrial (SA) node, (2) atrioventricular (AV) node, (3) bundle of His, (4) right and left bundle branches, and finally (5) subendocardial Purkinje network. The electrocardiogram (ECG) is a recording of this electrical activity. The primary anatomic pacemaker for the heart is the SA node, a crescent-shaped structure 9 to 15 mm long that is located at the junction of the superior vena cava and the right atrium. The SA node regulates the functions of the atria and is responsible for production of the P wave (atrial depolarization) on the ECG ( Fig. 5.2 ). The ends of the sinus nodal fibers connect with atrial muscle fibers. The generated action potential travels along the muscle fibers (internodal pathways) and eventually arrives at and excites the AV node, which serves as a gate that regulates the entry of atrial impulses into the ventricles. It also slows the conduction rate of impulses generated within the SA node. From the AV node, impulses travel along the AV bundle (His bundle) within the ventricular septum, which divides into right and left bundle branches. The bundle branches then terminate in the small Purkinje fibers, which course throughout the ventricles and become continuous with cardiac muscle fibers. Simultaneous depolarization of the ventricles produces the QRS complex on ECG. The T wave is formed by repolarization of the ventricles. Repolarization of the atria occurs at about the same time as depolarization of the ventricles and thus is usually obscured by the QRS wave.

FIG 5.1
The electrical conduction system of the heart. AV, Atrioventricular.
(From Hall JE: Guyton and Hall textbook of medical physiology, ed 12, Philadelphia, 2011, Saunders.)
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Sep 3, 2018 | Posted by in General Dentistry | Comments Off on Cardiac Arrhythmias
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