Cardiac Arrhythmias

Implanted Permanent Pacemaker

-A permanent, implanted pacemaker consists of a lithium battery-powered generator implanted subcutaneously in the left infraclavicular area that produces an electrical impulse that is transmitted by a lead inserted into the heart through the subclavian vein to an electrode in contact with endocardial or myocardial tissue -more commonly, bipolar (stimulating two chambers). With a bipolar pacemaker, one lead usually is inserted into the right atrium, and the second lead is positioned within the right ventricle. - In general, pacemakers are indicated to treat bradycardias in patients with acquired AV block, congenital AV block, chronic bifascicular and trifascicular block, AV block associated with acute MI, sinus node dysfunction, hypersensitive carotid sinus and neurocardiogenic syncope, and certain forms of cardiomyopathy. -Infective endocarditis rarely may occur; however, antibiotic prophylaxis for dental treatment is not recommended.

Implantable Cardioverter Defibrillators

-An ICD is a device that is similar to a pacemaker and is implanted in the same way as for a pacemaker. ICDs are capable not only of delivering a shock but of providing antitachycardia pacing (ATP) and ventricular bradycardia pacing. -Most ICDs have a single lead that is inserted into the right ventricle and function by continuously monitoring a patient's cardiac rate and delivering ATP or a shock when the rate exceeds a predetermined cutoff point, such as in VT or VF -CDs generally are larger than pacemakers, and their batteries do not last as long as those of a pacemaker, the life span of the latter being 5 to 10 years. -Antibiotic prophylaxis for dental treatment in patients with these devices is not recommended.

Anit-arythmetic drugs

-Antiarrhythmic drugs are therefore classified on the basis of their effect on sodium, potassium, or calcium channels and whether they block beta receptors -Class I drugs have "local anesthetic" properties or membrane-stabilizing effects and work by primarily blocking the fast sodium channels. -Class II drugs are β-adrenergic-blocking agents. -Class III drugs prolong the duration of the cardiac action potential and enhance refractoriness through their effects on potassium channels. -Class IV drugs are calcium channel blockers. -Many of the antiarrhythmic drugs have very narrow therapeutic ranges, so optimum blood levels that are not too high or too low may be difficult to achieve. -Patients with AF often are prescribed warfarin sodium (Coumadin) to prevent atrial thrombosis and embolism; the target INR (therapeutic range) is between 2.0 and 3.0.

Atrial tachycardias

-Any tachycardia arising above the AV junction for which the ECG shows a P wave configuration different from that for sinus rhythm is called atrial tachycardia -Atrial tachycardia is characterized by an atrial rate between 150 and 200 beats per minute -It commonly is seen in patients with coronary artery disease, myocardial infarction (MI), cor pulmonale (right ventricular hypertrophy and pulmonary hypertension), or digitalis intoxication

Atrial flutter

-Atrial flutter is characterized by a rapid, regular atrial rate of 250 to 350 beats per minute. -It is rare in healthy persons and most often occurs in association with septal defects, pulmonary emboli, mitral or tricuspid valve stenosis or regurgitation, or chronic ventricular failure. It ialso may be noted in patients with hyperthyroidism, alcoholism, or pericarditis.

Sinus bradycardia.

-Bradycardia is defined as a heart rate less than 60 beats per minute, with an otherwise normal ECG tracing -pathophysiologic causes of bradycardia include intracranial tumor, increased intracranial pressure, myxedema, hypothermia, and gram-negative sepsis -lithium, amiodarone, beta blockers, clonidine, and calcium channel blockers.

C.A. further info

-Disorders in automaticity and conductivity constitute the underlying cause of the vast majority of cardiac arrhythmias. -Disorders of conductivity (block or delay) paradoxically may lead to rapid cardiac rhythm through the mechanisms of reentry. Reentry arrhythmias occur when accessory or ectopic pacemakers reexcite previously depolarized fibers before they would become depolarized in the normal sequential impulse pathway, typically producing tachyarrhythmias.

Electromagnetic Interference

-Electromagnetic interference (EMI) from nonintrinsic electrical activity can temporarily interfere with the function of a pacemaker or ICD. -Examples of EMI sources in daily life are cell phones, metal detectors, high-voltage power lines, and some home appliances (e.g., electric razor) DENTAL • Electrosurgery, ultrasonic bath cleaners • Ultrasonic scalers, battery-operated curing light -Amalgamators, electrical pulp testers and apex locators, handpieces, electric toothbrushes, microwave ovens, and x-ray units did not cause any significant EMI with the pacemakers and ICDs tested. Internal shielding has been increased on newer generators to minimize the adverse effects of such interference.

Dental Manage cont.

-For patients with pacemakers or ICDs, antibiotic prophylaxis to prevent bacterial endocarditis is not recommended. Some antibiotics (e.g., metronidazole, extended-spectrum penicillins) are known to increase the INR in patients on warfarin (Coumadin); caution in their use is advised. -Establish good rapport, and schedule short morning appointments. Use anxiety reduction techniques: • Provide preoperative sedation (short-acting benzodiazepine the night before and/or 1 hour before the appointment). • Administer intraoperative sedation (nitrous oxide-oxygen). -In patients taking warfarin: • Review current INR lab results (within 24 hours of surgical procedure). • If INR is within the therapeutic range (2.0-3.5), dental treatment, including minor oral surgery, can be performed without stopping or altering the warfarin regimen. In patients taking dabigatran when major oral surgery is planned: • Review current thrombin clotting time, activated partial thromboplastin time or ecarin clotting time lab results. • Ensure patient has normal renal function. In patients taking digoxin, watch for signs or symptoms of toxicity (e.g., hypersalivation, visual changes); avoid epinephrine or levonordefrin.Because the therapeutic range for digoxin is very narrow, toxicity can easily occur -If a vasoconstrictor is deemed necessary, patients in the low to intermediate risk category and those taking nonselective beta blockers can safely be given up to 0.036 mg epinephrine (two cartridges containing 1 : 100,000 epinephrine); intravascular injections are to be avoided.

AV block

-Heart block is a disturbance of impulse conduction that may be permanent or transient, depending on the underlying anatomic or functional impairment. -During first-degree heart block, conduction time is prolonged, but all impulses are conducted. Second-degree heart block occurs in two forms: Mobitz type I (Wenckebach) and type II. Type I heart block is characterized by progressive lengthening of conduction time until an impulse is not conducted. Type II heart block denotes occasional or repetitive sudden block of conduction of an impulse without previous lengthening of conduction time. When no impulses are conducted, complete or third-degree block is present. -AV block occurs when the atrial impulse is conducted with delay or is not conducted at all to the ventricles at a time when the AV junction is not physiologically refractory -AV block may be caused by a multitude of conditions such as surgery, electrolyte disturbance, myoendocarditis, tumor, myxedema, rheumatoid nodules, Chagas' disease, * calcific aortic stenosis, polymyositis, and amyloidosis

Long QT syndrome

-Long QT syndrome is a disorder of the conduction system in which the recharging of the heart during repolarization (i.e., the QT interval) is delayed -The condition can lead to fast, chaotic heartbeats, which can trigger unexplained syncope, a seizure, or sudden death

Medical management

-Management of cardiac arrhythmias involves medications, cardioversion, pacemakers, implanted cardioverter-defibrillators (ICDs), radiofrequency catheter ablation, and surgery

Sinus tachycardia

-Tachycardia in an adult is defined as a heart rate greater than 100 beats per minute, with otherwise normal findings on the ECG. -This condition most often is a physiologic response to exercise, anxiety, stress, or emotion -Pathophysiologic causes include fever, hypotension, hypoxia, infection, anemia, hyperthyroidism, and heart failure. -atropine, epinephrine, alcohol, nicotine, and caffeine.

Lab findings

-The ECG is the primary tool used in the identification and diagnosis of cardiac arrhythmias

Radiofrequency catheter ablation

-The catheter is positioned in contact with the area determined by electrophysiologic testing to be the anatomic source of an arrhythmia. Radiofrequency energy is then delivered through the electrode catheter whose tip is in contact with the target tissue, which results in resistive heating of the tissue, producing irreversible tissue destruction of an area 5 to 6 mm in diameter and 2 to 3 mm deep, destroying the ectopic pacemaker.

Dental Management

-The keys to successful dental management of patients prone to developing a cardiac arrhythmia and those with an existing arrhythmia are identification and prevention. Even under the best of circumstances, however, a patient may develop a cardiac arrhythmia that requires immediate emergency measures. -This process is accomplished by obtaining a thorough medical history, including a pertinent review of systems, and taking and evaluating vital signs (pulse rate and rhythm, blood pressure, respiratory rate). -Patients who report palpitations, dizziness, chest pain, shortness of breath, or syncope may have a cardiac arrhythmia or other cardiovascular disease and should be evaluated by a physician.

Normal Cardiac Sequence

-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. -Repolarization of the atria occurs at about the same time as depolarization of the ventricles and thus is usually obscured by the QRS wave

Ventricular tachycardia

-The occurrence of three or more ectopic ventricular beats (PVCs) at a rate of 100 or more per minute is defined as ventricular tachycardia -Sustained VT that persists for 30 seconds or longer may require termination because of hemodynamic instability -A variant of VT called torsades de pointes is characterized by QRS complexes of changing amplitude that appear to twist around the isoelectrical line; this rhythm occurs at rates of 200 to 250 beats per minute. -Certain drugs such as digitalis, sympathetic amines (epinephrine), potassium, quinidine, and procainamide may induce VT.

Signs and Symptoms

-The symptoms most commonly associated with cardiac arrhythmias include palpitations, lightheadedness, feeling faint, syncope, and those related to congestive heart failure (e.g., shortness of breath, orthopnea). The only clinical sign of an arrhythmia is a pulse that is too fast, too slow, or irregular

Ventricular flutter and fibrillation.

-Ventricular flutter and ventricular fibrillation (VF) are lethal arrhythmias characterized by chaotic, disorganized electrical activity that results in failure of sequential cardiac contraction and inability to maintain cardiac output -VF occurs most commonly as a sequela of ischemic heart disease.

Premature ventricular complexes.

-characterized by the premature occurrence of an abnormally shaped QRS complex (ventricular contraction), followed by a pause -PVCs may be provoked by a variety of medications, by electrolyte imbalance, by tension states, and by excessive use of tobacco, caffeine, and alcohol. -The prevalence of PVCs increases with age; they are associated with male gender and are related to low serum potassium concentration. Among patients with previous MI or valvular heart disease, however, frequent PVCs are associated with an increased risk of death.

Preexcitation syndrome (e.g., Wolff-Parkinson-White syndrome)

-in some persons, additional electrical bridges connect the atria and ventricles, bypassing the normal pathways and forming the basis for preexcitation syndromes such as Wolff-Parkinson-White syndrome. -The basic defect in this disorder involves premature activation (preexcitation) of the ventricles by way of an accessory AV pathway that allows the normal SA-AV pathway to be bypassed. -This accessory pathway allows rapid conduction and short refractoriness, with impulses passed rapidly between atria and ventricles, and it provides a route for reentrant (backflow) tachyarrhythmias. Resultant paroxysmal tachycardia is characterized by a normal QRS complex, a regular rhythm, and ventricular rates of 150 to 250 beats per minute, along with sudden onset and termination.

Atrial fibrillation

AF is the most common sustained arrhythmia in adults. It is characterized by rapid, disorganized, and ineffective atrial contractions that occur at a rate of 350 to 600 beats per minute. -thereby promoting the formation of intraarterial clots, along with consequent embolism and stroke -Thus, patients with AF who are at risk for stroke (e.g., history of previous stroke, systemic emboli, valvular heart disease, hypertension, diabetes, coronary heart disease, heart failure) should be placed on a regimen of warfarin for antithrombotic therapy, with a target international normalized ratio (INR) of 2.0 to 3.0. -Patients who cannot take warfarin, as well as those who do not have risk factors for stroke, may be managed with dabigatran or aspirin therapy.

Perioperative risk and dental treatment with cardiac arythmias

Arrhythmias Associated with Major Perioperative Risk • High-grade atrioventricular (AV) block • Symptomatic ventricular arrhythmias in the presence of underlying heart disease • Supraventricular arrhythmias with uncontrolled ventricular rate Dental management: Avoid elective dental care. Arrhythmias Associated with Intermediate Perioperative Risk • Abnormal Q waves on electrocardiogram (ECG) (marker of previous myocardial infarction) Dental management: Elective dental care is appropriate. Arrhythmias Associated with Minor Perioperative Risk • ECG abnormalities consistent with: • Left ventricular hypertrophy • Left bundle branch block • ST-T wave abnormalities • Any rhythm other than sinus (e.g., atrial fibrillation) Dental management: Elective dental care is appropriate.

Premature atrial complexes

Impulses arising from ectopic foci anywhere in the atrium may result in premature atrial beats. Premature atrial complexes, or contractions, occur frequently in otherwise healthy people but often occur during infection, inflammation, or myocardial ischemia. 14 They may be provoked by smoking, lack of sleep, excessive caffeine, or alcohol. 13 They are common in conditions associated with dysfunction of the atria such as congestive heart failure.

Sinus arrhythmia

Sinus arrhythmia is characterized by phasic variation in sinus cycle length. In the respiratory type, heart rate increases with inhalation and decreases with exhalation. It is seen predominantly in the young and reflects variations in parasympathetic and sympathetic signals to the heart and is considered a normal event. Nonrespiratory sinus arrhythmia is unrelated to respiratory effort and is seen in digitalis intoxication.

Cardiac arrhythmia

which refers to any variation in the normal heartbeat, includes disturbances in rhythm, rate, or the conduction pattern of the heart 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. The most common type of persistent arrhythmia is atrial fibrillation (AF), which affects approximately 2.6 million people.