Cause: Mechanisms include increased automaticity of ectopic atrial focus (APC), triggered activity associated with disorders of repolarization, and reentrant arrhythmias involving accessory pathways between atria and ventricles (35-40%), within the AV node (60-65%), or within the SA node for SVT or in RA for Aflut, and macro-reentrant circuits within the atria. Afib may also be due to single, rapidly discharging focus, in which case elimination of the focus by radio-frequency ablation also eliminates the arrhythmia (Circ 1997;95:562).
Multifocal atrial tachycardia is typically seen in elderlypts with severe illnesses, most commonly COPD. The mechanism may be delayed after depolarization, leading to triggered activity (Chest 1998;113:203).
Epidem: Prevalence of PSVT is 225/1000 persons; incidence is 35/100,000 person-yr. Other CVD is present in 90% of malepts and 48% of femalepts. 90% ofpts have AV or AV node reentrant tachycardia (J Am Coll Cardiol 1998;31:150).
The lifetime risk of Afib is 1 in 4 for subjects > 40 yr old (Circ 2004;110:1042). Inpts > 65 yr, overall incidence of Afib is 192/1000 person-years (age 65-74: men, 176 and women, 101; age 75-84: men, 427 and women, 216). Use of diuretics, h/o valvular heart disease, CAD, advancing age, higher systolic BP, glucose, and LA size are all associated with increased risk of Afib (Jama 2001;285:2370; Circ 1997;96:2455).
SV arrhythmias occur in 76% ofpts undergoing noncardiac surgery. Correlates include male sex, age > 70 yr, significant valvular disease, h/o asthma, CHF, APC on pre-op EKG, and abdominal, vascular, and intrathoracic surgery (Ann IM 1998;129:279). Up to 33% ofpts will develop Afib after CABG. Predictors include age > 70 yr, male sex, HT, need for IABP, post-op pneumonia, mechanical ventilation > 24 hr, and h/oAfib or CHF (Circ 1996;94:390; Jama 1996;276:300). Post-op atrial pacing in conjunction with β-blockade reduces the incidence of Afib following CV surgery (J Am Coll Cardiol 2000;35:1411).
Up to 25% ofpts with ablation of Aflut develop Afib over 2 yr. The risk is 10% forpts with neither h/oAfib nor EF < 50%; 20% with either of these; and 74% with both (Circ 1998; 98:315).
Pathophys:
PSVT: In 90% ofpts with AV node reentrant tachycardia, anterograde conduction occurs over the slow atrioventricular nodal pathway and retrograde conduction over the fast pathway. In mostpts, posterior atrionodal input to the AV node serves as the anterograde limb of the reentry circuit, and anterior atrionodal inputs serve as the retrograde limb (Nejm 1995;332:162; 1999;340:534).
Aflut: Due to macro-reentry involving counterclockwise reentrant activation of RA. The critical element of the reentrant circuit is the isthmus between the IVC and tricuspid valve annulus.
Afib: Pts with AMI are prone to Afib. Predictors are 3-vessel CAD, advanced age, higher peak CK levels, worse Killip class (IV vs I), and increased heart rate. The unadjusted mortality rate is higher at 30 d (14.3% vs 6.2%) and at 1 yr (21.5% vs 8.6%) in patients with Afib (GUSTO-I; J Am Coll Cardiol 1997;30:406).
After cardioversion of chronic Afib to NSR, there is a gradual increase of 56% in CO over 4 wk, due to return and increasing strength of LA mechanical activity. CO decreases transiently after cardioversion of Afib in > 1/3 ofpts; the decrease may last 1 wk (Arch IM 1997;157:1070).
Sx: Palpitations; may be associated with lightheadedness, dyspnea, and nausea. Pts treated with radio-frequency ablation report an improvement in sx (Circ 1996;94:1585).
Si: Irregular heartbeat; tachycardia
Crs: In the Framingham Heart Study, Afib was associated with a 15-to 19-fold higher mortality risk after adjustment for preexisting CV conditions (Circ 1998;98:946).
Inpts with CHF and Afib, amiodarone produced conversion to NSR in 31% and reduced incidence of recurrent Afib. Pts who converted to NSR had a lower mortality rate than those who did not (Circ 1998;98:257).
Cmplc: 15% ofpts presenting with Afib will have atrial thrombi identified by TEE. Pts with Afib have an annual stroke rate of 45%; the rate is 14% for anticoagulatedpts. The risk of stroke in Afibpts is 15% for age 50-59 vs 23.5% for age 80-89 (Framingham). Pts with previous TIA, CVA, or systemic embolism; age > 75 yr; HT; poor LV function; prosthetic heart valve (mechanical or tissue valve); or rheumatic mitral valvular disease have an increased risk. Diabetes, CAD, age 65-75 yr, or thyrotoxicosis may also increase this risk (Chest 1998;114:S579).
Forpts with Afib clinically estimated to have lasted < 48 hr, the likelihood of cardioversion-related clinical thromboembolism is 0.1%. Approximately 67% will convert spontaneously (Ann IM 1997;126:615).
Inpts with Afib for < 2 wk before cardioversion, normal atrial mechanical function returns within 24 hr of cardioversion. Pts with Afib present for 2-6 wk require up to 1 wk, and those with Afib for < 6 wk require up to 3 wk for full recovery of atrial mechanical function (Circ 1998;98:479). Overall, effective mechanical atrial function is recovered by 68% ofpts by 3 and by 76% by 7 after cardioversion. Electrical cardioversion produces a greater degree and longer duration of mechanical atrial dysfunction than those who convert pharmacologically or spontaneously (J Am Coll Cardiol 1997;30:481).
Pts with Aflut are also at risk for thromboembolus postcardioversion (J Am Coll Cardiol 1997;29:582). In one series, TEE showed LA thrombus in 11% ofpts with Aflut for 4 ± 9 wk (Circ 1997; 95:962).
Lab: Thyroid function, electrolytes
EKG: (See Chapter 3 for EKG diagnostic criteria.) Wolff-Parkinson-White syndrome—ventricular depolarization through AV node and accessory pathways, with reentrant tachyarrhythmias and characteristic short PR interval and delta wave
TEE: Features independently associated with increased thromboembolic risk in Afib include LA appendage thrombi, dense spontaneous echo contrast, LA appendage peak flow velocity < 220 cm/sec, and complex aortic plaque. Pts with h/oHT have an increased incidence of atrial appendage thrombi on TEE. The presence of complex aortic plaque also distinguishespts with Afib at high risk from those at moderate risk of thromboembolism (J Am Coll Cardiol 1998;31:1622; Ann IM 1998;128:639).
PSVT: More than 90% of tachycardias due to AV or AV nodal reentry are terminated by a 12-mg dose of adenosine. Adenosine also frequently terminates sinus-node reentrant tachycardia and occasionally terminates unifocal atrial tachycardia (Nejm 1995;332:162).
Table 7.1 Acute Management of Stable Regulator Tachycardias
600 mg/day for 2 wk, then 200-400 mgqd (lower dose is preferable)
iv amiodarone moderately effective for conversion, but onset is slow. Good rate slowing in Afib. Not FDA approved for this indication.
Ibutilide
1 mgiv over 10 min in patients weighing ≥ 60 kg, or 0.01 mg/kg over 10 min in patients weighing < 60 kg; may be repeated once if arrhythmia does not end within 10 min after end of initial infusion
Not available for maintenance (iv formulation only)
Do not use in patients with hypokalemia, a prolonged QT interval, or torsades de pointes.
1. Iv flecainide and propafenone (the doses of which are given in parentheses) are not available in the United States.
Source: Reprinted with permission, Falk, Medical Progress. Atrial Fibrillation 2001;344:1067-1078, New England Journal of Medicine.
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