RFA of the AP is the treatment of choice. The most useful drugs are \202 e- cainide and p ropafenone, which slow conduction in the accessory pathway and the AV node. Verapamil, dilt iazem, and B-blockers should be used only when there is no history of atrial \201 brillat ion, there is no antegrade conduction during tachycardia, or the AP is known to have a long ante- grade refractory period. FP AVN SP Left side AP Figure 9.7 Mechanism of AVNRT and AVRT. Both AVNRT and AVRT have reentrant mechanisms. Orth odromic AVRT via a left-sided accessory pathway (AP) (above). Activation from A to V is dow n the atrioventricular node (AVN), then across the ventricular myocardium and back from V t o A up the AP, thus completing the circuit. The ventricle therefore is an essential part of the circuit. Antidromic AVRT (not shown) would activate in the opposite direction. Typical AVNRT (below) activates from the atrium to the AVN via the slow pathway (SP) and from the AVN to the atrium via the fast pathway (FP) thus completing the circuit. The ventricle is a ctivated as a bystander via the bundle of His and is not an essential part of the circuit. Atypical AVNRT (not shown) activates in the opposite direction. ATRIAL FIBRILLATION 377 Junctional tachycardia This term should only be used for focal tachycardias that originate from the AV nodal tissue directly. They are rare in adult cardiology. Distinction from othe r forms of narrow complex tachycardia is only possible at the EP study. RFA is high risk as the AV node may be damaged. B-Blockers and \202 ecai- nide, and propafenone are effective. Atrial \201 brillation Atrial \201 brillation (AF) is the most common sustained cardiac arrhythmia with a prevalence of 0.5% \200\2231% in the general population but 10-fold grea ter in those aged over 65. It is an atrial arrhythmia where uniform activation is replaced by chaos, such that coordinated contractile function is lost and the atria dilate. It is ch aracterized by an ECG lacking consistent P waves and a rapid, often irregular ventricular r ate. Classi \201 cation Previously, many terms were used to classify AF. However, now an inter- national consensus on nomenclature has been reached,1 allowing the cor- rect selection of management options for patients. All episodes of AF lasting >30 seconds should be described as follows: \200 or a recurrent episode \200 \200 \200 \200 First detected Self terminating Symptomatic Paroxysmal Persistent regardless of how it term inates) Permanent cardioversion) Lone idiopathic (in the absence of any disease) or not self terminating or asymptomatic (if self-terminating within 7 days) (if cardioverted to SR by any means or lasts >7 days (if it does not terminate or relapses within 24 hours of (in the absence of underlying structural heart disease) or Causes (see Table 9.2) AF is a common end point for many forms of cardiac disease where atr ial myocytes are damaged or subject to adverse stress generated by ischemia, cyanosis, elev ated intracavity, or pericardial pressures. These changes are hypothesized to alter the con duction properties of the myocardium facili- tating \201 brillation. 1 Levy S, Camm AJ, Saksena S, et al. (2003). International consensus on nomenclature and cl assi \201 ca- tion of atrial \201 brillation. J Cardiovasc Electrophysiol 14:443 \200 \223445. CHAPTER 9 Arrhythmias 378 Table 9.2 Causes of atrial \201 brillation Common \200 \200 Potentially reversible \200 \200 \200 \200 \200 \200 Rare \200 Congenital heart disease Autonomic \200\234vagal \200\235 overactivity Pericardial effusio n Cardiac metastases Myocardial in \201 ltrative diseases (e.g., amyloid) Atrial myxoma Alcohol binge Hyperthyroidism Acute MI Acute pericarditis Myocarditis Exacerbation of pulmo nary disease Pulmonary embolism Cardiac surgery Hypertension Left ventricular failure (any cause) Coronary artery disease Mitral or tricusp id valve disease HCM COPD \200 \200 \200 \200 Symptoms and signs Palpitations, dyspnea, fatigue, presyncope, syncope, and chest pains are common. However, 30% of patients present with AF as an incidental \201 nd- ing only. Amb ulatory monitoring reveals that even patients with sympto- matic paroxysmal AF have many as ymptomatic episodes. Physical \201 ndings are an irregular pulse (which, if rapid, will be faster at the apex than wrist), variable intensity of the \201 rst heart sound, and absent a-waves in the JV P. ATRIAL FIBRILLATION: EVALUATION 379 Atrial \201 brillation: evaluation A reversible cause should be sought early to allow app ropriate treatment. The most important investigations are the following: \200 ECG: on intact AV nodal function. In the presence of complete AV nodal block a slow regular junctional or ventricular escape rhythm is present. The QRS will be broad if there is aber rant conduction; ST-T wave changes may be due to rapid rate, digoxin, or underlying cardiac disease. CXR: calci \201 cation (MS) Chemistries: Cardiac enzymes: Thyroid function: Live r function tests Drug levels: Arterial blood gas (ABG): Echocardiogram (TTE TEE): perica rdial effusion, and to exclude intracardiac thrombus prior to conversion to SR. LA size is an important predictor of likely future maintenance of SR. Other investigations irregular ventricular rate and absence of P waves. V rate depends cardiomegaly, pulmonary edema, intrathoracic precipitant, valve \200 \200 \200 \200 \200 \200 hypokalemia, renal impairment; check Mg2+, Ca2+ ?MI. Small rise after DC shock thyrotoxicosis may present as AF only. especially if patient is taking digoxin if hypoxic, in shock or ?acidotic for LV function, valve lesions, and depend on suspected precipitant. Other investigations when patient is stable Use a 24-hour ambulatory monitor to assess hear t rate control and look for intermittent AF or bradycardia. CXR, exercise testing (or other ischemia stress test), and coronary angiography can also be used. Management There is some controversy regarding the ideal strategy for management of atrial \201 brillation. However, depending on the clinical situation and the patient \200\231s l evel of symptoms, a rate or rhythm control strategy may be preferable. Currently available antiarrhythmic drugs (AADs) are limited by their toxicity, including pr oarrhythmia, and if a rhythm control strategy is cho- sen, AAD administration should be und ertaken in concert with a specialist. Patients should remain on anticoagulation with warfar in to decrease the incidence of thromboembolic complications regardless of whether a rate o r rhythm control strategy is chosen. Emergency management If the patient is hemodynamically compromised, then urgent external sy nchronized DC cardioversion under general anesthesia or sedation is needed. This is rarely necessary; usually rate control is suf \201 cient to acutely control symptoms. CHAPTER 9 Arrhythmias 380 If symptoms persist despite rate control, cardioversion can be attempted pharmacologically with ibutilide 1 mg over 10 minutes repeated x1, \202 ecai- nide (2 mg/kg, max 150 mg, in fused via a peripheral line over 30 minutes) or if LV dysfunction is suspected, amiodarone (5 mg/kg, max 300 mg; gen- erally, 150 mg IV over 10 minutes repeated x 1). Patients must be monitored throughout for possible ventricular arrhyth- mia, bradycardia, a nd hypotension. If AF has been present for >48 hours, cardioversion should be preceded by a TEE to exclude atrial thrombus. All patients should be anticoagulated with Coumadin for at least 4 weeks post-cardioversion . Decisions regarding long-term anticoagulation should be made on the basis of the patient \200\231s risk pro \201 le. ATRIAL FIBRILLATION: MANAGEMENT 381 Atrial \201 brillation: management Rate control Drugs The \201 rst-line agents are B-blockers or nondihydropyridine calcium- channel antagonists (verapamil or diltiazem), which are effective during both exercise and rest. Digoxin is effective only at rest and should be considered a second-line agent. Rhythm control If symptoms are not improved by rate control alone, the restoration and main tenance of SR should be attempted. The trials of rate vs. rhythm control underrepresent you nger patients (<65 years old), so in this group an aggressive strategy of rhythm control ma y be warranted regardless of symptoms. Drugs Flecainide, sotalol, dofetililide, propafenone, disopyramide, and quinidine are more effective than placebo in maintaining SR. They may contribute to QT prolongation or prolong ation of the action potential duration and can be associated with the development of VT/VF. They should initially be administered while under the supervision of a specialist and are relatively contraindicated in patients with impaired LV function and/or underlying coronary artery disease. Amiodarone is the most effective antiarrhythmic drug and is not associ- ated with VT/VF, as seen in the other AADs. However its use is limited by noncardiac toxicities and is not tol erated in up to 25% of patients. Pacemakers While various pacemaker strategies are hypothesized to be useful in main- tainin g SR, the data are limited. Atrial pacing modes (AAI or DDD) are preferable to reduce the A F burden. \200 \200\234Vagal AF \200\235 is prevented by pacing. \200 SA node disease symptoms are improved by a \200\234block and pace \200\235 regimen: rate-controlling drugs for AF and pacing for bradycardic episodes. Trigger suppression. Atrial ectopy that initia tes AF may be prevented by use of pacemakers with speci \201 c algorithms to pace the atri um just faster than the native rhythm or brie \202 y pace rapidly following detection of a n atrial ectopic. This is currently a class III indication for implantation of a permanent pacemaker in the absence of another indication for pacemaker therapy. Multisite pacing. By reducing the intra- and interatrial activation time, the tendency to AF may be reduced. CHAPTER 9 Arrhythmias 382 Atrial de \201 brillators With limited data and not commonly used, they are thought to wor k by promptly cardioverting each episode of AF, preventing remodeling of the atria. AF epis odes may be reduced and quality of life may improve. However, even though shocks are low en ergy (1 \200\2232 J) they are painful. Careful patient selection is required, and current c linical use is limited. Catheter and surgical ablation Pace and ablate When adequate rate or symptom control is not possible with drugs or their side effects are not tolerated, a permanent pacemaker may be implanted followed by radiofrequency ablation of the AVN. This achieves rate control and th erefore symptom improvement but renders the patient pacer dependent and should only be chos en as a last resort. Anticoagulation Both aspirin (325 mg daily) and warfarin (INR 2 \200\2233) reduce strokes i n AF. Decisions regarding anticoagulation strategy depend on the patient \200\231s over- al l stroke risk, and no distinction should be made between paroxysmal, persistent or permanen t AF. The CHADs score is a clinical prediction tool used to estimate the risk of stroke in nonval vular atrial \201 brillation.1 Patients receive a risk score based on the presence of con gestive heart failure, hypertension, age >75, diabetes, and prior stroke or TIA. The risk i ncreases with the number of features present. Those patients having two or more features ar e catego- rized as having moderate to high risk of stroke per year ((cid:116)4%/year), and it is suggested that they be maintained on warfarin therapy. Those with one risk factor are at moderate risk (2.8%/year), and 0 are low risk. The ACC/AHA/ESC guidelines (Table 9.3) for anticoagulation in atrial \201 brillation take into account the risk factors included in the CHADs model as well as additional factors. 1 Gage BF, van Walraven C, Pearce L, et al. (2004). Selecting patients with atrial \201 b rillation for anticoagulation: stroke risk strati \201 cation in patients taking aspirin. Circulation 110(16):2287 \200\2232292. ATRIAL FIBRILLATION: MANAGEMENT 383 Table 9.3 Guidelines for anticoagulation in atrial \201 brillation (modi \201 ed from AC C/AHA/ESC guidelines for AF 2006 \200 ) Condition Recommendation <60 years old Normal heart (lone AF) Aspirin 81 \200\223325 mg/day or no therapy <60 years with heart disease but no other risk factors Aspirin 81 \200\223325 mg/day Age 60 \200\22374 with no risk factors Aspirin 81 \200\223325 mg/day Age 65 \200\22374 with diabetes mellitus or CAD Warfarin (INR 2 \200\2233) >75 years old Warfarin (INR 2 \200\2233) Age 65 or older, heart failure Warfarin (INR 2 \200\2233) LV ejection fraction <35% Warfarin (INR 2 \200\2233) Rheumatic heart disease Warfarin (INR 2 \200\2233 or higher) Prosthetic heart valves Warfarin (INR 2 \200\2233 or higher) Persistent atrial thrombus on TEE Warfarin (INR 2 \200\2233 or higher) Prior thromboembolism* Warfarin (INR 2 \200\2233 or higher) Risk factors for thromboembolism: heart failure, LV ejection fraction <35%, hypertension, p revious thromboembolic event. \200 Fuster V, Ryden LE, Cannom DS, et al. (2006). ACC/AHA/E SC Guidelines for the Management of Patients with atrial \201 brillation. Circulation 114 :e257 \200\223e354. CHAPTER 9 Arrhythmias 384 Ventricular tachycardia This section deals with diagnosis and pharmacological management. M echanisms and ablation are discussed in detail in Chapter 13. The most important distinctio n is the presence of structural heart disease. Impaired LV function is the strongest predic tor of a poor prognosis. VT IN THE NORMAL HEART ( \200\234BENIGN \200\235 VT) 385 VT in the normal heart ( \200\234benign \200\235 VT) Right ventricular out \202 ow tract ( RVOT) tachycardia This is due to the automatic \201 ring of cells in the RVOT, giving a c harac- teristic ECG pattern of LBBB with a strongly inferior axis (see Fig. 9.8). Paroxysms of palpitation may be related to exercise. The tachycardia is often adenosine sensitive. Usually symptoms are well controlled by verapamil or a B-blocker, but RFA is a potentially curative option. Care must be taken to exclude arrhythmogenic right ventricular car- diomyopathy (ARVC), par ticularly if the ECG or echocardiogram is not typical. LVOT tachycardia (RBBB + inferior ax is) is also recognized. Fascicular tachycardia This is a reentrant tachycardia emerging most commonly from the left posterior fascicle. ECG typically shows RBBB with superior axis (see Fig. 9.9). It is ofte n sensitive to IV verapamil (which normally slows then ter- minates it) but not adenosine. Symptoms are well controlled with oral verapamil or class Ic AADs, but RFA offers a cure. CHAPTER 9 Arrhythmias 386 Figure 9.8 Intermittent right ventricular out \202 ow tract (RVOT) tachycardia and sinus r hythm. During the tachycardia beats, notice the left bundle branch block appearance and the positivity in leads II, III, and aVF, indicating an inferior axis. Figure 9.9 12 lead ECG of fascicular tachycardia suggested by broad complex tachycardia wit h right bundle branch block appearance and superior axis. VT WITH IMPAIRED LV FUNCTION 387 VT with impaired LV function Symptoms Palpitations, chest pain, presyncope, syncope, dyspne a, pulmonary edema, and sudden death can all occur. How well patients tolerate the arrhythm ia depends mainly on their LV function and the tachycardia rate. Etiology Any cause of impa ired LV function can predispose to VT. Common causes are coronary artery disease, dilated c ardiomyopathy, and HCM. VT is often due to reentry around areas of scarred or diseased myoc ardium. VT may rapidly deteriorate to VF, and these patients may present with sudden death. General management It is essential to treat the underlying heart failure and cause (ACE in hibi- tors, B-blockers, diuretics, nitrates, statins). This reduces not only the symptoms b ut also the incidence of arrhythmia. Preventing SCD Implantable cardiac de \201 brillators (ICDs) have dramatically improved sur- vival for these patients and are indicated for both primary and secondary prevention. Long-term antiarrhythmic treatment B-Blockers may reduce arrhythmia and SCD, but the impact of other drugs is minimal and may be harmful. Flecainid e, propafenone, and sotalol have been associated with increased mortality and should be avo ided, except in patients with ICDs under supervision of an electrophysiologist. Amiodarone and mexilitine have a neutral impact on prognosis but may reduce the number of VT episodes and thus ICD therapy. RFA is possible in certain situations when the VT is slow and relatively well tolerated. CHAPTER 9 Arrhythmias 388 Arrhythmogenic right ventricular cardiomyopathy (ARVC) This is an uncommon genetic disorder resulting in fatty \201 broin \201 ltration of the RV myocardium. The scarring predispo ses to VT of RV origin. The ECG in tachycardia has an LBBB appearance but in SR it may be normal or have a terminal notch in the QRS (epsilon wave) or T-wave inversion in V1 \200\223V3. It is a progressive disease, associated with worsening RV function (lead- ing to symptoms of heart failure), arrhythmia, and sudden death. The diagnosis is indicated by a typical ECG VT appearance and evidence on echocardiogram (l ate) or MRI (early) of RV impairment, dilatation, and fatty in \201 ltration. RV biopsy is not necessary. Signal-averaged ECG is often abnormal and may be used to differentiate ARVC from RVOT VT. An ICD is warranted to decrease the risk of sudden cardiac death (SCD). Drug management inc ludes \202 ecainide, sotalol, amiodarone, and B-blockers. However, they have limited pote ntial in preventing SCD. Disarticulation of the RV from the LV (thus electrically isolating RV arrhythmias) has been used in dif \201 cult cases. BRUGADA SYNDROME 389 Brugada syndrome This is an important form of idiopathic VT and VF. It is an autosomal domi - nant condition with variable penetrance and is characterized by a defect in the SCN5A gen e, causing loss of function in the sodium channel. Patients are mainly found in Southeast A sia and are mostly men (M:F 8:1). The heart is otherwise normal and the \201 rst manifestation may be VF or a very rapid, u nstable VT. The hallmark feature is an RBBB appearance with ST elevation in leads V1 \200 \223V3. A \202 ecainide challenge will reveal the ECG abnormality if not already present (see Fig. 9.10). Perform serial ECGs after administration of \202 ecainide 2 mg/kg body weight IV in 10 mi nutes, or procainamide 10 mg/kg IV in 10 minutes. The test is positive if an additional 1 m m ST elevation appears in leads V1, V2, and V3. All positive individuals should undergo EP studies and further specialist evaluation. The primary therapy is ICD to prevent SCD, although there is a sugges- tion that quinidine may be helpful. Figure 9.10 Brugada ECG with \202 ecainide challenge. A typical Brugada ECG with arrows m arking the characteristic prominent coved ST-segment elevation in the right precordial lead s, (cid:116)2 mm at its peak, followed by a negative T wave with little or no isoelectric s eparation. Intravenous \202 ecainide (2 mg/kg, max. 150 mg; in 10 minutes) exaggerate the ST changes or reveals them if initially absent.1 1 Wilde AA, Antzelevitch C, Borggrefe M, et al. (2002). Proposed diagnostic criteria for th e Brugada syndrome. Consensus report. Circulation 106:2514 \200\2232519. CHAPTER 9 Arrhythmias 390 Bundle branch tachycardia This is a reentry circuit when activation circuits up one bundle branch and down the other (in either direction). It only occurs in diseased ventricles with delayed conduction in the bundles. It is con \201 rmed only during EP study and is treate d with RFA. Torsades de pointes (TdP) See Long QT Syndrome (p. 391). LONG QT SYNDROME 391 Long QT syndrome Long QT syndrome (LQTS) is a fascinating condition of which our under- sta nding of the genes, molecular function of the myocyte, and clinical expression of the disea se has evolved rapidly over recent years. The iden- ti \201 cation of genetic mutations th at code for protein elements of speci \201 c ion channels has taught us more about the lin k between genotype and phenotype than any other cardiologic disorder. Pathology LQTS is due to prolonged repolarization of the ventricular myocyte, which is mani fest as a lengthened QT interval on the ECG and predisposes to ventricular tachycardia in t he form of torsades de pointes (TdP), VF, and sudden cardiac death. The cardiac action potential is generated by at least 10 distinct but \201 nely balanced ionic currents (principally gating the \202 ow of Na+, K+, and Ca2+ ions across the cell membrane). A functional abnormality in any of these, whether acquired or genetic, that acce ntuates depolarizing currents or attenuates repolarizing currents, can potentially lead to LQTS. Congenital LQTS Two inherited forms of LQTS are well known. The more common Romano \200\223 Ward syndrome (autosomal dominant with variable penetrance) has no other phenotypic feature s, and the much rarer Jervell Lange \200\223Nielson syndrome (autosomal recessive) is assoc iated with deafness. A modern gene-based classi \201 cation, however, has now replaced the se eponymous syndromes, and 10 chromosome loci (LQTS1 \200\22310) coding for 10 genes have been identi \201 ed (see Table 9.4). Each genetic syndrome can also be characterized by di stinct clinical features. There is an interaction between congenital and acquired forms. Carriers of genetic abnormal ities may not manifest the overt ECG changes. However, if challenged by a QT-prolonging dru g such as erythromycin, they are at risk of developing torsades and sudden death. Acquired LQTS (see Table 9.5) Clinical features The unmistakable hallmark of LQTS is recurr ent syncopal episodes precip- itated by emotion or physical stress or at rest. The arrhythm ia is torsades de pointes, often preceded by a short \200\223long \200\223short cardiac cyc le (Fig. 9.11). This bradycardia-related phenomenon is more common in the acquired form. Th e clinical features of the congenital form are related to the spe- ci \201 c genetic mutat ion (see Table 9.4). Unfortunately, the \201 rst clinical event can be sudden cardiac dea th. ECG: QTc values are typically >460 ms but may be as long as 600 ms. The T-wave pattern may give a clue to the gene involved. In affected families a normal QT interval does not ru le out genetic carrier status. The degree of QT prolongation varies across the ventricle, s o QT dispersion, if measured, is also greater. QT 0.38 \200\2230.46 sec Normal QTc = = (cid:151)(RR interval) (9 \200\22311 small squares) 3 9 2 C H A P T E R Table 9.4 Characteristics of currently identi \201 ed congenital LQTS LQTS subtype Gene Frequency Effect dK+ ef \202 ux Clinical features ECG \201 nding 9 A r r h y t h m i a s 1 KVLQT1 30% \200\22335% Syncope with exercise or acute emotional reactions Broad, late-onset T wave Syncope with ex ercise, emotions, or awakening to an alarm Widely split, low-amplitude T wave Symptoms at r est rather than when excited. Young age and usually presents as sudden death Biphasic or pe aked, late-onset T wave Variable QT prolongation dK+ ef \202 ux 2 HERG 25% \200\22330% Prolonged Na+ in \202 ux 3 SCN5A 5% \200\22310% 4 Ankyrin-B 1% \200\2232% Increased Na+ within the cell and Ca2+ outside the cell dK+ ef \202 ux dK+ ef \202 ux dK+ ef \202 ux Prolonged Ca2+ in \202 ux Prolonged Na+ in \202 ux Prolonged Na+ in \202 ux 5 6 7 8 9 10 Mink MiRP1 KCNJ2 CACNA1C CAV3 SCN4B 1% Rare Rare Rare rare Extremely rare \200\2241 family Not de \201 ned Not de \201 ned Modest QT prolongation Exaggerated QT prolongation Not de \201 ned Not de \201 ned Potassium currents (Ik) are repolarizing and the sodium currents (INa) are depolarizing. Th e ankyrin-B gene codes not for an ion channel but for a cellular structural protein that bi nds sodium ion channels.1 1 Splawski I, Shen J, Timothy KW, et al. (2000). Spectrum of muta tions in long-QT syndrome genes. Circulation 102:1178 \200\2231185. LONG QT SYNDROME 393 Table 9.5 Common causes of acquired LQTS Drugs* Antiarrhythmics Quinidine, procainamide, disopyramide, \202 ecainide, propafenone, sotalol, ibutilide, do fetilide, amiodarone (rare) Antimicrobials Erythromycin, clarithromycin, trimethprim, ketoconazole, itraconazole, chloroquine Antihistamines Terfenadine Other drugs Amitriptyline, \202 uvoxamine, chlorpromazine, domperidone, cisapride, glibenclamide Other causes Electrolyte imbalance Hypokalemia, hypomagnesemia, hypocalcemia Severe bradycardia Complete heart block, sinoatrial node disease, hypothyroidism, hypothermia Note: This is not a comprehensive list, and LQTS is the most common single reason for new d rugs being withdrawn. 3 9 4 C H A P T E R 9 A r r h y t h m i a s Figure 9.11 Torsades de pointes. A continuous tracing from 3 leads of a patient monitored o n CCU. The \201 rst complex is a sinus beat followed by 2 ectopics. There is then a long pause (2s) followed by another sinus beat. LONG QT SYNDROME: MANAGEMENT 395 Long QT syndrome: management Usually episodes of torsades de pointes (TdP) are short-lived and termi- nate spontaneously. However, a prolonged episode causing cardiovascular compromi se needs immediate treatment with DC cardioversion. For recurrent bursts or following a cardiac arrest, give IV magnesium bolus and infusion, f ollowed by urgent temporary pacing (at rate 90 \200\223110) if necessary. An isoproterenol infusion may be used to increase the ventricu- lar rate and shorten the QTc while pacing is being arranged. Acquired The underlying cause should be identi \201 ed and reversed. Stop the offend- ing drugs. Give Mg2+ before getting blood results. K+ can be checked rap- idly with a blood gas analyzer; replace if <4 mmol/L and aim to achieve high normal levels. Long-term treatment is not usually necessary. However, a permanent pacemaker is required if nonreversible heart block was the cause or if there is signi \201 cant underlying bradyca rdia predisposing to TdP. Congenital As most events are triggered by sudden increases of sympathetic activ- ity, trea tment is aimed at preventing this. The \201 rst choice is B-blockade. Propanolol reduces events in symptomatic patients. If full B-blockade can- not be achieved or is not tolerated , surgical left cardiac denervation is an alternative. Cardiac pacing is useful to alleviate the B-blocker-induced bradycardia and where pauses ha ve been identi \201 ed to precipitate symptoms (LQT3). Pacing is never the sole treatment in congenital LQTS. ICDs should only be used with careful consideration, i.e., for patients at high risk of SCD or when a resuscitated cardiac arrest was the \201 rst event. ICDs prevent SCD but not T dP, and recurrent distressing shocks for non- sustained episodes can ruin a patient \200 \231s life. Careful patient selection, concomitant use of B-blockers, and shrewd device programming minimize inappropriate therapies. Asymptomatic patient Screening of affected families reveals patients with LQTS who have nev er had symptoms. Most patients do not die from LQTS but all are at risk (13% incidence of f atal events over a lifetime if untreated). A balance must be struck between lifelong treatm ent with associated side effects and the risk of sudden death. Predicting risk is extremely dif \201 cult but is helped by knowledge of the baseline QTc and of the genetic abnormality. A recent study suggested treatment in LQT1 if QTc >500 ms ( men + women); in LQT2 for all men if QTc >500 ms and all women; and in LQT3 for all patient s. All patients need individual counseling.1 1 Priori SG, Schwartz PJ, Napolitano C, et al. (2003). Risk strati \201 cation in the long -QT syndrome. N Engl J Med 348:1866 \200\2231874. CHAPTER 9 Arrhythmias 396 Arrhythmia in special situations Pediatrics Arrhythmia may occur at any stage in the pediatric population, from fetal life t o adolescence. Fetus and neonate AVRT and atrial \202 utter are the usual cause of tachycardia. If persi stent, hydrops fetalis may result. The majority of AVRT cases resolve spontan- eously in ut ero or by 1 year of age, although recurrences later in life may occur. Ablation may be nece ssary. Congenital heart block occurs mediated by maternal anti-Ro/SSA anti- bodies and if severe m ay also cause hydrops fetalis. This always persists after birth and usually requires perman ent pacing, although timing depends on the stability of the subsidiary pacemaker. Infancy and childhood AVRT is the usual (80%) cause of tachycardia. AVNRT is rare in infanc y, but becomes increasingly common in teenage years. Focal atrial tachycar- dias and a spec i \201 c form of AVRT mediated by a slow atrial septal acces- sory pathway (persistent jun ctional reciprocating tachycardia) both lead to incessant tachycardia and profound ventricu lar dysfunction (tachycardia- induced cardiomyopathy). This usually completely resolves with successful therapy. Radiofrequency ablation is now co mmonly performed in older children and may also be used in refractory arrhythmias in neonat es and young infants when necessary. Congenital heart disease Arrhythmias in association with congenital cardiac lesions are poo rly tol- erated, and if uncontrolled may lead to a rapid decline in ventricular func- tion and cardiac output. Supraventricular tachycardia These are a major cause of both morbidity and mortality in con genital heart disease. Accessory pathways are associated with Ebstein \200\231s anomaly and congenitally corrected transposition of the great arteries and this results in AVRT. Macro -reentrant \200\223atrial tachycardia is common late fol- lowing the Mustard, Senning, or F ontan procedures. This condition is notoriously dif \201 cult to control with medication, and although ablat ion (either percutaneous or surgical) is commonly successful acutely, arrhythmia recurrence is a problem. Pacing has also been used. Ventricular tachycardia VT is seen in Ebstein \200\231s anomaly and following repair of tet ralogy of Fallot. Treatment may involve radiofrequency ablation, antiarrhythmic drugs, or a n ICD. ARRHYTHMIA IN SPECIAL SITUATIONS 397 Pregnancy The hemodynamic and hormonal changes associated with pregnancy may unmask arrhyth mic substrates for the \201 rst time or exacerbate pre-existing arrhythmic conditions. Ge stational palpitations are common, and most frequently there is an increased awareness of p hysiological tachycardia. If new ventricular arrhythmias occur, peripartum cardiomyopathy should be actively excluded . Attention should be given to the safety of medica- tions and diagnostic procedures consid ered during pregnancy. CHAPTER 9 Arrhythmias 398 Permanent pacemakers Introduction Permanent pacemakers can pace and sense in one, two, and/or even three chamber s of the heart. There are two types of lead: unipolar, which has one electrode in the heart , the other being the casing of the pulse gen- erator ( \200\234active can \200\235), and b ipolar, where there are two closely spaced electrodes in the heart. International code This three-letter identi \201 cation code describes the basic function of the pacing system. The \201 rst letter is the chamber(s) paced and the second letter i s the chamber(s) sensed: V = ventricle, A = atrium, D = dual (i.e., A+V). The third letter indicates how the device responds to a sensed event: I = inhibits, T = triggers, D = dual ( i.e., I+T), and O = nothing. Often a fourth letter is used to describe added features of th e device, e.g., R = rate responsiveness. Implantation Most pacemakers are implanted transvenously using the cephalic or sub- clavian vein. An incision is made about 2 cm below the clavicle across the deltopectoral groove. T he cephalic vein is isolated and is often of suf \201 cient caliber to accept two pacing w ires. Alternatively, a guide wire can be introduced followed by introducer sheaths to provide acc ess. Sometimes the cephalic vein is not suitable and the leads have to be introduced via pu ncture of the subclavian vein using the Seldinger technique. The ventricular lead is most c ommonly placed in the RV apex. RV out \202 ow tract or on the septum, an active \201 xat ion lead is required. The atrial lead is placed in the right atrial appendage ideally, but any- where in the RA w ith adequate pacing parameters is acceptable although likely to require an active \201 xa tion lead (Table 9.6). After both leads are placed in acceptable positions, they are then secured and attached to the pulse generator, which is placed either subcu- taneously or beneath the pectoral muscle s. Indications for permanent pacing are listed in Box 9.8. Table 9.6 Acceptable pacing parameters for new leads Atrium Ventricle Threshold* <1.5 V <1.0 V Sensitivity >1.5 mV >4.0 mV Slew rate >0.2 V/sec >0.5 V/sec Impedance 400 \200\2231000 ohms 400 \200\2231000 ohms Using a pulse width of 0.5 ms. PERMANENT PACEMAKERS 399 Box 9.8 Indications for permanent pacing De \201 nite indications \200 Symptomatic third-degree heart block \200 \200 \200 Symptomatic advanced second-degre e heart block Third-degree or advanced second-degree heart block in patients with atrial \201 brillation and bradycardia with pauses of >5 seconds Advanced second-degree heart bloc k with pauses Bifasicular block with intermittent third-degree, second-degree block or alte rnating bundle branch block Trifasicular block with intermittent third-degree or second-deg ree block After STEMI in the presence of persistent high-grade AV block Symptomatic sinus n ode dysfunction Symptomatic chronotropic incompetence Carotid sinus hypersentivity with rec urrent syncope Sustained VT caused by pauses Conditions requiring drugs that result in symp tomatic bradycardia Bradycardia with symptoms Pauses (cid:116)3 seconds Awake ventricular rates <40 bpm \200 \200 (cid:116)3 seconds \200 \200 \200 \200 \200 Relative indications \200 Asymptomatic third degree block with V rate <40 or second degree (type II) with distal hear t block Sinus node dysfunction (SND) with HR <40 and where symptom \200\223 ECG correlation is not available Syncope and SND evident on EPS High-risk patients with long QT syndrome C hronic chronotropic incompetence (HR <40) Neurocardiogenic syncope with signi \201 cant br adycardia on tilt testing Symptomatic HCM with out \202 ow gradient \200 \200 \200 \200 Adapted from ACC/AHA/ \200\231NASPE 2008 Guidelines. J Am Coll Cardiol 2008; 51(21):2085 \200\2232105. CHAPTER 9 Arrhythmias 400 Which pacing modality? The vast majority of patients should have atrial-based pacing (i.e., either AAI or DDD) (see Fig. 9.12). Ventricular-only pacing leads to a greater incidence o f AF and potential pacemaker syndrome. Bradycardic Patient No P waves VVI(R) Permanent AF Yes Sinus bradycardia - Sick sinus syndrome (SSS) No Consider AAI(R) AV conduction abnormal? No Yes 2nd & 3rd degree HB - Bi & trifasicular block - Carotid sinus syncope No DDD(R) LBBB and poor LV function? Yes Biventricular Pacing Figure 9.12 Algorithm to select the optimal pacing mode. COMPLICATIONS OF PACING 401 Complications of pacing Pacemaker syndrome This occurs in patients with intact VA conductio n during VVI pacing. Symptoms include presyncope, syncope, lightheadedness, fatigue, exerci se intolerance, malaise, lethargy, dyspnea, headache, chest pain, and nonspe- ci \201 c sy mptoms. Loss of AV synchrony can decrease cardiac output by 20% at rest. There is atrial contractio n against a closed mitral and tricuspid valve, leading to cannon waves. There is also activ ation of atrial stretch receptors with release of atrial natriuretic peptide (ANP). The treatment is to restore AV synchrony by either reducing the pacing rate or inserting an atrial lead. Endless loop tachycardia (pacemaker-mediated tachycardia [PMT]) This occurs in dual-chamber pacing (VDD, DDD, or DDDR) and is caused by inappropriate sensing of retrograde P waves, w hich trigger a ventricular response. The treatment is to increase the postventricular atria l refractory period (PVARP) to prevent sensing of the retrograde P wave or activate a varie ty of anti-PMT algorithms. Other tachycardias Atrial \202 utter or \201 brillation can cause rapid ventricular pac ing in dual-cham- ber systems by sensing and tracking the atrial rate. To overcome this, th e pacemaker can either mode-switch to VVI or be reprogrammed to DDI so that the atrial rate cannot be tracked. Interference MRI is generally contraindicated in a patient with a pacemaker, as it can cause serious mal function. However, recommendations are changing and MRI-compatible systems are being develo ped. Radiation therapy can damage pacemaker electronics or result in erosion of the generator. T he radiation dose is cumulative. Shielding is mandatory. The pulse generator should be inte rrogated after therapy and may need to be replaced. Cautery pacemaker needs to be checked before and after surgery as the electronics of the ge nerator can be damaged. It should be reprogrammed to a non-sensing mode (VOO) prior to surg ery or have a magnet applied during cautery to force the device to pace (see below). CHAPTER 9 Arrhythmias 402 Magnet response When the pacemaker is within a suf \201 ciently strong magnetic \201 eld , it reverts to its magnet mode. This is non-sensing \201 xed pacing at the device \200 \231s \200\234magnet rate \200\235 usually 70 \200\22380 /min, i.e., DOO (dual chamber) or VOO/ AOO (single chamber). Additional potential complications of pacing include lead malfunction, device recalls, and device infection. Evaluation and management of these problems should be done in consultatio n with a cardiovascular specialist. Pacemaker follow-up The device is interrogated every 6 \200\22312 months. The battery volta ge is measured, and below a critical level the elective replacement indicator (ERI) activat es. There are approximately 6 months between ERI and the dangerous EOL (end of life). The lead(s) function is assessed by checking pacing threshold, sensitivity (the size of sen sed electrogram detected), and pacing impedance. Any change in these parameters could indic ate a problem, e.g., low impedance suggests an internal insulation break, while high impeda nce might suggest a conductor problem. Modern devices store the time and duration of many changes of pace- maker function, which i s helpful for arrhythmia detection. Most can also store electrograms that help in the diagn osis of arrhythmias and pace- maker malfunction. Remote or transtelephonic monitoring may also aid in careful patient follow-up. PACEMAKERS FOR CHRONIC HEART FAILURE 403 Pacemakers for chronic heart failure Cardiac resynchronization therapy (CRT) CRT is a novel treatment for symptomatic heart failure (NYHA Class III \200\223IV). In patients with a ve ntricular conduction delay, coordination of wall motion in the left ventricle can be improv ed by pacing the lateral LV (via the coronary sinus) and septum (via the RV) simultaneously . This improves cardiac output and symptoms. Ventricular \201 lling may be improved by op ti- mizing the AV delay. Current indications \200 \200 \200 \200 \200 \200 NYHA Class III \200\223IV heart failure On optimal medical therapy Sinus rhythm QRS duratio n >120 ms LVEF LVEDD (cid:100)35% (cid:116)55 mm