Investigation and risk strati \201 cation The diagnosis of LQTS is based on the clinical h istory and ECG. The QT interval should be measured in lead II or V 5 and should be correcte d for heart rate according to Bazzet \200\231s formula; QTc = QT/ \210\232(RR)(see Fig. 10. 14 ). Risk strati \201 cation is based on age, sex, QT interval, recent symptoms, and gene tic diagnosis . RR interval Tangent T P U Lead II or V5 Baseline QRS QTc = QT / \210\232RR (sec) QT Fig. 10.14 QT interval is measured in lead II or V 5 from the point of the \201 rst sharp de \202 ection away from the baseline of the QRS interval to the end of the T wave, de \201 ned as the intersection of the baseline and a tangent drawn to the steepest slope of t he last limb of the T wave. Reproduced with permission from Postema et al . (2008). Heart R hythm 5 : 1015 \200\22318. 520 CHAPTER 10 Arrhythmias Long QT syndrome, continued Table 10.5 Characteristics of currently identi \201 ed congenital LQTS Effect of mutation Clinical features LQTS Mutation Ion current a I ks Loss of function Exercise-related syncope I KVLQT1 (CW11) I kr Loss of function Syncope related to sudden emotional or auditory stress II HERG (CW7) I Na Gain of function Symptoms at rest rather than when excited. Young age and usually presents as sudden death III SCN5A (CW3) IV Ankyrin-B (CW4) See below Loss of function \200\224 V KCNE1 (CW21) I ks Loss of function \200\224 I kr Loss of function \200\224 VI KCNE2 (CW21) a Potassium currents ( I k ) are repolarizing and the sodium currents ( I Na ) depolarizing . The ankyrin-B gene codes not for an ion channel but for a cellular structural protein tha t binds sodium ion channels (Splawski I, Shen J, Timothy KW, et al. (2000). Spectrum of mut ations in Long-QT syndrome genes. Circulation 102: 1178 \200\22385.) Common causes of acquired LQTS Drugs *2 \200 Antiarrhythmics : quinidine, procainamide, d isopyramide, \202 ecainide, propafenone, sotalol, ibutilide, dofetilide, amiodarone (rare ) \200 Antimicrobials : erythromycin, clarithromycin, trimethoprim, ketoconazole, itraconazole, chloroquine Antihistamines : terfenadine \200 Other drugs : amitriptyline, \202 uvoxamine, chlorpro mazine, domperidone, cisapride, glibenclamide. Electrolyte imbalance \200 Hypokalaemia, hypomagnesaemia, hypocalcaemia. Severe bradycard ia \200 Complete heart block, sino atrial node disease, hypothyroidism, hypothermia. Note this is not a comprehensive list and LQTS is the commonest single reason for new drugs being withdrawn. When a patient is known to be at risk from LQTS or there is concern that interaction may occur with other QT-prolonging drugs, all drugs and potential interactions. LONG QT SYNDROME, CONTINUED 521 Fig. 10.15 Torsades de pointes. A continuous tracing from three leads of a patient monitore d on CCU. The \201 rst complex is a sinus beat followed by two ectopics. There is then a long pause (2 s) followed by another sinus beat. 522 CHAPTER 10 Arrhythmias Long QT syndrome: management Torsades de pointes (TDP) usually terminates spontaneously, al though it may degenerate to VF. A prolonged episode causing cardiovascular compro- mise nee ds immediate DC cardioversion. For recurrent bursts or following a cardiac arrest, use IV m agnesium bolus and infusion, followed by urgent temporary pacing (at rate 90 \200\223110/mi n) if necessary. Acquired LQTS The underlying cause should be identi \201 ed and reversed. Stop offending d rugs. Give Mg 2 + before getting blood results. K + can be checked rapidly with a blood gas analyzer, replace if less than 4 mmol/L, and aim to achieve high normal levels. An isopren aline infusion can be commenced while waiting to pace. Long-term treatment is not usually n ecessary; however, a permanent pacemaker is required if non-reversible heart block was the cause. Congenital As most events are triggered by sudden increases of sympathetic activity, treatm ent is aimed at preventing this. Beta-blockade is the mainstay and is especially effective in LQT1, although less so in LQT3. Patients should avoid precipitating symptoms. Cardiac pa cing is useful to alleviate the B-blocker- induced bradycardia, and, where pauses have been identi \201 ed, to precipitate symptoms (LQT3). ICDs should only be used with careful con sideration, i.e. for patients at high risk of SCD or where a resuscitated cardiac arrest wa s the \201 rst event. ICDs prevent SCD but not TDP, and recurrent distressing shocks for non-sustained episodes can ruin a patient \200\231s life. Careful patient selection, concom itant use of B -blockers, and shrewd device programming minimizes inappropriate therapies. In resistant cases, or where ICD is contraindicated, left cardiac sympathectomy may be high ly effective. Asymptomatic patients Once a diagnosis of LQTS has been made, screening should be offered t o all family members. Screening (clinical and/or genetic) of affected fami- lies reveals pa tients with LQTS who have never had symptoms and may have normal QT intervals. All patients must be carefully evaluated and the risk determined on an individualized basis. Most patie nts do not die from LQTS but all are at risk (13 % incidence of fatal events over a lifetim e if untreated). A balance must be struck between lifelong treatment with side-effects and the specter of sudden death. Further reading 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\223 74 . This page intentionally left blank 524 CHAPTER 10 Arrhythmias Arrhythmogenic right ventricular cardiomyopathy (ARVC) ARVC is an autosomal dominant disord er characterized by \201 brofatty in \201 ltration of ventricular myocardium, which clas sically affects the right ventricle but may also show biventricular involvement. ARVC predo mi- nantly relates to genetically encoded abnormalities in the desomsome, a transmembrane a ssembly of proteins involved in interceullular adhesion and communication. The disease is p rogressive and may be notoriously dif \201 cult to diagnose in its early phases. Diagnosis is made according to international criteria based on electrocardiography, echocardiography , cardiac MR, and histology (see Table 10.6 ). Ventricular arrhythmia typically show a left bundle morphology that is indicative of a righ t ventricular origin, often relating to areas of scar within ventricular myocardium. In sin us rhythm, the ECG may show a broadened QRS and T-wave inversion in leads V 1 \200\223V 3 , and epsilon waves indicating late ventricular activation. The predominant risk is arrhyth mia, although a small proportion of patients progress to heart failure requiring transplant ation. Drug management includes B -blockers, sotalol, amiodarone, and class 1 agents in those with preserved LV function, although as they have limited potential in preventing SCD, an ICD i s warranted in high-risk cases. VT ablation may be acutely successful, but due to continual disease progression, the rate of recurrence is high. Genetic analysis for mutations in the \201 ve major desmosomal proteins should be performed in those with clinical or familial evidence of the disease. ARRHYTHMOGENIC RIGHT VENTRICULAR CARDIOMYOPATHY 525 Table 10.6 Diagnostic criteria for arrhythmogenic right ventricular tachycardia International Task Force Criteria 1994 a Modi \201 ed Task Force Criteria 2002 b Major Minor Con \201 rmed case of familial ARVC in \201 rst-degree relative, plus one of: Mild RV dilatation and reduction of EF Mild RV dilatation and reduction of EF Structural abnormalities Severe RV dilatation and reduction of ejection fraction (EF) Localized RV aneurysms Regional RV hypokinesia Regional RV hypokinesia Mild RV segmental dilatation Severe RV segmental dilatation Mild RV segmental dilatation Tissue characterization Fibrofatty replacement of myocardium on biopsy Repolarization abnormalities T-wave inversion in V 2 and V 3 ( > 12 years of age and without bundle branch block) T-wave inversion in V 2 and V 3 ( > 12 years of age and without bundle branch block) Late potentials on signal-averaged ECG Depolarization abnormalities Epsilon waves Late potentials on signal- averaged ECG Localized QRS prolongation in V 1 \200\223V 3 LBBB VT Arrhythmia > 1000 ventricular ectopics/24 hours on Holter monitor LBBB VT > 200 ventricular ectopics/24 hours on Holter monitor Family history of sudden cardiac death due to suspected ARVC Family history Familial disease con \201 rmed on post-mortem or at surgery Family history of con \201 rmed ARVC a Adapted from McKenna WJ et al (1994). Diagnosis of arrhythmogenic right ventricular cardi omyopathy/dysplasia. Br Heart J 71 : 215 \200\22318. b Adapted from Hamid MS et al (2002). Prospective evlauation of relatives for familial arrhythmogenic right ventricular cardiomyo pathy/dysplasia reveals a need to broaden diagnostic criteria. J Am Coll Cardiol 40 : 1445 \200\22350. 526 CHAPTER 10 Arrhythmias Brugada syndrome Brugada syndrome is an increasingly recognized cause of SCD, character- iz ed by a pattern of J-point elevation > 2 mm in leads V 1 \200\223V 3 . The heart is struct urally and functionally normal. Approximately 30 % of patients will have identi \201 able mutations in the sodium channel gene ( SCN5A ). The disease is especially prevalent in Sout h-East Asian individuals, and shows both age- and sex-related penetrance, classically prese nting in males (M:F 8:1) in their 30s and 40s. Symptoms include syncope and VF leading to c ardiac arrest, although the ECG \201 ndings may be incidental. A type 1 pattern (coved ST elevation > 2 mm and inverted T wave) in \211 1 anterior preco rdial leads (V 1 \200\223V 3 ) is diagnostic, although these changes are dynamic. Conditio ns that should be actively excluded are atypical RBBB, acute MI, pericarditis, ARVC, and au tonomic and electrolyte disturbances. Type 2 (saddle-back ST segment elevation \211 1 mm) and type 3 ECG (saddleback/coved ST segment <1 mm) are non-diagnostic but suggestive of Br ugada syndrome, and may be converted to a diagnostic type 1 pattern using a class 1 antiarr hythmic agent challenge: ajmaline 1 mg/kg IV to max 50 mg; \202 ecainide 2 mg/kg IV, or p rocainamide 10 mg/kg IV (see Fig. 10.16 ). Similarly, a diagnotic ECG may be precipitated b y fever and different medications including class 1 antiarrhythmics, anti-depressant, antip sychotics, and cocaine. Patients with symptomatic Brugada syndrome (syncope, VT, VF) should undergo ICD implantatio n, No medical therapy is effective, although quinidine is under investigation. The role of programmed ventricular stimulation to identify high-risk, asymptomatic patients who should undergo primary prevention ICD implantation remains controversial. Catecholaminergic polymorphic VT Catecholaminergic polymorphic VT (CPVT) is an aggressive c ondition char- acterized by adrenergically stimulated polymorphic VT. Genetically encoded m utations in the cardiac ryanodine receptor (autosomal dominant) or calse- questrin (autosom al recessive) lead to abnormalities in myocardial calcium \202 ux, which, in the presence of catecholamines, trigger delayed afterdepolari- zations and VT. Patients present with pa lpitations, syncope, or cardiac arrest during exercise or emotional stimulation, often in t he \201 rst two decades of life. Baseline ECG and echocardiogram are normal. Investigatio ns include exercise testing, Holter monitoring, and adrenaline provocation that reveal the classical bidirectional or polymoprhic VT, usually once the heart rate reaches 110 \200\223 120 bpm. B -blockers are the mainstay of therapy, although verapamil and \202 ecainide ha ve also been used. Given the highly aggressive nature of the disease, ICD implantation shou ld be considered in patients with symptoms or persistent VT despite appropriate drug therap y. CATECHOLAMINERGIC POLYMORPHIC VT 527 1 Fig. 10.16 Brugada ECG with \202 ecainide challenge. A typical Brugada ECG with arrows ma rking the characteristic prominent coved ST-segment elevation in the right precordial leads , \211 2 mm at its peak folllowed by a negative T wave with little or no isoelectric sepa ration. Intravenous administration of either ajmaline (1 mg/ min) or \202 ecainide (2 mg/ kg, max 150 mg; in 10 minutes) exaggerate the ST changes or reveals them if initially absen t.1 1 Wilde AA, Antzelevitch C, Borggrefe M, et al . (2002). Proposed diagnostic criteria for t he Brugada syndrome. Consenus report. Circulation 106 : 2514 \200\22319. 528 CHAPTER 10 Arrhythmias Arrhythmia in special situations Pediatrics Arrhythmia may occur at any stage in the pediat ric population, from fetal life to 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 resolves spontaneously in utero or by one year of age, although recurrences later in life may occur. Ablation is rarely necess ary. Congenital heart block occurs mediated by maternal anti-Ro/SSA antibodies, and, if sev ere, may also cause hydrops fetalis. This always persists after birth and usually requires permanent 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 infa ncy, but becomes increasingly common in teenage years. Focal atrial tachycardias and a spec i \201 c form of AVRT mediated by a slow atrial septal accessory pathway (persistent junct ional reciprocating tachycardia) both lead to incessant tachy- cardia and profound ventricu lar dysfunction (tachycardia cardiomyopathy). This completely resolves with successful ther apy. Radiofrequency ablation is now commonly performed in older children, and may also be u sed in refrac- tory arrhythmias in neonates and young infants when necessary. Congenital heart disease Arrhythmias in association with congenital cardiac lesions are poo rly toler- ated, and, if uncontrolled, may lead to a rapid decline in ventricular func- tio n and cardiac output. Supraventricular tachycardia This is a major cause of both morbidity and mortality in conge nital heart disease. Accessory pathways are associated with Ebstein \200\231s anomaly and c ongenitally corrected transposition of the great arteries, and this results in AVRT. Macro- re-entrant-atrial tachycardia is common, late, following the Mustard or Fontan procedure. T his is notoriously dif \201 cult to control with medication, and although ablation (either percutaneous or surgical) is commonly successful acutely, arrhythmia recurrence is a probl em. Ventricular tachycardia VT is seen in Ebstein \200\231s anomaly and following repair of tet ralogy of Fallot. Treatment may involve either RFA or an ICD. Pregnancy The haemodynamic and hormonal changes associated with pregnancy may unmask arrhyt hmic substrates for the \201 rst time, or exacerbate pre- existing arrhythmic conditions. Gestational palpitations are common, and, most frequently, an increased awareness of physi ological tachycardia. If new ventricular arrhythmias occur, peripartum cardiomyopathy shoul d be actively excluded. This page intentionally left blank 530 CHAPTER 10 Arrhythmias Permanent pacemakers Introduction Permanent pacemakers play a central role in the management of bradycardia. In addition, they can be used to treat atrial and ventricular tachyarrhthmias (with ICDs), as well as to improve ventricular function and symptoms in heart failure (cardiac resynchroniz ation therapy). Basic pacemaker function involves sensing and pacing either the atria or ve ntricles or both. International code This is a three-letter identi \201 cation code describing the basic fun ction of the pacing system. The \201 rst letter is the chamber(s) paced and the second le tter is the chamber(s) sensed. V = ventricle, A = atrium, D = dual (i.e. A + V). The third letter is 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 t he device e.g. R = rate response. Implantation \200 Antibiotic prophylaxis : reduces risk of infection. Use a drug that is effective against staphylococci, e.g. \202 ucloxacillin (clarithromycin or clindamycin if pencillin allergic Site of implant : ususally infraclavicular (right or left); rarely, abdominal, axillary, or submammary Pocket : subcutaneous or submuscular (beneath pectoralis major) \200 Venous access : dire ct cutdown to the cephalic vein in the deltopectoral groove or Seldinger approach to the su bclavian vein. A venogram (from the ipsilateral brachial vein) is useful if access is dif \201 cult. Rarely, internal jugular or femoral veins are used Leads : active (screw-in) or passively \201 xed. Use an active \201 xation lead in the atrium post cardiac surgery Lead placement : RV apex/septum for the ventricular lead. RA appendage for atrium. See Fig. 10.17 for lead placement, and Table 10.7 for acceptable para meters Suturing : lead sleeves should be \201 rmly stitched to muscle with a non- resorbable sut ure (silk, surgilon). The pocket is closed in layers with vicryl. Skin closure is with prol ene or Dermabond glue Follow-up : ensure stitches are removed and the wound is healed. Pacing check within 1 month (see later). PERMANENT PACEMAKERS 531 Fig. 10.17 AP chest X-ray post permanent pacemaker implantation showing satisfactory placem ent of actively \201 xed leads into the right atrial appendage and right ventricular apex . The generator has been placed subcutaneously in the standard left infraclavicular positio n. 532 CHAPTER 10 Arrhythmias Indications for permanent pacing Class I \200 Sinus node disease with symptoms due to bradycardia, pauses, or chronotropic incompetence Third-degree or second-degree (Mobitz type 2) AV nodal heart block \200 Persistent AF and asymptomatic pauses \211 5 s \200 Pause-dependent VT (e.g. LQTS) \200 Recurrent sync ope caused by spontaneously occurring carotid sinus stimulation and when carotid sinus pres sure induces ventricular asystole > 3s Class IIa \200 Symptomatic sinus node disease with heart rate <40 bpm or unexplained syncope First- or second-degree heart block causing pacemaker syndrome \200 Chronic bifascicular block and unexplained syncope when other causes including VT have been excluded High-risk patients with LQTS \200 Hypertrophic cardiomyopathy with symptoms due to out \202 ow tract obstruction refractory to medical therapy Adapted from ACC/AHA/HRS 2008 guidelines. J Am Coll Cardiol 51 :2085 \200\223105. Table 10.7 Acceptable pacing parameters for new leads Atrium Ventricle Threshold a <1.5 V <1.0 V Sensitivity > 1.5 mV > 4.0 mV Slew rate > 0.2 V/s > 0.5 V/s Impedance 400 \200\2231000 ohms 400 \200\2231000 ohms a Using a pulse width of 0.5 ms. WHICH PACING MODALITY? 533 Which pacing modality? The vast majority of patients should have an atrial-based pacing (i. e. either AAI or DDD). Ventricular-only pacing leads to a greater incidence of AF and poten tial pacemaker syndrome (see Fig. 10.18 ). Bradycardic patient No P waves VVI(R) Permanent AF Yes Sinus bradycardia \200 Sick sinus syndrome(SSS) No AV conduction abnormal? Consider AAI(R) No Yes 2nd- and 3rd- degree HB \200 Bi- & trifasicular block \200 Carotid sinus syncope No DDD(R) LBBB and poor LV function? Yes Biventricular pacing Fig. 10.18 Which pacing modality? 534 CHAPTER 10 Arrhythmias Complications of pacing At the time of implantation The procedural complication rate is 5 % . Important complications are: \200 haematoma : most can be managed conservatively, but evacuation is required if very large or threatening the skin (usually due to an arterial bleed). Meticulo us haemostasis should be secured during the implant, and diathermy used if necessary. Bruis ing over the site is common, and resolves spontaneously pneumothorax : a small apical pneumothorax can be observed with serial X-rays. A chest drai n is required for anything larger. A haemothorax may co-exist pericardial effusion : more common with actively \201 xed leads, which can perforate thro ugh the thin-walled RA or RV (right ventricle). Pericardial tamponade can occur, requiring urgent pericardiocentesis infection : occurs at the time of implant but usually presents late. Minimized by aseptic technique and antibiotic prophylaxis air pulmonary embolism : care must be taken when using sheaths, as a signi \201 cant volume of air can be drawn into the vein axillary vein thrombosis : rare, can present with a swollen arm and is treated with systemic anticoagulation. Late complications \200 Lead displacement : this is common and requires lead repositionin g. \200 Infection : risk factors are fever within 24 h of implant, use of a temporary wire, prolonged procedure, any revision procedure shortly after the \201 rst im plant. Infection can manifest as localized pocket abscess/cellulitis, septicaemia, or endoc arditis with vegetations on leads. Treatment is urgent extraction of the entire system. Pro longed intravenous antibiotic therapy may be needed. Patients who are pacing dependent will need a temporary wire. New device implantation should be performed when there are no signs of infection on the contralateral site. Box or lead erosion : at implant, care must be taken to create a large enough pocket for the device and leads without causing tension on the skin. Indolent infect ion can cause erosion. If the skin is threatened, box repositioning may be attempted (to a submuscular pocket), but if the skin is breached the whole system needs to be explanted. Lead damage/failure : common causes are crush between the clavicle and \201 rst rib, or in the pocket if the leads have been over-coiled tightly. Fibrosis a t the lead tip results in higher pacing thresholds and poor sensing. Lead failure requires insertion of a new lead (see Fig. 10.19 ). Device failure is rare. \200 Venous obstruction : this is usually asymptomatic (due to co llateral formation) but may present a problem at system revision. COMPLICATIONS OF PACING 535 Other problems \200 Pacemaker syndrome : this occurs in patients who have sinus node function but are implanted with a VVI pacemaker. Symptoms include; presyncope, syncope, lig htheadedness, fatigue, exercise intolerance, malaise, lethargy, and dyspnoea. It is due to independent atrial and ventricular contraction. The treatment is to restore AV synchrony, b y either reducing the pacing rate or inserting an atrial lead. Endless loop tachycardia : this occurs in dual chamber pacing (VDD, DDD, or DDDR) and is caused by inappropriate sensing of retrograde P waves and hence trigge ring a ventricular response. The treatment is to increase the post-ventricular atrial refra ctory period (PVARP) so as not to sense the retrograde P wave. Atrial tachycardias can cause rapid ventricular pacing in dual-chamber systems by sensing t he atrial rate. To overcome this, the pacemaker can either mode-switch to VVI or be reprogr ammed to DDI mode. Fig. 10.19 Atrial lead fracture. A dual-chamber ICD was implanted 3 years prior to this PA CXR. At routine follow-up, the pacing impedance was very high and there was no atrial sensi ng or capture. The atrial lead has fractured (arrow). The inset shows a magni \201 ed view of the fracture (arrow). 536 CHAPTER 10 Arrhythmias Pacemaker follow-up 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\230magnet rate \200\231 usually 70 \200\22380/min, i.e. DOO ( dual chamber) or VOO/AOO (single chamber). Application of a magnet over the pacemaker can b e used during surgery to prevent device inhibition (and hence asystole) when dia- thermy is being used. Pacemaker clinic The device is interrogated every 6 \200\22312 months. At these visits, the function of the lead(s) is assessed by checking the pacing threshold, sensitivity (the siz e of sensed electrogram detected), and pacing impedance. Any change in these parameters cou ld indicate a problem, e.g. a low impedance sug- gests an internal insulation break, while a high impedance might suggest a lead fracture. The battery voltage is measured, and below a critical level the elective replacement indicator (ERI) activates. There is approximately 6 months between ERI and the dangerous EOL (end of life). A box change is usually arranged at the ERI time. Interference \200 Magnetic resonance imaging (MRI) : absolutely contraindicated in a patient with a pacemaker or ICD, as it can cause device malfunction and harm the patient. M RI- \200\230safe \200\231 pacemaker systems are available. \200 Radiotherapy : can damage pacemaker electronics or result in erosion of the generator. The damage is cumulative and the device should be shielded. Occasionally, the generator may need to be repositioned if i t overlies a tumor (e.g. lung cancer). Diathermy : may inhibit pacing. The device should be reprogrammed to a non-sensing mode (VO O) prior to surgery or have a magnet applied during surgery. The pacemaker needs to be chec ked after surgery to ensure normal function. Security gates : these will be activated by pacemakers. Patients are advised to carry their identi \201 cation card so that they can show staff. This page intentionally left blank 538 CHAPTER 10 Arrhythmias Cardiac resynchronization therapy Patients with heart failure and broad LBBB on their ECG w ill have uncoordinated contraction and relaxation of the ventricles because of the delayed and heterogenous depolarization of the LV. This is termed dys- synchrony. By pacing the RV and LV simultaneously, cardiac resynchro- nization therapy (CRT) improves co-ordinated vent ricular contraction, increases cardiac output, and reduces heart failure symptoms. Electrical or mechanical dys-synchrony? Accurate assessment of mechanical dys-synchrony by detailed echocar- diography, including tissue Doppler, does not predict reliably who will r espond to CRT, and therefore electrical dys-synchrony, i.e. LBBB on ECG, remains the standa rd measurement. CRT in patients with narrow QRS complexes even with evidence of mechanical dys-synchrony is con- troversial. Implantation The RA and RV leads (often an ICD lead) are inserted conventionally. The LV is paced epicardially via the coronary sinus (CS). Using a Seldinger technique, a guide cathe ter is introduced into the RA via the subclavian vein. The CS is intubated and a venogram p erformed to identify a suitable lateral tributary. The pacing lead is then inserted either with a stylet or using the over-the-wire technique, into a stable position with acceptable pacing parameters and no diaphragmatic stimulation (see Fig. 10.20 ). There are a number of tools to help place the lead, e.g. subselector sheaths, and different leads, e.g. steerabl e or \200\230active \200\231 \201 xation. If the anatomy is unfavour able (tortuous, sma ll veins) or there is inability to capture the LV, patients can be referred to a cardiac su rgeon for thoracoscopic-guided epicardial lead placement. Effects of CRT Some patients respond immediately, while the majority respond over a course of weeks. Bene \201 t can be dramatic, with a major improvement to quality of life, reduce d hospitalizations, and improved prognosis. There are improvements in LVEF and a reduction in ventricular dimensions (reverse remodeling). Indeed, implantation of devices in asymptom atic patients can delay symptom onset and reduce future hospitalization episodes for heart failure. 1 Non-responders Unfortunately, 30 \200\22340 % of patients who undergo CRT implantation fail to respond. Reasons for this are: suboptimal lead position, end-stage heart failure (New Y ork Heart Association (NYHA) IV), alternative causes of symptoms (e.g. chronic obstructive pulmonary disease (COPD)). There are a number of options for these patients: \200 ECHO-gu ided optimization : cardiac output is assessed for different AV and RV \200\223LV pacing intervals, with the optimal settings chosen 1 Moss AJ, Hall WJ, Cannom DS, et al . (2009). Cardiac-resynchronizationtherapy for the pre vention of heart-failure events. N Engl J Med 361 :1329 \200\22338. CARDIAC RESYNCHRONIZATION THERAPY 539 lead repositioning : the LV lead can be placed at a different site, or the RV lead moved, e.g. from the apex to the septum multisite pacing : implanting an additional LV lead via another CS branch, or if this is no t possible, then two RV leads can be implanted (apex and high septum). Fig. 10.20 A \202 uoroscopic image of the heart from the RAO projection. There is an acti ve \201 xation lead in the conventional right atrial appendage (RAA) and a lead in the ri ght ventricular apex. Dye has been injected from below retrogradely up the CS to demonstrat e the lateral left ventricular branches, from where pacing stimuli can capture the ventricl e. Current indications for CRT Class I \200 NYHA class III \200\223IV heart failure established on optimal medical thera py. Sinus rhythm with QRS duration > 120 ms and left ventricular ejection fraction (LVEF) < 35 % Class IIa \200 NYHA class III \200\223IV heart failure established on optimal medical the rapy. AF with QRS duration > 120 ms and LVEF < 35 % . AV nodal ablation to control the vent ricular rate may be needed NYHA class III \200\223IV and LVEF \211 35 % in patients who require frequent RV pacing Class IIb \200 NYHA class I \200\223II, LVEF \211 35 % in patients who are undergoing p ermanent pacemaker implantation who will require frequent RV pacing Adapted from ACC/AHA/HRS 2008 guidelines. J Am Coll Cardiol 51 : 2085 \200\223105. This page intentionally left blank 541 Chapter 11 Invasive electrophysiology Abbreviations 542 Mechanism of tachycardias 544 Mechanism of arrhythmias 546 The electrophy siology study 548 Uses of the electrophysiology study 550 Programmed ventricular stimulatio n 554 New technologies 556 Catheter ablation 558 Complications of catheter ablation 560 Tra ns-septal puncture 562 Atrial arrhythmias: mechanism 564 Ablation of atrial tachycardias 56 6 Catheter ablation of atrial \201 brillation 568 Complications of AF ablation 570 Mechan ism of AV re-entry tachycardias 572 Ablation of AV re-entry tachycardias 574 Accessory path ways (Wolff \200\223Parkinson \200\223White syndrome) 576 Accessory pathways: localization 578 Accessory pathways: management 579 Mechanism of ventricular tachycardia 580 Ablation of ventricular tachycardia 582 Automatic implantable cardioverter de \201 brillators 584 AIC D programming 586 AICD troubleshooting 588 542 CHAPTER 11 Invasive electrophysiology Abbreviations 3D ACT AD AF AICD AP ASD ATP AV AVN AVNERP AVNRT AVRT AWCL BBB BP CFAE CS CT DVT ECG EP ERP FAT FFP HCM HRA HSVPB IAP ICD ICegram IVC IVP LA LAA LAO LBBB LIPV LSPV three dimensional activated clotting time afterdepolarization atrial \201 brillation auto mated implantable cardioverter de \201 brillator accessory pathway atrial septal defect an titachycardia pacing atrioventricular atrioventricular node atrioventricular nodal effectiv e refractory period atrioventicular node re-entrant tachycardia atrioventricular re-entrant tachycardia anterograde Wenckenbach cycle length bundle branch block blood pressure comple x and fractionated atrial electrogram coronary sinus computed tomography deep vein thrombos is electrocardiogram electrophysiology effective refractory period focal atrial tachycardia fresh frozen plasma hypertrophic cardiomyopathy high right atrium His syndrome ventricular premature beat incremental atrial pacing implantable cardiac de \201 brillator intracardi ac electrogram inferior vena cava incremental ventricular pacing left atrium left atrial ap pendage left anterior oblique left bundle branch block left inferior pulmonary vein left su perior pulmonary vein INVASIVE ELECTROPHYSIOLOGY 543 LV MI MRI MV NYHA PE PV RAO RF RSPV RVA RVOT RWCL SA SAN SCD SR SVC SVT TIA TOE TV VERP VF V/Q VT WCL WPW left ventricle myocardial infarction magnetic resonance imaging mitral valve New York Heart Association pulmonary embolism pulmonary vein right anterior oblique radiofrequency right superior pulmonary vein right ventricular apex right ventricular out \202 ow tract right W enckenbach cycle length sinoatrial sinoatrial node sudden cardiac death sinus rhythm superi or vena cava supraventricular tachycardia transient ischaemic attack transoesophageal echoc ardiography tricuspid valve ventricular effective refractory period ventricular \201 bril lation ventilation \200\223perfusion ventricular tachycardia Wenckenbach cycle length Wolff \200\223Parkinson \200\223White (syndrome) 544 CHAPTER 11 Invasive electrophysiology Mechanism of tachycardias Knowledge of how arrhythmias are initiated and perpetuated is fun damental to understanding the techniques described in this chapter. The electrical wavefront The excitable impulse is generated at the cell membrane by the act ion potential. As one cell depolarizes, it causes a reduction in negativity of the resting potential in the adjacent cell such that it this cell also reaches the threshold potential and depolarizes. The shape, orientation, and pres- ence of gap junctions between myocardial cells allow rapid progression of this depolarization, which can be described as an electri cal wavefront . After a cell has depolarized, it cannot depolarize again until a \201 xed period of recovery time has passed, the refractory period . Cells that are able to depolar ize are excitable and those that cannot are refractory . In sinus rhythm (SR), the source of these wavefronts is the sinoatrial node (SAN), and they may be modulated between the atrium and ventricle by the atrioventricualar (AV) node. They are initiated (and therefore the heart rate is controlled) by regulation from the autonomi c nervous system and circulating cathecholamines. This control is lost in tachyarrhythmia, and heart rates are inappropriate. Conduction block A wavefront will propagate as long as there are excitable cells in its pat h. Anatomical barriers such as the mitral valve annulus, vena cava, aorta, etc. do not cont ain myocardial cells and therefore the progression of wave- fronts is halted there. This is described as \201 xed conduction block , as block is always present. Dead cells are anot her important source of \201 xed conduction block e.g. the left ventricular scar of a myo cardial infarction (MI). Functional conduction block describes the situation when block is only present under certai n conditions. An example is myocardial ischaemia, which may alter the electrical properties of myocytes so that they do not conduct. It is also functional block that prevents a wavef ront turning back on itself, as the cells behind the leading edge are temporarily refractor y and force the wavefront to continue in one direction. Other causes of functional block ar e: cyanosis, myocardial stretch, rate of wavefront, and direction of wavefront. Arrhythmia mechanism Three distinct mechanisms are described: \200 enhanced automaticity \200 re-entry \200 triggered activity. The \201 rst two account for nearly all clinic al tachycardias, and their charac- teristics are compared in Table 11.1 . MECHANISM OF TACHYCARDIAS 545 Table 11.1 Characteristics of automatic and re-entry tachycardiasa Re-entrya Automatic Autonomic sensitivity? (e.g. to exercise, emotion) Often Unusual No Yes Reproducible induction and termination by programmed pacing? Entrainment of the tachycardia by pacing (p)? No Yes Induced by atropine/isoprenaline infusion? Yes May augment induction by pacing a Related to metabolic causes Often Unusual Onset/offset May be gradual (warm up and down) Sudden Macroreentrant atrial tachycardia, AVNRT, AVRT, VT Speci \201 c tachycardias caused Focal atrial tachycardia, RVOT VT a The conduction properties of, e.g. the AV node, are in \202 uenced by autonomic tone. Sp ontaneous or drug-induced changes in this may then in \202 uence the development of re-ent ry tachycardias such as AV-nodal re-entry tachycardia (AVNRT); AF (atrial \201 brillation ); AVRT (atrioventricular re-entrant tachycardia); RVOT (right ventricular out \202 ow tra ct); VT (ventricular tachycardia). 546 CHAPTER 11 Invasive electrophysiology Mechanism of arrhythmias Enhanced automacity If a nidus of myocardial cells depolarizes fas ter (rapid phase 4 of the action potential) than the SAN, they will act as the source of wa vefronts that conduct through the heart. They may be atrial or ventricular, but if they occ ur in the atria they will override the SAN. As they occur from a single site they are often termed focal . Common sites are where myocardial cells suddenly change shape/size or those under abnormal pressures such as; the junction of veins/atrium (superior vena vava (SVC), pulmonary veins (PVs)), crista terminalis, coronary sinus (CS), AV node area, mitral/tricus pid ring, ventricular out \202 ow tracts. Re-entry Re-entry accounts for > 75 % of clinical arrhythmias. It is caused by a perpetu- a lly propagating wavefront that it is constantly meeting excitable myocar- dium. For re-entr y to occur, at least two distinct pathways must exist around an area of conduction block. T his is best described using the example of VT due to re-entry around a LV myocardial scar ( see Fig. 11.1). 1. A myocardial scar acts as an area of block, around which a normal sinus wavefront passes via normal myocardium (A) and slowly through it via diseased myocardium (B ) \200\224 hence there are two distinct pathways. 2. The sinus beat is followed closely by a ventricular ectopic, which is conducted around A normally but is blocked in B, which is still refractory following the last sinus beat. 3. The distal end of B, however, is now excitable and the wavefront passes backwards up B, which has had time to fully recover by the time it reaches the proximal end. Conduction is suf \201 ciently slow up B that now A is excitable again and the wavefront can pass down A . Thus, a re-entry wavefront has been formed that is constantly meeting excitable myocardium. Triggered activity This has features of both the above mechanisms. They are caused by spont aneous (hence automatic) afterdepolarizations (ADs) occurring late in phase 3 ( early ADs) or in phase 4 ( delayed ADs) of the action poten- tial. These ADs, however, are often trigg ered by premature beats and are therefore inducible (like re-entry). If these ADs reach the threshold level, then a single or burst of action potentials is set off. The ADs can be in duced experimentally by ischaemia, QT-prolonging drugs, cell injury, or low potassium. This mechanism underlies torsades de pointes and arrhythmias due to digoxin toxicity. MECHANISM OF ARRHYTHMIAS 547 Fig. 11.1 Re-entry as a mechanism of tachycardia. 1. Normal sinus beat passing around and t hrough scar 2. Ectopic beat passing around but blocked through scar 3. Re-entry circuit of tachycardia (Dark gray represents scar, light gray normal myocardium, and white arrows elec - trical wavefronts.) 548 CHAPTER 11 Invasive electrophysiology