Patent ductus arteriosus This may occasionally present in later life. If it is small or med ium sized with no pulmonary hypertension, it usually can be successfully occluded with a va riety of transcatheter occluding devices or coils. Pulmonary valve implantation Percutaneous transcatheter implantation of a bovine jugular ve nous valve mounted within a platinum-iridium stent into the right ventricular out- \202 o w tract is now possible. If it stands the test of time, this procedure will revolutionize o ur approach to management of patients with pulmonary regurgitation following right heart co ngenital surgery, offering a nonsurgi- cal approach. It may not be long before an implantable valve that can be used in the systemic circulation becomes widely available. SPECIFIC MANAGEMENT ISSUES 343 Speci \201 c management issues Complications of cyanotic CHD Chronic hypoxemia results in an increased red cell mass and total blood volume. This compensatory mechanism may initiall y enhance oxygen delivery; however, symptoms of hyperviscosity may develop. \200 Symptoms of hyperviscosity include headaches, visual disturbances (blurred or double vision ), impaired alertness, fatigue, parasthesia, tinnitus, myalgia, muscle weakness, and restle ss legs. Transient ischemic events or stroke may also occur. Measure hemoglobin and red cel l indices; most patients have a compensated erythropoesis with a stable hemoglobin. Therape utic phlebotomy should be reserved for symptomatic patients, e.g., with hemoglobin >20 g/dL or hematocrit >65%. Symptoms may be relieved by removal of 500 mL (maximum) of blood with concomitant \202 uid replacement of dextrose or saline. Phlebotomy should be performed no more than 2 times per year, as it increases the risk of stroke by causing iron de \201 ci ency. Intravenous line \201 lters should always be used. Iron de \201 ciency in a polycythemic patient should be treated with cautious iron supplem entation. Recheck hemoglobin 8 \200\22310 days later. Overaggressive treatment can result i n further increases in hematocrit. Skin Severe acne is common in cyanotic CHD. It can act as a source of infection and endocar ditis. Treat it aggressively. Gallstones These are common in cyanotic patients. Bilirubin is a product of hemo- globin br eakdown. Suspect them if a patient presents with severe abdomi- nal pain and discomfort. Renal function \200 \200 \200 Reduced glomerular \201 ltration rate Increased levels of creatinine Abnormalities in cle arance of uric acid frequently accompany chronic cyanosis and gout may result. Use contrast in angiography with caution and always prehydrate and premedicate the patient. Noncardiac surgery This should be undertaken in specialist centers and care delivered by a multidisciplinary team. Local anesthesia should be used, if possible; other- wise a cardiac anesthesiologist with experience in congenital heart disease should be consulted. Consider preoperative phlebotomy if hemoglobin >20 g/dL or hemat- ocrit >65%. Endocarditis prophylaxis and air line \201 lters should be employed. CHAPTER 8 Congenital heart disease 344 Pregnancy Box 8.7 The majority of women with CHD can tolerate pregnancy. Maternal congenital heart disease is now the major cause of maternal car- diac death in dev eloped countries. All patients need specialist counseling before embarking on pregnancy. Ca rdiologists are generally ill prepared to give such advice; pediatric cardiologists less so ! All young women of child-bearing age should undergo a detailed clini- cal and hemodynamic a ssessment that should include a formal exercise test and detailed echocardiography with emp hasis on systemic ventricular function. All women with complex CHD should be closely monitored in spe- cialist centers where delive ry should take place. Multidisciplinary input is essential. Pregnancy is contraindicated in some CHD patients (see Box 8.8). Attention to medications 1. Anticoagulation (warfarin embryopathy) must be balanced against the need for effective maternal anticoagulation in the setting of indications such as arrh ythmias or prosthetic valves. 2. ARBs and ACE inhibitors are contraindicated in pregnancy. 3. Assess the need for and cho ice of antiarrhythmic drug (e.g., chance for amiodarone-induced fetal thyroid dysfunction). Arrhythmia Arrhythmia is an important cause of morbidity and mortality and a major cause fo r hospitalization of CHD patients. It may lead to signi \201 cant hemo- dynamic deteriorat ion and is poorly tolerated. It may be due to the following: Underlying cardiac defect, e.g., atrial isomerism Part of n atural history, e.g., hemodynamic changes such as chamber enlargement or scarring Residual postoperative abnormalities \200 Box 8.8 Women with CHD in whom pregnancy is contraindicated \200 Pulmonary hypertension \200 E.g., Eisenmenger syndrome (50% maternal and fetal mortality; maternal death may occur up t o 2 weeks postpartum) \200 Heart failure secondary to failing Fontan circulation Women with severe cyanosis and polycy themia \200 If saturation is <80% at rest and hemoglobin is >18 g/dL, there is a greater incidence of m iscarriage and intrauterine growth retardation. SPECIFIC MANAGEMENT ISSUES 345 Management Specialist advice is essential. New presentation demands a complete hemodynamic reassessment including electrophysiological investigation. Correction of any underlying pos toperative hemodynamic abnormality may be one of the most important therapeutic interventio ns. \200 \200 Record a 12 lead ECG. Administer intravenous adenosine while recording the ECG. The mode of termination of the tachyarrhythmia may give very useful information on its etiology, e.g., pre-excitation. Urgent direct current cardioversion may be required if hemodynamic comprom ise is present. Ideally, transesophageal echocardiography should rule out intracardiac thro mbus. If the patient is on warfarin, always check the INR as well as the serum electrolytes prior to cardioversion. CHAPTER 8 Congenital heart disease 346 Atrial septal defect Atrial septal defect (ASD) is one of the most common lesions presentin g for the \201 rst time in adult life. It is often missed, as clinical signs of \201 xe d splitting of the second heart sound can be dif \201 cult to appreciate. It may present f or the \201 rst time with new-onset atrial \202 utter or \201 brillation. Consider the need for electrophysiological interventions, e.g., the Maze procedure for atri al \201 brillation. Shunting tends to increase with aging as the left ventricle stiffens. Closure is indicated in all symptomatic patients; few are truly asymptomatic when assessed by cardiopulmonary testing! There is no upper age limit. The vast majority of secundum def ects are amenable to transcatheter closure. Pulmonary hypertension needs to be excluded. Atrial arrhythmias are one of the common late medical problems. All other types such as sinus venosus defect (defect in upper atrial sept um associated with overriding of the superior vena cava and anomalous right pulmonary venou s drainage) and partial atrioventricular septal defect require surgical closure. A sinus ve nosus defect represents a major surgi- cal challenge involving redirection of anomalous pul monary vein(s). Risk of endocarditis is very low. Antibiotic prophylaxis is not indicated except for the 6 months post-repair with a prosthetic device or material. Ventricular septal defect The majority of cases are small, as larger defects are usually re paired in childhood. Eisenmenger syndrome (pulmonary vascular disease and hypertension associated with reverse, right-to-left shunting via intracardiac communi- cation \200\224VSD, ASD, PDA) is becoming increasingly rare. VSD should be closed if there is signi \201 cant shunt, previous endoca rditis, development of aortic regurgitation, or right ventricular out \202 ow tract obstru ction. It is always important to demonstrate reversibility of pulmonary hyper- tension prior to in tervention. This may be amenable to surgical or tran- scatheter closure. Ventricular arrhythmias may occur late during follow-up. Antibiotic prophylaxis is indicate d for 6 months post-repair or if a resid- ual defect exists adjacent to the prosthetic material. Atrioventricular septal/canal defect (endocardial cushion defect) This is a common defect in patients with Down syndrome. If unoperated, pulmonary vascular d isease (Eisenmenger syndrome) develops. Left atrio- ventricular valve regurgitation and ste nosis are the major determinants of need for further interventions. Valve replacement may b e necessary. Endocarditis prophylaxis is recommended if there is a prosthetic valve, cyanosis, or a defe ct adjacent to the prosthetic material or for 6 months post-repair. COARCTATION OF THE AORTA 347 Pulmonary stenosis This may present for \201 rst time in adult life. This can be successf ully treated by balloon valvuloplasty, which should be undertaken if the valve gradient exc eeds 30 mmHg on Doppler echocardiography. Surgery is reserved for calci \201 ed and dysplastic valves. The outlook is excellent. The risk of endocarditis is low. Left ventricular out \202 ow tract (LVOT) obstruction Aortic valve stenosis is especially common in association with a bicuspid valve. This is a complex lesion and an aortopathy is commonly present. There is a risk of aortic dilation and dissection. The degree of stenosis or regurgitation may increase over time. Effort intolerance, chest pain, or syncope, espec ially with exertion, need to be taken seriously and intervention considered. It may occasionally be amenable to balloon valvuloplasty but more com- monly requires surgi cal intervention. Aortic valve replacement (lifelong anticoagulation) or homograft insertio n or Ross operation (which requires no anticoagulation but potentially further intervention s and is critically operator dependent) can be offered. Subaortic stenosis is uncommon (no ejection click) and requires sur- gical resection if sev ere or if the patient is symptomatic. Recurrence is possible. Supravalvar stenosis is commo nly seen in patients with Williams syndrome. It may be associated with multiple stenoses in the origins of the coronary arteries and the aortic arch arterial branches. Reconstructive surgery is complex. Coarctation of the aorta Most patients seen in adult clinics will have already undergone su rgery. Some may present for the \201 rst time with hypertension. Always feel the femoral pulses! Consider Turner \200\231s syndrome in female patients. Coarctation of the aorta is a complex lesion usually associated with a bicuspid aortic valv e (ejection click at the apex) and aortopathy. During follow-up, upper (right arm) and lowe r limb blood pressure should be recorded and evidence of left ventricular hypertrophy on EC G and echocardiography should be noted. Re-coarctation may occur over time and should be suspected if there are reduced femoral pul ses or radiofemoral delay on examination. Doppler echocardiography can help by revealing an increased systolic velocity signal with forward \202 ow through the site of re-coarctati on during diastole. MRI with three-dimensional reconstruction is the imaging modality of ch oice. Transcatheter balloon dilatation and stenting is feasible in many patients, thus avoiding the risks of thoracic aortic surgery. Lifelong surveillance is necessary to rule out aneurysm formation or recurrence. Antibiotic prophylaxis is indicated for 6 months post-repair of if there is a defect associated with the prosthetic material. CHAPTER 8 Congenital heart disease 348 Anomalous pulmonary venous drainage Many patients will undergo surgery in early childhood. This may occur in association with Scimitar syndrome. If the patient is symptomatic (short- ness of breath, arrhythmia) and there is evidence of right heart volume overload, e.g., on the cross-sectional echocardiogram or MRI, consider surgery. There is a low risk of endoca rditis. Transposition of the great arteries The aorta arises from the right ventricle and the pulmo nary artery from the left ventricle. It is the most common cyanotic cardiac lesion presenti ng in the \201 rst few days of life. In the absence of mixing at the cardiac or great art ery level, this condition is uniformly lethal. The majority of adult survivors have undergone intra-atrial repair by Mustard or Senning pr ocedure. These produced excellent early survival but signi \201 cant late morbidity and mo rtality. Common late problems are sinus node dysfunction, atrial arrhythmias ( \202 utter/ \201 brillation), venous baf- \202 e narrowing, and right ventricular failure with tric uspid regurgitation. Arrhythmias are poorly tolerated, and prompt restoration to sinus rhythm is essential. Baf \202 e stenosis can be relieved by transcatheter balloon dilatation and stenting. Ventricular failure requires intensive medical therapy but may ultimately necessitate cardi ac transplantation. Patients who have undergone the arte- rial switch procedure are now rea ching early adulthood. Problems with coronary arterial stenoses at the site of reanastomosi s to the neo-aorta have been identi \201 ed in some. Antibiotic prophylaxis is required prior to repair and post-repair if there is a defect adjacent to the prosthetic material or for 6 months. FONTAN PATIENTS 349 Tetralogy of Fallot Tetralogy of Fallot (TOF) comprises a large nonrestrictive VSD, overrid ing aorta, right ventricular out \202 ow tract (RVOT) obstruction, and right ven- tricular hypertrophy. This is the most common cyanotic cardiac lesion pre- senting outside the neon atal period. If it presents with critical cyanosis in the neonatal period, the patient may undergo a palliative Blalock \200\223Taussig shunt prior to complete repair in early childh ood. Many centers now opt for de \201 nitive repair even in the \201 rst few months of life. The vast majority of adults will have undergone some form of repair with surgical closure o f the septal defect and relief of the RVOT obstruction. Arrhythmias are an almost inevitable consequence of surgery (scarring, ventriculotomy, and pulmonary regurgitation). Late arrhythmias (both atrial and ventricular) and sudden death o ccur. Pulmonary regurgitation, ignored for many years as a benign condition, is now known to be o ne of the most important causes of morbidity and mortality in patients following RVOT surge ry. The QRS duration >180 ms on the ECG has been used as a marker for patients at risk of a rrhythmia and late sudden death. Patients should be assessed with exercise testing and MRI. A percutaneous approach to pulmonary valve implantation is now avail- able using a bovine j ugular venous valve mounted within a platinum-iridium stent and is suitable for patients wi th severe pulmonary regurgitation and out \202 ow tracts <20 mm in size. Branch pulmonary arterial stenoses should be treated aggressively by catheter intervention. Surgical insertion of a homograft valve is currently performed with perioperative mortalit y <1% in specialist centers. The majority of such conduits need replacing within a 10-year period, i.e., the need for multiple reoperations. Aortic regurgitation may also occur. Endocarditis prophylaxis is indicated in all patients prior to repair and post-repair if th ere is a prosthetic valve, a defect adjacent to the repair, or for 6 months. Fontan patients This is the de \201 nitive palliation for patients born with \200\234sing le ventricle \200\235 physiology in which all the systemic venous return is directed back t o the lungs without the bene \201 t of a subpulmonary ventricle, e.g., mitral, tricus- pid , pulmonary, or aortic atresia. It produces excellent early and mid-term survival but late failure occurs even in the most carefully selected candidates. The late problems com- prise atrial arrhythmias, sinus node dysfunction and heart block, atriov- entricular valve regurgitation, ventricular failure, v enous obstruction, and protein-losing enteropathy (<50% 5-year survival). The failing Fontan is a major challenge; transplantation or conversion to a more streamline d modi \201 cation with concomitant arrhythmia surgery should be considered. All patients need endocarditis prophylaxis. CHAPTER 8 Congenital heart disease 350 Congenitally corrected transposition of the great arteries Cyanosis is present if there is an associated ventricular septal defect (VSD) and pulmonary stenosis (PS) or if there is pu lmonary vascular disease with VSD and no PS. This is a rare lesion with normal survival in some if the lesion is isolated. There is ongoing risk of complete heart block (2% per year) . Atrioventricular valve regurgitation in association with systemic right ventricular failure is a major long-term problem, leading to decreased survival. Ebstein \200\231s anomaly of the tricuspid valve This condition is associated with apical d isplacement of the tricuspid valve and is often associated with ASD. Cyanosis occurs via ri ght-to-left shunt at the atrial level. A wide spectrum of presentations occurs depending on the severity of tricuspid valve regurgitation and associated anomalies. In infancy this presents with heart failure and cyanosis, and prognosis is poor. In the old er child or young adult, the murmur may be an incidental \201 nding, and mild forms can b e asymptomatic. Atrial arrhythmias are common and associated with pre-excitation (accessory pathways). Inte rvention is warranted if the condition is sympto- matic with heart failure and severe tricu spid regurgitation or arrhythmias. Tricuspid valve replacement or repair can be offered. In teratrial com- munications causing cyanosis or paradoxical emboli can be closed percu- tane ously if hemodynamic assessment permits. EXTRACARDIAC COMPLICATIONS 351 Extracardiac complications Polycythemia Chronic hypoxia stimulates erythropoietin productio n and erythrocytosis. The ideal Hb level is 17 \200\22318 g/dL. Some centers advocate phle botomy to control the hematocrit and prevent hyperviscosity syndrome. Follow local guidelines. Generally, consider phlebotomy only with mod- erate or severe symptoms of hyperviscosity and hematocrit >65%. Remove 500 mL of blood over 30 \200\22345 minutes and replace volume simultaneously with 50 0 \200\2231000 mL saline or salt-free dextran (if there is heart failure). Avoid abrupt cha nges in circulating volume. If hyperviscosity symptoms are the result of acute dehydration or iron de \201 ciency, phl ebotomy is not required and the patient must be rehydrated and/or treated cautiously with i ron. Renal disease and gout Hypoxia affects glomerular and tubular function, resulting in protei nuria, reduced urate excretion, increased urate reabsorption, and reduced cre- atinine clea rance. Overt renal failure is uncommon. Try to avoid dehydration and use of diuretics or radiographic contrast. Asymptomatic hyperu ricemia does not need treatment. Colchicine and steroids are \201 rst-line agents for tre atment of acute gout. NSAIDs should be avoided. Sepsis Patients are more prone to infection. Skin acne is common with poor heal- ing of sca rs. Dental hygiene is very important because of the risk of endo- carditis. Any site of sep sis may result in cerebral abscesses from metastatic infection or septic emboli. Thrombosis and bleeding Causes are multifactorial and due to a combination of abnormal plat e- let function, coagulation abnormalities, and polycythemia. PT and aPTT values may be ele vated and secondary to a fall in factors V, VII, VIII, and X. Both arterial venous throm boses and hemorrhagic complications (e.g., petechiae, epistaxis, and hemoptysis) can occur. Dehydration or oral contraceptives are risk factors for thrombotic events. Spontaneous blee ding is generally self-limited. In the context of severe bleeding general measures are effe ctive, including platelet transfu- sion, fresh frozen plasma (FFP), cryoprecipitate, and vi tamin K. Aspirin and other NSAIDs should generally be avoided to decrease chances of spontaneous bruising and bleeding. Primary pulmonary problems include infection, infarction, and hemorrhage from ruptured arte rioles or capillaries. Stroke can be either thrombotic or hemorrhagic. Arterial thrombosis, embolic events (parado xical emboli in right-to-left shunt) and injudicious phlebotomy lead to spontaneous thrombo sis. Hemostatic problems, espe- cially when combined with NSAIDs or formal anticoagulation, can lead to hemorrhagic stroke. Any injured brain tissue is also a nidus for intracranial infection or abscess formation. CHAPTER 8 Congenital heart disease 352 Complications secondary to drugs, investigations, surgery Avoid abrupt changes in blood pre ssure or systemic resistance. Contrast agents may provoke systemic vasodilatation and cause acute decompensa- tion. They may also precipitate renal failure. Before noncardiac surgery, try to optimize hematocrit and hemostasis by controlled phleboto my and replacement with dextran. High- \202 ow oxy- gen is important before and after surg ery. Use extreme caution with IV lines. Consider \201 lters in IVs. Arthralgia Arthralgia is mainly due to hypertrophic osteoarthropathy. In patients with righ t-to-left shunt, megakaryocytes bypass the pulmonary circula- tion and become trapped in sy stemic vascular beds, promoting new bone formation. Hemoptysis Hemoptysis is common. Most episodes are self-limited and precipitated by infecti on. Differentiation from pulmonary embolism may be dif \201 cult. Try to keep the patient calm and ensure adequate BP control. Give high- \202 ow oxygen by mask. If there is clinic al suspicion of infection (fever, sputum production, leukocytosis, raised CRP, etc.) start broad-spectrum antibiot- ics. A VQ scan may help in the diagnosis of pulmonary embolism but is often equivocal. Avoid use of aspirin and NSAIDs, as these exacerbate the intrinsic plate- let abnormalities . There is anecdotal evidence for the use of low-dose IV heparin, Dextran 40 (500 mL IV inf usion q4 \200\2236h), acrid (Arvin reduces plasma \201 brinogen by cleaving \201 brin ), or low-dose warfarin therapy for reducing thrombotic tendency in these patients. Severe pulmonary hem- orrhage may respond to aprotinin or tranexamic acid. Breathlessness This may be due to pulmonary edema or hypoxia (increased shunt) sec- ondary to chest infection or pulmonary infarction. Do not give large doses of diuretics or nitrate s, as this will drop systemic pressures and may pre- cipitate acute collapse. Compare chest X-ray to previous \201 lms to assess if there is radiological evidence of pulmonary edem a. JVP in patients with cyanotic CHD is typically high and should not be used as a sole marker of heart failure. Patients need higher \201 lling pressure to maintain pulmonary blood \202 ow. Give high- \202 ow oxygen by mask. Start antibiotics with clinical suspicion of infection. Give oral diuret- ics if there is e vidence of pulmonary edema or severe right heart failure. Monitor hematocrit and renal func tion closely for signs of overdiuresis. Effort syncope should prompt a search for arrhythmias, in particular VT (Holter monitor/EPS ), severe valve disease, or signs of overt heart failure. Treat as appropriate. Chest pain Chest pain may be secondary to pulmonary embolism or infarction (spon- taneous t hrombosis), pneumonia, ischemic heart disease, or musculoskel- etal causes. It requires car eful evaluation with conventional diagnostic modalities as already described. 353 Chapter 9 Arrhythmias The cardiac conduction system 354 Bradyarrhythmias: general approach 356 Sinus bradycardia 358 Sinus pause 359 Sick sinus syndrome 359 Atrioventricular block 360 Bundle branch block 362 Tachyarrhythmias: general approach 363 Tachyarrhythmias: classi \201 cation 365 ECG di agnosis of tachyarrhythmias 367 Tachycardia: emergency management 369 Drug treatment of tac hyarrhythmias 371 Supraventricular tachycardia 372 Sinus tachycardia 373 Sinus nodal reentr ant tachycardia 373 Atrial tachycardia 374 Atrioventricular nodal reentrant tachycardia (AV NRT) 375 Atrioventricular reentrant tachycardia (AVRT) 376 Junctional tachycardia 377 Atria l \201 brillation 377 Atrial \201 brillation: evaluation 379 Atrial \201 brillation: management 381 Ventricular tachycardia 384 VT in the normal heart ( \200\234benign \200\235 VT) 385 VT with impaired LV function 387 Arrhythmogenic right ventricular cardiomyopathy ( ARVC) 388 Brugada syndrome 389 Bundle branch tachycardia 390 Long QT syndrome 391 Long QT s yndrome: management 395 Arrhythmia in special situations 396 Permanent pacemakers 398 Which pacing modality? 400 Complications of pacing 401 Pacemakers for chronic heart failure 403 CHAPTER 9 Arrhythmias 354 The cardiac conduction system Cardiac action potential The intracellular resting potential of the cardiac myocyte is electrically negative with a resting transmembrane voltage betwee n \210\22250 and \210\22295 mV. The transmembrane gradient is due to the relative distrib ution of the ions K+, Na+, Cl \200\223, and Ca2+ across the cell membrane. During phase 4 of the action potential, the voltage slowly increases until a threshold of \210\22270 to \210\22265 mV is reached, which opens voltage-gated Na+ channels and trigger s depolarization via an in \202 ux of Na+ ions. The resulting voltage changes are propagat ed to adjacent cells via gap junctions between myocytes, such that a wavefront of electrica l activation is propagated. At least 10 distinct ion channels modulate the voltage changes that occur in the action potential (Fig. 9.1). Automaticity Automaticity is the unique ability of myocytes to spontaneously depolarize. It is attributed to the in \202 ux of positive ions during diastole (phase 4). At potentials more negative than \210\22260 mV ion channels open, allowing in a slow in \202 ux of cat ions. In the sinoatrial node (SAN) the slow in \202 ux of Ca2+ allows it to depolarize mor e rapidly and thus suppress other potential pacemaker sites. Sinoatrial node The SAN is normally the dominant pacemaker site in the heart and sits high in the lateral right atrium (RA) just inferior to the superior vena cava (SVC) (Fig. 9.2). It is 1 \200\2232 cm long, 2 \200\2233 mm wide, and <1 mm from the epi- cardial surface. Th e impulses generated in the SAN are conducted out of the sinus node to depolarize the surro unding RA. The SAN is richly innervated with both adrenergic and cholinergic receptors, which alter th e rate of depolarization and therefore heart rate. Electrical impulses spread out from the SAN to the rest of the RA and left atrium (LA) via specialized interatrial connections incl uding Bachmann \200\231s bundle. Atrioventricular node The atrioventricular node (AVN) is found in the RA anterior to the os tium of the coronary sinus and directly above the insertion of the septal lea \202 et of t he tricuspid valve. It is normally the only electrical connection between the atrium and ve ntricle. Electrical impulses transmitted through the AVN subsequently traverse the His bundle, which , like the SAN, is also densely innervated with sym- pathetic and parasympathetic \201 be rs. His \200\223Purkinje system The electrical impulse conducts rapidly through the His bundle into the upper part of the interventricular septum where it divides into two branches. The right bundle branch continues down the right side of the septum to the apex of the right ve ntricle and the base of the anterior THE CARDIAC CONDUCTION SYSTEM 355 papillary muscle. The left bundle branch further splits into two fascicles, anterior and po sterior. The terminal Purkinje \201 bers connect with the ends of the bundle branches, forming an interweaving network on the endocardial surface so that a cardiac impulse is transmitted al most simultaneously to the entire right and left ventricles. 1 2 0 3 \200\22360mV 4 \200\22380mV Figure 9.1 The cardiac action potential. The action potential has \201 ve parts: 0 Rapid in \202 ux of Na, causing fast depolarization 1 Rapid early repolarization due to ef \202 ux of Na+ 2 Plateau phase where repolarization is slowed by an in \202 ux of Ca2+ 3 Repol arization due to the ef \202 ux of K+ 4 Diastole with a steady-state resting transmembrane voltage and diastolic depolarization in pacemaker cells The plateau phase distinguishes th e cardiac from neuronal action potential. The release of Ca2+ during phase 3 triggers mecha nical contraction of the cell. SAN AVN MV His bundle TV Left bundle branch Right bundle branch Left anterior and posterior hemi fasicles Figure 9.2 Anatomy of the normal conduction system. AVN, atrioventricular node; MV, mitral valve; SAN, sinoatrial node; TV, tricuspid valve. CHAPTER 9 Arrhythmias 356 Bradyarrhythmias: general approach Ask speci \201 cally about previous cardiac disease, pa lpitations, fainting or blackouts (syncope), dizziness, chest pain, symptoms of heart failu re (shortness of breath, edema, exercise intolerance, orthopnea, nocturnal dyspnea), and re cent use of drugs. Examine carefully, noting the BP, JVP waveform and height (?cannon waves), heart rate, sounds and murmurs, and signs of heart failure. Investigations \200 12 lead ECG and rhythm strip: between P waves and QRS complex. A long rhythm strip is somet imes necessary to detect complete heart block if atrial and ventricular rates are similar. Blood tests: Mg2+ (especially if on diuretics), biochemical markers of cardiac injury. Ches t X-ray: 24-hour ambulatory monitor (Holter/event monitor) about ambient heart rates, inter mittent or infrequent arrhythmia and associated symptoms if present. Event monitors, useful to identify even less frequent events. Look speci \201 cally for the relationship CBC, chemistries including glucose (urgently), Cr, K+, Ca2+, \200 heart size; evidence of pulmonary edema. provides information which patients may have for a month at a time, may be Management Hemodynamically unstable patients \200 \200 Give Keep NPO of aspiration in case of cardiac arrest or when the patient lies supine for t emporary wire insertion. Secure peripheral venous access. severe hemodynamic compromise (ca rdiac Bradyarrhythmias causing arrest, asystole, SBP <90 mmHg, severe pulmonary edema, evid ence of end-organ damage including renal or cerebral hypoperfusion) require immediate treat ment often including temporary pacing (technique is described on p. 692). Give a maximum 3 mg. Give isoproterenol 0.02 \200\2230.06 mg IV if there is a delay in pacing and the patien t remains unstable. Set up an infusion (1 mg in 100 mL bag normal saline starting at 2 \200 \22310 g/min titrating to HR). Set up transvenous pacing (see Box 9.1). Bradycardia in sh ock is a poor prognostic sign. Look for a source of blood loss and begin aggressive resusci tation with \202 uids and inotropes. oxygen via facemask if the patient is hypoxic on room air. until de \201 nitive therapy has been started to reduce the risk \200 atropine 0.5 \200\2231 mg IV (Min-I-Jet ) bolus; repeat if necessary up to external pacing system if available, and arrange for initiation of BRADYARRHYTHMIAS: GENERAL APPROACH 357 Hemodynamically stable patients \200 Admit to cardiac care unit (CCU) or step-down unit when appropriate with continuous ECG mon itoring. Keep atropine drawn up and ready in case of acute deterioration. Evaluate if the p atient requires a temporary wire immediately. It may be valuable to have appropriate centra l venous access (internal jugular vein or femoral) in place in case of the need for emergen cy temporary wire insertion or aggressive resuscitation. \200 \200 Box 9.1 External cardiac pacing In emergencies, external cardiac pacing may be used but is often painful for the patient (i f conscious) and should be viewed as a temporary meas- ure until transvenous pacing can be initiated. External cardiac pacing is useful in patients who have received thrombolysis for an acute m yocardial infarction (MI) when the risks of perforation and bleeding from transvenous pacin g are high. Hemodynamically stable patients with anterior MI and bifasicular block may be managed simpl y by application of the external pacing electrodes and having the pulse generator ready if necessary. Familiarize yourself with the machine in your hospital as soon as possible \200\224a cardiac arrest is not the time to read the manual. CHAPTER 9 Arrhythmias 358 Sinus bradycardia The sinoatrial node discharges <60/min. P waves are normal in appear- anc e. It is often normal in sleep and in athletes and healthy young adults. Causes \200 \200 \200 \200 Hypothyroidism Hypothermia Ischemia or infarction of the sinus node Chronic degeneration of sinus or AV nodes or atria Cholestatic jaundice Raised intracranial pressure Cervical and mediastinal tumors Young athletic individual B-blockers, calcium Drugs ( channel blockers, digoxin, morphine, amiodarone, lithium, propafenone, clonidine) Increased vagal tone \200 \200 \200 \200 \200 \200 \200 Vasovagal syncope Nausea or vomiting Carotid sinus hypersensitivity Acute MI (especially in ferior) Nasal or endotracheal suctioning Management If hypotensive or presyncopal \200 \200 \200 \200 \200 \200 Atropine 0.5 mg IV bolus repeating as necessary. Isoproterenol infusion 2 \200\22310 g/mi n. Theophylline infusion 0.2 \200\2230.7 mg/kg/hr. Temporary pacing. Avoid and correct prec ipitants. Stop drugs that may suppress the sinus or AV nodes. Long-term treatment \200 If all possible underlying causes have been removed and symptomatic bradycardia remains, re fer for permanent pacing. Consider Holter monitoring in patients with possible episodic bra dycardia. R-R intervals >2.5 seconds may require permanent pacing, especially if associated with symptoms. SICK SINUS SYNDROME 359 Sinus pause The SAN fails to generate impulses (sinus arrest) or the impulses are not condu cted to the atria (SA exit block). The PP interval with sinus pause does not equal a multip le of the basic sinus interval (PP). A single dropped P wave with a PP interval that is a m ultiple of the basic PP interval suggests exit block. A period of absent P waves suggests s inus arrest. Causes include excess vagal tone, acute myocarditis, MI, aging ( \201 brosis), stroke, digoxin toxicity, and antiarrhythmic drugs. Sick sinus syndrome This syndrome encompasses a number of sinus node problems: 1) persist- ent, inappropriate sinus bradycardia not caused by drugs; 2) sinus arrest or exit block; 3) SAN and AV conduction disturbances; 3) paroxysms of atrial, supraventricular, or junctiona l tachyarrythmias alternating with slow atrial or ventricular rates. It is usually diagnose d by ambulatory cardiac monitoring. CHAPTER 9 Arrhythmias 360 Atrioventricular block AV block occurs when an impulse from the atria is conducted with del ay or not conducted at all to the ventricle. This can occur at the level of the AVN (nodal) or His \200\223Purkinje system (infranodal). Common causes are ischemic heart disease, conduction system \201 brosis (aging), calci \201 c aortic stenosis, congenital, cardiomyopathy, hypothermia, hypothyroidism, trauma, ra diotherapy, infection, connective tissue disease, sarcoidosis, tick-born diseases, and anti -arrhythmic drugs (see Box 9.2). AV block is classi \201 ed as follows. First-degree AV block Every impulse conducts to the ventricle but the conduction time is pr o- longed. Every P wave is followed by a QRS but with a prolonged PR inter- val (>200 ms). If the QRS width is normal on ECG, then the delay is usually in the AV node. If the QRS sho ws aberration (RBBB or LBBB), then the delay may be in the AV node or His \200\223Purkinje system. Second-degree AV block Some, but not all, atrial impulses are conducted to the ventricle. Mobitz type 1 (Wenckebach) ECG shows a regularly irregular rhythm with grouped beating and progres- sive prolongation of the PR interval until the P wave is not conducted. The PR int erval following the dropped P wave is the shortest in the sequence. The RR interval is ther efore irregular. This block is characteristic of normal AVN physiology and generally is a stable rhythm that does not progress to advanced AVN block. Mobitz type 2 ECG shows a stable PR interval with periodic block of the atrial impulse at a ratio of 2:1, 3:1, or 4:1. Block is predominantly below the AVN at the His bundle and ther e is often an aberrant pattern to the QRS complex. Type 2 block is an unstable rhythm that often predates the development of complete AV block. Third-degree AV block (complete heart block) There is no conduction of atrial impulses to t he ventricle. The ECG shows no relationship between P and QRS complexes (dissociation). Generally, a ventricular pacemaker originating just below the site of the block takes over. A narrow QRS usually indicates block in the AVN and the His bundle is the pacemaker, which is faster and more stable than more distal sites. A wide QRS indicates infranodal block an d a distal, slower ventricular pacemaker. Distal block carries a worse prognosis and a greater risk of sudden asystole. ATRIOVENTRICULAR BLOCK 361 Box 9.2 Causes of atrioventricular block \200 Valvular disease (aortic stenosis, incompetence, endocarditis) Myocarditis (diphtheria, rhe umatic fever, viral, Chagas \200\231 disease, tick-borne) Associated with neuromuscular dis ease, i.e., myotonic dystrophy. Collagen vascular disease (SLE, rheumatoid arthritis, scler oderma) Cardiomyopathies (hemochromotosis, amyloidosis) Granulomatous disease (sarcoid) Con genital heart block Congenital heart disease (ASD, Ebstein \200\231s, PDA, L-transposition) Acute myocardial infraction or ischemia Drugs ( Ca2+-blockers) Conduction system \201 bro sis (Lev and Lenegre syndromes) Increased vagal tone Trauma or following cardiac surgery Hy pothyroidism (rarely thyrotoxicosis) Hypothermia Hyperkalemia and other electrolyte abnorma lities Hypoxia In \201 ltrative diseases (amyloidosis) B-blockers, digitalis, \200 \200 \200 \200 \200 CHAPTER 9 Arrhythmias 362 Bundle branch block Bundle branch block (BBB) is due to disease in the His \200\223Purkinje system resulting in conduction delay that manifests as a prolonged QRS on sur- face ECG (Q RS >120 ms). Common causes are conduction system \201 brosis (aging), ischemic heart dise ase, hypertension, cardiomyopathies, cardiac surgery, and in \201 ltrative diseases (see B ox 9.3). LBBB: left ventricular depolarization is delayed, giving large notched R waves in leads I a nd V6 and an inverted-M pattern in V1. Block con \201 ned to the anterior or posterior fas cicles of the left bundle gives left-axis or right-axis deviation, respectively, on the ECG . BBB leads to asynchronous contraction of the left and right ventricles, which worsens fun ction. RBBB: right ventricular depolarization is delayed, giving an RSR pattern in V1 and a promin ent S wave in I and V6. This can be a normal variant but more commonly is due to causes lis ted in Box 9.3 as well as atrial septal- defect (ASD), pulmonary embolism (PE), and cor pul monale. Bifascicular block = RBBB + left anterior hemiblock (left-axis deviation on ECG), RBBB + le ft posterior hemiblock (right-axis deviation on ECG) or LBBB. All of these may progress to complete AV block. Trifascicular block = bifascicular block + \201 rst-degree AV block.