Wednesday, August 18, 2010

Congenital heart disease: Complications

Complications of Cong. HD. include:
  • Congestive heart failure (CHF).
  • Cyanosis.
  • Pulmonary hypertension (PHT).
  • Infective endocarditis.
  • Impaired growth.
  • Acid-base abnormalities.
  • Syncope.
  • Chest pain.
  • Sudden death.



Congestive Heart Failure (CHF):

Reserve mechanisms in the neonate:

Neonates are more prone to CHF since the reserve mechanisms in the neonatal heart are limited:
  • Preload (Diastolic) reserve: Myocardial stiffness in the neonate is relatively high; thus little ventricular filling causes marked increase in wall stress, limiting the benefit from the Frank-Starling’s law of the heart.
Frank-Starling's law: Stroke volume increases with increasing preload, up to a limit, after which the stroke volume starts to decrease.
http://www.rcsed.ac.uk/journal/vol46_1/4610023.gif






Frank Starling curves under different conditions.
http://www.education.science-thi.org/edu_hf/images/fsm1a.jpg


  • Contractile (Systolic) reserve: This is also limited since the neonatal heart under basal conditions already functions near its peak performance because of:
    • Relatively less myofilaments.
    • Relatively higher O2 consumption.
  • Heart rate reserve: Again this reserve is limited since the intrinsic heart rate in neonates is normally quite high.


Incidence of CHF in neonates with Cong. HD:
  • CHF occurs in 20 % of all cases of Congenital HD.
  • And in 80 % of those requiring cardiac catheterization or surgery in their first year of life.


Onset of CHF in neonates with Cong. HD:
  • Onset of CHF almost always occurs during the 1st year of life.
  • Beyond the 1st year, CHF is rare and usually needs a precipitating factor such as:
    • Endocarditis,
    • Myocarditis,
    • Cardiomyopathy,
    • Pneumonia,
    • Arrhythmia,
    • Anemia.


Etiology of CHF in neonates with Cong. HD:
  • In the preterm: most commonly patent ductus arteriosus (PDA).
  • In the full-term: First day:
    • Volume overload: Left-to-right shunts, valve regurgitation.
    • Acute myocardial depression: Hypoglycemia, hypoxia, anemia, hypocalcemia, septicemia.
  • In the full term: First 2 weeks:
    • Pressure overload: Critical AS, aortic atresia, coarctation or interruption of the aorta.
  • In the full term: beyond 2 weeks:
    • Left-to-right shunt: Ventricular septal defect (VSD), Patent ductus arteriosus (PDA), Aorticopulmonary septal defect (APSD).
    • Transposition of the great arteries (TGA).


Clinical picture of CHF in neonates with Cong. HD:
  • Common manifestations:
    • Tachypnea & dyspnea (Feeding difficulty).
    • Tachycardia (160-180 beats/minute).
    • Failure to gain weight.
    • Basal crepitations (left ventricular failure: LVF).
    • Hepatomegaly (right ventricular failure: RVF).
  • Less common manifestations :
    • Edema.
    • Ascites.
    • Sweating.
    • Gallop rhythm.
    • Pulsus alternans.
  • Rare manifestations:
    • Pleural effusion.
    • Pericardial effusions.



Left-sided or right-sided heart failure?

Distinction between left-sided & right sided heart failure in the infant is usually difficult because:
  • Left-sided heart failure usually leads to right sided heart failure, due to:
    • Left-to-right shunt via PFO or PDA.
    • Development of Pulmonary Hypertension (PHT).
    • Bernheim effect: elevated LV pressure leads to push of the ventricular septum to the right encroaching on RV cavity.
  • Right-sided heart failure usually also leads to left-sided heart failure due to reversed Bernheim effect: elevated RV pressure leads to push of the ventricular septum to the left encroaching on LV cavity.



End-stage CHF:

At the end stage of CHF, marked tissue hypo-perfusion occurs with:
  • Renal hypo-perfusion & oliguria,
  • Cardiogenic shock will be the end with very poor prognosis.


Chest x-ray in neonates with Cong. HD and CHF:
  • Cardiomegaly is common.
  • Pulmonary venous congestion (PVC) and pulmonary edema are also common.
  • Lung collapse may occur, usually due to compression of the left bronchus.
  • Pericardial effusion is rare.
  • Pleural effusion is also rare.


Echocardiography in neonates with Cong. HD and CHF:

Echocardiography helps two main jobs:
  • Diagnosis of the underlying congenital heart disease.
  • Assessment of ventricular volumes and function.


Management of CHF in neonates with Cong. HD:
  • Etiologic treatment, i.e. management of the underlying Cong. HD.
  • General measures: rest, O2 therapy…etc
  • Standard anti-failure measures:
    • Inotropic drugs: Digoxin orally, Dobutamine iv infusion…etc
    • Diuretics, as needed.
    • Vasodilators, as needed.
  • Prostaglandin E1 to open the ductus or Endomethacin to close it, as per case.
  • Intra-aortic balloon pump may be needed.
  • Interventional catheterization may be needed.
  • Surgery may be needed.




Cyanosis:


Cyanosis is classified into 3 main types:
  • Peripheral cyanosis.
  • Central cyanosis.
  • Differential cyanosis.


Peripheral cyanosis:

Peripheral cyanosis is seen only in the skin, but not the mucus membranes, and improves with warming.


It occurs due to stagnation of blood, which increases O2 extraction from the blood by tissues, leading to higher Areteriovenous (AV) O2 gradient; Arterial blood O2 saturation is normal, while venous O2 saturation is very low.


Causes of peripheral cyanosis include:
  • CHF.
  • Shock.
  • Cold weather.
  • High Hemoglobin (Hb) Content of the blood.


Central cyanosis:

Central cyanosis may be due to cardiac, pulmonary or blood diseases:
  • Cardiac causes include: congenital cyanotic heart disease, and Eisenmenger’s syndrome. In congenital cyanotic heart disease inhalation of 100% O2 does not improve cyanosis. In those patients, exercise may intensify cyanosis by increasing O2 extraction by tissues, and increasing the right-to-left shunt, due to drop of systemic vascular resistance (RS).
  • Pulmonary causes: e.g. persistent fetal circulation, respiratory distress syndrome, parenchymal lung disease... etc. Pulmonary disease can interfere with oxygenation of pulmonary venous blood: thus inhalation of 100% O2 may reduce or abolish cyanosis.
  • Blood causes: e.g. abnormal hemoglobin.


Congenital cyanotic heart diseases may be classified into:
  • Vascular anomalies ( 4 T + 1):
    • Tetralogy, triology & pentalogy of Fallot.
    • Transposition & mal-position complexes including: Complete Transposition of the Great Arteries (TGA), isolated ventricular inversion, Corrected TGA, double-outlet right ventricle (DORV), double-outlet left ventricle (DOLV), and Single ventricle.
    • Truncus arteriosus: types I, II, III, and IV.
    • Total anomalous pulmonary venous drainage.
    • +1: Pulmonary AV Fistula.
  • Valvular anomalies: (4 At + 1):
    • Atresia of the mitral, aortic, tricuspid, or pulmonary valve.
    • +1: Ebstein’s anomaly.


Differential cyanosis:

In differential cyanosis; either the upper or the lower half of the body is cyanosed, while the other half is normal.
  • Lower body only is cyanosed in the following conditions:
    • Eisenmenger’s PDA: right-to-left shunt via PDA due to development of severe pulmonary vascular obstructive disease with marked PHT that exceeds the systemic pressure.
    • PDA plus severe coarctation of the aorta: the pressure in the descending aorta distal to the site of coarctation is very low & the descending aorta is supplied from the RV via the PDA.
    • Interruption of the aortic arch: upper body is supplied from LV while lower body from RV via PDA.
  • Upper body only is cyanosed in the following conditions:
    • This occurs in presence of a combination of PDA plus Coarctation plus TGA: upper body is supplied by RV to ascending AO. Lower body is supplied by LV to PA to PDA to descending AO distal to coarctation.



Complications of cyanosis:
  • Polycythemia, Fe-deficiency anemia, Abnormal Red Blood Cell (RBC) deformability.
  • Coagulation defects, Hemoptysis.
  • Paradoxical embolism from right-to-left.
  • Hyperuricemia.
  • Retinopathy.
  • Hypoxic spills.
  • Clubbing.


Treatment of hypoxic spills:
  • Knee-chest or Squatting position.
  • Oxygen therapy.
  • Morphine i.v. injection.
  • β-Blockers, particularly Propranolol.
  • α-Stimulants may be used to increase the RS and thereby reduce right-to-left shunting.
  • Na HCO3: For metabolic acidosis.





Pulmonary Hypertension (PHT):


In the fetus; the pulmonary artery (PA) pressure is equal to the aortic pressure.


By age 7 days after birth, PA pressure drops to the adult level, after ductal closure.


In the adult; the PA pressure is much lower than the aortic pressure:
  • PA Systolic pressure: 15-30 mmHg.
  • PA Diastolic pressure: 5-10 mmHg.
  • PA Mean pressure: 10-20 mmHg.


Etiology of PHT:


PHT results from increased blood volume contained in the pulmonary circulation, which later on leads to pathological changes in the pulmonary vasculature; i.e. Pulmonary Vascular Obstructive Disease (PVOD).




Excess pulmonary blood volume may result from either:
  • Excess flow of blood from the right side of the heart leading to pulmonary plethora.
  • Or obstruction to pulmonary venous return leading to pulmonary congestion.


Pulmonary Vascular Obstructive Disease (PVOD):


PVOD results from pathological changes in the pulmonary vasculature including: obliterative changes, vasoconstriction and endothelial injury. Immature pulmonary vessels are more prone to be affected by these pathological changes.




Histology of PVOD (Heath-Edwards classification):


According to Heath-Edwards classification, PVOD passes into six stages, some of them are reversible, if the cause is removed:
  1. Medial thickening: Reversible.
  2. Intimal proliferation: ? Reversible.
  3. Intimal fibrosis: Unlikely reversible.
  4. Plexiform dilatations: Irreversible.
  5. Medial fibrosis: Irreversible. 
  6. Medial necrotizing arteritis: Irreversible


Cong. HD. patients at increased risk of developing PVOD:


The following congenital anomalies are particularly at high risk of developing PVOD:
  • Transposition and mal-position complexes, especially: Complete TGA, DORV and single ventricle.
  • Persistent truncus arteriosus (PTA).
  • Big VSD.


Contraindications to surgical correction of Cong. HD:


Surgery for correction of Cong. HD. is contraindicated in the following conditions:
  • If Rp is already very high: the histology of PVOD is irreversible, right-to-left shunt is about to occur, and no benefit is expected from surgery, as occurs in patients with:
    • Rp of 11 U. or more.
    • Rp / Rs ratio of 0.7 or more.
  • When Rp is higher than Rs Eisenmenger's syndrome is already there and the right-to-left shunt is now essential for life. Closure of the shunt in these cases will be fatal.
  • Ratio of pulmonary blood flow (Qp)/ systemic blood flow (Qs) < 1.5: 
    • In patients with normal Rp, the disease is still mild, surgery is not yet needed, and the patient can be followed up safely.
    • In patients with elevated Rp, on the other hand, Qp/Qs < 1.5 indicates marked elevation of the right-sided pressures with decreasing left-to-right shunt that is going to reverse; thus no benefit is expected from surgery.


Clinical examination of the patient with PHT:
  • General examination:
    • Cyanosis & clubbing: in presence of right-to-left shunt.
    • Big a-waves in neck veins: in presence of high right ventricular pressure.
    • Big v-waves in neck veins: in presence of tricuspid regurgitation).
    • Signs of ystemic venous congestion.
  • Inspection & palpation may show:
    • Palpable PA expansion in pulmonary area.
    • Palpable pulmonary second sound (P2).
    • Signs of right ventricular hypertrophy (RVH).
  • Auscultation may reveal:
    • Systolic murmur & click and high P2 in pulmonary area.
    • Signs of pulmonary and/or tricuspid regurgitation.




Infective endocarditis with Cong. HD:


The following congenital cardiac anomalies are at particularly high risk of developing infective endocarditis:
  • Tetralogy of Fallot (TOF).
  • Congenital aortic stenosis (AS).
  • Ventricular septal defect (VSD).
  • Patent ductus arteriosus (PDA).


Arterial blood gases and acid-base abnormalities in Cong. HD:
  • Right-to-left shunts result in hypoxia.
  • Low cardiac output (e.g. left ventricular outflow tract obstruction & congestive heart failure) result in tissue under-perfusion with metabolic acidosis.
  • Pulmonary venous congestion may cause hypoxia & hypercapnia.
  • Severe hypoxia results in metabolic acidosis, hyperventilation & hypocapnia.


Causes of impaired growth in patients with Cong. HD:
  • Chromosomal abnormalities.
  • Anorexia & poor feeding.
  • Infections: Intra or extra uterine.
  • Chronic CHF.
  • ABG, Acid-base, and Electrolytes disturbances.
  • Mal absorption & protein loss.
  • Endocrine causes.


Causes of chest pain in patients with Cong. HD:
  • Angina: (manifested as irritability during feeds):
    • Anomalous coronary artery.
    • Severe aortic stenosis (AS).
    • Severe pulmonary stenosis (PS).
  • Non-anginal pain: pericarditis, pleurisy, musculoskeletal, mitral valve prolapse (MVP).


Causes of syncope in patients with Cong. HD:
  • Arrhythmia: as in cases of: Long QT syndrome, sick sinus syndrome (SSS), and complete heart block (CHB).
  • Severe AS and other causes of left ventricular outflow tract (LVOFT) obstruction.
  • Pulmonary hypertension (PHT).
  • Left atrial (LA) myxoma.


Causes of sudden death in patients with Cong. HD:
  • Arrhythmia.
  • Severe LVOFT obstruction.
  • Cardiomyopathy, myocarditis.
  • Severe PHT.
  • Endocardial fibroelastosis.
  • Severe cyanosis & hypoxia.
  • Coronary arterial anomalies.