Infantile hypertrophic cardiomyopathy masquerading as cardiac tamponade: A case report

Introduction

Hypertrophic cardiomyopathy (HCM) is a form of cardiomyopathy characterized by fibrosis and hypertrophy of the left ventricle (LV), most commonly found in boys. It accounts for 25%–40% of pediatric cardiomyopathy, with the highest incidence reported in children <1 year of age. ¹ Although the onset may vary, the incidence peaks during infancy and the pre-adolescent period. ² Infantile HCM, particularly, often progresses rapidly, with 30% of affected infants experiencing death or requiring heart transplantation. ² In addition, its clinical presentation is often nonspecific and difficult to distinguish from other causes of dyspnea and respiratory distress.^1,3 Therefore, meticulous diagnostic evaluation is essential to correctly identify HCM before initiating an appropriate treatment.

HCM yields a similar clinical presentation with massive pericardial effusion (PEF) manifesting as cardiac tamponade^2,3 because they share a similar pathophysiology of impaired diastolic filling that prevents blood from entering the heart. Impaired diastolic filling increases left ventricular end-diastolic pressure (LVEDP) and pulmonary capillary wedge pressure which in turn cause dyspnea and respiratory distress.^{2 –4} Even though HCM and PEF share similar pathophysiology, treatment strategies are hugely different. Thus, we aim to present a case of infantile HCM mimicking cardiac tamponade, emphasize shared pathophysiology between the two disease entities and underscore the importance of diagnostic strategy so that treatment can properly be initiated.

Case presentation

A 4-month-old female infant presented to our emergency department with worsening breathlessness 1 week prior to admission. She was born at term (39 weeks) to non-consanguineous parents of Asian origin, with no family history of cardiac disease. Delivery was via cesarean section due to cephalopelvic disproportion. Birth weight was 3148 g, and Apgar scores were 7, 8, and 9 at 1, 5, and 10 min, respectively. Maternal history was unremarkable. Physical examination revealed unobtainable blood pressure, tachycardia (180 beats/min), respiratory rate of 56 times per minute, intercostal retractions, nasal flare, muffled heart sounds, cold and clammy skin. Monitor ECG showed sinus tachycardia. Laboratory evaluation showed only mild anemia (hemoglobin 10.8 g/dL). Unfortunately, blood gas analysis couldn’t be performed since blood sample was unobtainable. Chest X-ray (CXR) demonstrated cardiomegaly with a globular cardiac silhouette (Figure 1). Considering severe respiratory distress, indiscernible heart sounds and globular heart morphology, we suspected cardiac tamponade and performed echocardiography immediately. Echocardiogram showed significant LV wall (18–24 mm) and interventricular septum hypertrophy (21 mm; Figure 2(a) and (b)), causing reduced LV cavity of 17 mm with preserved LV ejection fraction of 67%. Mild PEF was found at posterolateral LV and lateral right atrium (RA) with no signs of tamponade (Figure 3(a) and (b)). Additionally, there was insignificant dynamic gradient at left ventricular outflow tract (LVOT) around 10–13 mmHg (Figure 3(c)) and atrial septal defect of 4–5 mm (Figure 2(a)). Since we determined HCM as the patient’s main diagnosis, we focused the treatment strategy on relieving severe diastolic dysfunction and congestion by initiating intravenous furosemide 6 mg b.i.d. Despite preliminary treatment, the patient’s condition deteriorated rapidly and she ultimately passed away.

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Figure 1.

Chest X-ray showed cardiomegaly with globular heart morphology, prompting emergent TTE to confirm suspicion of massive PEF and cardiac tamponade.

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Figure 2.

(a) Apical four-chamber showed interventricular septum hypertrophy (IVSd 21 mm, +2 z-score 5.2 mm), right ventricular anterior wall hypertrophy (RVAWd 13 mm, +2 z-score 3.8 mm) and ASD of 5 mm. (b) Parasternal short axis view showed left ventricular posterior wall hypertrophy (LVPWd 18 mm, +2 z-score 5.1 mm). Left ventricular end-diastolic diameter (LVEDD) was smallish (17 mm, −2 z-score 17.4 mm). LVEDD measurement isn’t shown in Figure 3.

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Figure 3.

(a) and (b) Apical four-chamber view showed mild PEF at lateral RA (4–6 mm) and lateral LV (4–8 mm). (c) Pulsed wave Doppler showed a gradient of 13 mmHg. This doesn’t suit the criteria of significant LVOTO in HCM.

Discussion

HCM in infancy is rare with an estimated annual incidence of 1.24 per 100.000 children under 10 years of age. It often presents with atypical symptoms, which complicate diagnostic establishment, and carries a high mortality risk once diagnosed. ⁵ Our patient presented with severe respiratory distress which can occur due to various etiologies: airway obstruction, pulmonary, cardiovascular, or neuromuscular abnormalities. Of all abnormalities, the most frequently found are bronchiolitis, pneumonia, cardiogenic pulmonary edema, airway obstruction, and intracardiac or intrapulmonary shunting.^6,7

Physical examination demonstrated no stridor, wheezing, or crackles, so airway obstruction, bronchiolitis, and pneumonia were crossed out of possible working diagnosis. Indiscernible heart sounds and a severely distressed clinical presentation raised initial suspicion of cardiac tamponade and intracardiac shunt. Unexpectedly, the echocardiogram showed classical HCM with mild PEF surrounding posterolateral LV and lateral RA. Atrial septal defect was also identified, but that was insufficient to explain her symptoms. Diastolic LV posterior wall (18 mm; +2 z-score 5.1 mm) and interventricular septal (21 mm; +2 z-score 5.2 mm) were significantly hypertrophied, exceeding the +2 z-score threshold. Such extreme hypertrophy led to diastolic dysfunction and reduced LV capacity. Since LV became unable to accommodate pulmonary venous return, pulmonary capillary pressure increased and caused dyspnea. ⁴

Reduced LV filling due to HCM increases LVEDP, left atrial, pulmonary venous, and subsequently capillary pressures that serve as a compensatory mechanism to maintain forward flow to the LV. However, it also increases pressure in the RA, RV, and lymphatic system.^4,8 Since lymphatic system plays an important role in pericardial fluid drainage and clearance, such increased pressure disrupts pericardial fluid clearance and promotes PEF. ⁸ PEF will further impede ventricular filling, increase intracardiac pressure and aggravate the clinical manifestation of dyspnea. PEF also worsens diastolic dysfunction and begins a vicious cycle of HCM, pulmonary hypertension (PH), and PEF (Figure 4). Since less blood could get into the patient’s heart, less blood could also be ejected by the RV and LV, leading to hypotension, vital organ hypoperfusion, shock, and finally death, as can be seen in our case.

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Figure 4.

Vicious cycle of HCM, PH and PEF: diastolic impairment due to HCM creates an “obligatory” increase of pulmonary pressure resulting in PH which, in turn, transmit pressure increase resulting in lymphatic congestion and fluid accumulation surrounding the heart.

PEF typically arises from (1) increased production due to infectious or non-infectious inflammation (mostly exudate), (2) impaired reabsorption or drainage such as in heart failure (HF) or PH (mostly transudate), (3) systemic conditions (e.g., hypoalbuminemia, hypothyroidism), or (4) cardiac and/or great vessel injury (hemopericardium).^8,9 We didn’t perform pericardiocentesis in this case because there was only mild PEF so we can’t confirm whether it was transudate, exudate or hemopericardium. Yet, given the absence of infection and prior cardiac and/or great vessel injury, a transudative effusion secondary to HF and/or PH in HCM was most likely.

Studies about PEF in pediatric patients with HCM are limited. A study by Puwanant et al. ⁸ reported the prevalence of concomitant HCM and PEF in adults was 9%, with more than 50% being mild (<1 cm throughout the cardiac cycle). ⁸ The study also showed associations between PEF, PH, and RV hypertrophy. ⁸ Our patient showed both PEF and RV hypertrophy (13 mm; +2 z-score 3.8 mm), suggesting possible PH despite the absence of overt PH signs.

Physical examination and ECG are essential to distinguish HCM from cardiac tamponade because clinical symptoms and CXR may similarly demonstrate dyspnea and cardiomegaly. Indistinct heart sounds of cardiac tamponade and systolic murmur indicating the presence of LVOT obstruction (LVOTO) of HCM are helpful. ECG is also useful since low voltage QRS complex is typical for massive PEF, while signs of left ventricular hypertrophy and left bundle branch block are characteristic of HCM. However, echocardiography is still needed to visualize hypertrophied myocardium and PEF. Genetic or metabolic studies should have been performed to confirm HCM. Unfortunately, we had no access to such advanced diagnostic modalities and, therefore, relied primarily on an echocardiogram. We also didn’t perform an autopsy or histopathological confirmation. These should be noted as limitations of our study.

Our case revealed insignificant gradient at LVOT (<30 mmHg), thus, it was considered non-obstructive as in adult patients.^10,11 In case of preserved ejection fraction (>50%), treatment includes beta-blockers (BB) or non-dihydropyridine calcium-channel blockers (NDHP-CCB) to prevent dysrhythmia, reduce LVOTO and lower heart rate to improve diastolic filling. However, BB and NDHP-CCB were inappropriate in this case because the patient presented with shock. Initiating inotropic and/or vasopressor requires careful consideration. Dobutamine or vasoconstrictor with β-adrenergic agonism induces LVOTO by increasing contractility and HR. Calcium sensitizers like levosimendan enhance calcium sensitivity, fluxes and trapping, potentially leading to ventricular arrhythmia. Meanwhile, phenylephrine is preferred because of its α-1 agonism and reflex bradycardia effect that can improve diastolic filling and cardiac output. Vasopressin is also beneficial not only because of its α-1 agonist property but also selective pulmonary vasodilation through release of nitric oxide that enhances pulmonary blood flow, venous return, and consequently preload. ¹² Phenylephrine or vasopressin should have been initiated early because it could have improved preload, diastolic filling, and cardiac output. Before we could start phenylephrine or vasopressin, hemodynamic status deteriorated rapidly, and our patient ultimately passed away. Prior case of childhood HCM complicated by shock and PEF showed similar poor outcomes, but didn’t explain particularly the use of phenylephrine or vasopressin. ¹³

Generally, diuretics can be given for persistent symptoms of HF despite BB in non-obstructive HCM.^11,14 There hasn’t been any literature discussing whether diuretics can be given prior to BB. Because BB was inappropriate in this case due to the presence of shock, we decided to give diuretics first to manage severe congestion. We acknowledged the risk of reduced preload due to diuretics in our case, but we already anticipated this by securing adequate intravenous access. Unlike in non-obstructive HCM, diuretics are avoided in obstructive HCM.^3,15

BB should be administered in childhood HCM, provided there are no signs of shock, for patients at higher risk of sudden cardiac death: previous VT/VF, unexplained syncope, non-sustained ventricular tachycardia and extreme hypertrophy.^3,14,16 BB reduces septal hypertrophy, normalizes LV cavity size and improves LVOTO in infantile HCM as previously reported by Codazzi et al. ¹ Yet, some infants could still have markedly thickened interventricular septum with progressive increase of LVOTO despite BB as reported by Li et al. ⁵ who subsequently underwent alcohol septal ablation with good results: no systolic anterior motion causing LVOTO and normal ventricular wall motion. Specific guidelines on how to treat HCM complicated by PEF and shock are based only on observational data and expert consensus. The broad gap in knowledge should be covered in further study.

Conclusion

In summary, we report a case of a 4-month-old infant with HCM mimicking cardiac tamponade. HCM and cardiac tamponade may present with similar clinical presentation because they share a common pathophysiology of impaired LV diastolic filling. Echocardiography remains the diagnostic tool of choice to distinguish HCM from cardiac tamponade.