Vasopressin role in hypertrophic obstructive cardiomyopathy post-cardiac surgery: A case report

Abstract

BACKGROUND

Managing left ventricular outflow tract obstruction (LVOTO) and systolic anterior motion (SAM) of the mitral valve can be challenging, especially in the context of circulatory shock and pulmonary edema post cardiac surgery.

CASE SUMMARY

We describe a case of an 80-year-old female patient with a history of severe aortic stenosis and hypertrophic obstructive cardiomyopathy that underwent aortic valve replacement and myectomy. The patient presented with acute pulmonary edema and low blood pressure due to LVOTO and SAM post cardiac surgery in the intensive care unit. She was paced with an epicardial dual-chamber pacing system due to complete atrioventricular block and treated initially with norepinephrine, furosemide, and esmolol infusion and continuous positive pressure ventilation. The patient remained hypoxemic and kept deteriorating hemodynamically despite titrating up norepinephrine. The addition of vasopressin infusion and tapering of norepinephrine finally stabilized the patient with significant reduction of LVOTO, confirmed by transthoracic echocardiography assessment, improved oxygenation and increased urine output.

CONCLUSION

Vasopressin seems to be the preferred vasopressor for managing LVOTO and SAM post-cardiac surgery, because of its absence of inotropic effects. Echocardiography is crucial for early diagnosis and therapeutic management.

Key Words: Vasopressin; Hypertrophic obstructive cardiomyopathy; Aortic valve replacement; Cardiac surgery; Myectomy; Case report

Core Tip: Left ventricular outflow tract (LVOT) obstruction is a condition in which the LVOT is obstructed. Aortic valve stenosis and hypertrophic cardiomyopathy are the most common causes of LVOT obstruction. We report a case of severe aortic stenosis and hypertrophic obstructive cardiomyopathy that underwent aortic valve replacement and myectomy. Management of patients with hypertrophic obstructive cardiomyopathy and systolic anterior motion remains a clinical challenge. Bedside echocardiogram guided therapeutic decisions has central role in such complex case patients to improve outcome. Vasopressin has been shown to reduce LVOT gradient and seems to be the vasoconstrictive drug of choice in such patients.

INTRODUCTION

Left ventricular outflow tract obstruction (LVOTO) and systolic anterior motion (SAM) of the mitral valve (MV) are significant clinical manifestations of hypertrophic obstructive cardiomyopathy (HOCM) that can lead to important hemodynamic compromise. LVOTO is characterized by the narrowing of the left ventricular outflow tract (LVOT) due to remarkable cardiac anatomical characteristics noticed in HOCM, such as a hypertrophied interventricular septum. Concurrently, structural abnormalities of the MV, along with altered papillary muscle positioning, may precipitate SAM, defined by the anterior movement of the MV during systole[1]. These phenomena are generally linked to HOCM but may also occur in other contexts, including post-cardiac surgery[2].

Post aortic valve replacement (AVR), dynamic LVOTO may arise from alterations in ventricular loading conditions, myocardial contractility, septal morphology, or systemic vascular resistance. Timely recognition and management of this complication is essential. These entities should be promptly suspected, as delayed or inadequate treatment may have catastrophic consequences for the patient[3]. In this article, we describe a case of an elderly female patient who experienced dynamic LVOTO and SAM immediately after AVR surgery. We emphasize the crucial importance of regular transthoracic echocardiographic (TTE) evaluations and the therapeutic advantages of vasopressin in this context.

CASE PRESENTATION

Chief complaints

An 80-year-old female consulted a cardiac surgery ambulatory clinic with a history of deteriorating exertional dyspnea.

History of present illness

An 80-year-old female (height 168 cm; weight 72 kg) with a history of deteriorating exertional dyspnea due to severe aortic stenosis and HOCM (septum 14 mm, resting outflow gradient 70 mmHg) underwent AVR (Avalus Medtronic bioprosthesis, No. 21 mm) and septal myectomy. Perioperatively, reintroduction to cardiopulmonary bypass (CPB) and transfusion of blood products were necessary due to bleeding from the cannula insertion sites requiring surgical sutures, resulting in a CPB total time of 93 minutes.

Figure 1 Electrocardiogram on admission. Paced rhythm due to complete atrioventricular block.

History of past illness

The patient has a history of aortic stenosis and HOCM with regular echocardiographic follow-up.

Personal and family history

Patient had no other personal or family history.

Physical examination

Upon admission to the ICU the patient had a norepinephrine infusion of 0.1 μg/kg/minute. MBP was 70 mmHg and UO ranged from 150 to 200 mL/hour. Atrioventricular sequential pacing was necessary due to complete atrioventricular block (Figure 1). HR and atrio-ventricular delay modifications didn’t result in significant alterations in BP or CO, and they were stabilized at 70 beats per minute and 180 milliseconds respectively. Six hours later she was successfully weaned from mechanical ventilation according to our institute’s protocol, despite a slight impairment of UO (80 mL/hour). Gradually, the patient started becoming hypoxemic, exhibiting pulmonary congestion on X-rays (Figure 2A). Intravenous furosemide was given and oliguria improved (> 150 mL/hour) but with no improvement of oxygenation and a concomitant drop of BP (systolic BP = 100 mmHg, MBP = 60 mmHg). Given the history of left ventricular hypertrophy and LVOTO, 500 mL of N/S 0.9% was initially administered, esmolol was started with titration up to 160 μg/kg/minute, and norepinephrine dosage rose at 0.18 μg/kg/minute, aiming for MBP > 65 mmHg. The interventions failed to restore hemodynamics and oxygenation, and the use of non-invasive mechanical ventilation was initiated to prevent re-intubation.

Figure 2 Onset of hypoxemia. A: Chest X-ray demonstrates pulmonary congestion; B: Resolution of pulmonary congestion on chest X-ray following diuresis and vasopressin.

Laboratory examinations

Laboratory findings were as follows: White blood cells (ADVIA 2120i, SIEMENS) = 22580 K/μL, C-reactive protein (Atellica^® CH Revised C-Reactive Protein assay) = 202 mg/L, urea [Atellica^® CH Urea Nitrogen (UN_c) assay] = 81 mg/dL, creatinine [Atellica^® CH Enzymatic Creatinine_2 (ECre_2) assay] = 1.2 mg/dL, lactate = 3.2 mmol/L, lactate dehydrogenase (Atellica^® CH Lactate Dehydrogenase L-P) = 1151 IU/L, temperature = 38.3 °C. The arterial blood gas analysis (ABL800 FLEX, RADIOMETER) revealed a pH = 7.41, PaO₂ = 320 mmHg and PaO₂/FiO₂ > 250 mmHg, pCO₂ = 39 mmHg, Ca²⁺ = 1.19 mmol/L and normal lactate levels (< 1.6 mmol/L). A standard four-lumen Swan-Ganz catheter (model 131F7, size 7F, length 110 cm, Edwards Lifesciences, Irvine, CA, United States) was placed at the bedside for tailored therapy. Initial measurements revealed a cardiac index of 1.7 L/minute/m², a systemic vascular resistance index of 2115 dyn∙second∙m²/cm⁵, mean pulmonary artery pressure = 33 mmHg, pulmonary capillary wedge pressure = 18 mmHg and central venous pressure = 15 mmHg.

Imaging examinations

TTE revealed a hyperdynamic, hypertrophic left ventricle (LV) (Figure 3A, Video 1) SAM of the MV with severe regurgitation (Figure 3B), right ventricle with normal dimensions and systolic function, a plethoric inferior vena cava (24 mm, Figure 3C), medium-sized pleural effusions and a significant LVOT peak gradient = 71 mmHg with Vmax = 4.2 m/second (Figure 4A).

Figure 3 Hypertrophic left ventricle. A: Interventricular septum dimension in end-diastole = 1.4 cm; B: Plethoric inferior vena cava; C: Systolic anterior motion of mitral valve with severe mitral regurgitation and left ventricular outflow tract obstruction.

Figure 4 Five-chamber view on transthoracic echocardiographic. A: Left ventricular outflow tract peak gradient 71 mmHg (during noradrenaline infusion); B: Resolution of left ventricular outflow tract gradient after vasopressin infusion.

MULTIDISCIPLINARY EXPERT CONSULTATION

A multidisciplinary ICU team (including ICU cardiologists) discussed the case and confirmed diagnosis and treatment choice.

FINAL DIAGNOSIS

Finally, a hyperdynamic, hypertrophic LV (Figure 3A, Video 2) and SAM of the MV with severe regurgitation was diagnosed.

TREATMENT

Furosemide continuous infusion was started (6 mg/hour), and norepinephrine was gradually substituted by vasopressin at an infusion rate of 0.05 U/minute.

OUTCOME AND FOLLOW-UP

During the following hours, the patient was stabilized, UO increased (200-300 mL/hour), the LVOT peak gradient decreased to 16 mmHg (Figure 4B) and pulmonary edema resolved (Figure 2B). Four days later he had been weaned off vasopressors, a dual-chamber permanent pacemaker was inserted due to persistent complete heart block, and the patient was transferred to the ward.

DISCUSSION

LVOTO is usually described in patients with hypertrophic cardiomyopathy, but it can occur in various clinical scenarios in the ICU, such as septic shock, apical ballooning syndrome, sigmoid septum, myocardial infarction, and post-cardiac surgery. Changes in preload, afterload, heart rhythm and rate, atrio-ventricular synchronization, inotropy, LV shape, and regional wall contractility can cause dynamic LVOTO in susceptible patients[4,5]. In our case, LVOT gradient was possibly provoked by afterload reduction, either due to CPB and subsequent systemic inflammatory response syndrome or to AVR itself[6]. In patients with aortic stenosis, surgical correction induces a dramatic decrease in afterload that may decrease the volume of an already small and hypertrophied ventricle. An abnormal LV gradient has been reported in as high as 14% of patients submitted to AVR[7].

A second mechanism could be positive inotropism due to the inotropic effect of norepinephrine and the sympathetic stimulation caused by surgery/pain[8]. Norepinephrine, although usually considered as a purely vasoconstrictive agent, has strong intrinsic inotropic properties that can provoke or augment LVOTO[9,10]. Preload reduction as a cause has to be excluded in our case, as there was a combination of significant inferior vena cava dilatation and pulmonary congestion[4]. In addition, administration of fluids failed to restore BP and worsened pulmonary congestion. There is no established guidance for fluid balance in the context of LVOTO and acute pulmonary edema, and ICU management should take into account several parameters like central venous pressure, pulmonary capillary wedge pressure, inferior vena cava diameter, B-lines, and predominantly echocardiographic follow-up of SAM and mitral regurgitation.

Complete heart block and atrioventricular dissociation are frequent complications of AVR or septal myectomy that can worsen LVOTO, but they were restored in our patient by dual-chamber atrioventricular pacing. Although asynchronous pacing of ventricles might be beneficial in LVOTO, and dual-chamber pacing may improve gradient, this wasn’t the case in our patient[11]. Beta blockade is essential in the management of LVOTO either due to HOCM or other causes[12,13]. Any tachyarrhythmia that exacerbates SAM-related obstruction should be promptly managed with ultra-short-acting beta-blockers, such as esmolol or landiolol. Long-acting agents are not recommended due to the rapidly changing hemodynamic conditions. Its use was somewhat delayed in our case due to concerns about complete heart block. Due to its very short half-life, esmolol is the preferred agent in such cases, as long as temporary pacing is available[12]. Nevertheless, esmolol did not relieve the obstruction in our case.

Vasopressin has become very popular in the management of vasodilatory shock post cardiac surgery. Unlike norepinephrine, it lacks inotropic properties and vasoconstrictive action in the pulmonary vasculature, and its effects remain intact in hypoxic and acidotic conditions. Also known as antidiuretic hormone, it exerts its physiological effects via V1, V2, and V3 receptors. While its V2-mediated renal action promotes water reabsorption and may cause dilutional hyponatremia, its use in this context did not significantly reduce UO, likely due to preserved renal perfusion under adequate BP and CO[14].

Consequently, alpha-1 agonists such as norepinephrine, phenylephrine, and vasopressin are recommended to increase afterload, whereas vasodilators should be avoided[15]. Norepinephrine, although a potent vasoconstrictor, possesses modest beta-adrenergic activity that can enhance cardiac contractility and potentially worsen LVOTO, especially at higher doses. Phenylephrine is a pure alpha-agonist and lacks inotropic effects as well, but has pulmonary and renal vasoconstrictive properties. However, it may trigger reflex bradycardia and sudden fluctuations in hemodynamics, complicating management in frail cases[9]. These pharmacologic profiles render vasopressin as a more appropriate and safer choice in this specific clinical scenario. Indeed, vasopressin addition reduced LVOT gradient and mitral regurgitation in our patient too, reversing pulmonary edema and restoring hemodynamics[16]. Agents with nonselective arterial vasoconstrictive effects, like etilefrine, dopamine, dobutamine, and epinephrine should be avoided, as their positive inotropic and chronotropic actions through their action on beta-1 and beta-2 receptors can exacerbate LVOTO[15].

The clinical course of our patient is consistent with the phenomenon termed suicide LV (SLV), a rare yet critical postoperative complication. SLV occurs as a result of abrupt afterload reduction in a hypertrophied, hypercontractile LV, resulting in increased dynamic intraventricular gradients, SAM of the MV, and diminished CO[17,18]. While typically linked to aortic stenosis and AVR, isolated instances without aortic valve pathology have been reported, highlighting the significance of extreme left ventricular hypertrophy and sudden vasoplegia. Risk factors for SLV encompass small left ventricular cavity dimensions, septal hypertrophy, pre-existing SAM, and female gender[17-19]. Identifying SLV as an often-overlooked cause of postoperative cardiogenic shock is crucial for directing prompt diagnostic and treatment measures[17-19].

The management of SLV necessitates a comprehensive strategy focused on stabilizing hemodynamics and alleviating LVOT blockage. Therapeutic approaches focus on volume loading to enlarge the ventricular cavity, beta-blockade to decrease contractility and HR, and the administration of vasoconstrictors to elevate systemic vascular resistance without increasing myocardial oxygen consumption. Inotropes are generally contraindicated as they may exacerbate LVOTO. In refractory cases, procedural procedures such surgical myectomy or alcohol septal ablation are deemed appropriate[19,20]. Preventive techniques encompass meticulous preoperative TTE evaluation to identify high-risk patients, intra-procedural volume optimization, and, in specific instances, prophylactic septal reduction therapy to reduce the likelihood of SLV development[20]. Multidisciplinary perioperative care is essential for enhancing outcomes in these difficult scenarios.

CONCLUSION

Vasopressin seems to be the preferred vasopressor in instances of LVOTO and SAM post-cardiac surgery, likely due to its absence of inotropic effects relative to norepinephrine. Continuous bedside echocardiographic monitoring is crucial not only for early diagnosis and assessment, but also for guiding the selection and titration of vasopressor therapy.