What are the causes and characteristics of malignant hyperthermia and the most common cardiac anomaly found in adults?

Malignant Hyperthermia: Causes, Characteristics, and Cardiac Anomalies in Adults

Malignant Hyperthermia Triggers and Characteristics

Malignant hyperthermia is triggered by potent inhalational anesthetics and succinylcholine (depolarizing muscle relaxant), but NOT by local anesthetics, nondepolarizing muscle relaxants, or nitrous oxide. 1

Triggers of Malignant Hyperthermia

• Malignant hyperthermia is specifically triggered by potent volatile inhalational anesthetics (halothane, sevoflurane, desflurane, isoflurane) and the depolarizing muscle relaxant succinylcholine 1, 2
• Local anesthetics do NOT trigger malignant hyperthermia 3, 4
• Nondepolarizing muscle relaxants do NOT trigger malignant hyperthermia 3, 4
• Nitrous oxide does NOT trigger malignant hyperthermia 3, 4
• Safe anesthetic agents for MH-susceptible patients include nitrous oxide, barbiturates, opiates, tranquilizers, and nondepolarizing muscle relaxants 4

Pathophysiology

• MH is caused by dysregulation of calcium control in skeletal muscle, not disordered potassium metabolism 1, 2
• The underlying mechanism involves excessive release of calcium from the sarcoplasmic reticulum in skeletal muscle cells 5
• This leads to sustained muscle contraction, hypermetabolism, and heat generation 1
• Most cases are caused by genetic variants in the ryanodine receptor gene (RYR1) 2

Clinical Manifestations

• The earliest and most specific sign is an unexplained increase in end-tidal CO2 despite increased minute ventilation 6
• Other early signs include tachycardia and muscle rigidity 1
• Temperature elevation typically occurs later in the progression 6
• The syndrome can rapidly progress to acidosis, hyperkalaemia, arrhythmias, rhabdomyolysis, and death if untreated 1

Epidemiology

• MH affects approximately 1:10,000 to 1:250,000 anesthetics 2
• The genetic prevalence may be as high as 1:2000 in the general population 1
• MH is more common in children than adults 1
• There is a consistently higher incidence in males compared to females 1

Management

• Treatment involves immediate discontinuation of triggering agents, administration of dantrolene (2-3 mg/kg initially), hyperventilation with 100% oxygen, and active cooling 1, 7
• Activated charcoal filters should be available to adsorb inhalational anesthetics 1
• Mortality has decreased from >80% to <5% with prompt recognition and treatment 2

Most Common Cardiac Anomaly in Adults

The most common cardiac anomaly found in adults is bicuspid aortic valve, followed by atrial septal defect.

While the provided evidence doesn't directly address the most common cardiac anomaly in adults, based on general medical knowledge:

• Bicuspid aortic valve is the most common congenital cardiac anomaly in adults, affecting approximately 1-2% of the population
• Atrial septal defect is the second most common congenital heart defect found in adults
• Ventricular septal defect is more common at birth but many close spontaneously during childhood
• Transposition of great vessels and coarctation of the aorta are less common and often diagnosed and treated in childhood

Clinical Implications

• Adults with undiagnosed congenital cardiac anomalies may present with complications such as arrhythmias, heart failure, or endocarditis
• Patients with known cardiac anomalies require careful anesthetic planning, especially those with right-to-left shunts who may be at risk for paradoxical air embolism

Key Points for Clinical Practice

• Always take a thorough personal and family history of anesthetic problems before administering general anesthesia 1
• An unexplained progressive increase in carbon dioxide production should raise immediate suspicion for MH 1
• Dantrolene must be readily available wherever triggering anesthetics are used 7
• MH-susceptible patients can safely undergo surgery with non-triggering anesthetics 4
• Early diagnosis and prompt treatment are essential to reduce mortality from MH 1