How does hypocalcemia cause QT prolongation?
Hypocalcaemia is a recognised cause of QT prolongation via prolongation of the plateau phase of the cardiac action potential. This causes calcium ion channels to remain open for a longer period, allowing a late calcium inflow and the formation of early after-depolarisations.
How does hypokalemia cause prolonged QT interval?
Hypokalemia is another common risk factor in drug-induced LQTS. Low extracellular potassium paradoxically reduces IKr by enhanced inactivation [42] or exaggerated competitive block by sodium [43]. As a result, hypokalemia prolongs the QT interval.
What causes QT interval prolongation?
Causes of acquired long QT syndrome Certain antifungal medications taken by mouth used to treat yeast infections. Diuretics that cause an electrolyte imbalance (low potassium, most commonly) Heart rhythm drugs (especially anti-arrhythmic medications that lengthen the QT interval)
Does calcium shorten QT interval?
The QT shortening effects of rising serum calcium levels have been known for years. This observation is counterintuitive because increased extracellular concentrations of calcium would be expected to increase inward Ca flow during the late stages of repolarization, actually prolonging the QT interval.
How does hypocalcemia cause Torsades de Pointes?
Torsades de pointes (TdP) is a polymorphic ventricular tachycardia, which is characterized by twisting of the QRS axis around the points of the isoelectric line. An underrepresented cause of corrected QT (QTc) interval prolongation leading to TdP is hypocalcemia due to blood product transfusion.
Does hypocalcemia cause ventricular tachycardia?
Hypocalcemia can result in both ST segment modification and QT interval prolongation and, when severe, can predispose to life-threatening ventricular arrhythmias (3).
What electrolyte imbalance causes QT prolongation?
Abstract. Background: Prolonged QTc (corrected QT) interval and torsades de pointes (TDP) are associated with hypocalcemia, hypomagnesemia, hypokalemia, possibly alkalosis and may result in syncope and sudden cardiac death.
How does hyperkalemia cause QT prolongation?
As hyperkalemia progresses (6.5-7.5 mEq/L), the P-wave increases in duration and decreases in amplitude, and PR and QRS intervals widen. The QT-interval prolongs. Other changes include decreased amplitude of the R-wave with concomitant increased depth of the S-wave and ST-segment depression or elevation.
Which of the following are factors affecting the QT interval?
Factors that predispose to QT prolongation and higher risk of torsades de pointes include older age, female sex, low left ventricular ejection fraction, left ventricular hypertrophy, ischemia, slow heart rate, and electrolyte abnormalities including hypokalemia and hypomagnesemia.
What does hypocalcemia do to EKG?
The ECG hallmark of hypocalcemia remains the prolongation of the QTcinterval because of lengthening of the ST segment, which isdirectly proportional to the degree of hypocalcemia or, as otherwisestated, inversely proportional to the serum calcium level. The exactopposite holds true for hypercalcemia.
Why does hypomagnesemia cause prolonged QT?
Magnesium deficiency of any cause can lead to QT interval prolongation due to Na+-K+ pump inhibition and change in membrane potential which predisposes to life-threatening polymorphic ventricular tachycardia or Torsades de pointes (TdP).
What is Hypocalcemic Tetany?
Hypocalcemic tetany (HT) is the consequence of severely lowered calcium levels (<2.0 mmol/l), usually in patients with chronic hypocalcemia. The causal disease for hypocalcemic tetany is frequently a lack of parathyroid hormone (PTH), (e. g. as a complication of thyroid surgery) or, rarely, resistance to PTH.
Why does hypocalcemia prolong QT?
Answering why hypocalcemia would prolong QT is microbiologically equivalent to asking why low extracellular calcium prolongs the plateau phase of a cardiac myocyte. This is for several reasons. First, the waveforms present in the EKG are thought to be coincident with the phases of the cardiac action potential.
How does extracellular calcium affect QT interval?
As before, less extracellular calcium means calcium leaks in more slowly. But in this model, the slower influx means it takes longer for intracellular calcium to reach the threshold to close the L-type calcium channel, extending the action potential duration, and by extension, extending the QT interval.
How does hypocalcemia affect the EKG waveforms?
First, the waveforms present in the EKG are thought to be coincident with the phases of the cardiac action potential. Depolarization of myocytes is associated with the QRS complex and repolarization is associated with the T wave. Second, hypocalcemia would result in a low concentration of calcium in the extracellular fluid bathing the myocytes.
What is the role of calcium in the pathophysiology of hypocalcaemia?
Calcium has diverse roles in neuromuscular mechanisms. Within the cardiovascular system, hypocalcaemia is known to both impair myocardial contractility and prolong the QT interval, predisposing to ventricular arrhythmias. We present a case of chronic hypocalcaemia with prolonged QT interval associated with an atrial arrhythmia.
