166 articles
Tachyarrhythmias in pregnancy
Tachyarrhythmias in pregnancy are abnormally rapid heart rhythms, including supraventricular tachycardia, atrial fibrillation or flutter, and ventricular tachycardia, that occur during pregnancy or early postpartum, affecting 0.03% to 0.5% of pregnancies.
Tbx18 transduction
Tbx18 transduction delivers the T-box transcription factor 18 gene or mRNA to heart muscle to create a biological pacemaker, converting cardiomyocytes into sinoatrial-node-like cells; large-animal results exist but a 2026 AAV study found no genuine TBX18 pacemaker activity.
Tetralogy of Fallot
Tetralogy of Fallot is a congenital heart defect combining four abnormalities that cause low blood oxygen and bluish skin; surgical repair in infancy gives over 90% survival to adulthood.
Transcutaneous pacing
Transcutaneous pacing (TCP, external pacing): emergency noninvasive cardiac pacing via skin electrodes for symptomatic bradycardia; a short-term bridge to transvenous pacing, ineffective in asystolic arrest; pioneered by Paul Zoll, re-introduced 1981 with 40 ms pulses and 80 cm2 electrodes.
Tricuspid valve
Tricuspid valve (right atrioventricular valve): heart valve between right atrium and right ventricle with three leaflets, chordae tendineae, and the largest cardiac orifice (7-9 cm2); main disease is tricuspid regurgitation, treated by diuretics, surgery, or transcatheter repair/replacement.
Umbilical cord
Umbilical cord: fetal-placental conduit with two arteries and one vein in Wharton jelly, 50–60 cm at term; carries oxygenated blood via the vein; delayed clamping 30–60 seconds is now recommended; single umbilical artery affects under 1% of pregnancies.
Vagal maneuver
Vagal maneuvers (Valsalva, carotid sinus massage, diving reflex) are first-line physical techniques that raise vagal tone to terminate AV-node-dependent supraventricular tachycardia; the modified REVERT Valsalva converts about 43% versus 17% standard.
Vagal tone
Vagal tone is the vagus nerve's parasympathetic influence on the heart, estimated from HRV indices RMSSD, pNN50, and HF power; measured via ECG, tied to respiration, and distinct from wearable PRV.
Vasa praevia
Vasa praevia (vasa previa): unprotected fetal blood vessels run through the amniotic membranes over the cervix. Types I–III; risk factors include IVF and low-lying placenta; ultrasound diagnosis and planned cesarean cut fetal mortality from over 60% to under 5%.
Vascular ring
Vascular ring: congenital aortic arch anomaly, mainly double aortic arch or right arch with aberrant left subclavian artery, encircling and compressing the trachea and esophagus; about 1% of congenital cardiac anomalies, treated surgically when symptomatic.
Vasoconstriction
Vasoconstriction is narrowing of blood vessels by smooth muscle contraction, controlled by sympathetic vasomotor nerves and hormones such as angiotensin, vasopressin, epinephrine, and norepinephrine; it conserves heat, limits bleeding, raises blood pressure, and was discovered in 1851-1852 by Bernard and Brown-Séquard.
Vasodilation
Vasodilation is widening of blood vessels from smooth muscle relaxation, lowering vascular resistance and blood pressure while increasing flow. Key mechanisms: NO–sGC–cGMP signaling, K+ channel hyperpolarization; quantified by flow-mediated dilation (~6.4% healthy).
Velamentous cord insertion
Velamentous cord insertion (VCI): umbilical cord attaches to fetal membranes rather than the placenta, leaving vessels unprotected by Wharton's jelly; affects about 1.4% of singletons, more in twins and IVF, and raises risks of stillbirth, preterm birth, and vasa previa.
Ventricle (heart)
Ventricle (heart): the heart's two pumping chambers, the thick-walled left ventricle of the systemic circuit and the thin-walled right ventricle of the pulmonary circuit; differs from the atria, which only fill the ventricles.
Ventricular Function
Ventricular function: the hemodynamic and electrophysiological action of the heart ventricles, assessed by ejection fraction, global longitudinal strain, pressure-volume analysis, and diastolic indices; EF remains the heart failure classifier while GLS detects subclinical dysfunction.
Ventricular Pressure
Ventricular pressure, also called intraventricular pressure, is the pressure within a ventricle of the heart, measured by catheterization or imaging to evaluate heart and valve function.