Patent ductus arteriosus - physiology, pathology, clinical manifestations, diagnosis, treatment — Transcript

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1. 0:02With patent ductus arteriosus, or PDA,
2. 0:06patent comes from the Latin word patere,
3. 0:09meaning to lie open. While ductus
4. 0:11arteriosus refers to a blood vessel that
5. 0:14normally connects the pulmonary artery
6. 0:16to the aorta.
7. 0:18During fetal development, the ductus
8. 0:20arteriosus allows blood to bypass the
9. 0:22lungs, but normally it closes soon after
10. 0:25birth. So, in patent ductus arteriosus,
11. 0:28this blood vessel fails to close and
12. 0:31remains open.
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19. 0:51But before we proceed, first let's look
20. 0:53at how fetal circulation works.
21. 0:56During fetal development, the baby's
22. 0:58lungs are filled with fluid and not yet
23. 1:00involved in breathing. So, the fetus
24. 1:02relies entirely on oxygen-rich blood
25. 1:05from the mother.
26. 1:07This oxygen-rich blood travels from the
27. 1:09placenta through the umbilical vein and
28. 1:12eventually reaches the right atrium of
29. 1:14the heart.
30. 1:15From here, most of it takes a shortcut
31. 1:17through the opening between the right
32. 1:19and left atria, called the foramen
33. 1:21ovale.
34. 1:22This allows oxygen-rich blood to
35. 1:24completely bypass the lungs and enter
36. 1:27the left atrium directly.
37. 1:29From the left atrium, blood enters the
38. 1:31left ventricle, and from there it's
39. 1:33pumped into the aorta and systemic
40. 1:36circulation.
41. 1:38However, not all blood follows this
42. 1:40path. A small amount still reaches the
43. 1:43right ventricle and gets pumped into the
44. 1:45pulmonary artery. However, since the
45. 1:48fetal lungs are not yet functioning, the
46. 1:50pulmonary vessels are squeezed, creating
47. 1:53high resistance that makes it difficult
48. 1:55for blood to flow into the lungs.
49. 1:58As a result, most of the blood follows
50. 2:00the path of least resistance and slips
51. 2:02from the pulmonary artery through
52. 2:04another fetal shunt called the ductus
53. 2:06arteriosus into the aorta.
54. 2:11Anatomically, the ductus arteriosus sits
55. 2:14right on the aortic arch, just after the
56. 2:16arteries that branch off to supply the
57. 2:18brain and upper extremities.
58. 2:21This setup allows oxygen-rich blood from
59. 2:23the left ventricle to reach the brain
60. 2:26and upper extremities first, while blood
61. 2:28from the right ventricle, via the ductus
62. 2:30arteriosus, supplies the lower body.
63. 2:34This arrangement helps prioritize oxygen
64. 2:36delivery to the most important organs,
65. 2:38like the brain and heart, while the
66. 2:40ductus arteriosus sends the remaining
67. 2:43oxygenated blood to the rest of the
68. 2:44body.
69. 2:47During fetal development, the placenta
70. 2:49produces prostaglandin E2, which helps
71. 2:52keep the ductus arteriosus open.
72. 2:55At birth, everything shifts. The
73. 2:58placenta is no longer in play, so
74. 3:00prostaglandin E2 levels drop.
75. 3:03Next, the lungs take over as the primary
76. 3:06source of oxygen, increasing oxygen
77. 3:08levels from approximately 60% in the
78. 3:11uterus to over 90% after birth.
79. 3:15Higher oxygen levels also support the
80. 3:17closure.
81. 3:18At the same time, lungs begin releasing
82. 3:21bradykinin, which is a small peptide
83. 3:23that causes smooth muscle cells of the
84. 3:25ductus arteriosus to constrict, speeding
85. 3:28things up.
86. 3:30Together, the drop in prostaglandin E2,
87. 3:33the rise in oxygen, and the release of
88. 3:35bradykinin all help close the ductus
89. 3:38arteriosus, transforming it into a
90. 3:40fibrous band called the ligamentum
91. 3:43arteriosum.
92. 3:44This usually occurs within the first 3
93. 3:47weeks of life.
94. 3:50If the ductus arteriosus fails to close
95. 3:53after birth, the baby is left with a
96. 3:55patent ductus arteriosus.
97. 3:58Like in fetal life, blood flows from the
98. 4:00right atrium to the right ventricle and
99. 4:03then into the pulmonary artery.
100. 4:05But now that the lungs are up and
101. 4:06running, pulmonary vessels are wide
102. 4:08open, which makes resistance in
103. 4:10pulmonary circulation lower than in the
104. 4:13aorta.
105. 4:14Freshly oxygenated blood then comes over
106. 4:17into the left atrium, the left
107. 4:19ventricle, and into the aorta.
108. 4:22Some of the oxygenated blood in the
109. 4:24aorta follows the path of least
110. 4:25resistance across the ductus and shunts
111. 4:28into the lower pressure pulmonary
112. 4:30artery.
113. 4:31This creates a left-to-right shunt.
114. 4:34And because no deoxygenated blood enters
115. 4:37the systemic circulation, PDA is
116. 4:40classified as an acyanotic heart defect,
117. 4:43literally meaning not blue.
118. 4:46However, this inefficient circuit causes
119. 4:49volume overload in both the pulmonary
120. 4:51circulation and the left side of the
121. 4:53heart, which now must handle
122. 4:55significantly more blood returning from
123. 4:57the lungs.
124. 4:58Over time, this increased workload
125. 5:01strains the left ventricle, forcing it
126. 5:03to pump up to twice the normal cardiac
127. 5:05output.
128. 5:07Eventually, this chronic strain can lead
129. 5:09to heart failure.
130. 5:12PDA accounts for about 10% of all
131. 5:15congenital heart defects, of which about
132. 5:1790% are isolated heart defects, meaning
133. 5:20there are no other associated heart
134. 5:22problems.
135. 5:24PDA is more common in preterm infants,
136. 5:27where immature tissues and higher
137. 5:29prostaglandin levels delay ductal
138. 5:31closure.
139. 5:33It's strongly associated with neonatal
140. 5:35respiratory distress syndrome, where
141. 5:37poor lung expansion and low oxygen
142. 5:40tension make the ductus less likely to
143. 5:42constrict.
144. 5:44Another well-known association is
145. 5:46congenital rubella syndrome, where
146. 5:48maternal rubella infection during the
147. 5:50first trimester interferes with normal
148. 5:53vascular development and leads to PDA.
149. 5:56Finally, PDA can be seen in genetic
150. 5:59conditions like Down syndrome.
151. 6:04Usually, PDA is asymptomatic, especially
152. 6:07when the amount of blood flowing from
153. 6:09the aorta to the pulmonary artery is
154. 6:11small.
155. 6:12In fact, many small PDAs are discovered
156. 6:15only because they produce a continuous
157. 6:17machine-like murmur from the continuous
158. 6:20blood flow from the aorta to the
159. 6:22pulmonary artery through the whole
160. 6:24cardiac cycle.
161. 6:26In contrast, infants with a large PDA
162. 6:28may develop signs of heart failure
163. 6:31early, such as rapid breathing, poor
164. 6:33feeding, and hepatomegaly, because the
165. 6:36left heart must pump two or more times
166. 6:38the usual cardiac output to handle the
167. 6:41extra blood returning from the lungs.
168. 6:46Later in life, from years of increased
169. 6:48pulmonary blood volume, the pulmonary
170. 6:50arteries thicken and stiffen.
171. 6:53These changes increase the pressure in
172. 6:55the pulmonary circulation and eventually
173. 6:57lead to pulmonary hypertension.
174. 7:00If the pressure in the pulmonary artery
175. 7:02rises high enough to exceed the pressure
176. 7:05in the aorta, the shunt flips from left
177. 7:08to right to right to left.
178. 7:12When this happens, deoxygenated blood
179. 7:14from the pulmonary artery bypasses the
180. 7:17lungs and flows through the PDA into the
181. 7:20aorta and systemic circulation.
182. 7:23Because of the ductus arteriosus'
183. 7:24position, deoxygenated blood mainly
184. 7:27reaches the lower part of the body.
185. 7:29The result is differential cyanosis,
186. 7:32where the lower body appears bluish or
187. 7:34purple, while the upper body remains
188. 7:36pink and well perfused.
189. 7:39This late complication of PDA is called
190. 7:41Eisenmenger syndrome and marks an
191. 7:44irreversible stage where pulmonary
192. 7:46vessels have undergone permanent
193. 7:48remodeling.
194. 7:49So, what started as a harmless little
195. 7:51duct can turn into a serious condition
196. 7:54that deprives tissues of oxygen.
197. 7:59PDA is generally suspected upon
198. 8:01auscultation of the classic machine-like
199. 8:04murmur.
200. 8:05However, the diagnosis primarily relies
201. 8:07on Doppler echocardiography, which
202. 8:10visualizes flow through the ductus,
203. 8:12estimates the size, and detects signs of
204. 8:15pulmonary over circulation or pulmonary
205. 8:18hypertension.
206. 8:22Small PDAs may close spontaneously
207. 8:24within the first few months and often
208. 8:26don't require treatment. For larger or
209. 8:29symptomatic PDAs, first-line therapy
210. 8:32includes nonsteroidal anti-inflammatory
211. 8:35medications, or NSAIDs, like
212. 8:37indomethacin or ibuprofen, which inhibit
213. 8:40prostaglandin E2 synthesis to promote
214. 8:43closure.
215. 8:44If NSAIDs fail, closure can be done via
216. 8:47a minimally invasive transcatheter
217. 8:49procedure with an occlusion device, or
218. 8:52by surgical ligation.
219. 8:55All right, as a quick recap,
220. 8:57patent ductus arteriosus is an acyanotic
221. 9:01congenital heart defect caused by the
222. 9:03failure of the ductus arteriosus to
223. 9:05close after birth, resulting in a
224. 9:07persistent communication between the
225. 9:09aorta and pulmonary artery.
226. 9:12This creates a left-to-right shunt,
227. 9:15leading to pulmonary overload of the
228. 9:16left heart, and potentially heart
229. 9:19failure.
230. 9:23PDA is more common in preterm infants
231. 9:26and classically presents with a
232. 9:28continuous machine-like murmur.
233. 9:31Small PDAs are often asymptomatic, while
234. 9:34larger ones can cause symptoms like
235. 9:36tachypnea and poor feeding.
236. 9:39If left untreated, PDA can progress to
237. 9:42pulmonary hypertension and even
238. 9:44Eisenmenger syndrome with reversal of
239. 9:46the shunt to right to left.
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