Fig. 1-7B. Cardiac Dilatation. The dilated heart is #51 | | |
big and baggy, not thick and strong like the hypertro phied heart. Genetic diseases, drugs, alcohol, and viral myocarditis can cause dilated cardiomyopathy. Pathophysiologic circumstances can also lead to car diac dilatation. If hard work makes the heart get big and thick, in what pathophysiological situation would the heart become bigger and floppier? Dilata tion occurs when the heart needs to handle more blood than usual. When would the left ventricle end up with extra blood? In aortic regurgitation, when the left ventricle contracts, instead of sending all of the blood out to the body, some of the ej ected blood leaks back through the aortic valve into the ventri cle. If there is aortic regurgitation, the heart can di late over time to accommodate the extra blood leaking back into it across the aortic valve. #52 | | |
What is another reason that extra blood might leak back into the left ventricle? Hint: The aorta is one way out of the left ventricle- what's the only other way (as suming no holes)? The left atrium. What if instead of all of the blood going forward during systole, some of it squirted backward into the left atrium, then flowed back into the ventricle during diastole? This would have the same effect on the left ventricle as aortic regurgita tion: the left ventricle would have to handle extra blood. What normally assures that blood flows forward from the left ventricle through the aorta and not back into the atria? The mitral valve. So a leaky mitral valve can lead to mitral regurgitation into the atrium. This will increase the amount of blood that the left ventricle re ceives, which can cause it to dilate. #53 | | |
What could cause the right ventricle to be overloaded with extra volume? Similar to their analogues on the left, pulmonic or tricuspid regurgitation can lead to right ventricular dilatation. Additionally, an atrial sep tal defect (ASD) or a ventricular septal defect (VSD) will lead to increased blood in the right heart. Though sep tal defects are often birth defects, a VSD can also occur as a complication of a myocardial infarction. #54 | | |
Consequences of Cardiac Dilatation. Since it is "baggy," a dilated ventricle should have no problem relaxing. However, a dilated ventricle is weakened and thus gives a weaker squeeze during systole. This is called systolic dysfunction. Let's compare this situ ation to cardiac hypertrophy. In hypertrophy, the ventricle gets stiff and squeezes well but does not adequately relax. In contrast, in cardiac dilatation, the heart is too relaxed and does not give a good squeeze. The loss of a good squeeze leads to both diminished forward flow and backup of flow. #55 | | |
Systolic dysfunction like that caused by cardiac dila tation can also occur from weakening of heart muscle secondary to ischemia (decreased blood flow/oxygen supply). #56 | | |
Treatment of Cardiac Dilatation. Treatment is the same as for heart failure, aiming to increase forward flow and decrease backup of flow (Fig.l-5). Fig 1-8. Summary of diseases of the heart muscle. #57 | | |
The Valves and Their Diseases: Stenosis and Regurgitation #58 | | |
Review Fig. 1-2. The heart valves allow blood to flow fo r ward and prevent blood from flowing backward. What could go wrong with a valve? Valvular pathology can cause a valve to be bad at allowing blood to flow forward through it (stenotic) or bad at preventing back flow (re gurgitant). There are fo ur valves and two possible pathologies for each (stenosis and regurgitation), so there are eight basic valvular pathologies. Definitive treatment for any valvular pathology is surgical repair or replacement. Criteria for valve surgery can involve symptoms, severity of valvular dysfunction, and/or find ings on echocardiography, depending on the type of valve lesion, age of the patient, and other clinical factors. #59 | | |
Fig. l-9A. The normal cardiac cycle. The active contrac tion that ej ects blood from the ventricles is systole. As the ventricles contract, the mitral and tricuspid valves slam shut to prevent regurgitation into the atria. The sound produced by the closure of the atrioventricular valves is 81. #60 | | |
During systole, blood flows across the aortic valve to #61 | | |
the aorta and through the pulmonic valve to the pul #62 | | |
monary artery. Also during this time, blood fills the atria to prepare for the next cycle. When systole is complete, the open vs. closed status of the valves reverses. Now, the mitral and tricuspid valves must open to allow blood to pass from the atria to the ventricles for the next systole, and the aortic and pulmonic valves slam shut to prevent regurgitation back to the ventricles. 82 is the sound of the aortic and pulmonic valves slamming shut. S2 heralds the beginning of diastole, the relaxed phase of the cardiac cycle. During diastole, blood passes from the atria across the open mitral and tricuspid valves into the ventricles. The filled ventricles then contract (systole) again, and we are back where we began. #63 | | |
83 and 84 are extra heart sounds that can be heard in heart failure (S3 can also occur normally in young patients). If heard in the context of heart fail ure, S3 is associated with a dilated heartlsystolic dysfunction, and S4 is more typical with a hypertro phied heart/diastolic dysfunction. Since S3 occurs right after S2 (but well before S1), what could this sound represent? What happens during this phase of the cardiac cycle? Blood flows across the atrioventric ular valves into the ventricles. If there is still blood left in the ventricles (e.g., because it could not squeeze it all out due to its poor systolic function), a sound may be heard as blood flows in and splashes against the blood still left in the ventricle. Although this may not be exactly what produces the sound, it is a helpful way to remember that an 83 occurs in a dilated heart. Since there is still blood left in the ventri cle because ofa weaker ventricular contraction than nor mal, the blood flowing in from the atria makes noise. 84 comes after 82 (and 83 if present), and just before 81. What could this sound represent? At the very end of di astole, the atria contract, squeezing the last of their blood to the ventricles. The S4 is a sound produced when the atria squeeze against a stiff ventricle (i.e., in a hyper trophied heart with diastolic dysfunction). Mnemonic: The number 3 looks like a puffy dilated number, whereas the number 4 looks like a small chamber with rigid surroundings (hypertrophied ventricle). #64 | | |
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Aortic Stenosis can cause cardiac hypertrophy be #66 | | |
cause of the increased resistance it presents to left ven tricular contraction. Causes of aortic stenosis include aging (also called senile calcification), congenitally bicuspid aortic valve, and rheumatic heart disease. #67 | | |
Fig. 1-9B. The murmur of aortic stenosis. To deter mine the murmur of any type of valvular dysfunction, ask yourself, ''When does blood go across this valve?" Blood flows across the aortic valve when the left ven tricle contracts, i.e., during systole, between S1 and S2. Therefore, if there is aortic stenosis, where the blood does not flow normally across the valve, a mur mur will occur between S1 and S2. This is known as a systolic murmur. The murmur must stop at S2 since that sound signifies that the aortic valve is closed (i.e., no more blood can flow through it). #68 | | |
What would the shape of this murmur be? Imagine a stiff door with lots of screaming people behind it trying to push it open. At first it opens only slowly, letting in a few screaming people, but as the door opens more, more screaming people can get through. Still, although the door does not open completely, peo ple are always squeezing through. This is a good im age for aortic stenosis: The murmur starts off quietly since the valve is only slightly opened, allowing only some "murmuring" blood through. Gradually the valve opens more, but still not all the way. This allows more blood to flow through, but it is still "murmuring" blood due to the narrowed opening. Finally, as blood flow across the valve decreases, the volume of the mur mur decreases. This is called a crescendo-decrescendo murmur, because it gets louder as it proceeds and then diminishes before S2. The murmur of aortic stenosis is also referred to as a systolic ejection murmur. #69 | | |
One final detail about the sound of aortic stenosis is that the quality of S2 changes. Why would this be? What does S2 signify? S2 signifies the closing of the aortic and pulmonic valves. If the aortic valve is stiff, it opens poorly and closes poorly (i.e., it does not snap shut, but weakly closes). So how would the S2 change? S2 would be softer since it is the sound of only one valve (the pulmonic) slamming shut instead of two. #70 | | |
Other manifestations of aortic stenosis. Another classic physical finding in aortic stenosis involves how the carotid artery pulse feels (carotid upstroke). In stead of blood slamming up against the carotids at high pressure, it is sent up more slowly and with less fo rce because it is "held up" by the aortic stenosis. Thus, instead of brisk pulses, the pulses are called paruus et tardus, meaning weakened and delayed. What symptoms would be caused by reduced flow in the carotids? The carotids feed the brain, and when the brain does not get enough blood, syncope, light headedness, and/or dizziness can occur. Other mani festations of aortic stenosis are those that can occur as a result of the induced cardiac hypertrophy. To review, patients with cardiac hypertrophy can have angina and/or myocardial infarction (because the thicker ven tricular wall cannot be adequately perfused). They can also feel weak and fatigued because flow to the body is inadequate since the stenotic valve inhibits this flow. #71 | | |
Aortic Regurgitation can lead to a dilated left ven tricle. Aortic regurgitation can occur because of weak ening of the valves or dilatation of the aortic root. Dilatation of the root causes the valves to be farther apart from each other, leaving space through which backflow of blood can occur. Diseases that can lead to aortic root dilatation include Marfan's syndrome, Ehlers-Danlos syndrome, and syphilis. #72 | | |
Fig. 1-9C. The murmur of aortic regurgitation. When in the cardiac cycle could blood leak back through the aortic valve? S2 is the sound of the aortic valve clos ing. If there is aortic regurgitation, the valve allows re gurgitation after closure, so the murmur occurs after S2, during diastole. Thus, the murmur of aortic regur gitation is a diastolic murmur. #73 | | |
Other manifestations of aortic regurgitation. Aortic regurgitation affects blood pressure and pulses. First, let's review what blood pressure actually measures. There are two numbers, systolic pressure and diastolic pressure (e.g., 120/80). The top number, systolic pres sure, refers to the pressure during systole, i.e., when the heart is squeezing. The bottom number, diastolic pres sure, refers to the pressure being maintained when the heart is relaxed. The squeezed-out blood is normally prevented from falling too much in pressure because the aortic valve shuts behind it. This helps maintain pressure during diastole. In aortic regurgitation, after a forceful squeeze, some of the blood falls back down into the left ventricle. Which pressure (systolic or diastolic) will be affected and why? Assuming the squeeze is nor mal, the systolic pressure should be unchanged. How ever, when the aortic valve allows regurgitation, the diastolic pressure is not maintained since instead of supporting the column of blood in the aorta, the valve collapses. Since the diastolic pressure falls and the sys tolic pressure stays the same, the distance between the two numbers increases (widened pulse pressure). How would this widened pulse pressure manifest on physi cal exam? Imagine this gush of blood coming from the heart and then falling back ...gushing out, falling back. You can actually fe el this in the pulses (bounding pulses). This can sometimes be so drastic that it can be visible, for example in the carotids (Corrigan's pulse), or with the patient's head actually bobbing with each pulse (De Musset's sign). #74 | | |
Due to decreased forward flow and increased backup of flow in aortic regurgitation, heart failure symptoms can occur (e.g., dyspnea on exertion, etc., see Fig. 1-4). #75 | | |
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Mitral Stenosis. Nearly all cases of mitral stenosis #77 | | |
are caused by rheumatic fever, a disease much less common in the U.S. since the introduction of antibiotics, but more common in developing countries. De spite decreased prevalence in the U.S., some patients who had rheumatic fever as children are still alive and can have resultant mitral stenosis. More rarely, mitral stenosis can occur congenitally or in endocarditis. #78 | | |
What are the roles of the mitral valve? First, to allow blood to pass from the left atrium to the left ventricle during diastole, and second, to prevent back flow into the left atrium when the left ventricle con tracts during systole. If the valve is stenotic, it is the first of these functions that is impaired, and thus the upstream portion of the circuit is affected. What is upstream? Immediately upstream from the mitral valve is the left atrium. Mitral stenosis causes the left atrium to dilate. Because of the stretching of the electrical fibers induced by this di latation, atrial fibrillation can develop. Further up stream, the pulmonary vasculature is also affected by this backup, which can lead to shortness of breath. Eventually, the chronically elevated left atrial pres sure can cause pulmonary hypertension and even right heart failure. #79 | | |
Fig. 1-9C. The murmur of mitral stenosis. When does blood pass across the mitral valve? Between S2 and S1, during diastole. So this is a diastolic murmur. #80 | | |
Other manifestations of mitral stenosis. The sound of the stiff mitral valve snapping open can sometimes be heard (opening snap). When would you expect this to occur? Shortly after S2. The timing of this snap re flects the severity of the stenosis. If the mitral steno sis is severe, this leads to higher left atrial pressure than if the stenosis were less severe. What would this do to the opening of the valve? If the pressure is high, the valve will snap open quite quickly. If the stenosis is less severe and the left atrial pressure is relatively less, the valve will not open until later, since initially there is not enough pressure to snap it open. Thus, the timing of the opening snap is inversely proportional to the severity of mitral stenosis: the more severe the mi tral stenosis, the earlier the opening snap. #81 | | |
Mitral Regurgitation. During systole, the ventricles #82 | | |
contract, ejecting blood into their respective outflow tracts (Left Ventricle->Aorta, Right Ventricle->Pulmonary Artery). This contraction is quite forceful, and the job of the mitral and tricuspid valves is to shut tightly so as to prevent backflow and maximize forward flow. In mitral regurgitation, the mitral valve allows backflow into the left atrium during ventricular contraction. #83 | | |
Recall that if mitral regurgitation exists for a long time, the heart will compensate by dilating to accommo date the increased blood volume (which can cause sys tolic dysfunction, an S3, etc.). If cardiac dilatation exists for another reason (e.g., genetic, drugs, aortic regurgita tion), this dilatation stretches the ring-like mitral valve, preventing it from closing optimally. So mitral regurgitation can lead to left ventricular dilatation or it can be the result of ventricular dilatation. Aside from ventricu lar dilatation, mitral regurgitation can be caused by de generation of the valve (mitral valve prolapse, also known as myxomatous degeneration), rheumatic fever, endocarditis, or ischemic heart disease. #84 | | |
Where is the regurgitated blood going in mitral regurgitation? Back into the left atrium. So chronic mitral regurgitation can lead to left atrial dilatation. Forward flow is diminished since what was supposed to be part of the cardiac output is sent backward into the atria. Since pressure increases backward through the left atrium to the lungs, this can cause shortness of breath. If mitral regurgitation develops over a long period of time, dilatation of the atrium can allow it to adapt to accommodate the backflow, preventing signif icant elevations in pulmonary pressure. Alternatively, if mitral regurgitation occurs acutely (e.g., papillary muscle rupture secondary to ischemia), there is no time for compensatory dilatation of the left atrium to occur. Without the compensation of a dilated atrium, the pressure in the lungs acutely elevates due to the sudden onset of backward flow. Pulmonary conges tion is a prominent symptomatic feature in acute mitral regurgitation, whereas in more chronic mitral regurgitation, the fatigue/forward flow symptoms are more prominent. The acute problem is not well toler ated by the pulmonary system, and urgent surgical re placement of the valve is often necessary. #85 | | |
Fig.l-9B. The murmur of mitral regurgitation. Is the murmur of mitral regurgitation systolic or diastolic? In mitral regurgitation, blood flows backward across the mitral valve. This occurs during systole when the ventricles contract, so this is another systolic mur mur, occurring between S1 and S2. How can you dis tinguish it from the murmur of aortic stenosis, which is also systolic? A subtle difference is that mitral re gurgitation lacks the crescendo-decrescendo pattern that is present in aortic stenosis. Since the regurgi tant mitral valve flops back with the onset of systole, the murmur is usually relatively constant from S1 to S2 (holosystolic or pansystolic murmur).2 #86 | | |
Other manifestations of mitral regurgitation. Asso ciated findings can also help distinguish between aor tic stenosis and mitral regurgitation as causes of a systolic murmur. Mitral regurgitation can be accom panied by an S3. Why? S3 can be thought of as blood splashing against blood already in the ventricle. In mi tral regurgitation, all of the blood that got inappropri ately ejected back into the atrium then returns to the ventricle during diastole: splash! #87 | | |
Figure 1-10. From Chizner: Clinical Cardiology Made Ridiculously Simple, MedMaster, 2006 (Courtesy #88 | | |
ofW. Proctor Harvey, M.D.) #89 | | |
Atrial dilatation from mitral regurgitation can lead to atrial fibrillation, as in mitral stenosis. #90 | | |
Fig. 1-10. Sites of cardiac auscultation. Another dis tinguishing factor on physical exam is where the mur mur is heard best and where it radiates. Aortic stenosis is best heard over the aortic valve region in the right3 upper sternal border, and it radiates straight up to the carotids. One classically hears the murmur of mitral regurgitation over the cardiac apex, and it radiates to the left axilla. #91 | | |
Finally, another way to distinguish between the sys #92 | | |
tolic murmurs of aortic stenosis and mitral regurgita #93 | | |
tion is through physical exam maneuvers. While a full discussion of the cardiac physical exam maneuvers is beyond the scope of this text, a quick review of one ma neuver will be helpful. If you ask the patient to clench his/her fists, what does this accomplish? This is one way to increase the systemic vascular resistance by clamp ing down on the arteries in the hand/arm. Why would a change in systemic vascular resistance affect a mur mur? Given the choice of going through what is now a path with greater resistance (the body with clenched fists) and simply flowing back across the regurgitant mi tral valve, the blood chooses the mitral valve (the path of least resistance). Thus, this maneuver will increase the intensity of the mitral regurgitation murmur, while leaving the aortic stenosis murmur unchanged. Why would the aortic stenosis murmur remain unchanged? The main point of resistance responsible for the murmur in aortic stenosis is the valve itself, so changes in resist ance distal to this point (i.e., clenched fists) will have lit tle or no effect on the murmur of aortic stenosis. #94 | | |
Aside from aortic stenosis and mitral regurgitation, what other cardiac pathology could lead to a systolic murmur? Where else could the blood go during sys tole? If there is a ventricular septal defect, blood flow through this hole can also create a murmur, and this too would occur during systole. #95 | | |
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Tricuspid Stenosis. The pathophysiology in tricuspid #97 | | |
stenosis is essentially the same as in mitral stenosis, ex cept that it occurs on the right side of the heart. The mur mur is diastolic and best heard at the left lower sternal border. Just as mitral stenosis leads to left atrial dilata tion, tricuspid stenosis results in right atrial dilatation/ increased pressure. How can one see a barometer of this right-sided pressure? The jugular vein is connected to the superior vena cava, which is connected to the right atrium, and thus increased pressure in the right heart ЛИПСВА ТЕКСТ ЛИПСВА РЕД РЕД РЕД !!!!! #98 | | |
Tricuspid Regurgitation. Tricuspid regurgitation #99 | | |
also has a similar pathophysiology to its counterpart on the left, mitral regurgitation. Because of increased #100 | | |
