Cardiophile MD

Normal cardiac CT images: Coronaries on reconstructed views

Johnson Francis — Thu, 11 Mar 2010 17:25:59 +0000

Cardiac CT angiograms are increasing in popularity as a non-invasive screening tool for detecting significant coronary artery disease. The angiograms are reconstructions from 64 or more slice CT scans following intravenous injection of radiocontrast dye. As of now it cannot replace conventional coronary angiograms for assessing the detailed coronary anatomy.

LAD, LCX and Left main on reconstructed cardiac CT

Reconstructed cardiac CT scan image as viewed from the left anterior aspect, showing left main (LM) left main coronary artery, left circumflex (LCX) coronary artery and left anterior descending (LAD) coronary artery. Ao: aorta. Two diagonal branches are also seen arising from the LAD. LCX is occupying the atrioventricular (AV) groove.

LMCA, LAD, LCX and coronary sinus on reconstructed cardiac CT

Reconstructed cardiac CT image as viewed from the posterior aspect showing the left anterior descending (LAD) coronary artery, left main coronary artery (LMCA), left circumflex (LCX) coronary artery and the coronary sinus (Coron sinus). The main tributaries of the coronary sinus are also seen joining it. A diagonal branch is seen arising from the LAD and an obtuse marginal branch from the LCX (not marked).

RCA in the AV groove on reconstructed cardiac CT

Reconstructed cardiac CT image showing the right coronary artery (RCA) in the atrioventricular (AV) groove. The structure to the left of the RCA is the right atrium and that to the left is left ventricle. The left anterior descending (LAD) coronary artery is seen to the left extreme of the image, though it is not visualised well. A diagonal branch of the LAD is also visible.

Distal RCA and coronary sinus on on reconstructed cardiac CT

Distal right coronary artery (RCA) and coronary sinus seen in the atrioventricular (AV) groove seen on the posterior aspect view of reconstructed cardiac CT. Left circumflex coronary is seen adjacent the coronary sinus in the AV groove.

Tissue Doppler Imaging (TDI)

Johnson Francis — Wed, 10 Mar 2010 15:29:32 +0000

Tissue Doppler Imaging at the level of the mitral annuls, septal side.

(Click on the image for an enlarged view)

Tissue Doppler Imaging (TDI) measures the velocity of myocardial motion using Doppler principles. While the usual Doppler echocardiography measures the velocity of blood flow using the Doppler signals from the fast moving blood cells, which are of low amplitude, tissue Doppler measures low velocity, high amplitude signals from the myocardial tissue motion. Tissue Doppler is not able to differentiate between passive motion and active motion due to fibre shortening. But the newer technology of strain imaging is able to do so. Colour coded tissue Doppler imaging is sometimes called colour kinesis. Pulsed wave TDI is useful to measure myocardial velocities in the long axis as the movement is parallel to the Doppler beam. The mitral annular TDI has three waves: Sa, systolic myocardial velocity; Ea, early diastolic myocardial velocity and Aa, myocardial velocity during atrial contraction. While imaging from the apical view, systolic velocities are positive and diastolic velocities are negative. Systolic velocity at the lateral mitral annulus correlates with the longitudinal systolic function of the left ventricle. Diastolic velocities depend on ventricular diastolic function. TDI assessment of diastolic function is load independent compared to the conventional measurement using mitral inflow velocities which are highly sensitive to preload.

Aortic regurgitation – eccentric jet

Johnson Francis — Wed, 10 Mar 2010 15:11:26 +0000

Aortic regurgitation – eccentric jet

(Click on the image for an enlarged view)

Eccentric jet of aortic regurgitation cursing along the posterior margin of the left ventricular outflow tract (anterior mitral leaflet). Estimation of severity of eccentric jets may be erroneous as often the severity tends to be under estimated in case of eccentric jets. AR: aortic regurgitation; LA: left atrium; LV: left ventricle; RV: right ventricle. The frame to the left is a systolic frame and the right one is a diastolic frame. The systolic frame shows the mitral valve in the closed position while the diastolic frame shows it in the open position. The anterior mitral leaflet shows a reverse doming as the aortic regurgitation jet strikes it. Systolic frame also shows a trivial mitral regurgitation into the left atrium, just behind the mitral valve as a bluish mosaic jet.

Heart disease in women

Johnson Francis — Wed, 10 Mar 2010 13:27:02 +0000

Heart disease is being recognized more often in women. Heart disease causes one out of three deaths in women and about half of these is due to coronary artery disease. A forty year old female has a 32% lifetime risk of heart disease. Still only about 55% of women recognize heart disease as the most important risk. Some studies mention that 52% of women developing a myocardial infarction die before reaching a hospital and 2/3rd of those with a myocardial infarction never recover fully. But women are protected from coronary heart disease prior to menopause and the average age of occurrence of the first myocardial infarction is about 8-10 years higher in females. This difference in maintained globally even though the age of first myocardial infarction is different in various regions. The risk increases as the age advances. While men have higher risk before the fifth decade, risk is higher in women beyond the sixth decade. Hypertension, an important risk factor for coronary artery disease, is more prevalent in males before the age of 35 years while after the age of 75 years, it is more prevalent in females. Overall, hypertension is 15% more common in women and less well controlled. In women with diabetes mellitus, cardiovascular disease is twice as common and they are four times likely to be hospitalised, compared to men. There is a perimenopausal increase in LDL cholesterol and decrease in HDL cholesterol which increases the risk in post menopausal women.

NCX inhibitors (Na+ / Ca2+ exchange inhibitors) to limit ischemic injury

Johnson Francis — Tue, 09 Mar 2010 07:06:47 +0000

Elevation of calcium levels in the cells is an important mechanism of ischemic cellular injury and death. Na⁺ / Ca²⁺ exchanger (NCX) has the main role in elevating calcium levels within the myocardial cells during ischemia and reperfusion. Hence NCX inhibitors have been considered to be potential novel agents for limiting hypoxic cell injury.

Three genes encoding for NCX in the human genome are NCX1, NCX2 and NCX3. NCX1 is present in heart, brain and kidney. NCX2 and NCX3 are seen in brain and skeletal muscle. It is interesting to note that while NCX1 knockout is embryonically lethal, NCX2 knockout increases hippocampal long term potentiation and improves performance on learning and memory tests.

Though homozygous NCX1 knockouts are embryonic lethal, heterozygote NCX1 knockouts are viable. These transgenic mice have reduced NCX protein levels and have lesser rise of calcium levels within the cells after hypoxia and have a reduced susceptibility to ischemic injury.

Ultrarapid delayed rectifier potassium current (IKur) blockers in atrial fibrillation

Johnson Francis — Tue, 09 Mar 2010 06:41:36 +0000

Suppression of atrial fibrillation with drugs has always been a difficult issue. Most agents which suppress atrial fibrillation have certain problems like pro-arrhythmia or extra cardiac side effects. A novel strategy which has been proposed is the development of agents which act preferentially on the atria rather than on the ventricles. The ultrarapid delayed rectifier potassium current (I_Kur) is expressed in the atria, but not in the ventricles. Inhibition of I_Kur has been considered as an atrial selective antiarrhythmic treatment. Atrial selective sodium channel blockade with drugs like ranolazine is another approach which has been evaluated.

Kv 1.5 channels are responsible for the I_Kur and Kv 1.5 channels are encoded by the gene KCNA5. Some concern has been raised because I_Kur block may abbreviate atrial repolarization and loss of function mutations in KCNA5 has been associated with familial atrial fibrillation Heart Rhythm. 2008;5:1304-9.

Funny current: pacemaker current or If current

Johnson Francis — Tue, 09 Mar 2010 05:44:30 +0000

The funny current or pacemaker current is predominantly a feature of the sinoatrial node. It is also seen in atrioventricular node and the Purkinje fibres. It is a mixed sodium-potassium current which is inward and gets activated on hyperpolarization. The funny current is responsible for the spontaneous diastolic depolarization which ultimately leads to the automaticity of the sinus node. Since it controls the rate of the sinus node activity, it determines the heart rate. In addition to the diastolic voltage, the funny current activation is also dependent on cyclic AMP and hence can be modulated by the autonomic nervous system. HCN channel (hyperpolarization activated cyclic nucleotide) mediates the funny current (I_f). Four types of HCN channels (HCN 1-4) are known at present. HCN4 mutations have been implicated in sinus node dysfunction.

Though the funny current has been described over a quarter of a century back, it has come into attention recently due to the availability of selective I_f current blockers like ivabradine, a pure sinus node inhibitor without any other hemodynamic effect. Zatebradine and cilobradine are two analogues. A similar I_h current has been described in different types of neurons. I_f current has also been targeted in the development of a potential biological pacemaker.

I_f pacemaker current was discovered by Professor D. DiFrancesco in 1979.

Thrombus aspiration during primary angioplasty

Johnson Francis — Mon, 08 Mar 2010 16:11:07 +0000

Primary angioplasty is currently the best method for treating persons with acute ST elevation myocardial infarction presenting during the window period. Embolisation of atherothrombotic material during primary angioplasty often leads to obstructionof microvasculature and the well known ’slow flow phenomenon’. Various methods have been evaluated for reducing the chance for microvascular obstruction during primary angioplasty. Currently one of the popular methods is to aspirate the thrombus within the lumen of the artery and remove it. Thrombus aspiration produces better reperfusion and clinical outcomes. Aspiration is often considered when there is a visible thrombus on angiography. The device is introduced soon after the occlusive lesion is crossed by the guide wire. The aspiration catheter is introduced into the thrombus containing region under continuous aspiration. The whole unit is then withdrawn over the guide wire and the aspirated thrombus taken out. Care should be taken to avoid spillage of the thrombus into major proximal branches which can have catastrophic results. Negative suction is maintained while withdrawing the catheter. Care should be taken to prevent undue advancement of the guide catheter which may occur during this withdrawal process. NEJM article documenting the utility of thrombus aspiration is available here: http://content.nejm.org/cgi/content/full/358/6/557

Inherited Arrhythmias

Johnson Francis — Mon, 08 Mar 2010 00:49:24 +0000

Inherited Arrhythmias

Long QT Syndrome (LQTS 1-12)
Brugada Syndrome (BrS 1,2)
Catecholaminergic Polymorphic VT (CPVT 1,2)
Arrhythmogenic Right Ventricular Cardiomyopathy
Short QT Syndrome (SQTS 1-3)
Familial Atrial Fibrillation (FAF 1-4)
Sinus Node Disease (HCN4, SCN5A)
Progressive Cardiac Conduction Defect

Congenital Long QT Syndromes

LQT1: KCNQ1 (Alpha sub unit) Decrease in IKs (Slow component of delayed rectifier potassium current)
LQT2: HERG (Alpha sub unit) Decrease in IKr (Rapid component of delayed rectifier potassium current)
LQT3: SCN5A Increase in Late INa (Late sodium current)
LQT4: Ankyrin-B Anchoring protein which anchors ion channel to plasmalemma and sarcolemma
LQT5: KCNE1(minK) (Beta sub unit) Decrease in IKs
LQT7: KCNJ2 (Andersen syndrome) Associated with dysmorphic features and potassium sensitive periodic paralysis
LQT6 KCNE2 (MiRP1)(Beta sub unit) Decrease in IKrLQT7: KCNJ2 (Andersen syndrome)
LQT8: CACNA1c (Timothy syndrome) Associated congenital heart disease and syndactyly
LQT9: CAV3 (caveolin 3 – SIDS) Caveolin is the protein the caveolae (invaginations of the plasma membrane)
LQT10: SCNB4 (Beta subunit of sodium channel)
LQT11: AKAP9 (A-kinase anchor protein 9)
LQT12: SNTA1 (alpha-1 syntrophin)

Jervell-Lange-Nielsen Syndrome: Homozygous state causes defective endolymph secretion in the inner ear and deafness

JLN1 KCNQ1 (homozygous defect of alpha subunit) Decrease in IKs
JLN2 KCNE1(minK) (homozygous defect of beta sub unit) Decrease in IKs

Congenital Short QT syndromes

SQT1: Brugada et al – HERG (KCNH2) Gain in function of Iks
SQT2: Bellocq et al – KCNQ1 (KvLQT1) Gain in function of Ikr
SQT3: Priori et al – KCNJ2 Gain in function of Ik1

Other causes for shortening of QT interval

Tachycardia
Hyperthermia
Hypercalcemia
Digoxin

SQTS: Clinical Manifestations

Short refractory periods
Inducible VF at EP study
Family history of sudden death
Atrial fibrillation

Brugada Syndrome

Mutation in SCN5A / GPD1-L
Autosomal dominant, incomplete penetrance
5 to 66 per 10,000, male predominance
ST elevation in precordial leads, polymorphic VT
Cardiac arrest, syncope, family history

Arrhythmogenic Right Ventricular Dysplasia

Regional / global fibro-fatty replacement of myocardium
1:1000 to 1:10 000 incidence
Syncope, sustained VT, cardiac arrest
Familial in 30%
Autosomal dominant, incomplete penetrance
Epsilon wave on ECG
T wave inversion in anterior leads

Congenital long QT syndrome 12 (LQT12)

Johnson Francis — Sun, 07 Mar 2010 17:08:47 +0000

Congenital long QT syndrome 12 (LQTS 12) is caused by a mutation in the gene coding for alpha-1 syntrophin gene (SNTA1). The mutation was identified by evaluating a person with a QTC of 530 msec and negative for the 11 known LQTS susceptibility genes (LQT 1-11). A missense mutation A390V-SNTA1 was found in this person with recurrent syncope. SNTA1 links nNOS (neuronal nitric oxide synthase) to the nNOS inhibitor plasma membrane Ca-ATPase subtype 4b (PMCA4b). SNTA1 is also associated with SCN5A (cardiac sodium channel). This mutation causes an increase in the late sodium current in the myocardial cells. OMIM database has designated this gene (SNTA1) as LQTS 12 (LQT12) associated gene http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=612955.

[Ueda K, Valdivia C, Medeiros-Domingo A, Tester DJ, Vatta M, Farrugia G, Ackerman MJ, Makielski JC. Syntrophin mutation associated with long QT syndrome through activation of the nNOS-SCN5A macromolecular complex. Proc Natl Acad Sci U S A. 2008;105:9355-60. http://www.ncbi.nlm.nih.gov/pubmed/18591664]