Tuesday, June 28, 2016

Painful LBBB syndrome


A paper here describes this rarely encountered entity.

Monday, June 27, 2016

Lifestyle intervention, weight loss and atrial fibrillation incidence in type 2 diabetes


From the Look AHEAD trial:

A total of 5,067 overweight or obese individuals 45 to 76 years old with type 2 diabetes without prevalent AF were randomized to either an intensive lifestyle intervention (ILI) designed to achieve and maintain weight loss through caloric reduction and increased physical activity or a diabetes support and education usual care group. Atrial fibrillation was ascertained from electrocardiograms at study examinations and hospitalization discharge summaries. Multivariable Cox models were used to estimate the intention-to-treat effect of the intervention adjusting for baseline covariates. During a mean follow-up of 9.0 years, 294 incident AF cases were identified. Rates of AF were comparable in the ILI and diabetes support and education groups (6.1 and 6.7 cases per 1,000 person-years, respectively, P = .42). The intervention did not affect AF incidence (multivariable hazard ratio [HR] 0.99, 95% CI 0.77-1.28). Similarly, neither weight loss nor improvement in physical fitness during the first year of the intervention was significantly associated with AF incidence: multivariable hazard ratio (95% CI) comparing top versus bottom quartile was 0.70 (0.41-1.18) for weight loss and 0.88 (0.55-1.43) for physical fitness improvement.
Conclusion

In a large randomized trial of overweight and obese individuals with type 2 diabetes, an ILI that induced modest weight loss did not reduce the risk of developing AF.

This is a little disappointing. There is evidence that obesity is a risk factor for atrial fibrillation and it is appealing to believe that lifestyle modification is an effective treatment. In light of this study the best we can say at this point is that the evidence is mixed.

Fluid overload after fluid resuscitation


It happens and may be unavoidable. Strategies to deal with it in the post resuscitation period are needed. Review here.

Sunday, June 26, 2016

Environmental etiologic factors for eosinophilic esophagitis


Like many chronic conditions EO represents an interaction between genetics and environment. From a recent review:

Few studies have been conducted, however a consistent inverse association between EoE and H. pylori has been described. Several studies suggest a weak association between season and EoE diagnosis, but the evidence is inconclusive. EoE has also been associated with early life factors, including Cesarean delivery and antibiotic use. Larger studies are needed to evaluate these associations more thoroughly. Several papers have speculated the potential for anti-secretory agents to contribute to EoE.

Saturday, June 25, 2016

Mineralocorticoid excess and related syndromes


This was the topic of a recent review in Advances in Chronic Kidney Disease. Below are some take home points.

Hyperaldosteronism has deleterious effects beyond hypertension and hypokalemia such as hypertension independent LVH, myocardial fibrosis and an increase in other organ manifestations (eg hemorrhagic stroke) compared to the general population of hypertensive patients.

Sporadic primary aldosteronism

About a third are due to an adrenal adenoma for which unilateral adrenalectomy is the treatment of choice. About two thirds have bilateral adrenal hyperplasia in which the biochemical disturbances tend to be milder and for which medical management with aldosterone receptor antagonists is the treatment of choice.

Familial hyperaldosteronism type I

AKA glucocorticoid responsive hyperaldosteronism.

Reported in 1966.

Autosomal dominant.

Rare among causes of hyperaldosteronism but the most common form of monogenic hypertension.

As a result of the mutation aldosterone secretion is under the control of ACTH, thus treatment is with a glucocorticoid, preferably dexamethasone due to its long duration of action and minimal mineralocorticoid effect. Treatment may also include standard antihypertensive therapy including mineralocorticoid antagonists.

Familial hyperaldosteronism type II

Described in 1992.

Autosomal dominant.

Not suppressible by glucocorticoid.

Like sporadic hyperaldosteronism, it can be associated with adenoma or hyperplasia and the treatment is the same as in the sporadic form.

Familial hyperaldosteronism type III

Described 2008.

Not suppressible by glucocorticoid.

Massive hyperplasia.

Severe presentation with treatment resistance.

Liddle syndrome

Described 1963.

Though rare, second most common cause of monogenic hypertension.

Numerous mutations discovered, all of which cause increased activity of the epithelial sodium channel (ENaC).

Aldosterone levels low.

Treatment is with ENaC antagonists (triamterene, amiloride) but not mineralocorticoid antagonists such as spironolactone.

Apparent mineralocorticoid excess

Described 1977.

Autosomal recessive.

Third most common form of monogenic hypertension.

Local (renal tubular) deficiency of 11 beta hydroxysteroid dehydrogenase type 2 resulting in defective local conversion of cortisol to cortisone. The result is a local excess of cortisol, which has mineralocorticoid activity.

Treatment is with potassium sparing diuretics and possibly dexamethasone.

Licorice ingestion mimics this syndrome by causing inhibition of the intracellular enzyme.

Congenital adrenal hyperplasia

This is a group of diseases associated with numerous enzyme deficiencies. Only 17 alpha hydroxylase and 11 beta hydroxylase deficiencies cause mineralocorticoid excess syndromes. These result from an accumulation of precursors in the steroid biosynthetic pathway which possess mineralocorticoid activity. Glucocorticoid administration is the treatment.



Friday, June 24, 2016

Premature ventricular contractions: everything you wanted to know and more


A detailed review was recently published, which should be read in the original. Below are a few key issues covered.

Mechanisms:

Known or purported mechanisms include automaticity, triggered activity and re-entry. Automaticity causes ventricular ectopy (VE) by premature depolarization of pacemaker cells. This results from a shortening of the time it takes for phase 4 diastolic depolarization to reach threshold, due to an increased slope of diastolic depolarization or other mechanisms.

So called triggered activity is the result of afterdepolarizations, which could take the form of delayed (DAD) or early afterdepolarizations (EAD). DAD occur in phase 4 and are believed to be related to increased intracellular calcium concentrations due to a variety of mechanisms (eg catecholamine effects) with increased cAMP levels as a final common pathway. This in turn leads to a transient inward depolarizing sodium current generated by the Na/Ca exchanger. DAD is believed to be the mechanism of adenosine sensitive RVOT ectopy.

The mechanisms of EAD are less clear. Because EAD occur in phase 3 they increase repolarization time and appear to be instrumental in causing arrhythmias in the setting of a long QT interval.

Re-entry, once thought to be the primary mechanism of VE, is now in doubt as an important cause of PVCs.

The PVC coupling interval may provide a clue as to the mechanism but this is not entirely clear. A fixed coupling interval implies re-entry (if such exists in man) or triggered activity. Variable coupling intervals imply automaticity. Variable coupling intervals with equal or mathematically related inter-ectopic intervals are designated as parasystole which is usually associated with structural heart disease.


Are PVCs associated with harm?

It is useful to approach this question with respect to the presence or absence of structural heart disease. In both acute ischemia and chronic structural heart disease we know that they are associated with negative outcomes though it is less clear whether as a marker or a cause.

What about patients with no structural heart disease? In such patients VE was traditionally thought to be almost universally benign, based primarily on this paper from 1985 by Harold Kennedy and others. Drawing from a larger database that has accumulated since that time, this notion has been challenged, and there may be risk in some patients. This risk is poorly characterized with the exception of two categories: certain purely electrical heart diseases (channelopathies) and the potential for chronic frequent PVCs to cause a dilated cardiomyopathy (DCM). In purely electrical diseases a single PVC may trigger a life threatening event. From the article:

PVCs can trigger VF or polymorphic VT in patients with or without structural heart disease. 6 30 Some features of PVCs can help to identify “malignant PVCs” that have the potential of triggering VF in some patients. Most often PVCs are not tightly coupled to prior sinus beats; however, in certain conditions, tightly coupled PVCs have been described to trigger VF. This has been described for patients with Brugada syndrome, 31 early repolarization syndromes, 32 idiopathic VF, 33 or in the setting of acute myocardial infarction. 7 In the absence of these conditions, malignant ventricular arrhythmias are rare but have been reported and often have been triggered by tightly coupled PVCs. 6 34 No absolute cutoff value for a tight coupling interval has been defined, although most often the PVC coupling interval was less than 400 ms in these circumstances. 6 Other parameters that need to be assessed include the QT interval and the presence of nonsustained VT, including rate and morphology. More malignant arrhythmias have shorter cycle lengths, 35 and in 1 report, the coupling interval of the second beat of the nonsustained VT was found to be shorter in patients with VF compared with patients without VF. 36

It must be kept in mind that in some conditions (eg LQTS, hereditary and acquired) not all triggering PVCs are short coupled.

Concerning PVC induced DCM recent findings challenge the notion that this is caused chiefly by RVOT ectopy. Though RVOT ectopy is a known cause, DCM can result from VE originating from other foci. Also recently challenged is the idea that 15% of heartbeats is necessarily the ectopic frequency threshold for the development of DCM. The critical frequency is actually quite variable and is likely influenced by other risk factors, one of which is PVC QRS width, which is roughly directly proportional to the risk of DCM. A cutoff of 150 ms has been suggested. Epicardial origin of PVCs is associated with a wider QRS and greater DCM risk. Finally, interpolation of PVCs is also associated with a greater DCM risk. PVC induced DCM was once thought to be a variant of tachycardia mediated DCM but is now believed due to different mechanisms. It should be noted that in patients who already have structural disease for other reasons, frequent PVCs can lead to further deterioration of ventricular function.


Treatment:

Beta blockers are first line despite low efficacy due to their favorable safety profile. I-C antiarrhythmic drugs have stronger efficacy and are considered the next line of treatment provided the patient has no structural heart disease. The concern that these drugs increase the risk of SCD when used to treat PVCs is restricted to patients with structural heart disease. Careful assessment and appropriate expertise are required. Amiodarone is an option for patients who do have structural heart disease. Once DCM ensues due to frequent PVCs therapeutic options become limited for the above stated reasons. Suppression of VE with amiodarone has been reported to reverse DCM in that situation.

Catheter ablation is a preferred option in selected patients and is discussed in detail in the article.




Thursday, June 23, 2016

Vagal atrial fibrillation


This entity has long been known. It represents one group of mechanisms accounting for the increased risk of atrial fib with athletic conditioning. Review here.

Wednesday, June 22, 2016

How should we define valvular and non-valvular atrial fibrillation?


When the NOACs were first introduced atrial fibrillation associated with any hemodynamically significant valvular disease was considered valvular AF, excluding patients for treatment with a NOAC. Subsequently NOAC indications with respect to type of valve have been liberalized somewhat. The present consensus seems to be that patients considered to have valvular AF are those with rheumatic mitral disease, a valvular prosthesis (either tissue or mechanical) and possibly those with MV repair. Here is a recent review.