Chou's Flashcards
Progressive shortening of the PR interval with
corresponding widening of the QRS complex,
and vice versa, without change in the duration
of the P-end QRS interval is called
Concertina effect
The WPW ECG pattern with full preexciation
contains the following elements:
- A PR interval of less than 0.12 second,
with a normal P wave - Abnormally wide QRS complex with
a duration of 0.11 second or more - The presence of initial slurring of the QRS
complex, the delta wave - Secondary ST segment and T wave changes
A normal “septal” q wave is seldom found in
the preexcited complexes. Its presence in lead
__ is believed to exclude preexcitation.
V6
The WPW pattern occurs more often in males/females?
males
most important clinical manifestations in patients with WPW syndrome
Paroxysmal tachycardias
Paroxysmal supraventricular tachycardia is responsible for 75 to 80 percent of all paroxysmal tachycardias in patients with WPW syndrome.
Diagnostic criteria on the surface ECG and in the intracardiac electrogram during tachycardia include the following for orthodromic reentry tachycardia
(1) the P wave is negative in lead I
(2) PR is longer than RP when the retrograde pathway is fast (most common pattern) and shorter than RP when the retrograde pathway is slow
(3) the P wave is inscribed after, not during, the QRS complex; and
(4) the tachycardia cycle length is prolonged in the presence of functional ipsilateral bundle branch block (BBB).
(5) is an occasional occurrence of electrical alternans during tachycardia.
(6) is the sequence of the atrial excitation. The earliest excitation of the impulse conducted retrogradely via the AV node takes
place near the atrial septum
(7) the demonstration that the
impulse is conducted from the ventricle to the
atria at the time when the His bundle is refractory.
The effect of drugs is criterion (8). The effective
refractory period of the AV node and of the
AP is lengthened by different categories of drugs
(i.e., adenosine, b-adrenergic blockers, calcium
channel blockers, and digitalis for the AV node
and class 1A sodium channel blockers for the
AP). Therefore the response to a drug may be
helpful occasionally in the differential diagnosis
between AV node reentrant and AV reentrant
tachycardia
In some cases of AV reentrant tachycardia, the AP conducts the impulse as slowly as or slower than the normally conducting AV node. Such decremental conduction was found in 7.6 percent of APs in 653 patients.
Most of these atypical APs are located in the posteroseptal region and the associated tachycardia is called the ____________, as was first described by Coumel et al
permanent form of junctional reciprocating tachycardia
The tachycardia tends to be “incessant.” It is usually initiated by lengthening of the PR interval or a premature complex and can be produced or aggravated by antiarrhythmia drugs
Coumel and Attueldescribed a phenomenon called the _________ ” They showed that if BBB was present during tachycardia, a premature impulse elicited in the ventricle of the blocked bundle branch could be followed by a VA interval shorter than the VA interval of the tachycardia complexes because there is no delay caused by conduction around the blocked bundle branch.
“paradoxical capture.
The anterograde effective refractory period is the longest A1A2 interval recorded nearest the AP at which A2 conducts to ventricles without preexcitation.
the longest V1V2 interval recorded nearest the AP with the activation sequence compatible with retrograde conduction through the accessory bypass tract.
retrograde effective refractory period
An accessory AV pathway may be capable only of retrograde conduction. Anterograde block in the AP with preserved retrograde conduction results in an absence of the WPW pattern on the surface ECG (i.e., concealment of the bypass tract). This is AKA
The pathway is called concealed accessory pathway or bypass
However, the bypass tract can be utilized in the retrograde direction as a link in the AV reentrant circuit
When a reentrant tachycardia occurs in association with such a concealed bypass, the condition is called concealed WPW syndrome. It is the most common variant form of WPW syndrome and occurs in about 20 to 30 percent of patients with APs
findings during tachycardia to be suggestive of a concealed bypass tract
(1) negative P wave in lead I (because of left-sided bypass and early left atrial depolarization), (2) P wave during the ST segment, and
(3) increased cycle length if functional left bundle branch block (LBBB) develops
Conditions favorable for development of antidromic tachycardia include:
(1) short, effective refractory period of the entire retrograde VA conduction system
(2) short anterograde effective refractory period of the AP; and
(3) location of the bypass tract farther from the AV node
even if the term remains in use, it should not be applied to the ECG findings of short PR interval and normal QRS, with no history of paroxysmal tachycardia.
In 1941 Mahaim andWinston97 described muscular bridges connecting the AV node and ventricular myocardium, as well as discrete connections between the fascicles to the ventricles. Almost all Mahaim fibers are ____ sided (right or left?)
right
right atriofascicular fibers crossing the tricuspid annulus serve as the basis for typical Mahaim conduction in most if not all of these patients
In the absence of reentrant tachycardia, Mahaim fibers can be suspected when two different morphologies of the ventricular complex appear within a short time interval without any inter vening clinical events
Nodofascicular tachycardia should be suspected if:
(1) intermittent anterograde preexcitation is recorded
(2) the tachycardia can be initiated with a single atrial premature stimulus producing two ventricular complexes; and
(3) a single ventricular extrastimulus initiates supraventricular tachycardia without a retrograde His deflection
Drugs that can shorten effective refractory period of accessory pathways
Digitalis
beta blockers
CCB eg verapamil and diltiazem
Drugs that can prolong effective refractory period of accessory pathways
refractoriness is prolonged by class IA and class III antiarrhythmia drugs.
In most cases TDP is preceded by a sequence of a long RR interval of the dominant cycle followed by a short extrasystolic interval with premature depolarization interrupting the T wave AKA ____ phenomenon
(R-on-T phenomenon)
Kay and associates6 reported that such a sequence was seen during 41 of the 44 episodes of TDP that occurred in 32 patients. Such a sequence is not pathognomonic for TDP, however, as Gomes et al.7 also noted it frequently preceding ventricular tachycardia and ventricular fibrillation.
The risk is increased with increasing QTc duration and in the presence of
(1) hypokalemia, potassium deficiency, and perhaps hypomagnesemia
(2) impaired ventricular function
(3) severe bradycardia and second- or third-degree AV block
(4) T wave alternans; and
(5) R-on-T phenomenon.
Female gender is also a relative risk factor, as
in most series there is female preponderance of
this arrhythmia (ratio of female:male is about
3:1).
The clinical conditions known to predispose
to TDP are as follows:
1. Congenital long QT syndrome
2. Poisoningwith organophosphorus compounds.
3. Intracranial hemorrhage and complications
of air encephalography
4. Treatment with antiarrhythmic drugs.
5. Metabolic disturbances. TDP associated with significant QT prolongation has been reported in patients with hypothyroidism or anorexia nervosa and during treatment with “liquid protein” diets, other fad weightreducing diets, and therapeutic starvation.
6. Concomitant use of drugs that compete for or
inhibit the hepatic cytochrome P-450 3A4
7. Other drugs. Case reports of TDP associated
with QT lengthening incriminate a variety
of drugs. A partial list includes thioridazine,
amantadine, vincamine, ketanserin, astemizole,
pentamidine, trimethoprim-sulfamethoxazole,
vasopressin, and a mixture of Chinese medical herbs.
8. Transient QT prolongation often occurs
during the acute phase of (MI).
9. Other conditions. TDP has been reported in
several other conditions associated with
QT lengthening (e.g., after ionic contrast
injections into the coronary artery62) and
in patients with pheochromocytoma.
Many experimental studies suggest that TDP is initiated by a process known as ________ , which may also contribute to maintenance of the arrhythmia.
early afterdepolarizations
term applied to sudden death resulting from nonpenetrating chest wall impact in the absence of injury to the ribs, sternum, and heart, thereby differing from cardiac contusion.
commotio cordis
A regular tachycardia with a rate of 120 to 200 beats/min and a QRS duration of 0.12 second or longer may represent one of the following rhythms:
- Ventricular tachycardia
- Aberrant ve ntricular conduction
- Preexisting left (LBBB) or right (RBBB) bundle branch block
- Preexisting nonspecific intraventricular conduction defect
- Anterograde conduction through the bypass tract in patients with the Wolff-Parkinson- White (WPW) syndrome
- Anterograde conduction over an atriofascicular
or nodoventricular connection
An irregular wide QRS complex tachycardia may represent one of the following rhythms:
- Atrial fibrillation with aberrant ventricular conduction, bundle branch block, or intraventricular conduction defect.
- Atrial fibrillation with ventricular preexcitation. In the presence of a short refractory period of the bypass tract, the ventricular rate can be rapid. Indeed, if the ventricular rate in atrial fibrillation is >220 beats/min or the shortest RR interval is <250 ms, the presence of a bypass should be seriously considered because the AV node is not capable of conducting impulses at such rates in adults.
- Polymorphic VT (e.g., catecholaminergic tachycardia)
- Torsade de pointes.
In most instances, termination or slowing of
wide QRS tachycardia by vagal stimulation or
adenosine implies a supraventricular or ventricular origin?
supraventricular origin
although exceptions occur. Waxman and Wald83 reported well-documented episodes of VT that were terminated by carotid sinus massage after pretreatment with edrophonium. The subset of adenosine-sensitive idiopathic VT
criteria for VT with RBBB-like QRS morphology:
(1) in lead V1 are monophasic R or biphasic qR, QR, RS; (2) in lead V6 are rS, QS, qR.
criteria For VT with LBBB-like morphology Kindwall established the following diagnostic criteria:
(1) R wave in lead V1 or V2 >30 ms;
(2) any Q wave in V6;
(3) a duration of >=60 ms from the onset of QRS to the nadir of the S wave in V1 or V2; and
(4) notching of the downstroke of the S wave in V1 or V2.
Common to all these criteria for VT is the slow onset of the QRS complex or an abnormal Q wave.
Stierer et al analyzed the morphologic differences between VT and supraventricular tachycardia with anterograde conduction over an accessory pathway (preexcited tachycardia) with a QRS complex >0.12 second in 149 consecutive VTs and 149 consecutive preexcited regular tachycardia. They found that the following characteristics were specific for VT but were absent with preexcited tachycardia:
(1) predominantly negative QRS complexes in leads V4–V6;
(2) presence of a QR complex in one or more leads V2–V6; and
(3) more QRS complexes than P waves (when AV dissociation was present during VT).
The sensitivity and specificity of these three markers of VT were 75 percent and 100 percent, respectively.
In the so-called TYPICAL case of type I seconddegree AV block, the greatest increment of PR prolongation takes place in the _____ conducted impulse after the pause
second
Because of the periodic pauses, the rhythm has
a character of “group beating,” a finding that is an important clue to the diagnosis of Wenckebach
phenomenon.
how can atropine and carotid massage help distinguish infrahisian vs infranodal block?
Often intrahisian block can be distinguished from intranodal block on the body surface ECG, because with infrahisian block the AV conduction ratio worsens after atropine administration (which increases the sinus rate) and improves with carotid sinus massage (which decreases the sinus rate), whereas opposite effects are observed if the block is intranodal.
If the pacemaker is high in the AV junction, the ventricular rate may be increased/ decreased? by exercise or vagolytic agents?
increased
so basta sympathetic increases ventricular rate if pace maker is high in the av junc
An escape rhythm from the ventricle or low AV junction is generally not affected by such maneuvers
If the block is high grade or complete, the escape rhythm is usually junctional or his bundle vs ventricular in origin?
junctional
As a rule, the AV block is transient, and normal conduction resumes within less than 1 week after the acute episode
Most common cause of chronic AV block in Chous
Idiopathic bilateral bundle branch fibrosis
maximum heart rate usually occurs during _______ and the min heart rate at _____
The maximum heart rate usually occurs during late morning the minimum heart rate at 3 to 5 AM
thought to be the most common ectopic tachycardia seen on the ambulatory ECG
atrial tachycardia
The heart rate is generally 100 to 150 beats/min. The rhythm is often slightly irregular, with a gradual increase in rate (warming-up phenomenon), suggesting that the tachycardia is probably automatic.
The latter has been referred to as benign slow paroxysmal atrial tachycardia or ectopic atrial tachycardia The term suggested by Chou8 is accelerated atrial rhythm. With rare exception it is asymptomatic.
Arrhythmias capable of producing cardiogenic syncope include bradycardia of <___ beats/min, tachycardia of >___beats/min, and asystole longer than ___ seconds, depending on the patient’s body position and activity at the time of the arrhythmia.
< 40 bpm
> 150 bpm
3-5 sec
Because of the abnormal sequence of ventricular activation and contraction, ventricular tachycardia can often cause cerebral symptoms at a rate as low as ___ beats/min whereas patients with supraventricular tachycardia can tolerate faster rates.
120
it is generally agreed that transient ST segment elevation of ___ mm or more on the ambulatory ECG is a highly specific sign for myocardial ischemia, as it seldom occurs in normal persons without symptoms.
1mm
This study also demonstrated that isolated T wave inversion on the ambulatory ECG is a nonspecific finding, as 36 percent of the normal subjects had such a finding intermittently
Causes of MARKED qtc lengthening
