Davendra Mehta

SIGNIFICANCE OF SIGNAL-AVERAGED ELECTROCARDIOGRAPHY IN RELATION TO ENDOMYOCARDIAL BIOPSY AND VENTRICULAR STIMULATION STUDIES IN PATIENTS WITH VENTRICULAR-TACHYCARDIA WITHOUT CLINICALLY APPARENT HEART-DISEASE

Signal-averaged electrocardiography (ECG) was performed in 38 patients (mean age 38 years, range 15 to 70) with ventricular tachycardia who had no clinical evidence of structural heart disease. Spontaneous ventricular tachycardia was nonsustained in 23 patients and sustained in 15. None of the patients had symptoms of heart failure or ischemic heart disease, and at cardiac catheterization none had significant coronary artery disease or left ventricular wall motion abnormalities. In addition, all patients underwent left and right ventricular endomyocardial biopsy and ventricular stimulation studies. Signal-averaged ECG was performed and late QRS potentials were defined with use of Simsons method. Late QRS potentials were detected in a minority (18%) of patients including 2 of 23 with nonsustained and 5 of 15 with sustained (p = NS) ventricular tachycardia. Fifteen patients (40%) had abnormal endomyocardial biopsy results and these findings were more common in patients with sustained than in those with nonsustained ventricular tachycardia (9 of 15 versus 6 of 23, p less than 0.05). Late potentials were associated with abnormal endomyocardial biopsy findings (6 of 15 versus 1 of 23, p less than 0.01). An increase in fibrous tissue was the most frequent histopathologic abnormality; this increase was quantified by morphometric methods and compared with biopsy findings in normal control subjects. In the control group the proportion of collagen in relation to myocytes was less than 10%. All patients with both late potentials and abnormal biopsy findings had a greater than 15% ratio of collagen to myocytes in at least one specimen and the biopsies revealed marked interstitial fibrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Limitations of Rate Response of an Activity-Sensing Rate-Responsive Pacemaker to Different Forms of Activity

The responses of an activity‐sensing rate‐responsive system (Activitrax) to various forms of physiological activity were assessed in 15 individuals who had this pacemaker. Nine were patients with complete heart block and atrial arrhythmias; their mean age was 60 years (range, 41–85 years). Six were age‐matched healthy volunteers who were exercised with an external Activitrax system attached firmly to the chest wall. The pacemaker was programmed to achieve a pacing rate of about 100 bpm at the end of the first stage of the Bruce protocol (pacemaker settings; rate = 70–150 bpm; threshold = low to medium; response = 6–9). In the activity‐sensing ventricular pacing mode, oil patients achieved a significant increase in treadmill time compared to constant‐rate ventricular pacing (mean ± SD, 8.0 ± 3.3 vs 5.4 ± 2.3 minutes; p < 0.01), with a mean maximum pacing rate of 123 ± 18 bpm. Jogging in place produced a prompt increase in pacing rate, with the maximum achieved at the end of the exercise. However, physiological activities such as hand‐grip, the Valsalva maneuver and standing resulted in only minimal rate response. Pacing rate after ascending 4 flights of stairs was the same as that achieved after descending the same stairs (100 ± 8 vs 105 ± 4 bpm; p < 0.1). All 15 subjects were exercised from resting heart rate for 3 minutes on a treadmill at 1.2 mph and 2.5 mph with four gradients at each speed. Although the pacing rate increased with a faster treadmill speed (p < 0.005), it did not respond appropriately to a change in gradient compared to the sinus rate. We conclude that although activity‐sensing rate‐responsive pacing gives a prompt increase in pacing rate and improves maximum exercise tolerance, further refinement is necessary because: (1) physiological activities not associated with significant movement are not detected by this pacing system; (2) detection of vibrations as an indicator of activities does not correlate well with the level of exertion.

Echocardiographic and histologic evaluation of the right ventricle in ventricular tachycardias of left bundle branch block morphology without overt cardiac abnormality

The right ventricle was investigated by multiple biopsies and detailed echocardiographic evaluation, including measurement of cavity dimensions at the level of the inflow, body and outflow tract, in 27 patients with right ventricular tachycardia who had no clinical evidence of an underlying morphologic abnormality. Nine (33%) patients had abnormal biopsy results, with a quantifiable increase in interstitial fibrosis. Abnormal echocardiograms, defined as an increase in greater than or equal to 2 dimensions of the right ventricular cavity or wall motion abnormalities or both, were seen in 9 patients. There was a strong association between abnormal myocardial histologies and abnormal right ventricular echocardiograms (p less than 0.001). An abnormal echocardiogram was 94% specific and 80% sensitive for an abnormal biopsy. The findings of echocardiography and biopsy were correlated with the electrocardiographic features of the tachycardia. Evidence of right ventricular disease was seen in all 6 patients with superior frontal plane axis of clinical tachycardia as compared with 4 of 21 with inferior axis (p less than 0.001). Thus, 2-dimensional echocardiography is a sensitive means of diagnosing right ventricular disease in patients with nonischemic tachycardias of left bundle branch block morphology. A superior frontal plane axis of ventricular tachycardia in this group strongly suggests right ventricular disease, whereas an inferior frontal plane axis is frequently not associated with any morphologic or histologic abnormality of the right ventricle.

Ventricular tachycardias of right ventricular origin: Markers of subclinical right ventricular disease

The diagnosis of subclinical myocardial disease in patients with ventricular tachycardias of right ventricular (RV) origin and no overt cardiac abnormalities is important, inasmuch as the presence of RV cardiomyopathy or arrhythmogenic dysplasia can be associated with a poor prognosis. To this end the relative value of symptoms, ECG features of ventricular tachycardia, signal-averaged ECGs, and RV echocardiograms as compared with endomyocardial biopsy findings was prospectively evaluated. Twenty-seven patients with chronic ventricular tachycardias with a left bundle branch block-like morphology, presumed to be of RV origin, were studied. Clinical examination findings, 12-lead ECGs in sinus rhythm, radiographs of the chest, coronary angiograms, and left ventricular cineangiograms were normal in all patients. RV biopsies were abnormal in 11 patients (41%) with findings suggestive of RV dysplasia or cardiomyopathy. A multivariate analysis showed a significant correlation between an abnormal biopsy and sustained ventricular tachycardia (p < 0.05), tachycardia with a superior frontal plane axis (p < 0.001), an abnormal signal-averaged ECG (p < 0.05), and an abnormal RV echocardiogram (p < 0.001). An abnormal RV echocardiogram was both a sensitive (73%) and a specific (94%) indicator of an abnormal RV biopsy. Sustained tachycardia although sensitive (90%) had a low specificity (56%). In comparison, a superior frontal plane axis of ventricular tachycardia and an abnormal signal-averaged ECG were indicative of high specificity and low sensitivity for abnormal myocardial histologic findings.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative Evaluation of Chronotropic Responses of QT Sensing and Activity Sensing Rate Responsive Pacemakers

The rate responses of activity sensing (ATS) and QT sensing (QTS) rate responsive pacemakers to different forms and durations of exercises were compared. Nine patients with ATS and five with QTS were studied. All had complete heart block and atrial arrhythmias. At (he onset, (he pacemakers were programmed to achieve a pacing rate of 100–110 bpm by the end of stage 1 of the Bruce protocol, and to a pacing rate range of 70–150 bpm. With progressive exercise, using a treodmill (Bruce protocol), the maximum pacing rates in the two groups were not significantly different (mean ± SD; 123 ± 18 vs 129 ± 23 bpm, ATS vs QTS). The time taken to return to the baseline pacing rate during recovery was significantly longer with QTS (178 ± 70 vs 264 ± 68 s, p < 0.05). Brief exercise tests on a treadmill were performed for 3 min each with different combinations of treadmill speeds (1.2 and 2.5 mph) and gradients (0, 5, 10 and 15%). In both groups of patients, faster walking speed was associated with a faster pacing rate at each gradient. However, with increasing gradients, at each speed, there was a rise in the maximum pacing rate only in patients with QTS. During brief exercise tests, the maximum rate was achieved by the end of exercise in patients with ATS, but was delayed by 33 ± 20 s after exercise in patients with QTS. With very brief exercises lasting less than 1 minute (jogging on the spot), which require immediate rate response, patients with ATS had a rapid rate response and the maximum pacing rates were achieved by the end of the activities. The response of QTS was delayed and maximum pacing rate occurred during recovery. Ascending and descending four flights of stairs resulted in similar pacing rates in patients with ATS (100 ± 8 vs 105 ± 4 bpm, NS). Higher pacing rates were achieved on ascending stairs in patients with QTS (115 ± 24 vs 93 ± 28 bpm, p < 0.01). We conclude that with comparable pacemaker settings, ATS results in a more prompt rate response while the peak pacing rate of QTS is delayed. Rate responses are similar with gradually progressive exercise. However, the magnitude of rate response with QTS is more proportional to the level of exertion.

Multiple bilateral coronary arterial to pulmonary artery fistulae in an asymptomatic patient

We describe an asymptomatic patient with multiple fistulae between coronary arteries and the main pulmonary artery with an insignificant left-to-right shunt. Possible embryological basis of this anomaly is discussed.

Acute electrophysiologic effects of an HT2-serotonin antagonist, ketanserin, in humans

SummaryThe acute electrophysiologic effects of an intravenous bolus of ketanserin, a 5HT2 serotonin blocker, were studied in ten patients (four females, six males) during invasive electrophysiology. Following baseline electrophysiologic measurements during sinus rhythm and fixed-rate atrial pacing at 600 ms, a bolus of 0.2 mg/kg ketanserin was given over a 3-minute period. After 30 minutes all measurements were repeated. Systemic blood pressure was measured at regular intervals throughout. During sinus rhythm, there was no significant change in the basic cycle length or in the PA, AH, HV, QRS, QT, and QTc intervals. During atrial pacing there was a nonsignificant increase in the QT interval, from 342±13 ms to 366±16 ms, and a significant increase in the QTc interval, from 422±27 ms to 449±29 ms (p<0.05). There was no reduction in blood pressure. Thus ketanserin produced a significant prolongation of the QTc interval, in the absence of hypokalemia, in humans.

Clinical electrophysiologic effects of flecainide acetate.

SummaryFlecainide acetate depresses the rate of depolarization of action potential (Vmax), the so-called “membrane stablizing action.” In the intact heart it has a unique profile of substantial effect on conduction with modest effect on refractoriness. After intravenous administration, clinical electrophysiologic studies show that conduction through atrial myocardium, atrioventricular (AV) node, His-Purkinje system, and ventricular myocardium is depressed, the most prominent effect being on the His-Purkinje system. Refractorines of the normal atrial and AV nodal myocardium is not prolonged while that of the ventricular muscle is slightly increased. Atrial fibrillation (60% to 70%), atrial tachycardia (90% to 100%), and nodal and AV tachycardia (80% to 90%) are generally terminated, while flutter is usually slowed, but in a small proportion of patients (10% to 20%) might be terminated by the intravenous use of flecainide acetate. This drug has also been shown to be effective in terminating stable ventricular tachycardia (70%). However, it appears to be slightly less effective in suppressing inducibility of ventricular arrhythmias. Administered orally, flecainide is very effective in decreasing ventricular ectopic activity (80% to 95%) and nonsustained ventricular tachycardia. Thus, flecainide has a wide range of antiarrhythmic properties, making it a useful agent in the management of a variety of supraventricular and ventricular arrhythmias. In a small proportion of patients, however, its use can lead to apparent arrhythmogenic effects, the most dangerous being exacerbation of ventricular tachycardia.